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Research Paper C 833 Economic geology research Volume 1 1999–2000 Pär Weihed, editor Research Papers C 833 Economic geology research Volume 1 1999–2000 Pär Weihed, editor Sveriges Geologiska Undersökning 2001 ISSN 1103-3371 ISBN 91-7158-665-2 Cover: Augite oikocryst-bearing layers alternating with olivine–gabbro/troctolite layers in the Hoting mafic intrusion. Photo Birger Filén. © Sveriges Geologiska Undersökning Geological Survey of Sweden Layout: Agneta Ek, SGU Print: Elanders Tofters, Östervåla 2001 Preface The current volume is the result of a new attempt to continuously publish data from the work within the ore documentation programme at the Geological Survey of Sweden. Our aim is to publish various papers of interest to exploration and mining companies as well as the interested layman. The results within this volume stem from work carried out by scientists of the Geological Survey of Sweden during the years 1999 and 2000. One paper (Palaeoproterozoic deformation zones in the Skellefte and Arvidsjaur areas, northern Sweden by Jeanette Bergman Weihed) is the result of an external research project financed by the Geological Survey of Sweden. It is our ambition to continue to publish compilations and novel research based on the vast unpublished archives of the Geological Survey of Sweden. We will also try to publish new ideas on various aspects of earth sciences that can contribute to a better understanding of ore deposit geology and ore genesis. Dr Kjell Billström (Swedish Museum of Natural History, Stockholm) and Dr Olof Martinsson (Luleå University of Technology, Luleå) are acknowledged for thorough reviews of all papers in this volume. Uppsala, October 2001 Pär Weihed Content A review of Palaeoproterozoic intrusive hosted Cu-Au-Fe-oxide deposits in northern Sweden ................................ 4 Pär Weihed Swedish layered intrusions anomalous in PGE-Au .................................................................................................. 33 Birger Filén Palaeoproterozoic deformation zones in the Skellefte and Arvidsjaur areas, northern Sweden ................................. 46 Jeanette Bergman Weihed Geochemistry and tectonic setting of volcanic units in the northern Västerbotten county, northern Sweden .......... 69 Ulf Bergström Rock classification, magmatic affinity and hydrothermal alteration at Boliden, Skellefte district, Sweden – a desk-top approach to whole rock geochemistry .................................................................................................... 93 Anders Hallberg A review of the Fe oxide deposits of Bergslagen, Sweden and their connection to Au mineralisation .......................132 Magnus Ripa A review of Palaeoproterozoic intrusive hosted Cu-Au-Fe-oxide deposits in northern Sweden Pär Weihed Weihed, P,. 2001: A review of Palaeoproterozoic intrusive hosted Cu-Au-Fe-oxide deposits in northern Sweden. In Weihed, P. (ed.): Economic geology research. Vol. 1, 1999–2000. Uppsala 2001. Sveriges geologiska undersökning C 833, pp. 4–32. ISBN 91-7158-665-2. The present study is aimed at highlighting a new group of intrusive hosted Cu-Au-Fe oxide deposits in northern Sweden. Altogether 9 different deposits are briefly described: Tallberg, Granberg, Viterliden, Gråberget, Sarvasåive, Sadenåive, Vaikijaur, Iekelvare, and Sjisjka. Most deposits share common characteristics, such as being hosted by intermediate to felsic intrusive rocks. They are all also Cu±Au±Fe oxide dominated deposits with a similar ore mineralogy and they generally contain one or several of potassic, sodic and silicic alteration type assemblages. However, the host rocks belong to several different intrusive suites from early- to syn-orogenic suites like the Jörn-type through slightly younger GSM-type to young post deformation Lina and Revsund types. The mineralizations seem to be focused on high level or subvolcanic stocks, dykes, and sills that crystallised late in the evolution of the magmatic systems and hence the magmatic hydrothermal fluids possibly responsible for the formation of the deposits may have a magmatic origin. The deposits show similarities with porphyry style as well as Fe-oxide Cu-Au deposits and are here suggested to belong to the same general group of deposits. Genetic relationship with VMS, epithermal, and Kiruna type deposits can be inferred for some deposits. Pär Weihed, Geological Survey of Sweden, Box 670. Present address: Luleå University of Technology, 971 87 Luleå, Sweden. E-mail: [email protected] Introduction During the 1970’s and 1980’s, exploration for base metals was carried out by both the Swedish State, through SGU (later SGAB) and LKAB, and private companies, e.g. Boliden, in northern Sweden. In many cases, promising mineralizations were found although relatively little drilling was done. Many of the prospects contain Cu±Au±Feoxides and share many features although this was not emphasised at the time. From reports on individual prospects it is clear that many of the deposits are associated with intrusive rocks of felsic to intermediate composition and show similarities to porphyry style mineralization as well as to Proterozoic Cu-Au-Fe-oxide style deposits. Another striking observation is that the mineralizations have been considered sub-economic despite the fact that only few drillholes have been drilled, assaying of the core material 4 P. WEIHED is not consistently done (many mineralized cores are not assayed at all), and the mineralised systems are not known at depth. In this review of some of the interesting deposits a short description of each is given, the style of mineralization is described in macro- and microscopic scale, and a metallogenetic model is proposed for the deposits. It should be emphasised that it has only been possible to work with a very limited part of the vast material available from these deposits. Drill cores from the deposits described in some detail below have been logged and all available reports have been used in this study. In Figure 1 the location of all described deposits are shown. Deposit descriptions Below, each deposit is described separately from a regional setting point of view. Mineralization style, a summary section with some genetic considerations, and deposit characteristics are presented. In the final paragraph, all deposits are discussed in a metallogenetic framework for northern Sweden. Gråberget The Gråberget Cu-deposit is located on the mapsheet 24I, square 2d (Swedish nat. grid) c. 35 km northwest of the township of Malå (cf. Figs. 1 and 2). The first discoveries of glacial boulders in the area were made in the 1940ies during the county mapping by Gavelin (1955). During this period, some trenching was made and assays from trench samples indicated c. 3.1–3.6 % S and 0.8–1.4 % Cu which at the time was considered to be of no interest and consequently the exploration in the area ceased. Renewed interest in the area in 1974 through the ”Mineral hunt” in the county of Norrbotten, resulted in a new discovery of a glacial boulder that contained 3.2 % Cu. At the same time, regional geochemical sampling indicated anomalous Cu, Pb, and Mo in till samples. The area was investigated by SGU for NSG in 1975 with boulder tracing and geochemical and geophysical surveys. During 1975 to 1977 diamond drilling was carried out by SGU during which period 47 holes were drilled. The results from the drilling have been compiled in Claesson (1979). The map presented here is modified from Claesson (1979). 22˚E 20˚E Exposed Archaean v v v 69˚N Palaeoproterozoic greenstone belts Fin l v v v v v 24˚E v v v v v v v v v v v 9 Juvenile Proterozoic crust v v v v v v v v v v v v Reworked Archaean craton 68˚N v 16˚E v v v v v v v v v v v v Skellefte volcanic arc v v v v v v Kiruna porphyries Kiruna an d v v v 18˚E v 67˚N v v v Approximate Archaean– Proterozoic boundary defined by εNd values of 1.9 Ga intrusive rocks v v v Major shear zones v v v v No rwa y v v v v v v v v v v v 6 v v v v v v v S-type, anatectic, c. 1.80 Ga granites of Skellefte, Härnö, and Lina types, associated with minor Sn-W and Mo-Cu mineralizations v v v v 4 v v v v v v v v v v v v v v 5 v 2 v v vv v 3 v 1 Bothnian Bay v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v v Mainly subaerial volcanic rocks, c. 1.88 Ga, Kiruna and Arvidsjaur type. Disseminated Cu-Au deposits, Kiruna type Fe ores Mainly submarine volcanic rocks, c. 1.89–1.88 Ga, Skellefte type. VMS, epithermal Au-VMS, mesothermal gold lode deposits Calc-alkaline granitoids and mafic intrusions of Jörn type, 1.95–1.86 Ga, and GSM type, 1.87–1.86 Ga. Porphyry Cu-Au and mesothermal gold lode deposits, mafic and ultramafic hosted Ni v v 65˚N v v v v v v v v v v v Metagreywackes of the Härnö and Råneå Groups, >1.95–1.85 Ga mesothermal gold lode mineralizations v v TIB-related 1.80 Ga felsic volcanic rocks A- to I-type, 1.80 Ga felsic intrusive rocks of Revsund type, associated with minor Sn-W mineralization v v v v v 66˚N v v Caledonian rocks undivided, major thrusts indicated Precambrian basement cover undivided v v v v v v v v v v v v v v v v v v v Formlines of foliation 7 v v v v v v 14˚E v v v 8 64˚N v Palaeoproterozic greenstone belts, 2.5–2.0 Ga. Viscaria type Cu, disseminated Cu-Au, BIF, layered intrusion hosted Ni v Archaean rocks undivided Fig. 1. Simplified geological map of northern Sweden (modified from Stephens et al. 1994). The deposits described in the text are indicated on the map as follows: 1=Tallberg, 2=Granberg, 3=Viterliden, 4=Sarasåive, 5=Gråberget, 6=Lulepotten, Sadenåive, 7=Vaikijaur, 8=Iekelvare, and 9=Sijsjka. The present study is based on the report by Claesson (1979) with some additional core logging and microscopic investigations of thin sections. Regional geology The mineralization at Gråberget is spatially associated with a red quartz feldspar porphyritic phase of the Ledfat granite related to the Sorsele type intrusions. The Sorsele granite has been dated by U-Pb on zircons at 1791±22 Ma by Skiöld (1988) while the Ledfat granite at Gråberget has been dated at 1784±62 Ma and 1772±14 Ma respectively by U-Pb ages on zircons (Skiöld 1988). The red porphyritic phase of the Ledfat granite is intrusive into the Ledfat conglomeratic unit. This unit contains granitoid clasts, which have been dated at 1896±50 Ma and 1866±17 Ma by Skiöld (1988). Hence the Ledfat conglomerates must have been emplaced after c. 1.87–1.88 Ga and the Ledfat conglomerates have been paralleled with the Vargfors conglomerates in the Skellefte district which have been dated at 1875±4 Ma by U-Pb zircons from an intercalated felsic ignimbrite (Billström & Weihed 1996). The regional geology of the map sheet 24I is shown in Figure 2, which is compiled from the digital bedrock database at SGU. The oldest rocks in the area belong to the Skellefte Group and are found in the Adak area. Rocks are dominantly felsic to mafic volcanic rocks but are also intercalated with greywackes in higher stratigraphic positions in the Adak area. The volcanic rocks of the Skellefte Group are coeval and considered comagmatic with the calc-alkaline I-type intrusions generally in this area referred to as the Jörn type of intrusions. In the area southwest of Gråberget (Fig. 2) extensive units of mafic volcanic rocks are intercalated with greywackes. These mafic volcanic rocks are younger than the A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 5 V Kikkejaure Långträsket Storavan Naustajaure Ledvattnet Övre Bastuselet Sk ell eft Sorsele type granites (incl. Ledfat type), c. 1.80 Ga old Gabbroic intrusion, c. 1.89 Ga old Ledfat conglomerate, c. 1.75 Ga old Greywacke, c. 1.89 Ga old Ledfat sandstone, c. 1.75 Ga old Mafic volcanic rock, Skellefte type, c. 1.89 Ga old Mafic volcanic rock, Arvidsjaur type, c. 1.75 Ga old Felsic volcanic rock, Skellefte type, c. 1.89 Ga old Felsic volcanic rock, Arvidsjaur type, c. 1.75 Ga old Gråberget Cu-deposit GSM type intrusive rock, Arvidsjaur type, c. 1.88 Ga old Form line Mafic volcanic rock, c. 1.88 Ga old Deformation zone unspecified eä lve n 10 km Jörn type intrusive rock, c. 1.89 Ga Fig. 2. Simplified geological map of the Storavan mapsheet. The geology is modified from the digital database over the Norrbotten County available at the Geological Survey of Sweden. The Gråberget deposit is indicated. Skellefte Group but older than the Arvidsjaur Group. No age determinations exist from this rock unit. The mafic rocks, which informally have been called the Tjamstan 6 P. WEIHED formation, forms part of the Malå group on the Malå map sheet to the south (Bergström & Sträng 2000). The Arvidsjaur Group of mainly subaerial felsic with minor mafic volcanic rocks is generally considered to overlie the submarine Skellefte Group of volcanic rocks. The Arvidsjaur Group volcanic rocks are also considered to underlie the Ledfat Group of conglomerates and sandstones. The Arvidsjaur Group has been poorly dated at 1878±2 Ma (Skiöld et al. 1993) by U-Pb on zircons (only two fractions from Skyberget) and 1876±3 Ma (pooled zircon fractions from Skyberget, Bure, and Gråberget; Skiöld et al. 1993). The Arvidsjaur Group is also considered comagmatic with the Arvidsjaur type granitoids and age determinations of these granitoids fall within the same time span as the Arvidsjaur Group volcanic rocks. The structural evolution in the area is not clear and no thorough studies of the metamorphic evolution have been undertaken so far. However, in general all rocks but the Sorsele type intrusions have experienced ductile deformation in greenschist to amphibolite grade metamorphism during the svecokarelian orogeny. The timing of deformation and metamorphism is poorly constrained but regionally the peak of metamorphism is considered to have occurred between 1.86 and 1.80 Ga (cf. Billström & Weihed 1996). The main stages of penetrative deformation is generally in the same time span. However, regional ductile to brittle shear zones with a NNE strike have been active at c. 1.79 Ga and hence are coeval with the young Sorsele type intrusions. An important note in this respect is that the Gråberget area is extremely well preserved with very little penetrative deformation and lower greenschist facies metamorphism. It is possible that the Gråberget (and Ledfat area) forms part of a NNE trending downfaulted belt of supracrustal rocks that are bounded by the NNE striking c. 1.79 Ga shear system (cf. Fig. 2). 800 1000 1200 The geology of the Gråberget area is shown in Figure 3, which is modified from Claesson (1979). The host rocks to the mineralization are both granite and conglomerates, suggesting an epigenetic origin. As mentioned above, the main mineralization is located within the quartz-feldspar porphyritic border zone of the intrusion. The granite intrudes the conglomerate as irregularly shaped dykes of variable widths. The main dyke is c. 200–300 m wide in the mineralised area. The northern contact of the dyke is steep whereas the southern contact has a gentle dip towards south. Post mineralization diabase dykes intrude all other rocks in the area (Fig. 3). The textural changes, from clearly porphyritic at the contact to evengrained granite in the central parts of the granite dyke, appear gradual in drillcore even if it is probable that the dyke consists of several intrusive phases. The typical quartz feldspar porphyritic character of the marginal zone is shown in Figure 4 (sample 75007/8.00 m and 75007/10.30 m), whereas the more typical evengrained variety is shown in Figure 4 (sample 75001/130.50 m and 75001/155.00 m). The evengrained granite consists of microcline, oligoclase, quartz, biotite, and epidote as main minerals with accessory apatite, titanite, and opaques (Claesson 1979). The porphyritic variety is more microcline and quartz rich with euhedral quartz phenocrysts and tabular, zoned euhedral feldspar phenocrysts (Fig 5a). The plagioclase is variably sericitized and biotite is partly chloritized. Epidote is a common fracture mineral besides occurring as an alteration mineral after plagioclase. The conglomerates are polymict, grey to greenish grey with a fine matrix that consists of lithic fragments of vari- 1400 1600 1800 2000 2200 1400 Geology of the Gråberget Cu-deposit 1200 modified from Claesson (1979) 1200 B 1000 75007 1000 1400 600 Mineralization V 75001 I IV II III Mafic dyke Sorsele type granite 600 800 1000 800 800 A 1200 Ledfat conglomerate/ sandstone Outcrop 1400 Drillhole Fault 1600 IV Profile 1800 200 m 2000 2200 Fig. 3. The geology of the Gråberget Cu-deposit (modified from Claesson 1979). Drillholes and mineralizations A and B are indicated. A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 7 Fig. 4a. Photographs of drillcore specimens from the drillholes 75001 and 75007 (for location see Fig. 3). The white scale bar is approximately 35 mm long. Sample 75001/15.30 m – weak mineralization in biotized conglomerate, Sample 75001/23.60 m same as previous, Sample 75001/30.30 m – porphyritic granite typical of the rim of the major granitic dyke, Sample 75001/42.60 m – strongly altered granite with microcline, albite, quartz as major alteration minerals, Sample 75001/48.00 m – same as previous, Sample 75001/52.50 m – same as previous, Sample 75001/56.10 m – same as previous, Sample 75001/59.60 m – same as previous with early opaque (magnetite)biotite vein overprinted by late disseminated sulphides, Sample 75001/119.90 m – same as 75001/42.60 m, Sample 75001/130.50 m – well preserved even, medium-grained granite typical of the central parts of the granitic dyke, Sample 75001/155.00 m – same as previous but finer grained variety, ous supracrustal rocks as well as monomineralic quartz and feldspar. Clasts are generally well rounded and up to 20–30 cm in size. Supracrustal rocks, as well as scattered granite rocks, constitute the clast material. Silicification and epidote fracture fillings are common towards the contact with the granite (Claesson 1979). 8 P. WEIHED The mineralization consists of a dissemination and veinlets of chalcopyrite and pyrite (Fig. 4). The sulphides clearly overprint earlier magnetite veins and disseminations (Fig. 4). In Figure 5, micrographs are shown from the host rocks and mineralization. In Figure 5a, the microcline- Fig. 4b. Sample 75007/8.00 m – porphyritic phase of the granite, Sample 75007/10.30 m same as previous, Sample 75007/15 m – altered granite with very fine sulphide veinlets with fine-grained microcline, quartz, biotite, and sericite, Sample 75007/22.00 m – possible hematite stained granite with relatively strong microcline-quartz-albite alteration, Sample 75007/37.00 m – same as previous, and Sample 75007/46.50 m – late brecciation with epidote, opaques and chloritized biotite and tourmaline. albite-quartz phyric character of the host rock is clearly seen. A few larger chloritized grains of biotite are also visible. The sulphide vein-breccia in Figures 5b–c is representative of the style of mineralization. In this micrograph the porphyritic nature of the host rock is still seen. A slightly different style of mineralization is seen in Figures 5d–e where two generations of veins exist; a coarser grained vein composed of opaques and chloritized biotite and a parallel rim of secondary fine-grained biotite quartz-microcline. In Figures 5f–g a fine network veining of sulphides is associated with a fine-grained gangue of microcline, albite, quartz, biotite, and sericite. In mineralised parts of the conglomerate, a strong biotitization was evident in thin sections. Although this brief study has not identified any clear paragenetic zoning from the limited drill core material it seems plausible that early magnetite in veins is part of the mineralising system (Fig. 4 75001/59.60 m and Figs. 5e–g). The alteration associated with the mineralization is dominantly a potassic-sodic style of alteration with common bleaching (microcline-albite-quartz) or biotitization. Silicification and albitization may be part of the alteration style, but too few samples have been studied in order to understand the regional extent of these types of alteration assemblages. Brecciation with epidote and sulphide seems to record a late stage of mineralization. A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 9 Fig. 5. Micrographs from drillcore specimens shown in Figure 4. A) Sample 75001/30.30 m shows the typical porphyritic nature of the border of the granitic dyke. Euhedral microcline and albite phenocrysts together with anhedral subgrained quartz phenocrysts in a groundmass of similar composition. Also subhedral slightly chloritized biotite phenocrysts occur. Crossed polars. B) Sample 75001/48.00 m shows sulphide breccia vein in a microcline, quartz, and albite dominated groundmass. Some phenocrysts of microcline and albite are also visible. Crossed polars. C) same as B in reflected light. D) Sample 75001/59.60 m early opaque-biotite vein with finegrained microcline-albite-quartz rims. Crossed polars. E) same as D in reflected light. F) Sample 75007/15.0 m shows disseminated sulphides and sulphide veinlets in a fine-grained matrix of microcline, albite, quartz. Sericite and biotite occur together with the sulphides in veinlets. Reflected light. G) same as F with crossed polars. 10 P. WEIHED Iekelvare The Iekelvare Cu-Au-Fe oxide deposit is located on the map sheet 27I (cf. Figs. 1 and 6), square 1i–j (nat. grid). The mineralization was discovered in 1972 when SGU found mineralised boulders during exploration activities in the area. Subsequent geochemical sampling and geophysical ground surveys led to the drilling of 13 drillholes with a total length of 2063 m in the area between 1974 and 1977. The geophysical measurements include ground magnetics, EM, and IP. No thorough estimation of grade Pälkasjaure Bälkasjávrre and tonnage has been made, but Sundbergh et al. (1980) estimated the tonnage at 200 000–300 000 tonnes at a Cu grade slightly below 1 %. The deposit was re-assayed for gold in 1984 (Lundmark & Hålenius 1984) and high Au grades were found in several sections of the deposit. In drillhole 75002 1.3 g/t Au over 4.90 m and 1.6 g/t over 1.73 m and in drillhole 75004 7.8 g/t Au over 0.40 m was reported. The exploration activities are summarised in Sundbergh et al. (1980), Lundmark (1983), Lundmark & Parkijaure Tjähkkávrre Randijaure Asjkasluokta Pielnejaure Ladunjávrre Lulep Juksávrre Noarve jávrre Piertinjaure Bierddinjávrre Granite, Lina type, c. 1.80 Ga old Marble, Norvijaur group, c. 1.89 Ga old Gabbro–diorite, c. 1.80 Ga old ? Felsic volcanic rock, c. 1.89 Ga old Granitoid, GSM-type, c. 1.87 Ga old Older granitoid, Norvijaur type, c. 1.93 Ga old Granitoid, c. 1.89 Ga old Iekelvare deposit Metasedimentary rock, c. 1.89 Ga old Form line 10 km Deformation zone unspecified Fig. 6. Simplified geological map of the area NE of Randijaure. The geology is modified from the digital database over the Norrbotten County available at the Geological Survey of Sweden. The Iekelvare deposit is indicated. A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 11 Hålenius (1984), and Einarsson (1985). The presentation below is based on these reports together with relogging of cores and new thin sections from the drillcore material. Iekelvare area. Skiöld et al. (1993) published two U-Pb zircon ages from the Norvijaur granitoid situated in the southeastern corner of Figure 6 and the granitoid west of the Norvijaur group supracrustal rocks. The Norvijaur intrusion yielded an age of 1926 +13 –11 Ma whereas the granitoid to the west yielded an age of 1876±6 Ma (Juoksjokko granite). This implies that the Norvijaur granite may constitute a basement to the Svecofennian rocks in the area and, provided that the contact towards the Norvijaur group is intrusive, it also implies that the latter is an older sequence of supracrustal rocks. The Iekelvare area is dominated by red medium to fine-grained, foliated to non-foliated granites (cf. Figs. 7 and 8). According to Sundbergh et al. (1980), non-foliated finer Regional geology The regional geology of the Iekelvare area is relatively poorly known and beside regional compilations such as the Nordkalott map (1986) not much has been published. Unpublished exploration reports, for example Lundmark (1983), exist, but are difficult to evaluate since nomenclature is not consistent with present standards. In Figure 6, a regional geological map, modified from the SGU digital database from the area, is shown. No age determinations have been published from the Bälkajaure Iekelvare Modified from Sundbergh et al (1980) Mafic dyke Outcrop Altered diorite Foliation Diorite Fault Granite, foliated with abundant restites of supracrustal rocks Cu±Au±Fe-oxide mineralization 500 m Granite, foliated Fig. 7. The geology of the Iekelvare area (modified from Sundbergh et al. 1980). The location of the Iekelvare deposit is indicated. 12 P. WEIHED Fig. 8. Photographs of drillcore specimens from the drillhole 75002. The white scale bar is approximately 35 mm long. Sample 75002/55.0 m – a typical reddish Lina type granite which constitute the dominating rock type in the area, Sample 75002/70.0 m - same as previous, Sample 75002/79.85 m – foliated and mineralised rock dominated by finegrained quartz, microcline and biotite (weakly chloritized), sulphides along grain shape foliation, Sample 75002/81.30 m – strongly albite altered rock with veins and dissemination of sulphides. Minor microcline, Sample 75002/82.90 m – same as previous, Sample 75002/88.50 m – Weakly foliated mafic rock composed of clinopyroxene, plagioclase, albite, and minor quartz with a weak dissemination of opaque minerals with associated epidote and calcite, Sample 75002/89.10 m – Mafic intrusive rock with hornblende and plagioclase as major minerals, with epidote and minor quartz, microcline and sulphides, Sample 75002/90.10 m – Foliated and mineralised mafic rock with chloritized biotite, minor hornblende, epidote as mafic minerals and fine- grained quartz, albite and microcline as felsic minerals, Sample 75002/100.90 m – veins of clinopyroxene and quartz in matrix of plagioclase cut a plagioclase and hornblende dominated rock. Plagioclase sericite and epidote altered, Sample 75002/126.65 m – same as previous host rock, Sample 75002/146.90 m – foliated biotite, albite, microcline, and quartz schist with minor hornblende. Dissemination and thin veins of sulphides, and Sample 75002/153.10 m – same as previous. A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 13 grained granite is intrusive into a coarser foliated type. However, these types are not distinguished on the maps of Sundbergh et al. (1980), and on the Nordkalott map (1986) the granites are referred to as Lina type. Although no field mapping has been done within this project it is plausible that the non-foliated finer grained variety indeed can be classified as Lina type and hence has an age of c. 1.80 Ga, while the older coarser foliated granite should rather be classified as belonging to the older 1.89 Ga generation of granitoids. Sundbergh et al. (1980) and Einarsson (1985) report the common occurrence of restitic supracrustal material in the granite, which further supports a Lina type origin for the granite. In the mineralised area, the granite is intruded by a dioritic rock of unknown age. The foliated nature of the diorite may imply that is related to the older variety of granitic intrusion rather than the younger Lina type. In drillcore, Lundmark & Hålenius (1994) identified a porphyritic border phase of the diorite. The granite in the Iekelvare area can be seen in Figure 8, samples 75002/55.0 m and 75002/70.0 m, while the diorite is shown in Figure 8, samples 75002/88.5 m, 75002/88.5m, and 75002/89.1 m. Mineralization Besides the mineralization at Iekelvare, several minor occurrences of mineralised granite exist in the area, as indicated in Figure 7. None of these have been drilled and only scattered analyses of rock specimens from outcrops and from bedrock exposures from trenches exist. The results are reported in Einarsson (1985). As stated above, the mineralization at Iekelvare is associated with a foliated diorite which has intruded the regionally common red, foliated, medium grained granite. The mineralization is very scattered and heterogeneous in character and consists mainly of mm to cm wide sulphides veins, but disseminations of sulphides are also common. The bulk of the mineralization seems to be situated within a more or less pervasively altered diorite, but mineralization also occurs in the granite. The general macroscopic appearance of the mineralization is shown in Figure 8. The main ore minerals are chalcopyrite and pyrite, but sphalerite, galena, and molybdenite are also common locally. Magnetite is a ubiquitous constituent of the alteration assemblage and it is probable that the high magnetic areas on the ground-magnetic map (Fig. 9) can be attributed to the alteration system associated with the mineralization. Quartz veins, strong silicification, biotite, and chlorite are typical of the alteration assemblage as can be seen in Figure 8 and 10. Lundmark & Hålenius (1984) identified zones of higher grades of gold as stated above. They reported gold as part of a paragenesis consisting of fine-grained galena, sulfosalts, and arsenopyrite. They also noted that the gold grades do not follow the Cu grades. It should be noted that gold so far has mainly been assayed from Cu-rich parts (see introduction for grades) and thus the gold Fig. 9. Ground magnetic map of the Iekelvare area. Local grid in metres. 14 P. WEIHED Fig. 10. Micrographs of some of the specimens shown in Figure 8. A) 75002/100.90 m, Plagioclase and hornblende dominated rock with disseminated sulphides. Crossed polars. B) 75002/153.10 m, Foliated biotite, albite, microcline, quartz schist with minor hornblende. Dissemination and thin veins of sulphides. Crossed polars. C) same as B in reflected light. D) 75002/81.30 m, Strongly albite-quartz altered rock with disseminated sulphides. Crossed polars. E) same as D in reflected light. F) 75002/89.50 m, Weakly foliated mafic rock composed of clinopyroxene, plagioclase, albite, and minor quartz with a weak dissemination of opaque minerals with associated epidote and calcite. Crossed polars. potential of the mineralization has not been thoroughly evaluated. The more intensely mineralised parts of the Iekelvare deposit are characterised by a strong bleaching of the rocks (Fig. 8, samples 75002/81.30, and 82.90 and Figs. 10a, d, e). This is attributed to an addition of silica and potassium and mineralogically by a quartz-plagioclase- biotite±hornblende alteration assemblage (Figs. 10a, b, c). In the less intense mineralised parts, like in Figure 8 sample 75002/89.10, primary clinopyroxenes are preserved while in intermediate stages secondary hornblende and biotite are common (Fig. 10f ). The alteration is thus characterised by potassic (biotite-hornblende), sodic (albiteplagioclase), and silicic alteration styles. A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 15 Vaikijaur The Cu-Au-Fe-oxide-(Mo) deposit at Vaikijaur (cf. Figs. 1, 11, 12) is situated on the map sheet 27J square 0e (nat. grid). It was discovered in the early 1980ies and drilled between 1981 and 1983. Totally 16 drillholes were drilled during this period. The results are summarised in Sund- bergh & Niva (1981) and Lundmark (1982, 1983, 1984). The cores have only partly been assayed for copper and gold. Digital ground magnetic data is also available from the area (Fig. 13). No tonnage and grade calculations have been made but assays of 1.84 % Cu and 1.9 g/t Au over 2.0 m, and 2.28 % Cu and 3.0 g/t gold over 1.0 m were reported by Lundmark (1984). Ánájávrre Klubbuddsjön Fatjas sjön Vajkijaur Vájgájávrre Ö Ållojaure Hárrejávrre Jokkmokk NorrTjalmejaure Soarvásj Granite, Lina-type, c. 1.80 Ga old Metagreywacke, argillite, conglomerate, amphibolite (Norvijaur fm.) Granite, Jokkmokk-type, c. 1.80 Ga old ? Granitoid, Norvijaur type, c. 1.93 Ga old Granitoid, GSM-type, c. 1.87 Ga old Archaean gneisses Metadiabase, amphibolite (Muddus fm.) Cu-Au-Mo mineralization Granitoid, c. 1.89 Ga old Form line Gabbroid, c. 1.89 Ga old Deformation zone unspecified 5 km Felsic metavolcanic rock , c. 1.89 Ga old Fig. 11. Simplified geological map of the Jokkmokk area. The geology is modified from the digital database over the Norrbotten County available at the Geological Survey of Sweden. The Vaikijaur deposit is indicated. 16 P. WEIHED Vaikijaur Cu-Au-Mo deposit Cu Cu Mo Cu Cu 60 Mo Cu Cu Cu Mo Cu Cu 40 Mo Cu Cu Cu 65 Cu Mo Cu 80 Cu Cu Cu Cu Cu Cu Cu Mo Cu Lake Klubbuddsjön Foliation Porphyrite Granite, Jokkmokk-type Mo Pyrite dissemination Cu Irregular molybdenite dissemination Irregular chalcopyrite dissemination Magnetite dissemination Outcrop Chalcopyrite mineralization Drillhole 300 m Fig. 12. The geology of the Vaikijaur deposit (modified from Lundmark 1984). Regional geology The Vaikijaur area is situated totally within the Jokkmokk granite (Figs. 11 and 12), which is interpreted to belong to the c. 1.89 Ga old intrusive rocks in northern Sweden. No age determinations have been carried out in the area, but field relationships and the penetrative deformation support this interpretation. The Jokkmokk granite is generally greyish white, medium grained, and foliated and is mineralogically classified as granite s.s. to quartzmonzodiorite. The intrusion is elliptical with the approximate dimensions 10 x 5 km and is surrounded by other granites of similar age and supracrustal rocks, which are considered to be Svecofennian in age. Mineralization In Figure 12, the mineralised area within the Jokkmokk granite is shown (modified from Lundmark 1984). Based on outcrop appearance and information from drillcore, the Vaikijaur deposit displays a clear zoning from a central dissemination of dominantly pyrite through a thin shell of chalcopyrite rich Cu-mineralization which in turn is bordered by a characteristic magnetite dissemination. Molybdenum mineralization seems to be a more regional feature, but may constitute more distal parts in a concentrically zoned magmatic hydrothermal system. The mineralised area is beautifully displayed on the ground magnetic map (Fig. 13) where the concentric magnetic pattern is clearly visible. The Vaikijaur deposit is located in the northeastern part of the magnetic structure. According to Lundmark (1984), mineralization in outcrop is found south of the lake, which corresponds to the southern parts of the magnetic structure. It is thus plausible that the central parts of the hydrothermal system are beneath the lake and that Cu-mineralization occurs in the outer parts of the whole magnetic anomaly. In the case of Vaikijaur, as- A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 17 Fig. 13. Ground magnetic map of the Vaikijaur area. Note the sub-circular zonal magnetic pattern centred on the deposit. Local grid in metres. says indicate a good correlation between Cu and Au. The mineralization is dominated by veins and veinlets of sulphides, but with omnipresent weak disseminations. The main ore minerals are pyrite, pyrrhotite, and chalcopyrite. A few larger massive sulphide veins also occur. The style of mineralization is shown in Figure 14. Alteration associated with mineralization in the central zone of pyrite dissemination is sericitization and chloritization with 18 P. WEIHED some epidote. A potassic alteration with growth of K-feldspar is a general feature for the whole mineralised area. The microscopic appearance and style of mineralization can be seen in Figure 15. From these micrographs (Fig. 15) it is evident that the mineralization is associated with quartz-microcline-biotite alteration, epidote-biotite, and rare calcite in sulphide veinlets. Fig. 14. Photographs of drillcore specimens from the drillhole 83001. The white scale bar is approximately 35 mm long. Sample 83001/20 m – Typical Jokkmokk type granitoid in the Vaikijaur area. The rock is composed of glomeroporphyritic biotite-hornblende in a matrix of albite, microcline and quartz. Weakly porphyritic, Sample 83001/23.00 m – same as previous, but hornblende dominated and more microcline rich, Sample 83001/55.75 m – same as previous, but biotite dominates the mafic mineral phases. Thin sulphide veins with biotite and minor epidote and calcite, Sample 83001/63.30 m – Strong sulphide impregnation with a recrystallized matrix of albite and biotite, Sample 83001/68.70 m – weak foliation with microcline, albite and quartz as light minerals. Biotite aligned along grain shape foliation, Sample 83001/71.50 m – same as previous with biotite, epidote and quartz in sulphide veinlets, and Sample 83001/126.20 m – same as previous, but with accessory sericite and minor sulphides. Tallberg The best studied and documented porphyry style deposit in the Fennoscandian shield is the Tallberg deposit (cf. Weihed et al. 1987, Weihed & Schöberg 1991, Weihed 1993, Weihed & Fallick 1994), situated within the Jörn granitoid in the Skellefte district (map sheet 23J, square 4i–j). The deposit has been extensively drilled by Boliden Ltd and figures for tonnage and grade given by Weihed et al. (1992) are c. 44 Mt of 0.27 % Cu and 0.2 g/t Au (Weihed 1992). Substantially higher Au grade is found in shear zones that cut the mineralization. Below, a short review of results based on the papers referred to above is made. Regional geology The Skellefte district is somewhat loosely defined as a WNW trending, approximately 150 km by 50 km large (cf. Fig. 16), ore-bearing belt which is dominated by vol- canic rocks of Palaeoproterozoic age. It is generally regarded as a volcanic arc, which formed between a sedimentary basin to the south (Bothnian Basin) and a continental landmass to the north (volcanic rocks of the Arvidsjaur Group). Modern ideas favour some kind of destructive plate margin, either an island arc or a continental arc, and invoke a subduction towards the north. The Palaeoproterozoic intrusive rocks within and adjacent to the Skellefte district belongs to three main intrusive suites: 1) a syn-volcanic phase comprising granites to gabbros, 2) post-volcanic S-type granitoids, and 3) postvolcanic A/I-type granites to gabbros. The syn-volcanic intrusions are dominated by tonalites and granodiorites and have previously been considered as coeval and comagmatic with the Svecofennian volcanic rocks which host the massive sulphide ores (cf. Weihed et al. 1992), i.e. they fall in the age range 1890–1880 Ma. Within the Skellefte district, several age determinations have been carried out on the Jörn granitoid complex, which belongs to the syn- A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 19 Fig 15. Micrographs of some of the specimens shown in Figure 14. A) Strong sulphide impregnation with a recrystallized matrix of albite, biotite and minor quartz and microcline. Crossed polars. B) same as A in reflected light. C) weak foliation with microcline, albite and quartz as light minerals. Biotite aligned along grain shape foliation. Crossed polars. D) same as C in reflected light. E) weak foliation with microcline, albite and quartz as light minerals. Biotite aligned along grain shape foliation with accessory sericite and minor sulphides. Crossed polars. F) same as E in reflected light. volcanic suite. Wilson et al. (1987) dated zircons from three intrusive phases of this massif at 1888+20 –14 Ma (oldest +48 +18 outer zone GI), 1874 –6 Ma (GII), and 1873 –14 Ma (GIII). Weihed and Schöberg (1991) dated one of the porphyries associated with the Tallberg deposit at 1886 +15 –9 Ma. Furthermore, a monzonite and a gabbro in the Gallejaur intrusion (Fig. 16) have been dated at 1873±10 Ma (Skiöld 1988) and 1876±4 Ma (Skiöld et al. 1993), respectively. Post-volcanic S-type granitoids are referred to as Skellefte– Härnö-type granites south and east of the Skellefte dis20 P. WEIHED trict. These granites are minimum melt products often associated with pegmatites and aplites in areas of strong migmatitization. The Skellefte–Härnö-type has only been dated in two places: near Örnsköldsvik, approximately 200 km south of the Skellefte district (Claesson & Lundqvist 1995), yielding an age of 1822±5 Ma (monazite) and at Skellefteå (Weihed et al. in prep) yielding an age of 1798±4 Ma (titanite). Post-volcanic A/I-type granitoids are generally referred to as Revsund-type granites. These coarse, feldspar-phyric intrusive rocks occupy vast areas 165000 J 170000 K 725 000 725000 I Adak 2) Glommersträsk Malå Rakkejaur Holmtjärn 23 23 Näsliden Rävlidenmyran Kimheden Rävliden Kristineberg 1) Åkerberg Jörn Maurliden Norrliden Svansele Udden Kedträsk Petiknäs S Norsjö Petiknäs N Kankberg Renström Björkdal V Åkulla 720000 720000 Boliden Långsele Långdal I 165000 Post-volcanic granitoids of A- and I-type (Revsund type), c. 1.80–1.78 Ga Post-volcanic granitoids of S-type (Skellefte type), c. 1.82–1.80 Ga Gabbro and diorite Ultramafic intrusions Synvolcanic granitoids of I-type (Jörn III granit, Gallejaur monzonite), c. 1.87–1.85 Ga Synvolcanic granitoids of I-type (Jörn II granodiorite) c. 1.87 Ga Synvolcanic granitoids of I-type (Jörn I tonalite and ndivided) c. 1.89 Ga J 170000 Conglomerates and sandstones, polymict (Vargfors and Ledfat Groups) c. 1.87–1.85 Ga Basalt–andesite and minor dacite lavas and sills (Vargfors Group), c. 1.88–1.86 Ga Mudstone, black shales, sandstone and turbidites, (Bothnian Group, Vargfors Group, Skellefte Group)c. >1.95–1.85 Ga Subaerial to shallow water basalt–andesite (Arvidsjaur Group), c. 1.88–1.87 Ga Subaerial to shallow water rhyolite, dacite and minor andesite (Arvidsjaur Group), c. 1.88–1.87 Ga Basalt-andesite and minor dacite lavas and sills, mainly submarine (Skellefte Group), c. 1.89–1.87 Ga Rhyolite, dacite and minor andesite, mainly submarine (Skellefte Gro p), c. 1.89–1.87 Ga K Major VHMS deposits Major gold deposits Antiform with plunge Synform with plunge Major faults and shear zones 1) Tallberg deposit 2) Granberg deposits Fig. 16. Geology of the Skellefte district (modified from Weihed et al. 1992). Both the Tallberg and the Granberg deposits are indicated. in central Sweden and around the Skellefte district. Geochemically they display a monzonitic trend and a majority of the intrusions has a granitic to monzogranitic composition. Subordinate, often mingled or mixed, more mafic intrusions are also present. The Revsund granitoids intruded after the main phases of deformation and postdates the regional metamorphism. However, many ductile shear zones cut these granitoids indicating that greenschist facies deformation occurred at least locally in these rocks. Several age determinations have been carried out on these rocks yielding ages from 1.80 to 1.78 Ga (Patchett et al. 1987, Skiöld 1988, Claesson & Lundqvist 1995, Geological Survey of Sweden, unpublished results). The lowermost part of the supracrustal pile in the Skellefte district consists mainly of felsic volcanic rocks, which are included in the Skellefte Group (Allen et al. 1996). Ages of the Skellefte Group all fall within the range 1890 to 1880 Ma (Billström & Weihed 1996). The supracrustal rocks of the Vargfors Group overlie the volcanic rocks of the Skellefte Group with complex and variable contacts. The close spatial and chemical relationships be- tween the Vargfors mafic volcanic rocks and the Gallejaur intrusive rocks indicate that these rocks are comagmatic and genetically linked. Consequently, the published ages of 1873±10 Ma and 1876±4 Ma for the Gallejaur intrusive rocks (Skiöld et al. 1993) have been interpreted as indicating the age of the Vargfors Group. This was also confirmed by Billström & Weihed (1996) who dated an ignimbrite within the Vargfors Group at 1875±4 Ma. To the north of the Skellefte district, subaerial volcanic rocks of the Arvidsjaur Group have been considered to overlie the subaqueous volcanic rocks in the Skellefte Group. The Arvidsjaur volcanic rocks have been dated by Skiöld et al. (1993) and ages of 1878±2 Ma and 1876±3 Ma have been obtained. The fact that only the upper part of the Vargfors Group contains clasts of rocks of the Arvidsjaur Group indicates that these groups are most probably coeval. Mineralization The Tallberg porphyry deposit is situated in the outer and oldest GI phase of the Jörn granitoid and it is associated with high-level quartz-feldspar porphyritic dykes and in- A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 21 trusions (Fig. 17). The age of these porphyritic intrusions is 1886 +15 –12 Ma (Weihed & Schöberg 1991) which is, within errors, the same as the GI host rock and the age of the host rocks to most massive sulphide deposits in the district. The deposit is of a low grade (0.3 % Cu) and high tonnage (>50 Mt), disseminated type. Typical alteration zoning exists with a proximal zone of phyllic alteration with quartz, sericite, and pyrite grading out into a distal propylitic alteration with abundant chlorite. Ore miner- Mafic dykes als occur both disseminated and in a sulphide-quartz vein stockwork which is most intense in the central part of the deposit. Metals are also zoned with Cu concentrated to the central parts while Zn and Pb are concentrated to the marginal parts. Magnetite appears to be an early phase of the alteration system. Gold grades are low (<1 g/t), but in strongly sheared sericite alteration zones cutting the deposit the gold grades can reach >10 g/t. Stable isotope data and fluid inclusion studies indicate that the sulphides pre- Jörn GI Tonalite Älgliden ultramafic dyke Porphyry type deposit Granite porphyry Au-mineralizations 9 000 N 200 m 8 000 N modified from Weihed (1992) 11 000 W Fig. 17. Geology of the Tallberg deposit (modified from Weihed 1992). 22 P. WEIHED 10 000 W cipitated when magmatic fluids mixed with sea water at elevated temperatures of 450 to 500° C (Weihed et al. 1992). Other deposits Apart from the deposits described above, several minor and less well known occurrences of Cu±Au±Fe-oxide exist in northern Sweden which are intrusion hosted or show characteristics which indicate a possible magmatic hydrothermal origin. A few are briefly described below. Lulepotten and Sadenåive Although the deposits Lulepotten and Sadenåive are not strictly intrusion hosted, they are briefly described here. Both deposits are hosted by a sequence of felsic to mafic volcanic rocks of a probable, c. 1.88 Ga, Svecofennian age. Padget (1966) described the geology of the area and also briefly other minor mineralizations. The Lulepotten deposit is situated on the map sheet 25I square 6b and was drilled between 1960 and 1971 (Fig. 18). Altogether 77 drillholes with a total lenght of 17 500 m were drilled. Both the Lulepotten and Sadenåive areas are covered by groundmagnetic and IP measurements, which are not in digital format and therefore not shown. The deposit is estimated at 5.1 Mt with c. 0.73 % Cu and 0.25 g/t Au. Mineralization is disseminated and grades into non-mineralised host rocks. The supracrustal rocks are strongly foliated and the mineralization follows the schistosity. The main part of the mineralization is hosted by mafic porphyritic, volcanic rocks interpreted as lavas, but it also occurs in felsic volcanic rocks. A granitic rock classified as Lina type (c. 1.80 Ga), intrusive into the supracrustal rocks, is situated immediately west of the deposit and is also in some areas weakly mineralised (Figs. 18 and 19). The style of mineralization in the granite is vein type. Padget (1966) describes a biotite gneiss and diorite in close contact with the ore, but it is not clear whether this is a deformed part of the main granite or not. Mineralization is composed of chalcopyrite as main ore mineral with abundant bornite, pyrite, and chalcocite. Both Sandahl (1973) and Padget (1966) mention Fe-oxides as a common part of the mineralization. Sandahl (1973) calculated the Fe-oxides to 43.5 % of the total opaque phase. Magnetite dominates over hematite. Padget (1966) describes a K-metasomatism as a prominent feature and although he attributed this to ”granitization” he considers the granite as responsible for the alkali enrichment and the growth of microcline and biotite in what he refers to as biotite gneiss. Scapolitization is a common regional alteration product in mafic rocks throughout the area. The smaller Sadenåive deposit is located c. 1 km east of the Lulepotten deposit in the central part of the supra- crustal belt (Fig. 19). Ten drillholes with a total length of 1 730 m were drilled in 1978. Only Cu was analysed and no report on the gold content is available. The Cu grade was reported by Sandahl (1980) at 0.03–0.2 % without any tonnage figures given. The geology at Sadenåive is dominated by intermediate to felsic lavas and tuffs, which are intruded by numerous mafic dykes parallel to the regional NNE striking foliation (Sandahl 1980). The mineralization is disseminated in the intermediate porphyritic lava, while ”fracture fillings” are more common in the felsic tuff. The main ore mineral is chalcopyrite with subordinate bornite. Minor pyrite also occurs. The ore zones are less than 2 m wide and 80–140 m in length and known to 170–200 m depth. Pervasive magnetite dissemination is reported to occur in all volcanic rocks and a zone of hematite dissemination occurs c. 80 m to the west of the sulphide mineralization. The mineralization is parallel or sub-parallel to the regional strong foliation in NNE. Sanddahl reports ”pinch and swell” structures and minor folds which indicate that the whole unit is situated within one of the major crustal scale shear zones with a NNE to N–S strike which exist in northern Sweden. A relatively weak sericite and chlorite alteration associated with the mineralization is reported by Sanddahl (1980). Sjiska area In the 1980ies, the exploration division of LKAB explored an area situated c. 20 km SW of Kiruna on the map sheet 29J SW that they named the Sjiska granite area. After regional geophysical and geochemical surveys together with geological mapping and boulder tracing, an area situated at the Sierkavaare hill was drilled (Hedin 1984a, 1984b, 1985a, 1985b, 1986a, 1986b, Hedin et al. 1988). The mineralization found was named Sierkavaare or Pikkujärvi. During the exploration campaign, 37 drillholes were drilled on the deposit with a total length of c. 7 200 m. The tonnage was calculated at 11.4 Mt with 0.43 % Cu, alternatively 0.5 Mt with 1.19 % Cu, with only trace amounts of Au. The Pikkujärvi deposit is situated at the NW border of a monzonitic intrusion, which is interpreted as belonging to the Perthite-Monzonite suite, and thus have an age of c. 1.88–1.87 Ga (Fig. 20 and 21). No age determinations have, however, been performed on this intrusion. The monzonite is greyish red to red, unfoliated and variably magnetic. The mineralised area is dominated by volcanic rocks belonging to the coeval Kiruna porphyry Group. While intermediate to mafic rocks dominate regionally, the mineralised area close to the monzonite contact is dominated by intermediate to felsic volcanic rocks. The central parts are dominated by a quartz-phyric vol- A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 23 Båtsa Båhttsá V Rebraur Tjålmak Ö Rebraur Kakel Gáhkal Lullebådne Lina type granite, c. 1.80 Ga old Mafic volcanic rock, Arvidsjaur type, c. 1.75 Ga old Felsic volcanic rock, Arvidsjaur type, c. 1.75 Ga old GSM type intrusive rock, Arvidsjaur type, c. 1.88 Ga old Gublijaure Guoblajávrre Cu-Au mineralization Form line Deformation zone unspecified 5 km Haparanda type intrusive rock, c. 1.89 Ga Paragneiss, c. 1.89 Ga old Fig. 18. Simplified geological map of the Stensund area. The geology is modified from the digital database over the Norrbotten County available at the Geological Survey of Sweden. The Lulepotten and Sadenåive deposits are indicated. canic rock which, according to Hedin et al. (1988), is isochemical with the monzonite. This indicates a close genetic relationship between the two. The porphyry in the mineralised area is chemically a rhyolite to trachyte, greyish red to red with both white and red feldspar phenocrysts. 24 P. WEIHED In the porphyry, lamphrophyric dykes are interpreted as ring dykes associated with a cauldron and a subvolcanic complex. Some of the volcanic rocks are interpreted as lavas whereas others are of ignimbritic origin. Many of the porphyritic volcanic rocks are amygdaloidal with magnet- Granite 80 Diorite 85 Felsic volcanic rock 70 Foliation Bedding Lineation Felsic volcanic rock Fault Laminated felsic volcanic rock Way up Felsic volcanic breccia/ conglomerate Drillhole Quartz-feldspar porphyritic rhyolite Outcrop 75 80 70 85 Feldspar porphyritic dacite 70 Mafic volcanic rock 70 Laminated mafic volcanic rock Mafic volcanic breccia/ conglomerate Mafic lava, feldspar porphyritic Mafic lava, trachytic Mafic lava amygdaloidal Cu-deposit 75 1000 m Sadenåive Lulepotten 85 Lake Lullebådne 85 Fig. 19. Geological map of the Lulepotten and Sadenåive areas (modified from Sandahl 1980). A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 25 Siergajávri Kaitums domänreservat Nilakkajávri Vuotnajávri Kamasjaure Lina-type granites, c. 1.80 Ga old Conglomerate, Kiruna porphyry Group, c. 1.88 Ga old GSM-type granitoid rock, c. 1.88 Ga old Kiruna porphyry Group, undivided, c. 1.88 Ga old GSM-type gabbro-diorite, c. 1.88 Ga old Paragneiss, undivided Quartz porphyry, Kiruna porphyry Group, c. 1.88 Ga old Felsic volcanic rock, Porphyrite Group Intermediate Syenite porphyry, Kiruna porphyry Group, c. 1.88 Ga old Pikkujärvi Cu-deposit Mafic volcanic rock, Kiruna porphyry Group, c. 1.88 Ga old Form line Marble, Kiruna porphyry Group, c. 1.88 Ga old Deformation zone, unspecified 5 km Fig. 20. Simplified geological map of the Sjisjka area. The geology is modified from the digital database over the Norrbotten County available at the Geological Survey of Sweden. The Pikkujärvi deposit is indicated. 26 P. WEIHED 6000 N/4000 W 6000 N/8000 W 1000 m 3600 N/8000 W 3600 N/4000 W GSM-type granitoid rock, c. 1.88 Ga old Dark syenitic porphyry (Kiruna porphyry group) GSM-type gabbro-diorite Dark syenite-andesite porphyry (Kiruna porphyry group) Quartz-phyric felsic volcanic rocks (Kiruna porphyry group) Andesite-basalt (Kiruna porphyry group) Amygdaloidal felsic volcanic rock (Kiruna porphyry group) Metadiabase (Kiruna greenstone group) Cu-ore Fig. 21. Geology of the Pikkujärvi Cu-deposit (modified from Hedin 1984). ite as a typical constituent of the amygdales. According to Hedin et al. (1988), hydrothermal breccias are common in the mineralised area. The mineralization occurs as a dissemination and in thin sulphide veins. Chalcopyrite and pyrite are common with subordinate bornite. The alteration is not well described but a strong potassic alteration seems to be regional based on high K2O values of all reported chemical analyses from the area. Tourmaline, epidote, possible secondary biotite, and scapolite are typical alteration assemblages. The border zone surrounding the monzonite is highly magnetic and commonly contains quartz-bearing porphyries, which are similar to the central monzonite as well as the lamphrophyres. This led Hedin et al. (1988) to the conclusion that the entire Sjieska monzonite may be a subvolcanic complex with high-level intrusions and ring dykes associated with mineralization in the contact between the intrusion and the country rocks. The fact that mineralization is reported from other places within the monzonite and in other parts of the contact between the monzonite the the country rocks supports this idea. This also clearly suggests a genetic relationship between the monzonite (and the subvolcanic porphyries) and Cu±Au±Fe-oxide mineralization in the Sjieska granite area. Viterliden Immediately NE of the Kristineberg VMS-deposit in the eastern part of the Skellefte district, the felsic volcanic host sequence to the ore is intruded by a high level tonalitic intrusion (Fig. 22). This intrusion is part of the larger Kristineberg intrusion, which has been dated at 1907±13 Ma (Bergström et al. 1999). The Kristineberg intrusion is considered as comagmatic with the host sequence to the VMS ore and is furthermore geochemically and mineralogically very similar to the main Jörn batholith which hosts the Tallberg porphyry style deposit (see above). The high level intrusion NE of Kristineberg has been drilled both by SGU and Boliden AB. Logging of one core from this intrusion indicates weak pyrite-chalcopyrite minerali- A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 27 1625000 1645000 7225000 Strong hydrothermal alteration Granite (Revsund–Adak Suite) Gabbro–quartzdiorite, (Revsund–Adak suite) Sedimentary rocks (Malå Group) Basalt–andesite, lava or sill / dyke (Skellefte Group) Rhyolite–dacite, lava or subvolcanic intrusion, (Skellefte Group) Dioritoid Rhyolite–dacite (Skellefte Group) Basaltic komatiite, sill (Malå Group) Granite–tonalite Ultramafic rock (Malå Group) Fault, shear zone Dacite, subvolcanic intrusion left (Malå Group) Andesite–basalt, plagioclase porphyritic (Malå Group, Tjamstan Formation) 5 km Viterliden mineralization VMS deposit Fig. 22. Geology of the Kristineberg area (modified from Bergström et al. 1999). zation associated with quartz veins and strong propylitic alteration. Some sections of the core also indicate K-feldspar alteration associated with this weak mineralization 28 P. WEIHED (see Fig. 23 samples 101.5 m and 110.3 m). The logged core has not been analysed and the grade of Cu and Au is therefore not known from this mineralization. Fig. 23. Photographs of drillcore specimens from the drillhole 78002. The white scale bar is approximately 35 mm long. Sample 23.10 m – Typical tonalitic medium-grained intrusive rock with minor sulphide disseminations and hornblende dominating over biotite as dark minerals, Sample 48.20 m – same as previous but with characteristic quartz-sulphide veins with chloritic rims, Sample 61.30 m – foliated biotite, quartz, plagioclase, albite rock with disseminated sulphides. Possibly early dyke, Sample 101.50 m – microcline rich rock with albite phenocrysts. Glomeroporphyritic biotite and rare sulphides, and Sample 110.30 m – same as previous but with a strong foliation. The last two rock types have an unclear relationship with mineralization in the Viterliden area. Sarvasåive area A weak Cu-mineralization in outcrops was described by Sjöstrand (1982) from the Sarvasåive area on map sheet 24K, square 8a (see Fig. 24). This mineralization was so weak that it did not render continued exploration and no grades have been reported, although a few analysed outcrop specimens contained between 0.3 to 0.8 % Cu. The host rock is a reddish grey, non-foliated, medium grained granite which, according to Sjöstrand (1982), grades into red, felsic volcanic rocks to the north. This implies a close relationship between granites and volcanic rocks, which in turn indicates that the granite belongs to the c. 1875 Ma Perthite-Monzonite suite. Mineralization consists of weak dissemination of chalcopyrite with minor fluorite, scheelite, molybdenite, and arsenopyrite. The Laver Cu-deposit is situated c. 5 km north of the Sarvasåive mineralization. This deposit was mined between 1938 and 1946 and is the only mined Cu-ore sit- uated in southern Norrbotten. The deposit consists of both massive to semi-massive ore at the contact between felsic volcanic rocks and younger fine-grained sedimentary rocks, and disseminated sulphides within the volcanic rocks. The genesis and origin of the deposit remains open since no modern study of the deposit has been made. It is however, possible that the mineralization is epigenetic in character and a structural control or magmatic relationship cannot be excluded. Granberg A mineralization identical to Tallberg exists in the northern part of the Jörn batholith (Fig. 16). This mineralization shows all characteristics described for the Tallberg deposit above, but no published data exist on the deposit. The deposit was drilled during the 1970ies by Boliden AB who also evaluated the area in the late 1980ies and early 1990ies. No information is available from this work. A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 29 Pite älve n Ljusträsket Manjärv Laver Stor-LaverLill-Laver Städdje jaure St Idträsket Sarvasåive Vis tå n Vuotnersjön Laukersjön Finn träsket Brännträsket Ö Kikkejaure Bänkerträsket 228 Lyckoträsket Granite, Lina type, c. 1.80 Ga old Mafic volcanic rock, Arvidsjaur type, c. 1.87 Ga old Granite, Storliden type, c. 1.80 Ga old (?) Granodiorite, Haparanda type, c. 1.89 Ga old Granite, Edefors type, c. 1.80 Ga old Metasediment, biotite gneiss, c. 1.89 Ga old Syenite, monzonite, GSM type, c. 1.87 Ga old Cu-mineralization Gabbro, diorite, GSM type, c. 1.87 Ga old Form line Felsic volcanic rock, Arvidsjaur type, c. 1.87 Ga old Deformation zone unspecified 10 km Fig. 24. Simplified geological map of the Laver and Sarvasåive areas. The geology is modified from the digital database over the Norrbotten County available at the Geological Survey of Sweden. The Laver mine and the Sarvasåive prospect are indicated. 30 P. WEIHED Conclusions Most deposits described above show a strong spatial relationship with intrusive rocks of early Proterozoic age. They also occur in various tectonic settings throughout northernmost Sweden. As this is a first attempt to highlight this style of mineralization, no thorough, genetic model or classification has been proposed for these deposits. Since several of the deposits are of definite economic interest and deserves further attention, it is proposed here that they should be classified as a group of deposits called intrusive hosted Cu±Au±Fe-oxide deposits as a nongenetic name. It is still poorly understood how some of these deposits genetically relate to their host rocks, whereas others, like Tallberg, have been well documented and described as a porphyry Cu-Au style mineralization in genetic terms. In deposits like Iekelvare where the mineralization occurs in deformed and metamorphosed host rocks, the direct link to the host intrusive and hence to evolved magmatic hydrothermal style mineralization still needs to be proved. In deposits like Gråberget, where the mineralization is associated with late to postorogenic granites of Sorsele-Revsund type, it is more clearly a magmatic-hydrothermal genesis for the mineralization. In the case of Vaikijaur, the age of the host intrusive is not known, but the subcircular shape of the hydrothermal alteration system, seen in the ground magnetic map from the mineralised area which is situated totally within the Jokkmokk granite, strongly suggests that it was a magmatic, intrusive-centred hydrothermal system that gave rise to the mineralization. Although the mineralization is situated immediately outside the main intrusion in Sjieska (typical of many porphyry style mineralizations), several minor mineralised systems occur within the intrusion which suggests a possible magmatic hydrothermal origin for this mineralisation type. In the case of Lulepotten and Sadenåive, the magmatic connection is less clear although the area is characterised by porphyritic volcanic rocks which have been interpreted as lavas. However, these could be dykes, sills, and other subvolcanic intrusions that may have introduced both heat, fluids, and possibly metals to the volcanic pile. The weak mineralization in the granite at Lulepotten at least rules out a syngenetic origin for these deposits. The described deposits are hosted by intrusive rocks that in age span the entire Svecofennian orogeny in this part of Sweden. The Tallberg mineralization hosted by calc-alkaline tonalites has been dated at 1886 +15 –9 Ma (Weihed & Schöberg 1991) and is thus coeval with the VMS-deposits in the Skellefte district. The Boliden deposit in the Skellefte district has recently been suggested to be an epithermal-VMS deposit (Bergman Weihed et al. 1996) and thus the temporal link between major mag- matic hydrothermal porphyry style mineralization, epithermal and VMS deposits is possible in the Skellefte district. The deposits in Norrbotten, Iekelvare and Vaikijaur, are both characterised by early magnetite (as is Tallberg and Gråberget where hematite after magnetite is reported) which indicates a possible resemblance with Cu-AuFe-oxide style mineralization and also a possible link with Kiruna type deposits. The mineralization at Gråberget, which is associated with I- to A-type, c. 1.80 Ga granitic, sensu stricto, magmatism highlights this generation of granites as prospective for magmatic Cu and possibly Au. A common feature to many of these deposits is the association with high level, subvolcanic and porphyritic phases of the magmatism. This indicates that the mineralising processes are attributed to crystallising magmas and late stage fluids evolving from oxidised magmas. The mineralizing style is in most cases disseminations and veins, which are associated with potassic, sodic, and silicic alteration. References Allen, R.L., Weihed, P. & Svenson, S-Å., 1996: Setting of ZnCu-Au-Ag massive sulfide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc, Skellefte district, Sweden. Economic Geology 91, 1022–1053. Bergman Weihed, J., Bergström, U., Billström, K. & Weihed, P., 1996: Geology and tectonic evolution of the Paleoproterozoic Boliden Au-Cu-As deposit, Skellefte district, northern Sweden. Economic Geology 91, 1073–1097. Bergström, U. & Sträng, T., 2000: Berggrundskartorna 23I Malå. Sveriges geologiska undersökning Ai 114–117. Bergström, U., Billström, K. & Sträng, T., 1999: Age of the Kristineberg Pluton, western Skellefte District, northern Sweden. Sveriges geologiska undersökning C 831, 7–19. Billström, K. & Weihed, P., 1996: Age and provenance of host rocks and ores of the Paleoproterozoic Skellefte District, northern Sweden. Economic Geology 91, 1054–1072. Claesson, L.-Å., 1979: Gråberget kopparmineralisering. Rapport över prospekteringsarbeten utförda för NSG under åren 1974-1977. Sveriges geologiska undersökning BRAP 79001. (In Swedish.) Claesson, S. & Lundqvist, T., 1995: Origins and ages of Proterozoic granitoids in the Bothnian Basin, central Sweden; isotopic and geochemical constraints. Lithos 36, 115–140. Einarsson, Ö., 1985: Iekelvare – Prospekteringsarbeten utförda under 1984. SGAB PRAP 85035. (In Swedish). Gavelin, S., 1955. Beskrivning till berggrundskarta över Västerbottens län. Urbergsområdet inom Västerbottens län. Sveriges geologiska undersökning Ca 37, 7–99. Hedin, J.-O., 1984a: Sjisjka granitområde 1983. Unpublished exploration report LKAB K-84-3. (In Swedish.) Hedin, J.-O., 1984b: Sjisjka granitområde 840101-841231. Unpublished exploration report LKAB K-84-48. (In Swedish.) Hedin, J.-O., 1985a: Sierkavare – en kopparmineralisering på kartbladet 29J Kiruna SO. Unpublished exploration report LKAB K-85-22. (In Swedish.) A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN 31 Hedin, J.-O., 1985b: Preliminär geologisk modell över Sijsjka granitoidkomplex. Unpublished exploration report LKAB K-85-25. (In Swedish.) Hedin, J.-O., 1986a: Sjisjka granitområde 850101-851231. Unpublished exploration report LKAB K-86-4. (In Swedish.). Hedin, J.-O., 1986b: Sijsjka granitområde. Unpublished exploration report LKAB K-86-48. (In Swedish.) Hedin, J.-O., Hansson, K.-E. & Holme, K., 1988: Sjisjka granitområde – Slutrapport stödetapp III. Unpublished exploration report LKAB K-88-01. (In Swedish.) Lundberg, B., 1980: Aspects of the geology of the Skellefte field, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar 102, 156–166. Lundmark, C., 1982: Vaikijaur – Resultat av borrningsarbeten 1981–1982. Unpublished exploration report SGAB PRAP 82064. (In Swedish.) Lundmark, C., 1983: Vaikijaur – Resultat av borrningsarbeten okt-dec 1982. Unpublished exploration report SGAB PRAP 83048. (In Swedish.) Lundmark, C., 1984: Vaikijaur – Resultat av borrning 1983. Unpublished exploration report SGAB PRAP 84041. (In Swedish.) Lundmark, C. & Hålenius, U., 1984: Iekelvare – Guldanalysering. SGAB PRAP 84040. (In Swedish.) Lundqvist, T., Bøe, R., Kousa, J., Lukkarinen, H., Lutro, O., Roberts, D., Solli, A., Stephens, M., & Weihed, P., 1996b: Bedrock map of Central Fennoscandia. Scale 1:1 000 000. Geological Surveys of Finland (Espoo), Norway (Trondheim) and Sweden (Uppsala). Öhlander, B., 1986: Proterozoic mineralizations associated with granitoids in northern Sweden. Sveriges geologiska undersökning Ca 65, 39 pp. Öhlander, B. & Markkula, H., 1994: Alteration associated with gold-bearing quartz veins at Middagsberget, northern Sweden. Mineralium Deposita 29, 120–127. Öhlander, B., Skiöld, T., Elming, S-Å., BABEL Working Group, Claesson, S. & Nisca, D.H., 1993: Delineation and character of the Archaean-Proterozoic boundary in northern Sweden. Precambrian Research 64, 67–84. Padget, P., 1966: The geology and mineralization of the Radnejaure area, Norrbotten county, Sweden. Sveriges geologiska undersökning C 609, 60 pp. Rickard, D., (ed.) 1986: The Skellefte Field. Sveriges geologiska undersökning Ca 62, 52 pp. Rickard, D.T. & Zweifel, H., 1975: Genesis of Precambrian sulfide ores, Skellefte District, Sweden. Economic Geology 70, 255–274. Sandahl. K.-A., 1973: Lulepotten kopparfyndighet. Rapport rörande resultaten av SGU:s undersökning under åren 1960-1971. Unpublished exploration report BRAP 585. (In Swedish.) 32 P. WEIHED Sandahl, K.-A., 1980: Projekt Sadenåive. Unpublished exploration report. Sveriges geologiska undersökning 1980-01-23. (In Swedish.) Sjöstrand, T., 1982: Sarvasåive. Unpublished exploration report. SGAB BRAP 82034. (In Swedish.) Skiöld, T., 1988: Implications of new U-Pb zircon chronology to early proterozoic crustal accretion in northern Sweden. Precambrian Research 38, 147–164. Skiöld, T., Öhlander, B., Markkula, H., Widenfalk, L. & Claesson, L.-Å., 1993: Chronology of Proterozoic orogenic processes at the Archaean continental margin in northern Sweden. Precambrian Research 64, 225–238. Stephens, M.B., Wahlgren, C.-H. & Weihed, P., 1994: Bedrock map of Sweden. Scale 1: 3 000 000. Sveriges geologiska undersökning Ba 52. Sundbergh, S. & Niva, B., 1981: Vaikijaur. Unpublished exploration report. Sveriges geologiska undersökning BRAP 81006. (In Swedish.) Sundbergh, S., Persson, G. & Niva, B., 1980: Kopparmineraliseringen vid Iekelvare. Unpublished exploration report. Sveriges geologiska undersökning 1980-02-25. (In Swedish.) Weihed, P., 1992: Lithogeochemistry, metal- and alteration zoning in the Proterozoic Tallberg porphyry type deposit northern Sweden. Journal of Geochemical Exploration 42, 301–325. Weihed, P. & Schöberg, H., 1991: Timing of porphyry type mineralizations in the Skellefte District, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar 113, 289–294. Weihed, P. & Fallick, A., 1994: Stable isotope study of the Palaeoproterozoic Tallberg porphyry-type deposit, northern Sweden. Mineralium Deposita 29, 128–138. Weihed, P., Isaksson, I. & Svenson, S-Å., 1987: The Tallberg porphyry copper deposit in northern Sweden: a preliminary report. Geologiska Föreningens i Stockholm Förhandlingar 109, 47–53. Weihed, P., Bergman, J. & Bergström, U., 1992: Metallogeny and tectonic evolution of the early Proterozoic Skellefte District, northern Sweden. Precambrian Research 58, 143–167. Welin, E., 1987: The Depositional evolution of the Svecofennian Supracrustal Sequence in Finland and Sweden. Precambrian Research 35, 95–113. Wilson, M.R., Claesson, L-Å., Sehlstedt, S., Smellie, J.A.T., Aftalion, M., Hamilton, P.J. & Fallick, A.E., 1987: Jörn: An early Proterozoic intrusive complex in a volcanic arc environment. Precambrian Research 36, 201–225. Swedish layered intrusions anomalous in PGE-Au Birger Filén Filén, B,. 2001: Swedish layered intrusions anomalous in PGE-Au. In Weihed, P. (ed.): Economic geology research. Vol. 1, 1999–2000. Uppsala 2001. Sveriges geologiska undersökning C 833, pp. 33–45. ISBN 91-7158-665-2. A Platinum Group Element (PGE)-Au exploration programme was carried out in Sweden between 1985 and 1990. During this period a large number of cumulus textured mafic–ultramafic layered intrusions were identified. Ten percent of these intrusions have so far proved anomalous in PGE´s. This paper provides descriptions of the known targets for PGE-Au exploration in Sweden. It gives a summary and history of the exploration works. It also shows the importance of studying a mafic intrusion with respect to its emplacement, igneous stratigraphy and possible ore forming processes. A thorough investigation is essential in exploring mafic–ultramafic layered intrusions potential as the host rock for PGE-Au, Ni-Cu, titanium, and vanadium ores. Luleå 3 4 5 Caledonides 6 Phanerozoic sedimentary rocks Proterozoic rocks Archaean rocks 7 Key Words: PGE, gold, chromium, titanium, vanadium, layering, layered intrusion, mafic, ultramafic, cumulate. Birger Filén, Geological Survey of Sweden, Mineral Resources Information Office, Skolgatan 4, SE-930 70 Malå, Sweden. E-mail: [email protected] Layered mafic intrusions Stockholm Göteborg Introduction Platinum Group Elements, PGE, have never been primarily mined in Sweden. Small amounts have, however, been produced from anode slimes in Boliden’s Rönnskär plant. Most of the PGE’s produced nowadays come from scrap, either domestic or imported. A PGE-exploration program was carried out in Sweden between 1984 and 1990 at the request of the State Mining Property Commission (NSG). The contractor for the work was Swedish Geological Co (SGAB). Of some 80 proved layered intrusions eight showed anomalous PGE and/or gold values. If an intrusion was found to exhibit prominent layering, a sampling program was carried out. The criteria for a proper sampling were the presence 1 2 0 100 1 Kukkola 2 Notträsk 3 Näsberg 4 Hoting 5 Kläppsjö 6 Bottenbäcken 7 Flinten 200 km Fig. 1. Mafic intrusions anomalous in PGE and Au in Sweden discussed in this review. of ultramafic or leucocratic layers or cumulates with or without sulphides. Both boulders and outcrops were sampled. Six layered intrusions (Fig. 1) with anomalous precious metal tenors will be described below. Bottenbäcken (Storsjö Kapell) although no layered intrusion, has been added because of its anomalous PGE-Au values. SWEDISH LAYERED INTRUSIONS ANOMALOUS IN PGE-AU 33 Classification of Swedish PGE-anomalous layered intrusions Based on the age of the mafic-ultramafic host intrusions, the PGE-anomalous deposits can be subdivided into two groups: 1) Deposits in Early Proterozoic layered mafic intrusions (2440 Ma), emplaced between the Archean basement and overlying supracrustal rocks, and 2) Svecofennian synorogenic deposits, hosted by mafic–ultramafic intrusions, emplaced during the main stage of the orogeny (1900–1860 Ma) within highly metamorphosed mica gneisses. Kukkola (Location: Mapsheet 25N, x7338750 y1877000 ) Exploration history The 25 km long hookshaped Kukkola intrusion (Fig. 2) was mainly studied during an intermittent chromium exploration campaign between 1981 and 1984. The work started with hints from Finnish geologists concerning the similarity in the aeromagnetic patterns of the newly dis- covered Tornio layered intrusion and the patterns on the Swedish side. The Finnish geologists also claimed to have found cubic metre big chromitite boulders close to the Swedish–Finnish border. Exploration works soon started and included boulder tracing, geological mapping, geochemical till sampling, ground geophysics, and altogether 4676 m diamond drillings in profiles (Lundmark 1984). Geology The Kukkola intrusion is the westernmost part of the Early Proterozoic mafic-ultramafic layered complex, which stretches through Finland into Russia. The intrusions were emplaced at 2440 Ma, shortly after the cratonization of the Archaean crust (Alapieti & Lahtinen 1989). Smallscale pilot mining for platinum group elements has been performed at Kirakkajuppura NE of Kemi. Beside their PGE-Au potential, these intrusions have had and still have great economic significance because of the chromium mining at Kemi and past mining of vanadium and titanium at Mustavaara. 1875 1850 Late orogenic granite, 1.75–1.8 Ga ed Sw Early orogenic diorite–granodiorite, 1.85–1.9 Ga en Phyllite Pelite, basalt, dolomite, quartzite 7350 Greenstone d lan Fin Layered mafic intrusion, 2.44 Ga Granitic gneiss, 2.67 Ga Kukkola ? Fault Präntijärvi 10 km Fig. 2. Simplified geology of the Kukkola area, Claesson et al. (1982). 34 B. FILÉN Compared with the Finnish layered complexes in the east, the Kukkola intrusion is very thin, only 10– 200 m (Claesson et al. 1982, Lundmark 1984). It is very heterogeneous and consists of strongly altered mafic to ultramafic rocks emplaced between updomed granitic gneisses of the Archaean basement and Proterozoic schists (Fig. 2). Only in a drill profile close to the border, leucocratic rocks (anorthosites-leucogabbros) have been encountered. In some profiles, up to 15 cm wide seams with chromitite occur. They are poor in chromium – the best section gives 22.8 % Cr2O3 with a Cr/Fe ratio close to 1. In the profile close to the border, one 10 cm long section of a metapyroxenitic rock with 7 % Cr2O3 holds 0.64 ppm Pt, 1.1 ppm Pd, and 0.08 ppm Au. A single 2.7 m wide metaperidotite section with disseminated chromite shows 3.6 ppm Au (Claesson et al. 1983). In the western part of the big hook, a small mafic intrusion is situated in the basement. This has been considered as a feeder for the intrusion. A grab sample from a sulphide-disseminated metapyroxenitic rock gave 0.84 ppm Au. The Präntijärvi mafic intrusion is situated 6 to 10 km to the SW. It has almost the same aeromagnetic signature as the Kukkola intrusion. No outcrops are known, but it could be an analogue to Kukkola. Except for boulder tracing nothing has been done in the area. Notträsk (Location: Map sheet 25L, x7321000 y1774000) Exploration history The gabbroic intrusion at Notträsk east of the town of Boden has long attracted the attention of prospectors and geologists. A nickel-copper-sulphide mineralization was found at the end of the 19th century. The intrusion has thereafter at several occasions been the subject for scientific studies and exploration activities (Sundin 1977, Svensson 1981, Arvanitides 1982, Enmark 1982, Widenfalk et al. 1985). Most of these activities have focused on nickel and copper in the southeastern part of the intrusion. Exploration has included geological mapping, boulder tracing, ground geophysics, biogeochemistry, and diamond drillings. So far, the exploration results have not been successful. Though impressive looking in hand specimens, the nickel content in the massive sulphides hardly ever exceed 1 % in the sulphide phase. Between 1986 and 1989 SGAB intermittently explored the intrusion for PGE-Au. Unlike other organisations and companies, SGAB concentrated its efforts mainly on the inner parts of the intrusion. Rock sampling was carried out during the winter 1988–1989 and followed up by five diamond drill holes in a profile (Filén et al. 1989). Geology The Notträsk gabbro (Fig. 3) is a funnel-shaped layered intrusion, which has intruded into gneisses of metasedimentary origin (Arvanitidis 1982, Filén 1987, Filén et al. 1989). The intrusion has by Arvanitidis (1982) been divided into four major zones: Marginal Border Group (MBG) Ferrogabbroic Series (FGS) Troctolitic-Anortositic Series (TAS) Gabbroic Series (GS) The intrusion belongs to the Perthite monzonite suite, a suite of differentiated and synkinematic intrusions in folded supracrustal rocks of Svecofennian age. The supracrustal rocks are mainly metasedimentary. The gabbroic rocks of the Haparanda type are of the same age as the synkinematic Svecofennian intrusive rocks in the Västerbotten County (Näsberg), Jämtland County (Hoting), Västernorrland County (Kläppsjö), and Dalarna County (Flinten). The main intrusion is 6 x 4 km large, oval-shaped, and consists of concentric layers. At the margins, the layers are steeply dipping but gradually become shallower towards the centre, where they are flat-lying. The intrusion has a complicated structure with often very abrupt lithological changes as seen in Figure 4 (olivine–gabbro–anorthosite– olivine–gabbro–dunite–troctolite). In his Ph.D.-thesis, Arvanitides (1982) presents proofs for the existence of two magmas at the time of emplacement of the intrusion. One was Al-rich and formed the TAS-GS-series, and the other was Fe-Ti-rich and tholeiitic and formed the FGS-rocks. The magmas are thought to have a common ultramafic source. The separation into different magmas and the emplacement was caused by flow differentiation, oscillating nucleation, and filter pressing. The higher density, Fe-Ti-rich magma intruded late during the formation of the TAS-GS. Gravitational crystallisation differentiation played a crucial role. Later studies (Filén 1987, Filén et al. 1989) have discarded the existence of the Gabbroic Series. No clearly defined pyroxene-rich core has been identified, and no outward dipping troctolitic core as proposed by Widenfalk et al. (1985) can be seen in the numerous outcrops. When sampling an abandoned quarry in 1987, one specimen was highly anomalous in precious metals. Sample number BMNA 87488 (nat. grid. coordinates x7320160, y1773930) contains 2.74 ppm Pt, 1.33 ppm Pd, 0.21 ppm Au, and 20 ppm Ag. A subsequent diamond drilling programme in a profile planned to go from TAS-FGS into the (non-existing) GS gave the results presented in Table 1. The anomalous values are most often found in anorthositic olivine gabbro. SWEDISH LAYERED INTRUSIONS ANOMALOUS IN PGE-AU 35 177500 732500 60 42 55 53 62 75 28 47 Skogså 27 62 28 45 35 5 25 40 32 25 25 38 27 35 18 26 40 65 Notträsket 0 Metasediment Magnetite-gabbro Granite Norite Olivine-gabbro Diorite 2 km Ultramafic layers 40 Magmatic layering Fault Fig. 3. Geology of the Notträsk layered intrusion, Widenfalk et al. (1985), Filén et al. (1988). Fig. 4 Layers with olivine–gabbro, anorthosite, olivine–gabbro, dunite and troctolite. 36 B. FILÉN Table 1. Sections with anomalous PGE-Au values (ppm) in the Notträsk gabbroic intrusion. Drillhole 88001 ” ” ” ” ” 89001 ” ” ” ” ” ” ” ” ” ” ” ” ” ” ” ” 89002 89003 89004 ” ” ” ” Section 16.20–16.85 16.85–17-85 65.40–66.03 115.40–116.40 139.70–140.63 186.44–187.44 31.00–32.00 60.17–61.17 61.17–62.13 102.33–103.05 120.75–121.75 124.35–124.61 129.92–130.92 130.92–131.92 131.92–132.60 132.60–133.15 133.15–134.26 134.26–134.45 147.53–148.45 148.45–149.40 149.40–150.10 160.50–161.30 161.30–161.80 45.13–45.65 14.00–14.13 108.00–109.00 109.00–110.00 110.00–111.00 114.00–114.20 115.29–115.49 Pt 0.05 0.05 0.05 0.17 0.05 0.05 0.05 0.07 1.11 - Pd 0.03 0.04 0.04 0.30 0.13 0.08 0.05 Au 0.02 0.05 0.06 0.02 0.05 0.15 0.20 0.17 0.09 0.36 0.29 0.19 0.41 0.68 0.47 0.33 0.09 0.14 0.01 0.02 0.02 0.03 0.02 0.03 0.02 Ag 4 4 7 7 8 6 10 8 - The analytical results indicate that the mineralization is clearly subeconomic. Today, aggregates are produced in a dioritic-noritic satellite intrusion to the south-west. Näsberg (Location: Map sheets 24J, 24K, 23J, 23K, x7251000 y1699000) Exploration history The Näsberget mafic intrusion is 9 x 4.5 km large and is situated on both sides of the Byske River in the northernmost part of the Västerbotten County. Iron ore was found here as early as 1832 (Anon. 1986). As iron ores are scarce in Västerbotten and with a favourable location close to the river not too far from the coast, high expectations linked up with the discovery. A company was established and mining started five years later. Already in 1833 the Mine Inspector had visited the discovery and he had noticed that the ore occurred as veins which often were contaminated with pyrite. By careful hand sorting a better ore was produced, but falling iron prices and high transport costs soon forced the company to close the mine. Several later attempts were made – but with almost the same result. The last ore was mined in 1908. When old rock samples were rechecked, some samples from the Näsberg intrusion were found to contain cumulates. This resulted in field visits and rock samplings and later in small scale trenching. Geology The Näsberget intrusion is mainly surrounded by older Jörn granitoids. Felsic volcanic rocks, which are older than the granitoids, occur to the west and to the north (Claesson 1980). Volcanic rocks of different ages exist in the area. The intrusion is, in the north, in many places intruded by porphyritic dykes. The intrusion is clearly layered, the layering normally striking NE and dipping steeply NW, but especially in the north and along the Byske River local variations occur (Fig. 5). The most common type of layering is igneous lamination but, especially in the south and south-east, modal layering occurs. Ultramafic layers have not been encountered except for some thin altered hornblendites in the south-east (Filén 1987, Filén et al. 1988). Altogether 95 samples have been analysed for precious metals. At one locality (nat. grid coordinates x7248680, y16974009), a 0.2 m3 sulphide-bearing pyroxene gabbro boulder with cumulus textures was found. This boulder contained 1.2 ppm Pt, 3.9 ppm Pd, and 0.2 ppm Au. A later reassaying of the boulder was performed on different modal rock types. Chemical analyses gave 1.3 ppm Pt, 4.5 ppm Pd, and 0.3 ppm Au in one half of the boulder but only 0.05 Au in the other half which indicates a strong nugget effect. Microscope studies showed small amounts of gold in the PGE-empty part but no PGM’s could be found in the other part. Chips sampling from a weekly rusty outcrop 250 m to the north-west gave 0.05 ppm Pt and 0.02 ppm Au over 0.30 m. A grab sample from the old iron workings gave 0.4 ppm Au. Hoting (Location: Map sheet 21G, x7117500 y1523500) Exploration History Åhman (1967) and Lundqvist et al. (1990) have described the Hoting (Rörström) gabbro. During SGAB’s PGE-exploration campaign it was studied and described by Filén (1985, 1987) and Filén et al. (1988b). When checking old samples from Hoting it soon became clear that rocks with cumulus textures were abundant. Even Åhman in his paper of 1967 wrote about ”diffuse fluidal texture” though typically enough without mentioning layering. So when the PGE-exploration started it was more or less clear that Hoting was a layered mafic intrusion. In many ways it resembled Notträsk, and Hoting was thus given a high priority. Geology The Hoting massif is one of the largest layered intrusions in Sweden, with a diameter of 10 km and an 11 km long panhandle towards the south (Fig. 6). Early orogenSWEDISH LAYERED INTRUSIONS ANOMALOUS IN PGE-AU 37 Hej B y l eä k s n ve The Näsberg Fe-deposit 85 70 50 60 45 1700000 Sör-Abborrträsket 60 7250000 45 Snorum 0 Jörn granitoids and felsic volcanic rocks Näsberg mafic intrusion 50 2 km Magmatic layering Boulder of mafic layered rock anomalous in PGE Fig. 5. Layering in the Näsberg mafic intrusion, Claesson (1980), Filén et al. (1988). ic tonalitic and granodioritic gneisses in the east and in the south-west surround the intrusion. Elsewhere, the intrusion is bordered, often with tectonic contacts, by gneissic granites, metasedimentary rocks, and post-orogenic Revsund granite. Zones of weakness, which commonly are seen as valleys, streams, or cliffs with faults scarps, cut the massif and have acted as feeder channels for both the granites and for pegmatites and dolerites. As in the Notträsk intrusion, the layers are concentrically developed with steeply dipping outer layers and a flat layering in the 38 B. FILÉN central part. Layering can be seen all over the intrusion. Modal layering is the most common type. Oikocryst bearing layers alternating with gabbroic (± olivine) cumulates are quite frequent (Fig. 7). Ultramafic layers on the other hand are rare. Sulphides such as chalcopyrite, pyrrhotite, and pentlandite occur mostly in the southern part of the main intrusion, which also contains nickel-copper grades between 0.10–0.15 % Ni and 0.20–0.28 % Cu. One single sample contains 0.47 % Ni, 0.39 % Cu, and 0.09 % Co. As the 75 55 65 60 60 75 35 20 60 20 70 40 75 70 65 45 35 45-60 Hoting 60 30 40 75 Rensjön 20 40 60 60 60 56 Sundsjön 75 Hotingsjön 55 Granite 75 65 Revsund granite Granite-pegmatite Pegmatite Granodiorite Hoting mafic intrusion Metasedimentary rock Metamafic rock Foliation Magmatic layering 5 km Fig. 6. Simplified geology of the Hoting area, Filén et al. (1988b). sample contains much sulphur, 14.2 %, the nickel tenor in the sulphide phase will be rather poor. This is, however, typical for sulphide mineralizations in the marginal zone of a layered intrusion. A gabbro pegmatite east of the village Hoting shows a week platinum anomaly (0.2 ppm) and several gold anomalous boulders have been found in the area. In the central part of the intrusion, an 8 cm thick, gently dipping layer with almost massive magnetite was found. One sample contained 68.1 % Fe2O3, 21.9 % TiO2, and 0.49 % V. SWEDISH LAYERED INTRUSIONS ANOMALOUS IN PGE-AU 39 Fig. 7. Augite oikocryst-bearing layers alternating with olivine–gabbro/troctolite layers in the Hoting mafic intrusion. Kläppsjö (Location: Mapsheet 20H x7065000 y1569000) Exploration history The Kläppsjö intrusion was investigated already in the early days of SGU’s nickel exploration campaign, in the beginning of the 1970’s. Sulphide bearing samples were collected, but they contained only small amounts of nickel. However, some of them were anomalous in palladium. When the PGE project started, the Kläppsjö intrusion was thus a natural target. The Kläppsjö area has been the subject of sampling, mapping, trenching, airborne and ground geophysics and geochemistry. Altogether 1845 m of diamond drillings in 22 drill holes has been carried out during two drilling campaigns. The Kläppsjö layered intrusion has been described in several SGAB exploration reports: Filén (1985, 1987, 1990), Filén & Lundmark (1988a, 1988b), Filén et al. (1988a, 1988b, 1989), Ekström (1988), and also by Lundqvist et al. (1990). Geology The Kläppsjö massif is a 6x4 km large layered intrusion situated 15 km east of the village Junsele in the Västernorrland County. Just like Hoting, the main part of the Kläppsjö massif forms a topographic high and is mostly relatively well exposed. The intrusion is mainly surrounded by paragneisses, and in the north-west and south-east by the late orogenic Härnö granite. In the eastern part, remnants of felsic volcanic rocks occur. The Kläppsjö massif (Fig. 8) shows a megacyclic internal structure with ultramafic, gabbroic, leucogabbroic, and anorthositic units, less than ten to more than hundred meters thick. The cyclic composition is thought to be the result of multiple magma injections. A section in a 20 m thick ultramafic layer in the southern part has showed highly anomalous platinum values. Samples from 40 B. FILÉN a harzburgitic layer in contact with a metapyroxenite layer contained between 1.1 and 21.0 ppm Pt. In November 1987, a 14-hole diamond-drilling program started. Extensive analyses of drill core samples from the ultramafite only revealed four sections with weak Pt-anomalies (0.06–0.16 ppm). Low Au-values, between 0.01 and 0.17 ppm, were encountered in three drill-cores. Almost half way up in the theoretical stratigraphy, a 110 m thick ultramafic unit occurs, which was diamond drilled during a second campaign. Eight holes were drilled in two profiles 170 m apart. 238 Pt-Pd-Au-Ag analyses were made. Already during the field work, some anomalous PGE sections had been recorded in outcrops. Anomalous sections with PGE-Au (Ag) analysed from diamond drillholes are presented in Table 2. The precious-metal content is sub-economic, but the gold values suggest that Kläppsjö might also be a pure gold exploration target. As in Hoting, boulders with anomalous Ni-Cu tenors (0.63–0.85 % Ni, 0.37–1.03 % Cu), but poor in the sulphide phase, have been encountered in the south-eastern part of the intrusion where marginal zone sulphide mineralizations might occur. Ilmenite-containing boulders with approx. 10 % TiO2 have also been found. Bottenbäcken (Storsjö Kapell) (Location: Map sheet 18D x6973500 y1359000) Exploration history The existence of a copper mineralization in a gabbro complex situated in the Storsjö Precambrian window (Fig. 9) in the Caledonides was first noticed by a private prospector, but also by a SGU uranium exploration team in the mid-1970’s. Exploration started soon thereafter. Twenty boulder and outcrop samples contained an average of 1.20 % Cu and 0.5 ppm Au (Tirén 1979). The mineralization which has been called both Bottenbäcken and Storsjö Kapell has later been studied intermittently by different Kläppsjö Kläppsjön 75 70 70 65 70 70 70 70 75 Mjövattnet Rängsjön 60 00 0 15 70 69 00 0 Dolerite Gabbro Granite Ultramafic layers Tonalite Mica schist, phyllite Granodiorite Sedimentary gneiss Felsic volcanic rocks 75 2 km Magmatic layering Foliation Fig. 8. Geology of the Kläppsjö mafic intrusion, Filén et al. (1988b). organisations and companies by means of geological mapping, ground geophysics, geochemistry, and diamond drillings (Hålenius et al. 1985, Toverud 1987, Andersson 1990). Geology The copper was first thought to have been enriched in deformation zones in a gabbro complex (Tirén 1979). The mineralized gabbroic host rocks were later reinterpreted (Hålenius et al. 1985) as metabasaltic tuffs and lavas within granitic mylonites. The mineralizations showed anomalous Pd-values with grades between traces and 4.2 ppm and were interpreted as hydrothermal in character. Analytical results from two of the best drill-holes can be seen in Table 3 (Toverud 1987). Only in a few cases has Pt been encountered. The precious metal analytical results are usually hard to reproduce which could indicate a strong nugget effect. SWEDISH LAYERED INTRUSIONS ANOMALOUS IN PGE-AU 41 Table 2. Sections with anomalous PGE-Au values (ppm) in the Kläppsjö massif. Table 3. Analytical results from Bottenbäcken. PGE-Au values in ppm, Cu in %. Drill hole 88101 ” ” ” 88102 ” ” ” ” 88105 ” ” 88106 ” ” ” ” ” ” ” 88107 ” ” ” ” ” ” Drill hole 86012 ” ” ” ” ” ” ” ” ” 86013 ” ” ” ” Section 4.50–5.50 5.50–6.50 18.50–19.50 24.50–25.50 15.00–16.00 27.00–28.00 28.00–29.00 30.00–31.00 38.00–39.00 11.00–12.00 14.00–15.00 15,00–16 00 2.20–2.70 3.70–5.00 5.00–6.25 6.25–7.50 7.50–8.50 8.50–9.50 9.50–10.50 10.50–11.50 36.50–38.00 48.50–50.00 50.00–51.10 68.00–69.00 69.00–70.00 70.00–71.00 71.00–72.00 Pt 0.11 0.15 0.13 0.05 0.06 0.05 0.06 0.07 0.21 0.20 - Pd 0.05 0.07 0.05 0.09 0.06 - Au 0.01 0.04 0.08 0.01 0.20 0.34 0.11 0.39 1.17 0.63 0.86 0.01 0.26 0.03 0.23 0.04 0.10 0.25 0.04 Ag 6 8 6 Section 34.70-37.05 37.05-39.40 39.40-40.40 40.40-41.40 48.50-50.00 69.20-70.70 70.70-71.70 71.70-72.20 73.50-76.20 76.20-77.20 58.80-59.65 59.65-60.55 60.55 -61.45 64.50-65.20 65.20-68.05 Cu 0.84 0.44 2.30 0.51 0.61 0.24 2.88 0.20 0.32 0.81 3.28 0.64 2.71 2.88 0.43 Au 0.48 0.24 1.15 0.23 0.12 0.12 0.83 0.08 0.11 0.34 1.30 0.34 0.77 0.95 0.20 Pd 0.83 0.34 1.38 0.38 0.34 0.06 1.35 0.07 0.13 0.35 2.65 0.45 4.18 2.88 0.26 Pt 0.15 - 4 5 ÖverRöversjön YtterRöver sjön 1363000 6971000 ÖsterRotsjön Storsjön Storsjö Särv rocks Phyllonitic rocks Granitic mylonites Mafic extrusive rocks 42 B. FILÉN Thrusts 0 1 2 3 km Fig. 9. Map of the Storsjön window with the Bottenbäcken mafic extrusions (after Hålenius et al. 1985). Flinten (Svärdsjö) (Location: Map sheet 13G x6727000 y1510000) Exploration History Mafic intrusions have for long been known to exist in the central parts of the ”Svärdsjö Circular Structure”. Some geophysical work has earlier been carried out in the northeastern part of the complex, but the mafic rocks have not generally drawn any attention. During a regional field visit in 1988 it was concluded that the intrusion exhibits different kinds of beautiful layering as seen in Figure 10. Except for rock sampling, only a minor geochemical study has been performed in the south-eastern part of the intrusion (Lindholm 1990). Faults and dislocations cut the complex, which consists of several separate blocks or lobes (Fig. 11). Layering is very well developed. A continuous series of ultramafic and mafic to leucocratic rocks can be found ranging from dunites, lherzolites, troctolites and pyroxenites to gabbros, leucogabbros and anorthosites (Filén et al. 1988b, Filén et al. 1989). The width of the layers, which in places can be intensly folded, varies from 2 mm to hundreds of metres. In many places, small amounts of sulphides can be seen. Some of the sulphide-bearing rocks also contain anomalous amounts of PGE and Au. The most anomalous sample with 1.8 ppm Au (Table 4) was taken from a weakly sulphide-bearing metapyroxenite layer close to the locality shown in Figure 10. The other anomalous samples came from local troctolitic, websteritic and gabbroic boulders, also in the southeastern part of the intrusion. Table 4. Analytical results from samples from the Svärdsjö area. PGE-Au values in ppm, Cu and Ni in %. Sample PGBA88664 88667 88668 PGBA89307 89310 89311 89602 89604 89605 89608 89645 Au 0.03 0.09 0.02 1.8 Pd 0,18 0.14 0.20 0.05 0.06 0.19 - Pt 0.04 0.04 0.10 0.05 0.04 0.11 0.13 - Ni 0.05 0.06 0.05 0.2 0.09 0.08 0.05 0.06 Cu 0.4 0.1 0.15 0.19 Remarks Fig. 10. Graded bedding in the Flinten layered intrusion, Geology The ”Svärdsjö Circular Structure” is situated in an area with a low aeromagnetic signature. The inner part, Flinten, where the patterns are more variable, has been interpreted as a volcanic centre and the ”stock formed” high magnetic gabbros as feeder channels for the surrounding, mainly mafic volcanic rocks (Hammergren 1986). When the potential for a future PGE-exploration was evaluated in 1984, the results showed that only layered mafic intrusions could be the primary targets. At that time only a handful of layered intrusions were known to exist in Sweden. The name layered mafic intrusion was mainly restricted to very large complexes like Bushveld or Stillwater or to the classical Skaergaard. During the exploration work it was soon concluded that probably most of the larger mafic massifs showed some kind of layering. One of the few larger intrusions that did not show any true layering is the circular Kärkejaure structure (x7584000 y1708000) in the northernmost part of Sweden. The very few outcrops (mostly in the east), gravity high, extreme highmagnetic anomalies, geochemical patterns (Geol. Surv. of Finland et al. 1986), and in places dense shrub vegetation (salix and juniperus) indicate that the intrusion is more likely an analogue to the Sokli carbonatite in north-eastern Finland. SWEDISH LAYERED INTRUSIONS ANOMALOUS IN PGE-AU 43 Hinsen 50 50 60 60 30 20 60 45 30 Hinsen 45 70 60 40 60 60 40 40 50 70 75 50 50 40 Toxen Håsjön 60 80 Logärden 1510000 6722000 Younger granite Foliation Older granite Magmatic layering Flinten mafic layered intrusion Way up, inverted Felsic metavolcanic rocks Sulphide mineralization Mafic metavolcanic rocks 2 km Fig. 11. Geology of the Flinten area, Hammergren (1986), Filén et al. (1989). It is the hope that this short review will lead to a systematic investigation of layered mafic intrusions, which in turn will give insight in petrogenesis and differentiation of mafic magmas and how ores are formed in these 44 B. FILÉN magmas. Layered intrusions will also in the future be the natural targets in exploration for PGE’s, gold, chromium, titanium, and vanadium, and hence deserve a continued research interest also in Sweden. References Åhman, E., 1967: Hoting – Rörströmgabbron i Västernorrlands län. Sveriges geologiska undersökning C 607, 3–26. Alapieti, T.T. & Lahtinen, J.J., 1989: Early Proterozoic layered intrusions in the northeastern part of the Fennoscandian Shield. Geological Survey of Finland, Guide 29, 3–41. Andersson, L-G. 1990: Bottenbäcken – arbeten 1989 inkl. summering arbeten 1988. SGAB b 9002. Anon., 1986: Järn i Jörn – Näsbergsgruvan. Markkontakt Nr 2 13–18. Arvanitidis, N., 1982: The geochemistry and petrogenesis of the Notträsk mafic intrusion, northern Sweden. Meddelanden från Stockholms Universitets Geologiska Institution, Nr 253. Claesson, L-Å., 1980: Åselet. Prospekteringsarbeten utförda av SGU 1979–1980. Sveriges geologiska undersökning BRAP 80032. Claesson, L-Å., Filén, B. & Ekström, M., 1982: Delrapport över krommineraliseringen vid Kukkola. Sveriges geologiska undersökning BRAP 82100. Claesson, L-Å., Ullberg, A., Magnusson, J., Wiberg, B. & Ekström, M., 1983: Prospekteringsrapport, 1981–1982, Kukkola. SGAB PRAP 83042. Ekström, M., 1988: Kläppsjö – Mineralogi SGAB PRAP 88023. Enmark, T., 1982: Development and optimization procedures for gravity and magnetic interpretation and their application to some geological structures in northern Sweden. University of Luleå, 1982:019 D. Filén, B., 1985: PGE-prospektering Etapp II. SGAB PRAP 85111. Filén, B., 1987: PGE-prospektering 1986 Etapp II. SGAB PRAP 87003. Filén, B., 1990: PGE-Prospektering i Sverige 1985-1990. SGAB 90026. Filén, B. & Lundmark, L.-G,. 1988a: Kläppsjö Borrning, Etapp I. SGAB PRAP 88022. Filén, B. & Lundmark, L.-G., 1988b: Kläppsjö Borrning Etapp II. SGAB PRAP 88056. Filén, B., Gerdin, P., Lundmark, L.-G. & Renberg, A., 1988a: PGE – 1987 Etapp II. SGAB PRAP 88005. Filén, B., Gerdin, P., Lundmark, L.-G. & Renberg, A., 1988b: PGE-Ni-Prospektering 1988. SGAB PRAP 88066. Filén, B., Ekström, M. & Lundmark, L.-G., 1989: Notträsk 1989 Diamantborrning. SGAB PRAP 89025. Filén, B., Ekström, M., Lundmark, L.-G. & Renberg, A., 1989: PGE-Prospektering 1989. SGAB PRAP 89061. Geological Surveys of Finland, Norway and Sweden, 1986: Geochemical Atlas of Northern Scandinavia, 1:4 milj. Hålenius, U., Lund, L.-I. & Westerberg, S., 1985: Storsjöfönstrets koppar- och ädelmetallmineralisering. SGAB PRAP 85535. Hammergren, P., 1986: PI Projekt. Komplexa sulfidmalmer i Falu – Hoforsområdet. SGAB PRAP 86549. Lindholm, T., 1990: Flinten Djupmorän- och bergkaxprovtagning. SGAB PRAP 90007. Lundmark, C., 1984: Kukkola Resultat av diamantborrningen 1984. SGAB PRAP 84122. Lundqvist, T., Gee, D.G., Kumpulainen, R., Karis, L. & Kresten, P., 1990: Beskrivning till Berggrundskartan över Västernorrlands Län. Sveriges geologiska undersökning Ba 31, 429 pp. Sundin, N.O., 1977: Geofysiska mätningar i Notträsk. University of Luleå, 1977:120E. Svensson, R., 1981: Mineralogisk undersökning av Notträskgabbron. University of Luleå, 1981:072E. Tirén, S.A., 1979: Bottenbäckens kopparmineralisering. Sveriges geologiska undersökning BRAP 79519. Toverud, Ö., 1987: Resultat från utförd diamantborrning, oktober-november 1986, inom objekten Kalberget, Bottenbäcken och Nynäsberget i Jämtlands län. LKAB Prospektering s 8701. Widenfalk, L., Elming, S.-Å. & Enmark, T., 1985: A multidisciplinary investigation of the Notträskgabbro, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar107. SWEDISH LAYERED INTRUSIONS ANOMALOUS IN PGE-AU 45 Palaeoproterozoic deformation zones in the Skellefte and Arvidsjaur areas, northern Sweden Jeanette Bergman Weihed Bergman Weihed, J,. 2001: Palaeoproterozoic deformation zones in the Skellefte and Arvidsjaur areas, northern Sweden. In Weihed, P. (ed.): Economic geology research. Vol. 1, 1999–2000. Uppsala 2001. Sveriges geologiska undersökning C 833, pp. 46–68. ISBN 91-7158-665-2. large areas of the counties of Västerbotten and southern Norrbotten. Identification of metamorphic variations connected with the shear zones and at least the relative age of the shear zones were also aims of the study. A detailed investigation of a number of major shear zones and faults in northern Västerbotten and southern Norrbotten has resulted in new information on timing and kinematics of the deformation in this area. The observed shear zones and faults cut through the Svecofennian c. 1.95–1.80 Ga supracrustal sequence and intrusive rocks spanning ages between 1.95 Ga and 1.78 Ga. Approximately north striking, both semi-ductile and brittle deformation zones dominate the studied area. These zones are generally characterized by retrograde greenschist facies mineral assemblages and have a reverse sense of movement. They affect all intrusive rocks and must have formed during or after the regional D3 deformation (after c. 1.80 Ga) and after peak metamorphism. The dominantly dip slip reverse movements indicate an east-west shortening during this deformation. Older shear zones were found in the central part of the studied area where they commonly parallel axial surfaces of the regional D2 folds and surround lower strain lenses. These shear zones normally show a reverse oblique slip movement, commonly with the south side up, and they are overprinted by later S3 crenulations and display statically recrystallised textures. The shear zones formed late during the main D2 folding (between 1.87 and 1.82 Ga) in response to oblique convergence from the south-east. Regional geology Jeanette Bergman Weihed, Department of Earth Sciences, Villavägen 16, SE-752 36 Uppsala, Sweden. Present address: Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden. E-mail: [email protected] Introduction and background Many shear zones have been recognised during the last ten years of mapping in research projects and by the Geological Survey of Sweden in the Skellefte and Arvidsjaur areas, but the shear zones have not previously been studied in detail. They probably played an important role in the geological evolution of the area, but it has so far been unknown to what extent and during what time periods the shear zones were active. A research project was therefore initiated with the purpose to identify and describe shear zones, with special emphasis on regional zones and associated deformation in an area encompassing the map sheets 22–24 H–L in the Swedish national grid, covering 46 J. BERGMAN WEIHED The Skellefte district, broadly coincident with the area of Skellefte Group volcanic rocks in Figure 1, contains part of the Svecofennian c. 1.95–1.80 Ga supracrustal sequence and associated intrusive rocks in the northern part of Sweden. The rocks in the Skellefte district itself have been divided into a lower sequence dominated by subaqueous volcanic rocks (the Skellefte Group) and an overlying sequence dominated by shallow-water to subaerial sedimentary and volcanic rocks (the Vargfors Group). These rocks are bordered to the south and east by a vast area of strongly metamorphosed greywackes (Bothnian Group) and to the north by subaerial volcanic rocks (Arvidsjaur Group) which are similar in age to the rocks of the Vargfors Group. The supracrustal sequence is intruded by 1.95–1.85 Ga calc-alkaline I-type granitoids (Jörn type), by S-type anatectic granites at c. 1.82–1.80 Ga (Skellefte granites), and by younger post-volcanic A- to I-type granitoids at c. 1.80–1.78 Ga (Revsund granitoids). For a more detailed discussion of the rocks in the area, see Weihed et al. 1992, Allen et al. 1996, Billström & Weihed 1996 and references in these papers. Previous work Previous structural studies have mostly concentrated on smaller areas within the Skellefte district and very little attention has focused on shear zones in particular. Edelman (1963) presented the structural evolution in the Kristineberg area and this area was also studied in detail by Joseph Hull (unpubl. data). The central part of the Skellefte district has been structurally mapped by Bergman Weihed (unpubl.) and some results have been presented in Bergman (1989, 1991) and Weihed et al. (1992). Detailed studies of mineralizations and associated deformational structures are presented in Talbot (1988), Assefa (1990), Bergman (1992), and Bergman Weihed et al. (1996). Two major phases of folding have been proposed for most of the area. The early folds (here called D2) are tight to iso- Fig. 1. Map of the whole region with geological information from the bedrock map of central Fennoscandia (Lundqvist et al. 1996b) and major low-magnetic lineaments interpreted as shear zones and/or faults (black lines). PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 47 7300000 24 7250000 23 7200000 22 7150000 1550000 1550000 Syn-volcanic granitoid (Jörn and Haparanda types) c. 1.89–1.88 Ga 1700000 Mudstone, sandstone & turbidite, (Bothnian, Vargfors and Skellefte Groups), c. 2.0–1.85 Ga J Fig. 9 Post-volcanic granitoid (Skellefte type), c. 1.82–1.80 Ga Fig. 12 Kars träsk Mainly submarine rhyolite & dacite (Skellefte Group), c. 1.89–1.88 Ga 1650000 Fig. 7 1700000 Conglomerate, sandstone & volcanic rocks (Vargfors Group), 1.75 Ga I Arvidsjaur J Post-volcanic granitoid (Revsund type), c. 1.80–1.78 Ga 1600000 Lycksele Fig. 5 1650000 Caledonides Archaean Karelian province Svecofennian province Fig. 4 I Mainly subaerial to shallow water rhyolite, (Arvidsjaur Group), c. 1.88–1.87 Ga Fig. 2 1600000 Perthite monzonite c. 1.88–1.86 Ga H Caledonides Neoproterozoic and Fanerozoic rocks Sveconorvegian province Transscandinavian Igneous Belt Main map Sorsele H K K Piteå Mainly mafic volcanic rocks, (Knaften Group), c. 1.95 Ga Supracrustal rocks, (Kalevian Group), c. 1.9 Ga Gabbro and diorite (undivided) 1750000 Skellefteå 1750000 L L 1800000 Low magnetic lineaments, faults and shear zones Archaean granitoid 25 km Bothnian Bay Luleå 1800000 7300000 24 7250000 23 7200000 22 7150000 clinal, with upright axial surfaces and variably plunging fold axes (cf. Weihed et al. 1992). Axial surfaces strike north-east in the eastern and western parts of the Skellefte district and west-northwest in the central part of the district. An axial planar cleavage is developed and shearing along this is common. Late folds (here called D3) are open with north- to northeast-striking axial surfaces and fold axes coaxial with the early folds. Talbot (1988) and Assefa (1990) report an earlier recumbent phase of folding in the Långdal area and Allen et al. (1996) reports an early foliation which is subparallel to bedding. This foliation may have formed during a D1 deformation although no folds related to this foliation have been recognised. One shear zone, which parallels the axial surfaces of early folds in the central part of the Skellefte district, was reported in Bergman (1991). This shear zone dips steeply south and stretching lineations plunge moderately southwest. An s-c fabric indicates south side up reverse movement. An east-striking, steep shear zone also deforms the ore in Boliden (Bergman Weihed et al. 1996) and the stretching lineation plunges about 50° east. No oriented samples could be obtained from this zone so the shear sense is unclear. Both of these shear zones are overprinted by the second regional deformation and have thus formed during, or somewhat after, the first major regional D2 phase of folding. No published structural studies exist in the areas outside of the Skellefte district which are considered in the present study (Fig. 1) and, in many cases, the structures are poorly known. Some structural information is, however, reported in publications dealing with the general geology of the areas. The relevant publications are referenced in each section below. Tectonic interpretations of the area have generally focused on the Skellefte district. Hietanen (1975) proposed a subduction zone dipping north beneath the Skellefte district and after that, many similar models have been proposed (e.g. Rickard & Zweifel 1975, Lundberg 1980, Pharaoh & Pearce 1984, Berthelsen & Marker 1986, Gaál 1986, and Weihed et al. 1992). A more regional geophysical study was presented by Nisca in 1995. A northward subduction is supported by a magnetotelluric survey (Rasmusen et al. 1987) which found a low-resistivity slab dipping north under the Skellefte district and by a seismic reflection profile in the Bothnian Bay (BABEL group 1990) which shows a north-dipping reflector east of the Skellefte district. The Skellefte Group volcanic rocks are generally interpreted to represent some kind of volcanic arc whereas the subaerial volcanic rocks (Arvidsjaur Group) to the north may represent a continental environment coeval with the volcanic arc. The large area of metamorphosed greywackes to the south (Bothnian Basin) may be interpreted as a fore-arc environment (Weihed et al. 1992). Archaean detrital zircons and negative εNd values (at 1.9 48 J. BERGMAN WEIHED Ga) in the greywackes indicate that an Archaean crust, present somewhere in the area, provided material for the sediments in the Bothnian Basin (cf. Claesson & Lundqvist 1995, Lundqvist et al. 1998). Towards the northeast, around Luleå (Fig. 1), Archaean granitoid intrusions have recently been discovered (Lundqvist et al. 1996a). A study by Mellqvist (1997) has focused on delineating the boundary between juvenile rocks and rocks with an Archaean component. Results from this study indicate that tectonic contacts may be common between Archaean and younger rocks (Mellqvist 1997 & 1999). Methods During the present study, a few new deformation zones were identified using a combination of aeromagnetic interpretation and outcrop information. Interpretation of aeromagnetic maps was done to identify regionally important shear zones or faults. This information was then combined with outcrop information in order to locate the shear zones in areas which have not yet been mapped in detail. These interpreted shear zones were then studied in the field in addition to shear zones identified during mapping by the Geological Survey of Sweden. Aeromagnetic grey tone and relief maps on a scale of 1:250 000 were used for the geophysical interpretation of the entire area. This was complemented by interpretation of maps on a scale of 1:80 000 and 1:100 000 in areas where more detail was necessary. Low-magnetic, narrow zones can be found in most parts of the study area, but they are most easily seen where the bedrock is relatively high-magnetic. Therefore, very few low-magnetic zones were found e.g. on map sheets 22 H–I and 23H (Fig. 1). Other parts of the area appear complex with a large number of anastomosing low-magnetic zones (e.g. western part of 23–24 K). Apart from low-magnetic lineaments, magnetic boundaries (commonly representing boundaries between intrusive and supracrustal rocks) and high-magnetic narrow zones (often representing form lines of bedding in sedimentary units) were noted. All this information was correlated with geological maps of the area. Results The most striking feature of the interpretation of lowmagnetic lineaments shown in Figure 1 is the dominance of north- and northwest-striking zones on map sheets 23–24 H–I, whereas east to northeast striking zones dominate the southeastern-most part of the area. Northweststriking zones occur mainly within the central Skellefte district (23 J–K), and these are less obvious on aeromag- netic maps of the scale used in this project. These zones are, however, very clearly seen when interactively working with the aeromagnetic data on a computer. Kinematic indicators in the deformation zones were found in the field in approximately 20 shear zone localities. Nearly all observed shear zones are subvertical and have steep stretching lineations. In general, most northstriking zones show that the eastern side has moved upwards in relation to the western side, and most northwest-striking zones indicate that the southern side has moved upwards relative to the northern side. A few zones with dominantly horizontal movements have also been found, e.g. along the northern contact of the Karsträsk dome (Fig. 1). Below, results from all identified and studied shear zones are presented by area. The geological maps are based on the recently published Mittnorden map (Lundqvist et al. 1996b) supplemented by more detailed information from published papers and, in a few cases, ongoing mapping by SGU. In the discussion, an attempt will be made to integrate all the data into a tectonic interpretation of the area. The Bure area The Bure area (Fig. 2) is located a few kilometres east of Sorsele (Fig. 1). The rock sequence in the area has recently been described by Perdahl & Einarsson (1994) as constituting an example of the boundary between submarine and subaerial depositional environments, i.e. the stratigraphical boundary between the Skellefte and Arvidsjaur volcanic arcs. The exposed rock sequence constitutes a 4–8 km wide syncline (Perdahl & Einarsson, 1994) composed of sedimentary and mainly mafic volcanic rocks. The supracrustal units are intruded by the Sorsele granitoid to the west and by a Revsund granitoid to the east. Perdahl & Einarsson (1994) divide the supracrustal rocks of the area into three formations: the lowermost Stalo formation comprising basaltic to andesitic sedimentary units and rhyolite, the overlying Bure formation which consists of rhyolite–dacite lavas and clastic units and basaltic to andesitic lavas and clastic units, and the uppermost Loito conglomerate (Fig. 2). Two distinct low-magnetic lineaments appear on aeromagnetic maps of the Bure area and both are interpreted as shear zones. A prominent NNE-striking lineament cuts through the centre of the proposed supracrustal syncline. Field observations show that this lineament is caused by a ductile shear zone, here called the Loito shear zone. The continuation towards the south-west through the lowmagnetic granitoids is unclear but towards the north-east the shear zone continues via Jokkmokk to north of Pajala. A subparallel low-magnetic lineament cuts the Sorsele granitoid to the west of the supracrustal sequence. The surface expression of this lineament could not, however, be found in the field due to lack of exposure. The Loito shear zone was observed along the eastern margin of the Loito conglomerate and also in andesitebasalt of the Bure formation immediately east of the conglomerate (Fig. 2). Several more intensely sheared zones were observed and these were separated by areas of relatively well preserved rocks. Bedding surfaces were visible in an andesitic siltstone between two shear zones and east of the eastern-most shear zone almost undeformed amygdules were observed in andesite lavas or intrusions. The magnetic susceptibility is generally high in the less deformed supracrustal rocks in the area, whereas within the shear zones the susceptibility varied considerably from nearly zero to 9000x10-5 SI-units. Clasts in the Loito conglomerate are extremely stretched within the shear zone (Fig. 3a) and are really only visible on surfaces parallel to the very strong cleavage. The conglomerate is polymict but most clasts are felsic and fine-grained and probably have a volcanic origin. All clasts are both strongly flattened and stretched with a steep stretching lineation plunging north and a cleavage which dips 86° west. A later crenulation lineation is parallel to the stretching lineation and the associated crenulation cleavage strikes north-east. Asymmetric s-type tails on small crystals were observed in the field and they indicate that the eastern side has moved upwards relative to the western side. This observation was corroborated in thin section where both asymmetric wings on small clasts and crystals and shear bands indicate this sense of movement (Fig. 3b). The matrix in the conglomerate is composed of sericite, chlorite, fine-grained feldspar, quartz, and opaque phases. Calcite is common in veinlets parallel to the cleavage and also in stretched and fractured feldspar crystals. The andesite–basalt is feldspar porphyritic with a very fine-grained matrix of feldspar, sericite, and chlorite. Most of the feldspar phenocrysts are altered to chlorite, epidote, and calcite (Fig. 3c) near the shear zones whereas the feldspar phenocrysts are better preserved at some distance from the shear zones. Chlorite is common in strain shadows on epidote. Shear bands and asymmetric s-type tails on phenocrysts indicate that the eastern side has moved up relative to the western side also in the andesite (Fig. 3c). In the eastern splay of the shear zone a protomylonitic zone was found in a feldspar porphyritic dacite. Asymmetric tails on feldspar phenocrysts and shear bands (Fig. 3d) indicate that this splay has a west side up sense of movement. The alteration of feldspars to epidote and calcite in the andesite–basalt and the common occurrence of sericite in the matrix in both the andesite-basalt and the conglomerate indicates that the shearing took place under green- PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 49 1584000 1586000 1588000 1590000 7278000 1582000 7278000 1580000 67 50 7276000 7276000 69 Heden 7274000 7274000 71 63 86 78 77 83 77 71 80 50 70 61 NorrSvergoträsket 60 65 7272000 55 70 70 Sorsele 23 87 7268000 7270000 7268000 77 62 7270000 30 88 72 7272000 SörSvergoträsket 85 85 7264000 7264000 7266000 7266000 70 1580000 1582000 Sorsele and Revsund granite 1584000 1586000 1588000 Rhyolite Shear zone, barb on upthrown side Loito formation Polymict conglomerate and sandstone Basalt/andesite lava and conglomerate Bure formation Schist-greywacke 88 Bedding Schist dominating? 87 Foliation Mg-basalt Rhyodacite/rhyolite lava and conglomerate 1590000 Stalo formation 78 83 Shear fabric with stretching lineation 30 Fold axis Andesite tuff Andesite lava 2 km Fig. 2. Map of the Bure area. Geology based on observations by Perdahl & Einarsson (1994) complemented with results from recent mapping by the Geological Survey of Sweden and observations from this study. Shear zones are interpreted in this study. Small grey squares represent observed localities. 50 J. BERGMAN WEIHED Fig. 3. a) Outcrop in the Bure area showing extremely sheared Loito conglomerate. View towards south. b) Asymmetric wings on a small opaque clast indicating east side up. Width of view 2.7 mm. c) Feldspar phenocryst with asymmetric tails indicating east side up. Feldspar is strongly altered to epidote, chlorite, and calcite. Width of view 5.4 mm. d) Sheared feldspar porphyritic dacite with shear bands indicating west side up. Width of view 2.7 mm. schist facies conditions. These assemblages are also common in the country rocks and indicate that the shearing took place during or somewhat after peak metamorphism. Västra Kikkejaure to Jan-Svensamössan The north-eastern part of the Storavan map sheet is dominated by early orogenic granitoids of different types (Fig. 4). The Arvidsjaur granite occurs in the easternmost part of the area. These early orogenic granitoids intrude subaerial volcanic units of the Arvidsjaur Group which consist of rhyolitic to andesitic intrusions and lavas, and rhyolitic ignimbrites. These rocks were then intruded by post-orogenic granitoids of both Adak type (mediumgrained) and Revsund type (coarse-grained). The volcanic units are very well preserved and commonly contain only a weak cleavage indicating that the ductile deformation of these rocks is limited. Peak-metamorphic assemblages indicate upper greenschist to lower amphibolite facies in the southern parts of the map sheet (Bergström & Triumf 1996). Interpretation of aeromagnetic maps shows a large number of approximately north-striking low-magnetic lineaments which cut through the rocks of the area. These are interpreted to be faults or shear zones since they displace lithological contacts. In the central part of the Stor- avan map sheet these north-northeast striking faults contain many subeconomic uranium mineralizations (Adamek & Wilson 1979). A few short profiles were mapped across two of these approximately north-striking low-magnetic lineaments in the north-eastern part of the Storavan map sheet. In this area, the lineaments cross mainly synorogenic granitoids. Along Långträskälven to Stenträsket (area A in Fig. 4), an east-west profile across the eastern-most low-magnetic lineament on the Storavan map sheet covers volcanic rocks of dacitic to andesitic composition, intruded in the east by an Arvidsjaur granite. A penetrative grain shape foliation is present in the volcanic rocks but lacking in the coarse granite. Locally, the rock is cut by numerous closely spaced vertical north-striking fractures that are filled with epidote and, in these areas, the magnetic susceptibility decreases considerably. In general, however, the volcanic rocks are very well preserved with amygdules in andesite/ basalt, perlitic cracks in dacite, possible ignimbrite structures, and well developed porphyritic textures, indicating a limited amount of ductile deformation. The supracrustal sequence in this area is interpreted by Adamek (1987) to form a syncline. Around Tjålmak (area B in Fig. 4) a low-magnetic lineament crosses an area of early orogenic granitoid. This is a light grey, medium grained granitoid with a magnetic PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 51 1625000 1630000 1635000 1640000 ke ja 1655000 1660000 ure 7295000 Kik 1650000 7295000 V 1645000 Lå ng trä ske t 7290000 7290000 C Ava vike 7285000 7285000 B A n Ar vid sja ur sjö 7275000 7275000 7280000 7280000 n Arvidsjaur D 1625000 1630000 1635000 1640000 1645000 1650000 1655000 Post-volcanic granitoid (Revsund type), c. 1.80–1.78 Ga Mainly subaerial to shallow water rhyolite, (Arvidsjaur Group), 1.88–1.87 Ga Post-volcanic granitoid (Adak type), c. 1.80–1.78 Ga Mainly subaerial to shallow water dacite and andesite (Arvidsjaur Group), 1.88–1.87 Ga 1660000 Synvolcanic Arvidsjaur granitoid c. 1.87–1.85 Ga Synvolcanic granitoid c. 1.89–1.88 Ga Major faults and/or shear zones Gabbro, undivided Form lines of tectonic banding 5 km Fig. 4. Map of Storavan NE and parts of Arvidsjaur NW. Geology on Storavan map sheet from unpublished map by Adamek and on Arvidsjaur map sheet from Kathol & Triumf (1995). Most shear zones and all form lines interpreted in this study. Small grey squares represent observed localities. susceptibility of around 1800x10–5 SI-units. Fine-grained angular to sub-rounded dioritic fragments are present in the granitoid. The only observed deformation structures are locally closely spaced fractures in many orientations, some of which have epidote infill. In one outcrop the fractures are so closely spaced that they define a spaced cleavage. The orientation of this cleavage is subparallel to the low-magnetic lineament. However, lack of outcrop did not allow observation on the interpreted lineament. Nordanås and Jan-Svensamössan to Skogberget (areas C and D in Fig. 4, respectively) are two outcrop areas on the same low-magnetic lineament. In Nordanås (area C), the lineament crosses a flesh-coloured to pink mediumgrained granitoid with high magnetic susceptibility (av. 52 J. BERGMAN WEIHED 2000x10–5 SI-units). On either side of the lineament, the granitoid is well preserved with only a few fractures and contains fragments of mafic volcanic rocks with preserved bedding. At the position of the low-magnetic lineament, however, the granitoid is strongly brecciated with closely spaced fractures and epidote as an infilling mineral. The magnetic susceptibility is substantially reduced in this area and averages 100x10–5 SI-units. A similar pattern is found at Jan-Svensamössan and Skogberget (area D in Fig. 4) where granitoid is well preserved on either side of the lineament but strongly brecciated with epidote infill and a locally developed spaced cleavage at the position for the lineament. These observations all indicate that the north-striking low-magnetic lineaments in this area correspond to brittle faults where the rocks cut by the faults have been brecciated and infiltrated with fluids that deposited mainly epidote. The brecciation also led to a marked decrease of the magnetic susceptibility. Observations from northstriking low-magnetic lineaments on the western part of the Arvidsjaur map sheet show similar features (Benno Kathol, pers. comm. 1996). The brittle nature of the faults excluded the determination of sense of movement and amount of displacement on the probably steep slip surfaces (steep fracture cleavage). However, on aeromagnetic maps of the area a sinistral strike component is visible from a displaced gabbro body and also from other displaced magnetic markers. No information is available on the vertical component of movement. Deppis–Näsliden shear zone A locally diffuse low-magnetic lineament occurs on aeromagnetic maps of the western parts of map sheets 23J and 24J (Fig. 1). Sheared rocks were observed in the field at several localities along this lineament and the shear zone will here be called the Deppis–Näsliden shear zone. The northern part of this shear zone strikes north-east to north-northeast whereas in the southern part it strikes more north-northwest (Fig. 5). The shear zone is composed of at least three separate splays in the northern part of the area, whereas in the central part of the area the shear may be more localised to one zone. In the southern part of the area the shear zone again divides into two splays. The Deppis–Näsliden shear zone cuts through an area dominated by supracrustal rocks of the Arvidsjaur, Skellefte, and Vargfors Groups. Rocks of the Arvidsjaur Group occur in the northern part of the area where they are intruded by synvolcanic granitoids which are also cut by the Deppis–Näsliden shear zone (Fig. 5). Farther south, the shear zone occurs along the boundary between the central and western parts of the Skellefte district where mainly felsic volcanic rocks of the Skellefte Group and sedimentary units of the overlying Vargfors Group appear. These rocks are in the south intruded by post-volcanic granitoids of the Revsund and Skellefte types which may be unaffected by the Deppis–Näsliden shear zone, since the shear zone cannot be traced farther south on aeromagnetic maps. However, this may be due to the low-magnetic character of the Revsund and Skellefte granitoids. The rocks of the Skellefte and Vargfors Groups are folded into upright tight folds with steep axial surfaces striking northwest and variable fold axes. Late open folds have steep axial surfaces striking north to north-east and fold axes which are in general coaxial with the main upright folds. Ductile structures in the commonly well preserved Arvids- jaur Group are less well known and only weak fabrics are present. Within the Deppis–Näsliden shear zone, the sheared rocks always have a very strong cleavage with pronounced stretching lineations that plunge steeply west to north-west indicating movement mainly in the vertical direction. On the Arvidsjaur map sheet around Kilisåheden (A in Fig. 5), the Deppis–Näsliden shear zone was observed in an area with volcanic rocks belonging to the Arvidsjaur Group. These are finely flow-banded feldspar porphyritic dacites, rhyolitic very crystal-rich ignimbrites and mass flows, and siltstone units. Peperitic contacts were observed between dacite and siltstones in two localities. In this area the shear is localised into at least three zones separated by low-strain lenses. The shear fabric strikes 180–200° and has a steep dip towards the west. A strong stretching lineation plunges steeply west to north-west indicating mainly dip-slip movement. Primary structures like bedding and flow banding in the low-strain lenses often strike subparallel to the shear fabric but have a less steep dip. Flow banding in the dacites is locally intensely folded with axial surfaces parallel to the shear zone and shallowly plunging fold axes. Good shear sense indicators were observed in a few outcrops and in most thin sections. Asymmetric tails on feldspar phenocrysts (Fig. 6a) and weak shear bands indicate western side up on the westernmost shear zone, whereas east side up was indicated by asymmetric tails on feldspar phenocrysts (Fig. 6b) in the eastern-most shear zone (Fig. 5). The shear fabric is defined by bands of muscovite+chlorite alternating with bands of very finegrained feldspar±quartz. Feldspar phenocrysts are variably altered to sericite and, in the more mafic rocks, to epidote+calcite. The alteration of feldspar phenocrysts is strongest in the shear zone and decreases outwards from the zone. Farther south, the Deppis–Näsliden shear zone was encountered in rocks around the Grytfors dam (B in Fig. 5). In this area, the shear zone cuts mainly sedimentary units of silt/mudstone and volcanogenic mass flows belonging to the Skellefte Group. Bedding surfaces in the sedimentary units outside the shear zone are folded with axial surfaces striking north-west whereas towards the shear zone bedding is transposed into an orientation parallel to the zone itself. Stretching lineations on the steeply west-dipping shear surfaces plunge west to north-west indicating dominantly dip-slip movement. Shear sense indicators could not be found in the silt/mudstones, neither in the field nor in thin section, but in the somewhat coarser units, asymmetric tails on megacrysts and weak shear bands (Fig. 6c) indicate that the western side has moved up. In the area around Småberg–Hälträsket (C in Fig. 5), the Deppis–Näsliden shear zone cuts through an area of PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 53 Post-volcanic granitoid (Revsund type), c. 1.80–1.78 Ga 7300000 7300000 1650000 Post-volcanic granitoid (Skellefte type), c. 1.82–1.80 Ga Gabbro and diorite, undivided Ultramafic intrusion, undivided Synvolcanic intrusion (Gallejaur monzonite) c. 1.87–1.85 Ga Synvolcanic granitoid (Jörn & Arvidsjaur types) c. 1.89–1.88 Ga Arvidsjaur Conglomerate & sandstone (Vargfors Group), 1.88–1.87 Ga 63 80 Basalt & andesite (Vargfors Group), 1.88–1.87 Ga 78 78 Abborrträsk 70 71 73 Mudstone, sandstone & turbidite, (Bothnian, Vargfors & Skellefte Groups), 2.0–1.85 Ga A 76 Mainly subaerial to shallow water rhyolite, (Arvidsjaur Group), 1.88–1.87 Ga Mainly submarine basalt-andesite, (Skellefte Group), 1.89–1.88 Ga 7250000 7250000 Mainly submarine rhyolite & dacite (Skellefte Group), 1.89–1.88 Ga 86 69 78 70 B Major VHMS deposits Shear zone, barbs on upthrown side Glommersträsk 74 Faults and/or shear zones Form lines of tectonic banding and/or bedding 83 85 C 63 80 Shear fabric with stretching lineation 73 68 Rakkejaur 75 80 Näsliden Holmtjärn D Maurliden 10 km Norrliden 7200000 7200000 Norsjö 1650000 Fig. 5. Map of the geology around the Deppis-Näsliden shear zone. Geology compiled from Allen et al. (1996), Kathol & Triumf (1995) and the Mittnorden map (Lundqvist et al. 1996b). Shear zones and form lines interpreted in this study. Small grey squares represent observed localities. 54 J. BERGMAN WEIHED Fig. 6. a) Asymmetric wings on feldspar phenocryst in feldspar porphyritic dacite indicating west side up. Width of view 5.4 mm. b) Asymmetric wings on feldspar phenocryst in crystal-rich mass flow indicating east side up. Width of view 5.4 mm. c) Weakly developed shear bands in sheared crystal-rich dacitic mass flow indicating west side up. Width of view 5.4 mm. d) Well developed s-c fabric indicating west side up, in strongly altered feldspar porphyritic andesite. Width of view 5.4 mm. e) Same as d) but also showing the rounded epidote crystals that overgrow feldspar phenocrysts. Width of view 5.4 mm. mainly mafic volcanic rocks. East of the shear zone, very well preserved pillow lavas can be found. The shear zone itself was observed in an outcrop of a feldspar porphyritic mafic rock of unclear origin (possibly a crystal-rich mass flow or a shallow intrusion). The very strong shear fabric in this locality strikes north-northeast with a steep dip to the west and the stretching lineation plunges steeply north. An s-c fabric observed in outcrop indicates that the western side has moved up. This shear sense was confirmed by thin sections which all contain asymmetric tails on epidote and feldspar crystals and shear bands indicating the same sense of movement (Fig. 6d). The original feldspar phenocrysts have been strongly altered to epidote and calcite (Fig. 6e). The epidote is commonly rimmed by zoisite. The matrix between epidote and feldspar megacrysts is composed of very fine-grained feldspar, muscovite, and chlorite. The bedrock around Rakkejaur and Näsliden (D in Fig. 5) consists of folded volcanic and sedimentary rocks of the Skellefte and Vargfors Groups (Svenson 1982, Trepka-Bloch 1989). The volcanic units are mainly rhy- olitic to dacitic shallow intrusions and mass flows, and the sedimentary units are finely laminated mud- and siltstones. Axial surfaces of the main isoclinal folds are steep and strike north to north-northwest with fold axes plunging steeply west (Svenson 1982). Narrow zones with strong deformation and a steep stretching lineation were observed in a few outcrops north of Näsliden in a crystalrich volcaniclastic unit with andesitic fragments. In thin section the feldspar phenocrysts are partially altered to sericite and stretched with boudin necks infilled by calcite. The very fine-grained matrix is composed of feldspar, sericite, chlorite, and calcite and the cleavage is defined mainly by the alignment of micas. Slightly asymmetrical tails on some plagioclase phenocrysts may indicate east side up. The eastern splay of the Deppis–Näsliden shear zone, interpreted from aeromagnetic maps (Fig. 5), should pass close to the Rakkejaur deposit but it was not found in outcrop. In summary, the observed shear sense indicators show that the main Deppis–Näsliden shear zone had dominantly dip slip movement where the western side moved up PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 55 relative to the eastern side. An easterly splay in the northern part of the area shows the opposite sense of movement. All observations indicate that shearing along the zone took place after the main folding of the area and probably at greenschist facies conditions. The amount of movement, however, has not been possible to determine. Central Skellefte District In the central part of the Skellefte district (Fig. 7) a number of shear zones have been identified during previous mapping (Bergman 1991). A few of these zones were studied in more detail in this project. The central part of the Skellefte district consists of a sequence of volcanic and volcaniclastic units of mainly rhyolitic to dacitic composi1690000 1700000 7220000 7220000 1680000 tion which belong to the Skellefte Group. Mafic sills have intruded into the sequence at some stage before deformation. These rocks are overlain by siltstones, sandstones, grits, and conglomerates of the Vargfors Group. All of these rocks are relatively well preserved and greenschist facies mineral assemblages are normal. Towards the south, however, the metamorphic grade increases and north of the Karsträsk intrusion, amphibolites and strongly recrystallized meta-volcanic rocks occur. The main deformational structures are upright tight folds with fold axes plunging around 45° SE in most of the area. An axial planar cleavage developed as a penetrative grain shape foliation in the volcanic units whereas it is a crenulation cleavage in the fine-grained sedimentary units. This indicates that there, at least locally, is an earlier bedding-parallel Sk e Riv llefte er G 45 47 Norrliden A 32 52 Svansele E 88 D Udden 87 83 C 55 82 Petiknäs N 82 Petiknäs S F B 87 82 80 87 47 H rst räs 24 Renström I 84 ke t 7200000 7200000 Ka 7210000 7210000 Kedträsk 1680000 1690000 1700000 Post-volcanic granitoid (Revsund type), c. 1.80–1.78 Ga Conglomerate &sandstone (Vargfors Group), 1.88–1.87 Ga Major VHMS deposits Gabbro and diorite, undivided Basalt & andesite (Vargfors Group), 1.88–1.87 Ga Shear zone, barbs on upthrown side Ultramafic intrusion, undivided Mudstone, sandstone & turbidite, (Bothnian, Vargfors & Skellefte Groups), 2.0–1.85 Ga Form lines of tectonic banding and/or bedding Synvolcanic granitoid (Jörn type) c. 1.89–1.88 Ga Mainly submarine basalt-andesite, (Skellefte Group), 1.89–1.88 Ga Mainly submarine rhyolite & dacite (Skellefte Group), 1.89–1.88 Ga 63 80 Shear fabric with stretching lineation 5 km Fig. 7. Geological map of the central part of the Skellefte district compiled from unpublished maps by Bergman Weihed and Allen et al. (1996). Most shear zones and form lines interpreted in this study. Small grey squares represent observed localities. 56 J. BERGMAN WEIHED foliation (cf. Allen et al. 1996) and this was also observed in a few outcrops with mudstones. Later deformation caused gentle folds with steep axial surfaces striking north to north-east and largely coaxial with the first folding. Locally a spaced crenulation cleavage developed along the axial surfaces to these late folds. Revsund granitoid cuts most of the structures in the eastern and western parts of the area (Fig. 7). Shear zones occur mainly subparallel to the axial surfaces of first folds but in the eastern part of the area, north-striking shear zones are also present along the western contact between supracrustal rocks and a Revsund granitoid intrusion. A quartz-feldspar porphyry is strongly sheared around Övre Krokforsen (area A in Fig. 7). The shear zone is at least 20 m wide and there is a 2 m wide intensely sheared zone. The shear fabric strikes east and dips around 50° south and the stretching lineation plunges 30° towards WSW. All feldspar phenocrysts have been almost entirely obliterated during the shearing due to previous sericite alteration of the feldspars whereas the quartz phenocrysts remain, although they are strongly deformed. The shear foliation is defined by bands of very fine-grained muscovite alternating with bands of quartz, biotite, and chlorite. Asymmetric tails on quartz phenocrysts and an s-c fabric can be seen both in the field and in thin section (Fig. 8a), and they both indicate that the southern side has moved up relative to the northern side. With the shallow plunge of the stretching lineation this also gives a sinistral strike component of the movement. The shear foliation is subparallel to axial surfaces of major upright folds in the region. In a horizontal section, a north-striking slight crenulation of the shear foliation is visible. This corresponds to the second regional deformation in the area and indicates that shear along the zone occurred some time during or immediately after the main first folding event, but before the second deformation. South of Kusfors, in a 200 m long railroad cutting (B in Fig. 7), a Jörn-type granitoid which is cut by a number of quartz-feldspar porphyritic and mafic dykes is deformed by at least five separate shear zones. The steep zones are less than 10 m wide and they strike SE to SSE. A strong stretching lineation plunges about 60° north-west. Much of the deformation is brittle but incipient s-c fabric and weak shear bands in thin sections (Fig. 8b) indicate that the south-western side of the shear zone has moved up. In addition, there are also shear sense indicators (shear bands, tiled feldspar crystals, and oblique foliation) on horizontal surfaces and they all indicate a sinistral sense of movement. This is in agreement with the expected horizontal displacement. The shear fabric is overprinted by crenulations formed during the second regional phase of deformation. North of the Skellefte river in railroad cuttings (C, D & E in Fig. 7), shear zones were observed in volcanic units. These shear zones are all steep, strike ESE, and have a strong subvertical lineation. In the southern-most of these outcrops (C in Fig. 7), there are two 4 m wide zones and several narrower zones through a chloritic rock. Narrow quartz veins are parallel to the strong foliation between shear planes and fuchsite was observed in outcrop. In thin section, remains of biotite can be seen in the chloritic parts. Feldspar crystals have both a strong grain shape fabric and a strong lattice preferred orientation indicating dynamic recrystallization. Calcite is common and cloudy patches in the calcite may represent ghosts of feldspar phenocrysts. Weak shear bands are present throughout and they indicate that the north-northeast side has moved up relative to the SSW side (Fig. 8c). The strong shear fabric was crenulated during the second regional deformation. This outcrop is separated from an outcrop with shear zones farther north by an area of rather well preserved volcanic rocks with lithological contacts that strike 140° (D in Fig. 7). In the northern-most outcrop (E in Fig. 7), a strongly deformed 20 m wide zone and two narrower 1.5–5 m wide zones were observed in a fragmental rock of andesitic composition with angular, 1 mm to 10 cm large fragments in a very fine-grained matrix composed mainly of chlorite. These deformed zones are also steep, strike ESE, and have a pronounced subvertical stretching lineation. Shear sense indicators could not be found in these shear zones, neither in the field nor in thin section. A pronounced shear zone is present in the Petiknäs N mine (Fig. 7) and it may be traced towards the WSW in topography to Harahukberget (area F in Fig. 7) north of the Rengård dam. In the Petiknäs mine the shear zone cuts through volcaniclastic rhyolitic rocks. The zone is several meters wide and contains a 50 cm wide clay zone. The orientation of this clay zone is 083/45 and the boundaries to less deformed rock are rather sharp. Both horizontal and down-dip striations have been observed on shear planes (Joseph Hull pers. comm. 1992). However, on a vertical surface in a less clay-rich part, an s-c fabric was observed which indicates reverse movement. Outside the clay zone, the volcaniclastic rocks have a strong subvertical cleavage with a pronounced subvertical stretching lineation. This strongly cleaved zone is about 50 m long. Late closely spaced subhorizontal fractures have movements of less than 1 m. At Harahukberget (F in Fig. 7) a shear zone was observed in a Jörn-type granitoid. Several strongly deformed zones were observed, especially along contacts between the granitoid and mafic and quartz-feldspar porphyritic dykes, but the strongest deformation was found in the northernmost part of the outcrop towards the contact to volcanic rocks. There, a more than 5 m wide protomylonite to mylonite is exposed. In the mylonitic part the rock is banded with alternating light and dark bands composed of muscovite and chlorite, feldspar, and calcite, PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 57 Fig. 8. a) Asymmetric tails and weakly developed s-c fabric indicate south side up in strongly deformed quartz-feldspar porphyry. Most of the feldspar phenocrysts are completely altered to sericite. Embayments in quartz grain indicate the volcanic origin. Width of view 5.4 mm. b) Weak shear band indicates south side up in protomylonitic Jörn granitoid. Width of view 5.4 mm. c) Weak shear bands indicate north side up in strongly chlorite altered volcanic rock. Width of view 2.7 mm. d) Strong mylonitic foliation with shear bands indicating south side up in strongly sheared Jörn granitoid. Width of view 5.4 mm. e) Sandstones below the Vargfors dam which are locally strongly folded with shear zones parallel to axial surfaces of the upright folds. f) Weakly developed s-c fabric indicating dextral strike slip in granitic gneiss. Width of view 5.4 mm. g) Foliation defined by alternating bands of quartz+feldspar and biotite+muscovite. Width of view 5.4 mm. respectively. The east-striking mylonite is steep and has a stretching lineation plunging steeply north-east. Shear sense indicators, as shear bands (Fig. 8d) and asymmetric tails on phenocrysts, all indicate that the southern side has moved up. It is probable that the more gently dipping 58 J. BERGMAN WEIHED brittle fault in Petiknäs is overprinting and partly following an earlier shear zone which is represented by the shear zone observed at Harahukberget. Similar shear zones to the above were also observed below the Vargfors dam (G in Fig. 7) in the Skellefte river in siltstones of the Vargfors Group. The siltstone beds dip 40–50° NE and are generally well preserved with ripples and cross bedding indicating stratigraphic younging towards north-east. In localised, up to 2 m wide zones, however, the siltstones are intensely folded into tight folds and subvertical bedding surfaces are found. Along the subvertical, southeast-striking axial surfaces a cleavage is developed which have strongly sheared zones with reverse displacements up to 50 cm (Fig. 8e). The observed stretching lineations plunge about 45° towards 030° which is more or less perpendicular to the fold axes observed in the folded siltstones. In the Renström–Karsbäcksliden area, two shear systems intersect which results in a complex pattern of shear zones. This is very obvious on aeromagnetic maps of the area. The northwest-striking shear zones, which dominate the central part of the Skellefte district, encounters an anastomosing system of north-striking shear zones immediately west of the Renström mine. This north-striking shear system can be traced southwards along the western contact of the Revsund intrusion and northwards towards the Jörn batholith. North-striking shear zones have been observed within the ore in the Renström mine (Duckworth & Rickard 1993) and they also cut volcanic units around the Renström mine (Wanhainen, 1997). The north-striking shear zones are inferred to cut smaller Jörn-type bodies and amphibolites farther south although no shear zones were observed in the field in these rocks. Northwest-striking shear zones were observed mainly in rocks of somewhat higher metamorphic grade than the rocks in the Skellefte district described above. One of these shear zones was observed in the elliptical, granitic Karsträsk intrusion, and supracrustal rocks along the northern edge of the dome (H in Fig. 7). This shear zone is steep with a subhorizontal stretching lineation which plunges gently north-west. A locally developed s-c fabric (Fig. 8f ) and small shear zones observed in outcrop show a dextral dominantly strike-slip component of movement. In thin section all minerals are recrystallized during regional metamorphism (Fig. 8g), which indicates that shearing along this zone occurred before or during peak-metamorphism. A sheared Jörn granitoid was observed in the south-eastern part of the area (I in Fig. 7). The steep shear fabric strikes north-west and the stretching lineation plunges 50° south-east. A well developed s-c fabric with asymmetric tails on feldspar porphyroclasts indicates that the southern side has moved upwards relative to the northern side. These outcrops were located close to a long system of bogs in the same direction as the shear zone and local boulders of much more intensely sheared granitoid than observed in outcrop indicate that the shear zone is fairly wide and intense. The north-striking shear system was observed in the Renström mine (Fig. 7) in the drift at the 800 m level from the Renström mine towards the Petiknäs mine. Two well-defined, steep, about 20 m wide shear zones cut through feldspar porphyritic andesitic rocks which may originally have been shallow intrusions. Immediately east of the shear zones, fine-grained sedimentary units with preserved bedding structures occur. Both the shear fabric and the stretching lineations are subvertical and shear sense indicators (mainly a weak s-c fabric) show that the eastern side has moved up relative to the western side. The andesitic rocks in the shear zones are strongly altered and now consist dominantly of chlorite and calcite which almost completely obscures the original rock texture (Wanhainen, 1997). The age relationships between the north-west striking shear zones and the north-striking anastomosing shear system is not firmly established. However, the north-west striking shear zones formed prior to the second deformation and before or during peak-metamorphic conditions whereas the north-striking shear zones indicate retrograde conditions during shearing. This may indicate that the north-striking shear system formed after the north-west striking shear zones. All shear zones observed in the central part of the Skellefte district are overprinted by crenulations of the second regional deformation and shearing must thus have occurred prior to the second folding. There are, however, no absolute constraints on the age of the deformations in the Skellefte district. The first major phase of folding occurred prior to the intrusion of Revsund granitoids at 1800–1780 Ma (Skiöld 1988) and after the intrusion of the Sikträsk granitoid at about 1880 Ma (Weihed & Vaasjoki 1993, Billström & Weihed 1996, K. Billström & P. Weihed pers. comm. 2001). The second deformation affects, at least locally, the Revsund granitoid and must thus have occurred after 1800–1780 Ma. The Vidsel–Röjnoret Shear System The western parts of map sheets 22–24 K are dominated by a sedimentary sequence composed of schists and greywackes, locally with interlayered pillow lavas. This sedimentary sequence overlies volcanic rocks of the Skellefte Group in an area around Kankberg and Boliden (Fig. 9). The volcanic rocks contain a number of mineralizations with associated hydrothermal alteration but they are commonly well preserved and characterised by greenschist facies mineral assemblages. In the sedimentary sequence, in contrast, the metamorphic grade increases eastwards to upper amphibolite facies, and migmatites are common in the eastern-most parts of the area. In the north-western part of the area, volcanic units of the Arvidsjaur Group occur (Fig. 9). These are commonly subaerial rhyolites and dacites. The supracrustal rocks PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 59 Post-volcanic granitoid (Revsund type), c. 1.80–1.78 Ga 1750000 7300000 1725000 7300000 1700000 Älvsbyn Post-volcanic granitoid (Skellefte type), c. 1.82–1.80 Ga Gabbro and diorite, undivided I Perthite monzonite c. 1.88–1.86 Ga 7275000 7275000 Syn-volcanic granitoid (Jörn type) c. 1.89–1.88 Ga Conglomerate &sandstone (Vargfors Group), 1.88–1.87 Ga Mudstone, sandstone & turbidite, (Bothnian, Vargfors & Skellefte Groups), 2.0–1.85 Ga Mainly subaerial to shallow water rhyolite, (Arvidsjaur Group), 1.88–1.87 Ga Mainly submarine basalt-andesite, (Skellefte Group), 1.89–1.88 Ga Lillpite Långträsk Mainly submarine rhyolite & dacite (Skellefte Group), 1.89–1.88 Ga 7250000 7250000 Major VHMS deposit Major gold deposit Shear zone, barbs on upthrown side H 05 Form lines of tectonic banding and/or bedding 42 57 Fällfors 77 55 Åkerberg 65 80 Drängsmark Petiknäs N Björkdal Renström Boliden 70 Ersmark Långsele 18 87 Långdal l l l l l l l l l 81 C Myckle B Skellefteå Medle 58 l l l l Röjnoret structure Kåge 83 J Bastuträsk 5 km Ostvik Kusmark D V Åkulla 7200000 Kankberg 7200000 Post-glacial fault K F E Shear fabric with stretching lineation 7225000 7225000 G l l 63 80 1700000 57 17 A 77 76 1725000 1750000 Fig. 9. Geological map of the eastern part of the Skellefte district with the Vidsel–Röjnoret shear system, compiled from Allen et al. (1996) and the Mittnorden map (Lundqvist et al. 1996b). Small grey squares represent observed localities. 60 J. BERGMAN WEIHED Fig. 10.a) Tiling of feldspars and an oblique foliations indicating west side up in sheared Skellefte type granite. Width of view 5.4 mm. b) Titanites aligned in the foliation. Width of view 1.4 mm., c) Strongly sheared pegmatite with s-type wings on a feldspar crystal indicating west side up. Width of view 5.4 mm. d) Oblique foliation and tiled feldspar phenocrysts indicating west side up in same shear zone as in c). Width of view 5.4 mm. are intruded in the west by the syn-volcanic Jörn batholith and in the north by perthite-monzonites of a similar age. In the east, vast areas of post-volcanic granites of the Skellefte and Revsund types intrude the sedimentary sequence. Many low-magnetic lineaments were observed on aeromagnetic maps of the area. These form a complex array of anastomosing and splaying lineaments which are interpreted as shear zones or faults. This array of shear zones will here be called the Vidsel–Röjnoret shear system (VRSS) and it forms a diffuse boundary between rocks of lower metamorphic grade to the west and rocks of higher metamorphic grade to the east. The shear zones cut through nearly all rock types present in the area. Most zones are present in sedimentary and volcanic units but one splay of the zone cuts through the Björkdal granitoid and farther south, one shear zone forms the eastern margin of the Röjnoret structure. In the north the shear zone system also affects the eastern margin of the Jörn batholith. It is known that at least a part of the VRSS has been tectonically active even after the last glaciation since postglacial faults have been observed (Rodhe 1987) in an area around Röjnoret (west of B in Fig. 9). Outcrops were mapped in areas where the shear zones were expected to appear on the surface (areas B–I on Fig. 9), and a few outcrops where shear zones had previously been observed were visited (eg. area A on Fig. 9). Sheared rocks were encountered only in a few localities, and shear sense indicators could be determined in only three localities. Observations will be described from south to north. Around Rismyrliden (area A in Fig. 9) a Skellefte type granitoid with lath-shaped feldspar megacrysts has an almost north-striking steep protomylonitic fabric with a stretching lineation plunging 77° towards 102°. This shear zone was first noted by Nilsson & Kero (1998). An s-c fabric is developed with asymmetric tails on feldspar megacrysts but in the field, the shear sense criteria give conflicting slip directions. In thin section the deformation is semi-brittle and a shear foliation, which is defined by minute broken grains of feldspar, is slightly anastomosing around large, very fractured, rounded grains of feldspar. Bands between the larger feldspar megacrysts consist of fine-grained quartz with a slight ribbon texture. Shear sense criteria are tiling of feldspar grains and an oblique foliation in fine-grained quartz and feldspar between brittle shears (Fig. 10a). These criteria indicate that the western side has moved up relative to the eastern side. Tiling of megacrysts is considered an unreliable shear criterion whereas the oblique foliation is probably more reliable (Passchier & Trouw 1996). The regional extent of this shear zone is essentially unknown. It is shown on the Mittnorden map (Lundqvist et al. 1996b) to continue southwards for some distance and to connect northwards to the more continuous shear zone described below, but the zone is not visible on aeromagnetic maps of the scale used in this project. PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 61 a) very weak S2 quartz phenocryst pegmatite b) N poles to S1 (n=15) stretching lineation and fold axes (n=8) axial surfaces π-axis S1 20 cm fold axis 189/23 feldspar phenocryst Fig. 11. a) Sketch of outcrop from area B in Figure 9. Vertical surface looking north. b) Stereogram showing orientations of structural elements in area B in Figure 9. The eastern margin of the Röjnoret structure (area B in Fig. 9) appears to be bounded by a shear zone which continues for a considerable distance to the north (compare Fig. 9). The outcrops in the Röjnoret structure observed in this project are all rather similar with a quartz and feldspar porphyritic rock, which probably is rhyolitic in composition. The rock contains about 5 %, in average 3 mm large, subhedral to euhedral feldspar phenocrysts and <1%, rounded, 7 mm large, blue quartz phenocrysts in a fine-grained matrix composed of quartz, feldspar, and biotite. The rock is invariably strongly foliated with feldspar phenocrysts aligned along the foliation which is also defined by the orientation of biotite aggregates. The foliation is folded, at least on a small scale, into open folds with moderate dips of the fold limbs and gentle fold axes. Quartz phenocrysts are stretched parallel to the fold axes and flattened along the axial plane, whereas the feldspar phenocrysts remain aligned to the folded foliation (Fig. 11a). Axial surfaces to the folds are steep. The orientations of structural elements are shown in Figure 11b. In the easternmost outcrop a more than 2 m wide strongly foliated zone with extremely stretched quartz phenocrysts is present. The shear foliation in this outcrop strikes 018° and dips 57° east and the stretching lineation plunges 20° south. Narrow pegmatites occur along the foliation and deformation is concentrated to the margins of these, although pegmatites are also deformed. In a slightly less deformed zone around Aftonsmyran the shear fabric strikes 017° and dips 58° east with a down-dip stretching lineation. Asymmetric tails on quartz phenocrysts indicate that the eastern side has moved upwards relative to the western side. In thin section it is clear that the foliation is also defined by bands of euhedral to subhedral titanite and epidote with cores of allanite (Fig. 10b). Zircons are also present. Both the titanites and the zircons have been dated by Kjell Billström (pers. comm. 1997). The preliminary age of the titanites is around 1790 Ma whereas the zircons give a preliminary age closer to 1870 Ma. 62 J. BERGMAN WEIHED Outcrops between Finnforsberget and Pultarliden (areas C–F in Fig. 9) were mapped in order to find the continuation northwards of the above described shear zone. Around Finnforsberget and Silvgruvberget (area C in Fig. 9) the rocks are mainly mudstones and siltstones, commonly with a rusty appearance. No clearly sheared rocks were identified but the bedding surfaces are tectonically disturbed and commonly transposed into a steeply eastdipping, rather strong cleavage with a strike of 020°. Quartz veins are common parallel to the cleavage and en échelon tension gashes were also observed. At Fölmyrberget (area D in Fig. 9), volcanogenic metasedimentary rocks are exposed. Bedding in these grits, impure limestones, and mass flows strikes in average eastwest and it is folded with steep axial surfaces striking north-east and fold axes plunging 50° north-east. A spaced and anastomosing axial planar cleavage is developed and felsic fragments in the impure limestone are stretched parallel to the fold axis. No evidence of shearing was found in this area. At Björklidberget (area E in Fig. 9) feldspar porphyritic, probably coherent dacites were observed in the eastern part of the area. These are well preserved and contain only a weak but penetrative northeast-striking grain shape cleavage. The western-most outcrop consists of a mass flow with volcanic clasts, some of which are pumiceous. Anastomosing, north-northwest striking zones of stronger cleavage have a weakly developed s-c fabric on surfaces parallel to the lineation which plunges 65° north. This s-c fabric indicates that the western side has moved up. Individual sheared zones are rather narrow (<20 cm) and no similar structures could be found in neighbouring outcrops so the significance of this shear zone is unknown. Immediately east of this outcrop, however, there is a pronounced topographical low (along Lill-Häbbersbäcken) striking in the same direction as the narrow shear zones. At Pultarliden (area F in Fig. 9), there is a very crystalrich mass flow with about 30 %, 1–6 mm large, euhedral to subhedral feldspar crystals and about 10 %, 1–5 mm large, blue quartz crystals in a fine-grained matrix composed mainly of sericite and chlorite. One to five centimetre large fragments of a quartz-porphyritic rock also occur. Bands with more fragments define a faint layering which strikes 040° with an unknown dip. A strong steep cleavage strikes 020° and is defined by bands of chlorite and sericite and also the orientation of feldspar crystals. Towards the east the cleavage increases in intensity and a protomylonitic fabric is developed. A stretching lineation plunges down-dip in the cleavage indicating mainly dipslip movement but the sense of shear could not be determined. A large number of open fractures occur in the same orientation as the shear fabric. In the area around Furuberget (area G in Fig. 9), a number of southeast-striking lineaments are linking two north-striking lineaments. One of the southeast-striking zones outcrops along the Klintån in Jörn-type granitoid. This shear zone is more than 1 m wide and the shear fabric dips 60° south-west with a strong stretching lineation that plunges 57° south-east. A well defined s-c fabric is developed which indicates that the southern side has moved upwards. Some less than 10 cm wide, steep, semi-brittle shear zones were observed in several orientations (mainly north-northeast and east). Stretching lineations could not be observed in these small shear zones due to outcrops without relief and therefore no shear sense could be deduced. Sinistral strike separation was, however, observed in some of these zones. In other outcrops in the area very little deformation was observed and only a weak foliation is present in the Jörn granitoid. Similar observations were made in the area around H in Figure 9. In general, the Jörn granitoid is very little deformed and only narrow discrete faults and fractures cut the rock in many orientations. One outcrop, however, differs from the above in that it is a gneissic diorite with a strong linear fabric that plunges 5° north and a planar, NNW-striking component. Farther north in area I on Figure 9, outcrops close to the interpreted surface location of one of the larger north-striking lineaments were mapped. The main rocktype in the area is a medium- to coarse-grained pink granitoid with abundant fragments and cross-cut by later mafic dykes. Contacts to these dykes, which have many orientations, are commonly cleaved. Apart from this, very little semi-ductile to ductile deformation was noted. One <20 cm wide, steep zone with intense cleavage strikes southeast and has a steeply plunging stretching lineation. A weakly developed s-c fabric is seen both in outcrop and in thin section and it indicates that the south-western side has moved up relative to the north-eastern side. Late fractures and quartz veins are common, however, and most of these strike 060° and 120°. A more than 5 m wide shear zone was observed at J in Figure 9. This protomylonitic zone cuts across a Skellefte granite. The mylonitic fabric is steep and strikes north-west. A strong subhorizontal stretching lineation and a well developed s-c fabric indicates sinistral strike slip movement. East of Åkerberg at V. Selet (area K in Fig. 9) a more than 10 m wide mylonite cutting a pegmatite was observed. The mylonitic foliation is steep and strikes 189° and the stretching lineation plunges 70° north-west. Asymmetrical tails on mantled feldspar porphyroclasts (Fig. 10c) all indicate that the west side has moved up relative to the east side. The mylonitic banding is defined by alternating layers of fine-grained feldspar with some muscovite and recrystallized quartz ribbons. Other shear sense indicators observed in thin section were an oblique foliation in the fine-grained layers (Fig. 10d) and tiling of feldspar porphyroclasts. All indicate the same shear sense. The continuation of this shear zone is unclear since it is not visible on aeromagnetic maps of the scale used in this study. In summarising all information on the VRSS, very limited kinematic data is still available. Shear sense indicators were only found in the southernmost part of the VRSS on the north-striking zones and one observation is available on the northwest-striking zones that link the north-striking zones in the centre of the area. These observations indicate east side up reverse movements on the north-striking zones and south side up reverse movements on the northwest-striking zones. Very few observations on shear zones were made also during the regional mapping of the area. This may be due either to the lack of outcrops or that the shear zones simply were not recognised as such. Kalvträsk map sheet (22J) The south-eastern part of the Kalvträsk map sheet is dominated by low-magnetic granitoids which results in an aeromagnetic map with few visible structures. During the regional mapping (Weihed & Antal 1998a, b, c, d) in the area, some shear zone localities were found. These have been studied in some more detail in this project. Near Slipstensjön (A in Fig. 12), the western outcrop exposes a tectonic contact between Revsund and Skellefte granitoids. A steep protomylonitic foliation with a steep stretching lineation is present and a weak s-c fabric indicates east side up, reverse movement. In thin section, the feldspars are extremely deformed with microcracks and deformation lamellae. Dynamic recrystallization has reduced the grain size of the quartz considerably and some strongly deformed dark brown biotite is present. The eastern outcrop exposes a serorogenic granitoid (Skellefte PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 63 170000 Post-volcanic granitoid (Revsund type), c. 1.80–1.78 Ga 720000 720000 167500 Sikträsket Post-volcanic granitoid (Skellefte type), c. 1.82–1.80 Ga Gabbro and diorite, undivided Synvolcanic granitoid (Jörn type) c. 1.89–1.88 Ga Mudstone, sandstone & turbidite, (Bothnian, Vargfors & Skellefte Groups), 2.0–1.85 Ga 85 Mainly submarine rhyolite & dacite (Skellefte Group), 1.89–1.88 Ga B Faults and shear zones, barb on upthrown side 717500 717500 81 36 Form lines of tectonic banding and/or bedding 78 83 Shear fabric with stretching lineation Åmsele A 715000 715000 81 10 km Hällnäs 167500 170000 Fig. 12. Geological map of the eastern parts of the Kalvträsk map sheet. Simplified from Weihed & Antal (1998a, b, c, d). Small grey squares represent observed localities. type) with a strong subvertical protomylonitic fabric and a steep stretching lineation. Asymmetric pressure shadows on feldspars and an s-c fabric also here indicate east side up, reverse movement. The deformation in this zone is semi-brittle with bands of very fine-grained muscovite and feldspar alternating with coarser quartz-rich bands with minor biotite and muscovite and a weakly developed s-c fabric (Fig. 13a). At area B in Figure 12, mylonitic zones were observed in Skellefte type granitoid in two localities. In the northern outcrop, a more than 10 m wide mylonitic zone has a well developed steep s-c fabric with a steeply plunging stretching lineation. In thin section feldspars (both plagio64 J. BERGMAN WEIHED clase and K-feldspar) are strongly fractured and slightly altered to sericite. Quartz is dynamically recrystallized and muscovite and biotite are deformed. In the southern outcrop, a couple of narrower (about 30 cm) mylonitic zones are present. A well developed steep mylonitic fabric with a steeply plunging stretching lineation is present also here. In thin section, rounded, about 2 mm large s-type feldspar megacrysts are surrounded by a very fine-grained foliated matrix of quartz, muscovite, chlorite, and opaque phases. Shear bands are also developed locally (Fig. 13b). In all studied thin sections and outcrops the same east side up reverse movement is observed. Fig. 13. a) Semi-brittle deformation zone with a weakly developed s-c fabric indicating east side up in a Skellefte type granite. Width of view 5.4 mm. b) Mylonite with shear bands and asymmetric tails on feldspar grains indicate east side up in a Skellefte type granite. Width of view 5.4 mm. Discussion In the discussion below, each area presented above will be briefly discussed with special emphasis on the relative timing of shearing. The previously unrecognised (?) Loito shear zone through the Bure area (Fig. 2) shows well developed shear sense indicators that indicate mainly east side up reverse movement. On the north-eastern splay, west side up reverse movement was indicated in one locality. The structural block between the two splays of the Loito shear zone in the northern part of the area could thus be interpreted as a pop-up structure. The appearance of Loito conglomerate on the western side of both splays of the fault may indicate a fault repetition of the unit. However, the amount of displacement on the Loito shear zone is unknown. The timing of shearing can only be loosely constrained. The interpretation of aeromagnetic maps indicates that the shear zones cut through also the Sorsele granitoid which has been dated at 1766±8 Ma and 1791±22 Ma by Skiöld (1988). The latest shearing must thus have occurred some time after the intrusion of this granitoid. No other age constraints exist at this stage. The low-magnetic lineaments on the Storavan map sheet (Fig. 4) appear to be caused by dominantly brittle faults with strong brecciation of the rock and fluid infiltration causing alteration and infill by epidote. Sense of movement and amount of displacement on the faults could not be determined. Displaced lithological contacts indicate a sinistral strike component of movement but the vertical component is unknown. On aeromagnetic maps, the lineaments in this area cut both supracrustal rocks and older granitoids (1.89–1.87 Ga), whereas no cross-cutting relationships could be observed with the younger granitoids. The faulting can therefore only be constrained to some time after 1.87 Ga. The brittle nature of the faults, however, indicates a much later movement, probably after the intrusion of the youngest granitoids. Deformation on the Deppis–Näsliden shear zone (DNSZ, Fig. 5) and the north-striking zones around Renström mine (central Skellefte district, Fig. 7) occurred after the main, tight to isoclinal folding (D2) in the area since these fold structures are deformed by the northstriking shear zones. The mineral assemblages in these shear zones is dominated by chlorite, sericite, epidote, and calcite, depending on original rock composition, and this indicates deformation during greenschist facies conditions. The regional D3 folding produced open folds with steep axial surfaces striking north to north-east and many small shear zones have been observed along these axial surfaces (Bergman Weihed unpublished data). Since the north-striking shear zones show no evidence of later ductile deformation, it is possible that they may have initially formed during, or somewhat after, the regional D3 folding. The regional D2 folding occurred after the intrusion of the Sikträsk granitoid at c. 1.87 Ga (Weihed & Vaasjoki 1993, Billström & Weihed 1996) and before the intrusion of Revsund granitoid at c. 1.80 Ga (Skiöld 1988) whereas the F3 folding episode occurred during or after the intrusion of the Revsund granitoid at c. 1.80 Ga (Skiöld 1988). The amount of displacement on the north-striking shear zones is unknown. The northwest-striking shear zones in the central Skellefte district (Fig. 7), in contrast, are overprinted by crenulations and a local weak cleavage which can be related to the regional D3 folding. In general, the metamorphic grade in the central Skellefte district increases from greenschist facies rocks in the northern part of Figure 7 to amphibolite facies rocks in the south. This is reflected in the mineral assemblages observed from shear zones. The shear zone observed in area H in Figure 7 has a mineral assemblage that indicates deformation above greenschist facies conditions. Most of the observed northwest-striking shear zones have oblique-slip south side up displacement. An effect of this is that progressively deeper parts of the crust are exposed towards the south and this is also what is PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 65 observed. In contrast to most of the northwest-striking shear zones in the northern part of the area, shear zones with the same orientation north of the Karsträsk intrusion have subhorizontal stretching lineations indicating mainly strike-slip displacement. This may be caused by a transpressive regime in this area during deformation (see below). Very limited kinematic data is available for the Vidsel– Röjnoret Shear System (VRSS, Fig. 9). However, in the southern-most part of the VRSS, east side up reverse dipslip movements are indicated. This deformation is preliminarily dated at c. 1.79 Ga (Kjell Billström pers. comm. 1996) which is close in time to the intrusion of Revsund granitoid. The dated shear zone locality probably represents a slightly deeper section of the crust since titanites have formed during the shearing. This was not observed anywhere else along the VRSS where greenschist facies assemblages are most common. The metamorphic grade increases in the metasedimentary rocks towards the east and south, and the rocks in the southern-most part of Figure 9 commonly have a gneissic structure. Vargfors Group has been dated at 1875 Ma (Billström & Weihed 1996). These rocks are affected by both D2 and D3 structures and, consequently, both these deformation phases must be younger than c. 1.87 Ga. On the other hand Rutland et al. (1997) propose that migmatization occurred before 1.89 Ga and at c. 1860 Ma south of the Skellefte district in the Burträsk shear zone. Furthermore, Lundström et al. (1999) propose that intrusions east of the VRSS, dated at 1870 Ma, contain xenoliths with an earlier deformation fabric which therefore must predate 1870 Ma. It is thus possible that earlier deformational fabrics exist, but must be minor in the investigated area. The pre-1890 Ma deformation of Rutland et al. (1997) could of course not affect the rocks concerned here since all rock units studied are younger than 1890 Ma. The D2 of Rutland et al. (1997), dated at c. 1860 Ma by age of monazites in pegmatitic neosome granitoids intruding late during D2, for the Burträsk shear zone, may correspond to the D2 discussed in this paper. This necessitates a reinterpretation of the zircon ages of 1.85–1.86 (Weihed & Vaasjoki 1993, Billström & Weihed 1996) for the deformed Sikträsk intrusion. The peak of metamorphism in the area has not been accurately dated but is closely related to the S-type minimum melt granitoids of Skellefte- and Härnö type, dated at 1.80 to 1.82 Ga (Weihed et al. in prep, Claesson & Lundquist 1995). It is therefore likely that the best estimate of the age of peak metamorphism comes from a diopside skarn in the Burträsk shear zone where Romer & Nisca (1995) dated titanites at c. 1825 Tectonic implications A crucial point for tectonic implications of the results reported above is the timing of shearing and faulting in relation to metamorphism and magmatism in the area. The age of the Skellefte volcanic rocks has been constrained to between 1880 and 1890 Ma whereas the overlying H I J K L Sorsele 24 24 Luleå Piteå amphibolite facies amphibolite facies 23 23 greenschist facies Shear zone, barbs on upthrow side Orientation of main D2 folds Skellefteå Convergence during or after D3 (post 1.80 Ga) 22 22 Approximate boundary between metamorphic facies Lycksele Convergence during or after D2 but before D3 (1.85–1.80 Ga) H I J K L Fig. 14. Simplified structure map. Brown irregular area in centre represents the Jörn batholith. Arrows indicate an early oblique convergence, probably from the south-east, and late east-west shortening. 66 J. BERGMAN WEIHED Ma. Since the early structures discussed here seems to contain peak metamorphic assemblages it could be argued that the D2 must not be younger than 1825 Ma while the latest deformation in D3 structures, which affects the Revsund granitoids, must be 1.80 Ga or younger. Summarizing the observed kinematic indicators in the whole study area (Fig. 14), north-striking shear zones generally have a reverse dip slip sense of movement and have formed during or after the regional D3 deformation (after c. 1.80 Ga) and after peak metamorphism. In contrast, the northwest-striking shear zones observed in the central Skellefte district have a reverse oblique slip movement, commonly with the south side up, and these zones have formed prior to the regional D3 deformation and before the metamorphic peak. It is therefore probable that the northwest-striking shear zones formed late during the main D2 folding (between 1.87 and 1.82 Ga). The older shear zones may have formed late during the regional D2 deformation which caused the upright folds which are present everywhere in the Skellefte district. In the western and eastern parts of the district, axial surfaces to these folds strike north-east whereas in the central part of the district they strike north-west parallel to the southern contact of the large Jörn batholith north of the Skellefte district (Fig. 14). The folds occur in lower-strain lenses between shear zones in the central part of the district and areas to the east and west are less intensely deformed and have less shearing parallel to axial surfaces of the folds. It is proposed here that these regional F2 folds in the whole Skellefte district and the northweststriking shear zones in the central district formed in response to oblique convergence from the south-east and that the northwest-striking structures in the central Skellefte district were constrained in orientation by the presence of the large Jörn batholith which acted as a large block resisting deformation. This deformation occurred between 1.87 Ga and 1.82 Ga before or during peak metamorphism. The north-striking shear zones (and faults) formed after the D3 deformation, i.e. after 1.80 Ga and affect all intrusive rocks that are present in the area (except maybe the diabase dykes that are present in the south-western part of the studied area). The dominantly dip slip reverse movements observed on these shear zones indicate an east-west shortening during this period of deformation (Fig. 14). Nironen (1996) proposes that the TIB in central Sweden and the Revsund granitoids in the north formed during east–west extension. However, no indications of east-west extension at the time immediately after the emplacement of Revsund granitoids were found in this study. An interesting possibility that emerges from this study is that most structures discussed here, which are considered to belong to the Svekocarelian orogeny, temporally may be related to the intrusion of Skellefte-Härnö and Revsund granitoids which normally are considered as lateor post-orogenic in relation to the Svecokarelian orogen. It is possible that early Svecokarelian deformation and metamorphism, related to accretionary processes and calcalkaline magmatism at 1.95 to 1.88 Ga, in some areas are overprinted by the younger structures observed in this study related to southeast convergence at c. 1.87–1.82 Ga and to east-west shortening at c. 1.82–1.80 Ga. Acknowledgements This research project has been conducted with the support of many geoscientists active in the Skellefte district and its surroundings. I would especially like to thank Ildikó Antal, Ulf Bergström, Kjell Billström, Leif Björk, Thomas Eliasson, Benno Kathol, Leif Kero, Ingmar Lundström, Thomas Sträng, and Lars Kristian Stølen for sharing their information gathered during regular mapping for the Geological Survey of Sweden. My deepest thanks go to Pär Weihed for endless support during field work and in the office. Thanks are also due to Stefan Bergman, Lena Albrecht, Kjell Billström, Olof Martinsson, and Pär Weihed for reviews of earlier versions of this manuscript. This research project was funded by the Geological Survey of Sweden, external research grant 03-862/93. References Adamek, P. & Wilson, M., 1979: The evolution of a uranium province in northern Sweden. Philosophical Transactions Royal Society of London 291, 355–368. Adamek, P., 1987: Geological map over 24 I Storavan in 1:50 000 with legend. Sveriges geologiska undersökning, Berggrundsbyrån. Allen, R.L., Weihed, P. & Svenson, S.-Å., 1996: Setting of ZnCu-Au-Ag massive sulfide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc, Skellefte district, Sweden. Economic Geology 91, 1022–1053. Assefa, E., 1990: The geology of Långdal mine, Skellefte district, N Sweden. Uppsala University, Department of Mineralogy and Petrology Research report 64, 1–50. BABEL Working Group, 1990: Evidence for early Proterozoic plate tectonics from seismic reflection profiles in the Baltic shield. Nature 348, 34–38. Bergman, J., 1989: Structural geology of some sulphide bodies. STU-report 85-05350 and 87-02758. Bergman, J., 1991: Two structural profiles across the central part of the Skellefte district, northern Sweden. Final report of NUTEK project 88-03154P, 1–11. Bergman, J., 1992: Structural geology of Grundfors, a quartz vein related gold deposit in the Skellefte district, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar 114, 227–234. Bergman Weihed, J., Bergström, U., Billström, K. & Weihed, P., 1996: Geology, tectonic setting, and origin of the Paleopro- PALAEOPROTEROZOIC DEFORMATION ZONES IN THE SKELLEFTE AND ARVIDSJAUR AREAS, NORTHERN SWEDEN 67 terozoic Boliden Au-Cu-As deposit, Skellefte district, northern Sweden. Economic Geology 91, 1073–1097. Bergström, U. & Triumf, C.-A., 1996: Kartbladen 24I Storavan. In C.-H. Wahlgren (ed.): Regional berggrundsgeologisk undersökning. Sveriges Geologiska Undersökning Rapporter och meddelanden 84, 104–110. Berthelsen, A. & Marker, M., 1986: 1.9-1.8 Ga old strike-slip megashears in the Baltic Shield, and their plate tectonic implications. Tectonophysics 128, 163–181. Billström, K. & Weihed, P., 1996: Age and provenance of host rocks and ores in the Paleoproterozoic Skellefte district, northern Sweden. Economic Geology 91, 1054–1072. Claesson, S. & Lundqvist, T., 1995: Origins and ages of Proterozoic granitoids in the Bothnian Basin, central Sweden; isotopic and geochemical constraints. Lithos 36, 115–140. Duckworth, R.C. & Rickard, D., 1993: Sulphide mylonites from Renström VMS deposit, Northern Sweden. Mineralogical Magazine 57, 83–91. Edelman, N., 1963: Structural studies in the western part of the Skellefte district, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar 85, 185–211. Gaál, G., 1986: 2200 million years of crustal evolution: the Baltic shield. Bulletin of the Geological Society of Finland 58, 149–168. Hietanen, A., 1975: Generation of potassium poor magmas in the northern Sierra Nevada and the Svecofennian of Finland. Journal of Research of the USGS 3, 631–645. Kathol, B. & Triumf, C.-A., 1995: Kartbladen 24J Arvidsjaur. In C.-H. Wahlgren (Ed.): Regional berggrundsgeologisk undersökning. Sveriges Geologiska Undersökning Rapporter och meddelanden 84, 111–116 Lundberg, B., 1980: Aspects of the geology of the Skellefte field, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar 102, 156–166. Lundqvist, T., Vaasjoki, M. & Skiöld, T., 1996a: Preliminary note on the occurrence of Archaean rocks in the VallenAlhamn area, northern Sweden. Sveriges Geologiska Undersökning C 828, 48–55. Lundqvist, T., Vaasjoki, M. & Persson, P.-O., 1998: U-Pb ages of plutonic and volcanic rocks in the Svecofennian Bothnian Basin, central Sweden, and their implications for the Palaeoproterozoic evolution of the Basin. GFF 120, 357–363. Lundqvist, T., Boe, R., Kousa, J., Lukkarinen, H., Lutro, O., Roberts, D., Solli, A., Stephens, M. & Weihed, P., 1996b: Bedrock map of central Fennoscandia. Finland, Norway, and Sweden Geological Surveys. Lundström, I., Persson, P.-O. & Bergström, U., 1999: Indications of early deformation events in the northeastern part of the Skellefte field. Indirect evidence from geologic and radiometric data from the Stavaträsk-Klintån area, Boliden mapsheet. In S. Bergman (Ed.): Radiometric dating results 4. Sveriges Geologiska Undersökning C 831, 52–69. Mellquist, C., 1997: Proterozoic crustal growth along the Archaean continental margin in the Luleå area, northern Sweden. Luleå University of Technology, Licentiate thesis 1997:40. Mellquist, C., 1999: Proterozoic crustal growth along the Archaean continental margin in the Luleå and Jokkmokk areas, northern Sweden. Luleå University of Technology, Doctoral thesis 1999:24. Nilsson, G. & Kero, L., 1998: Berggrundskartan 22K Skellefteå NV, skala 1:50 000. Sveriges Geologiska Undersökning Ai 67. Nironen, M., 1996: A geotectonic model for the evolution of 68 J. BERGMAN WEIHED the Svecofennian Orogen. GFF 118, A21–A22. Nisca, D., 1995: Nya litologiska-tektoniska modeller för regionen Västerbotten-södra Norrbotten. Luleå University of Technology, Doctoral thesis 1995:182D. Passchier, C.W. & Trouw, R.A.J., 1996: Microtectonics. Springer-Verlag, Berlin. 1–289. Perdahl, J.-A. & Einarsson, Ö., 1994: The marine-continental transition of the Early Proterozoic Skellefte–Arvidsjaur volcanic arc in the Bure area, northern Sweden. GFF 116, 133–138. Pharaoh, T. & Pearce, J.A., 1984: Geochemical evidence for the tectonic setting of early Proterozoic metavolcanic sequences in Lapland. Precambrian Research 25, 283–308. Rasmussen, T.M., Roberts, R.G. & Pedersen, L.B., 1987: Magnetotellurics along the Fennoscandian long range profile. Royal Astronomical Society Geophysical Journal 89, 799–820. Rickard, D.T. & Zweifel, H., 1975: Genesis of Precambrian sulfide ores, Skellefte District, Sweden. Economic Geology 70, 255–274. Rodhe, L., 1987: Kvartärgeologiska kartan 22K Skellefteå och 22L Rönnskär. Sveriges Geologiska Undersökning Ak 3. Romer, R.L. & Nisca, D.H., 1995: Svecofennian crustal deformation of the Baltic Shield and U-Pb age of late-kinematic tonalitic intrusions in the Burträsk Shear Zone, northern Sweden. Precambrian Research 75, 17–29. Rutland, R.W.R., Skiöld, T. & Page, R.W., 1997: Age and Regional Significance of Deformation Episodes in the Svecofennian Province South of Skellefte. AGSO record 1997/44, 103–105. Skiöld, T., 1988: Implications of new U-Pb zircon chronology to early Proterozoic crustal accretion in northern Sweden. Precambrian Research 38, 147–164. Svenson, S.-Å., 1982: Näsliden, a volcanogenic massive sulphide deposit in the Skellefte district northern Sweden. Sveriges Geologiska Undersökning C 790, 1–81. Talbot, C., 1988: A desk analysis of the tectonic history of the Långdal mine, Skellefte district, Sweden. Economic Geology 83, 647–656. Trepka-Bloch, C., 1989: Volcanogenic and tectonic features of the Rakkejaur sulfide deposit, Skellefte district, Sweden. Mineralium Deposita 24, 279–288. Wanhainen, C., 1997: Kinematics and mineralogy of two shear zones in the Renström and Petiknäs north mines, Skellefte district, northern Sweden. Uppsala University, Institute of Earth Sciences, B.Sc. thesis. Weihed, P. & Antal, I., 1998a: Bedrock map Kalvträsk 22J NV, scale 1:50 000. Sveriges Geologiska Undersökning ser Ai 92. Weihed, P. & Antal, I., 1998b: Bedrock map Kalvträsk 22J NO, scale 1:50 000. Sveriges Geologiska Undersökning ser Ai 93. Weihed, P. & Antal, I., 1998c: Bedrock map Kalvträsk 22J SV, scale 1:50 000. Sveriges Geologiska Undersökning ser Ai 94. Weihed, P. & Antal, I., 1998d: Bedrock map Kalvträsk 22J SO, scale 1:50 000. Sveriges Geologiska Undersökning ser Ai 95. Weihed, P. & Vaasjoki, M., 1993: Age determination of a gneissoise granitoid south of the Skellefte district: implications for the early Svecofennian evoluation in the Skellefte district. Geologiska Föreningens i Stockholm Förhandlingar 115, 189–191. Weihed, P., Bergman, J. & Bergström, U., 1992: Metallogeny and tectonic evolution of the early Proterozoic Skellefte district, northern Sweden. Precambrian Research 58, 143–167. Geochemistry and tectonic setting of volcanic units in the northern Västerbotten county, northern Sweden Ulf Bergström Bergström, U,. 2001: Geochemistry and tectonic setting of volcanic units in the northern Västerbotten county, northern Sweden. In Weihed, P. (ed.): Economic geology research. Vol. 1, 1999–2000. Uppsala 2001. Sveriges geologiska undersökning C 833, pp. 69–92. ISBN 91-7158-665-2. The Precambrian bedrock in the northern Västerbotten county in northern Sweden includes a number of volcanic litostratigraphic units, which can be grouped according to their unique geochemical composition. The Bothnian Group, exposed south of the Skellefte District includes two volcanic units: one older homogeneous basalt lava and volcaniclastic assemblage with a MORB signature, and one younger (c. 1.95 Ga) fractionated basalt to rhyolite assemblage, formed in a volcanic arc setting. The Skellefte Group is a heterogeneous unit of basalt to rhyolite, deposited in an extensional continental margin arc at c. 1.90–1.88 Ga. The stratigraphically uppermost unit is composed of primitive basalts and andesites of the Tjamstan Formation and mudstones–siltstones of the Elvaberg Formation, reflecting the peak evolution of the extensional environment. The Vargfors Group succeds the Skellefte Group and indicates varying depositional environments at c. 1.88–1.87 Ga. The western part is dominated by greywackes, overlain by primitive Mg-basalts, which indicate renewed volcanic activity. The Vargfors Group in the eastern part is also dominated by greywacke deposition, which is succeded by evolved MORB-type volcanic rocks of the Varuträsk Formation. The latter probably reflects the initiation of a rift basin east of the Skellefte District. Erosion of the uplifted Skellefte Group rocks characterizes the stratigraphic sequences of Vargfors Group in the central part of the Skellefte District. The Arvidsjaur Group is concentrated to the Arvidsjaur district north of the Skellefte District, and may at least partly be stratigraphically equivalent to the Vargfors Group rocks. The Arvidsjaur Group is a heterogeneous unit of subaerial basaltic– rhyolitic volcanic rocks, formed in a mature, compressional, continental margin arc. Ulf Bergström, Geological Survey of Sweden, Earth Science Center, Guldhedsgatan 5a, SE-413 20 Göteborg, Sweden. E-mail: [email protected] Introduction Large parts of the Fennoscandian Shield are composed of rocks formed in Palaeoproterozoic analogues to modern destructive plate margin settings. These rock assemblages include volcanic units of various petrological, geochemical, and isotopic characteristics, associated granitoid suites, and sedimentary rocks. The Skellefte District in the northern part of the Västerbotten county, northern Sweden, is one such area where volcanic and intrusive units formed in what has been interpreted as a destructive plate margin. Plate tectonic interpretations of ancient metamorphosed, hydrothermally altered, and deformed volcanic units by the means of major and trace element geochemistry are frequently used. A number of discrimination plots based on different immobile trace elements are available as well as techniques for reconstruction of original compositions in altered rocks. In the Skellefte District, Claesson (1985), Vivallo (1987), Vivallo & Claesson (1987), Vivallo & Willden (1988), and Weihed et al. (1992) have presented geochemical data of volcanic rocks. Other geochemical interpretations of different volcanic rocks in the surrounding areas include Wasström (1990, in prep.) on basaltic rocks of the Knaften area south of the Skellefte District, Bergström (1996) on the Mg-basalts of the western Skellefte District, and Perdahl (1993, 1995) on the volcanic rocks in the Arvidsjaur area, north of the Skellefte District. In this paper a summary of the geochemical properties of the different volcanic units in the Skellefte District and the surrounding areas are presented including a proposal on how these volcanic units can be defined and discriminated. Regional Geology A compilation of the regional geology of northern Västerbotten County is presented in Figure 1. The Skellefte District forms a c. 150 x 50 km large belt situated in the northern part of the Västerbotten County in northern Sweden. It is characterized by the presence of the Skellefte Group volcanic rocks, which host a number of important volcanogenic massive sulphide deposits, and the associated Jörn Suite granitoids. The Jörn Suite is composed of the large composite Jörn pluton, which forms a conspicuous feature in the north-central part of the Skellefte District, and a number of smaller plutons. The age of the Skellefte District is suggested by Billström & Weihed (1996) to be c. 1900–1880 Ma. The volcanic rocks of the Skellefte Group have been dated at1882±8 Ma (Welin 1987), 1884±5.5 Ma and 1889±4 Ma, (Billström & Weihed 1996), and the age of the Jörn G1 has been dated at +15 1888+20 –14 Ma, (Wilson et al. 1987), and 1886 –9 Ma (Wei- GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 69 70 U. BERGSTRÖM 21 22 23 24 G G Caledonides Fig. 1. Geology of the Skellefte District and surrounding areas with the different volcanic units discussed in the text indicated. Skarvsjöby H Sorsele Barsele Storuman H Pauliden Bjurås Vinliden Bure I I Malå Knaften Lycksele Kristineberg Adak Norsjö J Skatan Jörn Granbergsliden Gallejaur Risliden Arvidsjaur J Långdal K Boliden K Burträsk Varuträsk Skellefteå L L Sedimentary rocks Sedimentary rocks Bothnian Group Skellefte Group Tjamstan Formation Bjurås Formation Gallejaur Formation Varuträsk Formation Arvidsjaur Group Volcanic rocks Pre- to synorogenic granitoids Postorogenic granitoids Doubblon Group Interpreted contact zone – Bothnian and Skellefte terrains Deformation zones Luleå M 21 22 23 24 hed & Schöberg 1991). An age determination of a typical Jörn type pluton in the Kristineberg area in the western part of the Skellefte District gave an age of 1907±13 Ma (Bergström et al. 1998). The Vargfors Group, which stratigraphically overlies the Skellefte group volcanic rocks, is a heterogeneous unit of sedimentary rocks with minor volcanic intercalations. In the central Skellefte District, the Vargfors Group is composed of coarse clastic rocks, sandstones, and finegrained argillites, which occur at the base of the Group (Dumas 1986). The Vargfors Group also includes thick greywacke units in a number of synformal basins at the margins of the Skellefte District. The volcanic intercalations are volumetrically small compared to the sedimentary rocks, and include mainly mafic units. The age of the Vargfors Group is close to c. 1875 Ma, as suggested by an age determination at 1875±4 Ma (Billström & Weihed 1996) of a dacitic ignimbrite intercalation in conglomerate from the central Skellefte District. In the central Skellefte District, the Vargfors sedimentary and volcanic units are related to the Gallejaur intrusive complex, dated by Skiöld (1988, 1993) at c. 1876–1873 Ma. To the north of the Skellefte District, the Arvidsjaur Group volcanic rocks and the Arvidsjaur granitoid Suite are exposed in the so-called Arvidsjaur district. The Arvidsjaur Group shows east–west compositional variations and grades into the volcanic areas further to the north in the Norrbotten County (Perdahl 1994). The Arvidsjaur granitoid Suite is intimately related to the Arvidsjaur Group volcanic rocks and occurs as large batholithic intrusions of heterogeneous composition, although more homogeneous plutons like the Arvidsjaur Pluton (Muller 1980) also exist. The age of the Arvidsjaur district rocks is c. 1875–1880 Ma, according to age determinations of Arvidsjaur Group volcanic rocks at 1876±3 and 1878±2 Ma (Skiöld et al. 1993), and Arvidsjaur granitoids at 1877+8 Ma (Skiöld et al 1993) and 1879 +15 Ma (Kathol & Persson 1997). To the south of the Skellefte District within the Bothnian Basin (Hietanen 1975, Lundqvist 1987), minor volcanic intercalations form part of the predominantly sedimentary Bothnian Group. The sedimentary and volcanic rocks of the Bothnian Group are intruded by several generations of granitoids, often with unclear relationship to the volcanic units. An age determination of a quartz-feldspar-porphyritic dacite from the Barsele area southeast of Storuman (Fig. 1) gives an age of 1959±14 Ma (Eliasson & Sträng 1998), which is interpreted as a rough estimate of the age of the Bothnian Group. Similar ages for intrusive rocks have been obtained from the Knaften area (Wasström 1993, 1996). As the Bothnian Group includes similar sedimentary rocks as the Vargfors Group to the north in the Skellefte District, the nature of the contact zone may be graditional. The suggested position of the contact zone between the two sedimentary Bothnian and Vargfors Groups is outlined in Figure 1 and the position is discussed below. It is probable that the sedimentary deposition in the Bothnian Group continued beyond the magmatic ages mentioned above, at least until the Skellefte Group volcanic episode was initiated (Fig. 2). All the above mentioned rocks have been deformed and metamorphosed at c. 1840–1800 Ma, and intruded by a late- to postkinematic granitoid suite at c. 1780–1810 Ma (Billström & Weihed 1996). The Skellefte, Vargfors, and Arvidsjaur Groups have been metamorphosed in the greenschist facies, whereas the Bothnian Group is variably metamorphosed in amphibolite facies. Veined gneisses, migmatites, and anatectic granites are common within the Bothnian basin. Characterization of volcanic units Stratigraphic, petrographic, geochemical, petrophysical, and isotopic parameters have been used to identify a number of volcanic units within the Bothnian, Skellefte, Vargfors, and Arvidsjaur Groups. In some cases these units may be correlated chrono-stratigraphically and form facies components rather than individual units. The individual volcanic units are briefly presented below. Bothnian Group The volcanic rocks of the Bothnian Group have been studied by Wasström (1990, in prep.) in the Knaften area and brief reports can be found in Eliasson & Sträng (1998) for Bothnian group volcanic rocks in the Storuman area, in Björk (1995) for the Lycksele–Vilhelmina area (map sheets 22 G–I), and in Weihed & Antal (1998) from the Kalvträsk map sheet (22J). The volcanic rocks occur as intercalations in the dominating sedimentary rocks, mainly greywacke-mudstone turbidites, which have been deformed and metamorphosed in amphibolite facies. The volcanic rocks may form volumetrically important local centers including lava flows, subvolcanic intrusions and volcaniclastic rocks, surrounded by mixed volcanicsedimentary units. Other parts of the Bothnian Group sedimentary rocks are virtually devoid of volcanic rocks. The restricted areal extent of the volcanic intercalations and the lack of stratigraphical markers prohibit any major interpretations of the physical volcanology of these rocks and the proposed tectonic setting is highly tentative. Wasström (1990) studied the mafic volcanic rocks of the Knaften area (Fig. 1) and identified two principal volcanic facies: more or less homogeneous massive and pillowed basaltic lava flows with minor interflow volcani- GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 71 72 U. BERGSTRÖM 1,95 1,90 1,88 1,87 Fig. 2. Stratigraphic subdivision of the different volcanic rocks into the Bothnian, Skellefte, Vargfors, and Arvidsjaur Groups. Granitoids Greywackes Greywackessiltstones Conglomerates Gallejaur Fm basalt to rhyolite volcanics and the Gallejaur intrusive complex Conglomerates Vargfors Group central Basalt lavas Basalt volcanoclastic rocks intercalated with greywackes Greywackes and mudstones Basalt-rhyolite lavas and volcanoclastic rocks Knaften granitoids and porphyry dykes Bothnian Group Ongoing sedimentation and magmatism in the Bothnian Group Greywackes Bjurås Fm lavas and volcanoclastics Vargfors Group west Dacite-rhyolite subvolcanic intrusion/lava domes and volcanoclastics –breccias Intercalated mudstones–siltstones Basalt-andesite lavas, volcanoclastics and sills Jörn granitoid suite Skellefte Group Mud- and siltstones with Tjamstan Fm basalt-dacites Conglomerates Varuträsk Fm basalts Stavaträsk suite granitoids Vargfors Group east Intercalated basalts-andesites Dacites-rhyolite ignimbrites, lavas and breccias Arvidsjaur Suite granitoids Conglomerates Arvidsjaur Group clastic sediments, and volcaniclastic rocks of similar composition mixed with greywackes and with only minor lava flows. In the north-eastern part of the Knaften area, the basalts are succeded by andesites, dacites, and rhyolites, which form another volcanic unit. These two principal compositional units can also be identified further to the north-west, in the Pauliden and Barsele areas, the former unit with massive and pillowed basalt lava flows and associated volcaniclastics (HBA) and the latter with more fractionated rocks with a compositional range from basalt to rhyolite (FBRA). Basaltic rocks are frequently found as more or less continuous intercalations in Bothnian Group greywackes outside the Knaften and Barsele type-areas. In the Skatan area, a pillow lava is associated with a gabbro (Weihed & Antal 1998), and similar associations of basalts and mafic intrusions were identified by Nilson & Kero (1986) on the Vindeln map sheet (21J). Small, scattered and rare occurrences of felsic volcanic rocks with the fractionated basalt-andesite-dacite-rhyolite compositions may also be found in the whole area. In the Knaften area, Wasström (1994) suggests a genetic link between rhyolitic tuffites, granitoid intrusions, and porphyritic dykes. The well-preserved HBA basaltic lavas from the Knaften area are mainly ophitic and locally amygdaloidal (Wasström 1990). They are mainly pyroxene porphyritic and altered to amphibole, but plagioclase porphyritic varieties are locally abundant. Hornblende and plagioclase with accessory ore minerals, sphene, epidote, calcite, and chlorite dominate the matrix. Chert horizons have been identified as associated with the basaltic lava flows. The volcaniclastic basaltic rocks from the Knaften area are mainly epiclastic deposits with different types of volcanic and sedimentary clasts, including ultramafic clasts (Wasström 1990). Most volcaniclastic rocks are laminated with local graded beds and imbricate structures. Rounded quartz phenocrysts are present in some beds. Wasström (1990) describes the felsic volcanic rocks of the Knaften area as tuffites, derived from fine-grained ash deposited in water, because of their laminated character. Quartz, plagioclase, microcline, and biotite with accessory epidote, ore minerals, and chlorite dominate the rock. The tuffites are underlain by dacitic to andesitic lava flows, which are different macroscopically from the basaltic lavas by their grey colour, higher abundance of quartzfilled fissures, and quartz phenocrysts. The FBRA fractionated assemblage in the Storuman area (Fig. 1) includes andesitic lava flows and dacitic volcaniclastic rocks, lavas, and dykes, similar to the porphyritic dykes of the Knaften area. Skellefte Group The Skellefte Group volcanic rocks are exposed along the Skellefte River in a well-defined area associated with minor sedimentary intercalations and Jörn Suite granitoid plutons (Fig. 1). Allen et al. (1995, 1996) have investigated the physical volcanology of the Skellefte Group, and Weihed et al. (1992) and Billström & Weihed (1996) summarized the isotopic features. Claesson (1985), Vivallo (1987), Vivallo & Claesson (1987), Vivallo & Willdén (1988), Weihed et al. (1992), Bergman Weihed et al. (1996). and Allen et al. (1996) have published petrographic and geochemical data of the Skellefte Group. Due to the presence of pervasive hydrothermal alteration related to numerous massive sulphide deposits in the Skellefte Group, textural interpretations of the volcanic rocks are locally seriously hampered. Otherwise, the rocks of the Skellefte Districts. are generally well preserved. Felsic compositions dominate in the Skellefte Group. The most common volcanic rocks are dacitic to rhyolitic, variably porphyritic, coherent subvolcanic intrusions/lava domes or pumiceous, syn-volcanic mass flows (Allen et al. 1995, 1996). The Boliden area is one type area for dacites, where subvolcanic intrusions and related mass flows occupy a stratigraphically high position in the Skellefte Group (Bergman Weihed et al. 1996). A plagioclase phyric texture is characteristic for the dacites and the wholerock composition is partly controlled by the phenocryst abundance. Mafic phenocrysts are rare. A stronger hydrothermal alteration is evident in the originally more porous mass flows compared to the coherent intrusions, which is expressed as plagioclase breakdown and a high sericite content. A heterogeneous group of coherent lavas, subvolcanic intrusions, and related mass flows with a rhyolitic composition, dominate the volcanic stratigraphy in various parts of the Skellefte District. The subvolcanic intrusions show a variable amount of quartz and plagioclase phenocrysts, which also vary in shape and size. Siliceous, glassy-looking, quartz phyric lava/crypto domes and subvolcanic intrusions form a rather distinct group of rhyolites. The mineralogical composition of the Skellefte Group rhyolites is dominated by quartz and albite, and the amount of potassic feldspar is typically very low. The rhyolitic mass flows are commonly redeposited coarse breccias and sandstones. Mafic volcanic rocks in the Skellefte Group are generally subordinate and mainly occur as subvolcanic sills or lava flows. Thicker mafic units are found for example in the Långdal area (Vivallo 1987, Allen et al. 1996), and the Holmtjärn–Granbergsliden area (Nicolson 1993, Allen et al. 1996). The mafic volcanic rocks include substantial amounts of andesites and basaltic andesites. Stratigraphical studies (Vivallo 1987, Nicolson 1993, Bergman Wei- GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 73 hed 1996) suggest that the basalt–andesite units normally occur high up in the stratigraphy, immediately below the contact to the younger Vargfors Group. Most basalts and andesites at lower stratigraphic levels may be regarded as feeder dykes or sills to the extrusive units further up in the stratigraphy. Generally the mafic volcanic rocks in the Skellefte group are plagioclase and pyroxene phyric. The pyroxenes are altered to chlorite and actinolite. Sedimentary intercalations in the Skellefte Group are not uncommon, but generally very limited in thickness and strongly volcanogenic in nature. Thin intercalations of black mudstones are locally found in the upper parts of the stratigraphy. Carbonate lenses may also be found, for example in the eastern part of the Skellefte District, and adjacent to massive sulphide ores. Tjamstan Formation The Tjamstan Formation (Bergström & Sträng 1997, 1998) is exposed in the western part of the Skellefte District. The unit occurs stratigraphically above the felsic volcanic rocks of the Skellefte Group and appears to be coeval with fine-grained black mud- and siltstones of the Elvaberg Formation (Allen et al. 1996), which defines the stratigraphic contact zone to the younger Vargfors Group (Fig. 2). The reason for referring the Tjamstan Formation to the Skellefte Group rather than to the sediment-dominated Vargfors Group, which would be natural considering the relation to the Elvaberg Formation, is simply the similar mineralogical and geochemical composition relative to the Skellefte Group volcanic rocks. A large area with well-preserved basalts and andesites of the Tjamstan Formation occurs around Malå (Fig. 1). The rocks are characterized by abundant plagioclase phenocrysts and well preserved volcanic syn-eruptive graded beds, where the plagioclase phenocrysts are concentrated into the base of the bed. Lava intercalations with the same composition are common and become volumetrically more important in some areas. Thick units of polymict breccias occur locally. Away from Malå (for example in the Adak area), distal facies are intercalated with sedimentary rocks. The Tjamstan Formation also includes some dacitic subvolcanic intrusions, dykes, and mass flows. Vargfors Group Allen et al. (1995, 1996) defined the Vargfors Group as the unit of dominantly sedimentary rocks which overlies the Skellefte Group volcanic rocks. The graphite- and sulphide bearing black mudstones of the Elvaberg Formation, which forms a magnetic and electric marker horizon in the Skellefte District, constitute the top of the Skellefte Group and thereby defines the transition into the Vargfors Group mud-, silt- and fine-grained sandstones and 74 U. BERGSTRÖM greywackes. In some areas, for example in the central Skellefte District, parts of this stratigraphic level are composed of lithological units characterized by different volcanic and sedimentary breccias, conglomerates, and sandstones. Along the western, southern, and eastern margins of the exposed Skellefte Group volcanic rocks, thick units of greywackes dominate the Vargfors Group. Within the Vargfors Group, there are substantial volcanic components with a local provenance. In the central Skellefte District, basalts and andesites dominate in the Gallejaur area (Fig. 1) where the volcanic rocks belong to the Gallejaur Formation. In the western part of the Skellefte District, the thick Vargfors Group greywackes have intercalations of ultramafic–mafic volcanic rocks of the Bjurås Formation. Basaltic intercalations are also found in the Vargfors Group sedimentary rocks of the eastern part of the Skellefte District, and these are termed the Varuträsk Formation. Gallejaur Formation The coarse conglomerates and sandstones along the Skellefte River, in the Gallejaur area and in the central Skellefte District (Dumas 1985), were included in the original definition of the Vargfors Group. These units overlie the Skellefte Group volcanic rocks and the fine-grained sedimentary rocks of the lower Vargfors Group. Mainly basaltic and andesitic volcanic rocks occur within the coarse conglomerates and sandstones in the Gallejaur area. The mafic volcanic rocks envelop the Gallejaur Complex (Fig. 1), a laccolithic gabbro with a thin central core of quartz monzonite (Enmark & Nisca 1983). Dacitic to rhyolitic volcanic intercalations are found in the coarse clastic rocks. Both lavas and volcaniclastic rocks are common in the Gallejaur Formation. The andesites are often coarsely amphibole phyric, but plagioclase phyric types are also found. The felsic volcanic rocks are normally ignimbrites, but lavas are also found locally. The Varuträsk Formation Minor occurrences of mafic volcanic rocks are intercalated with Vargfors Group sedimentary rocks in the Varuträsk area east of Boliden (Fig. 1) and further to the north. These rocks are compositionally similar to the Bothnian Group basalts to the south, but the host sedimentary rocks east of Boliden are included in the Vargfors Group because they show a continuous younging direction eastward from the exposed Skellefte Group rocks. The basalts of the Varuträsk area are normally massive and pillowed lava flows. Intercalated clastic units, as well as thin massive sheets, probably sills of similar basaltic composition, occur in the surrounding sedimentary rocks. The rocks of the Varuträsk Formation are nor- Table 1. Geochemical analyses of representative samples of mafic volcanic rocks. References to data; TEN960101: HBA basalt, Bothnian Group, Knaften area (Eliasson et al., in press), TEN930220: FBRA andesite, Bothnian Group, Barsele area (Eliasson et al., in press), L-56: basalt, Skellefte Group, Långdal area (Vivallo 1987), UJB940001: basalt, Tjamstan Formation, Näsudden area (Bergström & Sträng, 1999), KWI990089, Basalt lava, Gallejaur Formation, Gallejaur area (Antal, Bergström & Weihed, unpublished), MGN940135: Mg-basalt, Bjurås Formation, Bjurås area (Bergström & Sträng, 1999), UJB980399: basalt, Varuträsk Formation, Klubbfors area, (Kathol et al., unpublished), CHB950168: andesite, Arvidsjaur Group, Brunmyrheden area (Kathol & Triumf, in press), AFT950183: basalt-andesite, Arvidsjaur Group, Sjnjerra area (Bergström & Triumf, in press.). TEN960101 SiO2 TiO2 Al2O3 FeO Fe2O3 MgO CaO Na2O K2O P2O5 LOI Σ Ba Co Cr Cu Ga Hf Nb Ni Pb Rb Sc Sr Ta Th U V Y Zn Zr La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu TEN930220 50.5 1.135 13.5 10.9 1.386 7.48 9.28 3.16 0.12 0.07 1.3 55.1 0.786 14.7 6.4 1.834 6.2 7.66 3.73 1.4 0.23 0.95 99.9 20 45 160 143 16 1 2 80 688 23 410 49.2 17 3.3 10 77 5 45.9 120 0.2 0.2 0.1 372 20 85 67 2.5 7.5 1.2 7.1 2.3 0.82 1.7 0.82 4.2 0.82 2.5 0.4 2.6 0.35 42 23 428 1 3.6 4 180 18 81 153 17.6 39.4 5 21.4 4.8 1.25 0.6 3.7 0.72 2.1 0.3 1.9 0.29 L-56 49.73 0.89 18.09 7.21 1.9 4.8 11.73 3.04 0.29 0.15 1.29 29 59 121 10 4 28 15 7 48 617 293 17 91 21 7.22 16.61 11.88 2.87 1.10 2.65 2.70 1.59 1.39 0.20 UJB940001 KW1990089 MGN940135 UJB980399 50.5 1.68 14.9 14.3 48.9 0.34 18.8 50.9 0.659 15.7 44.2 0.53 9.54 9.5 3.53 13.7 2.06 0.46 0.0489 2.2 10.4 7.88 6.78 3.91 0.703 0.219 1.6 12.1 18 12.7 0.51 0.59 0.15 0.75 99.26 149 33.8 43.3 142 27.5 2.4 2 17 198 41.4 274 28.2 20.8 1.87 3.19 75.1 16.6 36.8 206 0.078 0.77 0.43 206 12.9 49.5 20.2 3.9 9.38 <1.17 5.34 1.21 0.443 1.25 0.257 1.74 0.257 0.936 0.163 1.1 0.155 21.1 29.6 624 0.298 1.74 1.48 191 16 678 62.3 10 24.4 3.29 15.2 2.67 1.15 2.73 0.401 2.81 0.613 1.53 0.217 1.6 0.195 mally strongly deformed and metamorphosed in amphibolite facies. The basaltic sills and lavas have few phenocrysts and are dominated by metamorphic hornblende and plagioclase. The Bjurås Formation Thick sills of ultramafic–mafic composition intrude the greywackes in the Vindelgransele area in the western part of the Skellefte District. These sills represent feeder systems to lavas further up in the stratigraphy, exposed in the 241 75 1600 63 1.3 4 571 15 32.9 127 1.2 2 14 90 60 10.2 22 11 2.5 0.7 0.4 1.3 0.22 7.11 8.68 2.11 0.243 0.17 0.8 CHB950168 54.2 1.48 18.1 8.31 1.59 6.11 3.59 4.14 0.792 2.3 AFT950183 51.6 0.742 15.4 8.24 7.84 7.42 3.19 2.06 0.259 3.9 57.1 47.1 223 184 23.5 3.39 8.19 129 995 28.2 28.1 121 11 6.86 17.2 37 765 30.7 408 23.8 15.9 3.65 4.86 94 12.7 35.2 143 0.718 0.634 0.234 322 25.2 113 106 8.19 25.2 3.24 17.2 3.88 1.67 4.94 1.21 5.06 1.36 3.24 0.618 2.77 0.412 133 20.9 510 1.31 8.45 6.02 121 47.3 93.9 330 57.9 124 16.2 66.9 1.5 2.2 10.7 1.4 7.02 1.38 3.29 0.565 3.78 0.568 38.5 21.6 671 0.50 5.82 5.13 115 18.2 138 136 22.3 47 6.14 25.9 4.89 1.29 4.33 0.744 3.58 0.661 1.68 0.248 1.89 0.276 Bjurås area (Fig. 1). Similar rocks exist in the Adak area to the north. Further to the north-west in the Vinliden area, the lavas are overlain by a thick package of similar volcaniclastic high-Mg basalts and basalts. The mafic volcaniclastic rocks are intercalated with and overlie greywackes of the Vargfors Group. Bergström (1997) proposed the name Malå Group for this greywacke-Mg-basalt package, but it can be stratigraphically correlated with the central Skellefte District greywackes, conglomerates, and sandstones of the Vargfors Group. Thin intercalations of volcanic rocks, similar to the Arvidsjaur Group can also be ob- GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 75 Table 2. Geochemical analyses of representative samples of felsic volcanics. References to data; JPN940254: dacite, Bothnian Group, Barsele area (Eliasson et al. in press), LAB930128, rhyolite, Bothnian Group, Mejvankilen area (Björk & Kero, 2001), 91105: dacite, Skellefte Group, Boliden area (Bergman Weihed et al. 1996), b-37: rhyolite, Skellefte Group, Boliden area (Vivallo, 1987), UJB940036: quartz porhyry rhyolite, Skellefte Group, Storliden area, (Bergström & Sträng 1999), KWI990080: dacite, Gallejaur Formation, Gallejaur area (Antal, Bergström & Weihed, unpublished), HLU980119: quartz latite, Arvidsjaur Group, Hornliden area, (Bergström & Triumf, in press), KBK970062: quartz latite/rhyolite/trachyte, Arvidsjaur Group, Skarpljugaren area (Kathol & Triumf, in press), MGN950271: rhyolite, Arvidsjaur Group, Fiskträsk area, (Bergström & Triumf, in press). SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O P2O5 LOI Σ Ba Co Cr Cu Ga Hf Nb Ni Pb Rb Sc Sr Ta Th U V Y Zn Zr La Ce Pd Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu JPN940254 LAB930128 68.1 0.509 13.9 1.15 72.6 0.129 13.9 1.97 0.0247 0.556 1.97 2.89 5.22 0.0395 1.3 2.5 3.45 1.11 3.26 0.13 2.1 99.0 222 5 29 3.5 16 6.9 13 6 3 43 10 87 3.9 1.8 38 33 51.2 184 20.2 41.2 4.8 19.6 5.3 1.2 5.4 0.9 6 1.3 3.8 0.6 4 0.63 208 18.2 40.6 37 6.75 21.7 7.43 155 45.5 1.6 14.8 5.16 7.75 39.2 8.63 168 25.3 66 6.72 25.5 5.72 0.246 5.26 0.99 6.66 1.63 5.24 0.814 6.62 0.9 91105 b-37 70.1 0.49 15.0 3.58 0.05 2.07 3.43 3.12 1.46 0.15 1.31 76.41 0.2 11.55 0.44 0.09 0.69 1.46 2.75 2.61 0.03 296 59 13 7 UJB940036 787 19 3 6 9 10 4 34 11 441 17 134 3 2.1 34 19 70 122 14.2 33.0 24 38.1 100 172 32.08 63.58 12 14 18.2 4.8 1.46 4.06 33.24 7.59 1.68 6.42 3.8 6.04 2.0 3.75 2.08 3.54 0.53 served in the Malå Group, at a stratigraphically higher position than the Mg-basalt lavas. The ultramafic–mafic sills and lavas are dominated by actinolite, both as pseudomorphs after the characteristic pyroxene phenocrysts and in the glassy matrix, which reflects the upper greenschist facies metamorphism that has affected the rocks in the western Skellefte District. In well-preserved samples, primary augite phenocrysts can be distinguished. The volcaniclastic rocks commonly contain a higher amount of magnetite, which results in a distinct high magnetic signature, and they also contain plagioclase both as phenocrysts 76 U. BERGSTRÖM 70.0 0.388 15.9 3.25 0.0709 1.83 1.65 1.03 4.11 0.118 1.6 99.9 567 9.64 15.6 28.4 13.7 4.74 3.61 12.5 40.8 15.7 56.8 0.435 2.5 3.31 14.5 38.6 107 162 10.5 25.7 3.55 16.4 3.74 0.792 5.28 1.03 6.27 1.45 4.4 0.72 4.82 0.776 KWI990080 67.4 0.639 14.7 5.06 0.095 1.13 2.71 4.89 2.81 0.19 0.4 1210 6.4 54.9 25.3 HLU980119 KBK970062 62.4 0.916 14.6 6.91 0.226 1.34 3.3 4.47 4.05 0.361 0.3 98.9 1200 34.5 6.16 14.2 26.6 20.6 8.28 7.73 14.4 54.5 9.97 327 0.918 5.39 3.97 27.9 29.5 64.8 260 33.8 80.7 10.2 40.1 6.72 1.45 5.57 0.809 4.78 0.827 2.38 0.287 2.8 0.322 83 11.3 212 0.867 6.51 5.55 56.9 35.2 121 247 31.7 74.0 9.47 40.0 6.71 2.98 6.85 1.03 7.26 1.6 3.2 0.408 4.67 0.695 68.8 0.598 13.0 4.73 0.086 0.362 1.47 3.88 4.64 0.131 1.6 1150 2.6 14 17.1 20 9.33 13.9 5.4 115 7.59 123 1.34 9.72 6.26 9.81 31.3 81.9 315 43.3 82.1 10.4 42 7.38 1.55 7.09 1.14 5.72 1.22 3.32 0.471 3.32 0.491 MGN950271 77.0 0.192 10.7 2.84 0.021 0.06 0.295 3.77 4.13 0.2 125 17.6 71.9 25.8 18.9 24 132 18 1.92 13.4 11 6.15 68.2 37.6 561 57.5 128 15.3 64.1 12.5 0.714 13.8 2.4 13.7 2.84 7.82 1.5 8.35 1.4 and in the matrix, which results in more basaltic and andesitic compositions. Arvidsjaur Group The volcanic rocks of the Arvidsjaur Group have been studied by Perdahl (1994), who emphazised the resemblance to the volcanic rocks further to the north in the Kiruna area, and the evident east–west compositional zoning. Lilljeqvist & Svenson (1974) described textural characteristics, which identify the majority of the rocks of the Arvidsjaur Group as subaerial. The Arvidsjaur Group volcanic rocks are intimately related to the Arvidsjaur Suite of granitoid intrusions and many of the exposed volcanic rocks occur adjacent to or are intruded by fine-grained subvolcanic granites. The major part of the Arvidsjaur Group volcanic rocks are rhyolitic in composition, commonly welded ash flow tuffs. Quartz, microcline, and plagioclase phenocrysts are very abundant. Some rare lava domes and subvolcanic sills or dykes occur, and probably reflect local volcanic centers. Ignimbrites normally form rather monotonous packages and it is not always possible to identify individual flows. In many cases, the flows probably form very thick units. The rhyolites may grade into alkali feldspar rhyolite compositions with lower plagioclase content and trachytic compositions with lower quartz content. The colour is normally red to violet, but may grade into reddish grey. Volcanic rocks of dacitic composition with plagioclase phenocrysts are present, both as lava domes and volcaniclastic rocks. Silica undersaturated rocks, commonly characterized by microcline phenocrysts, are also found in the Arvidsjaur Group, mainly as sporadical occurrences of dark grey, trachy-andesitic or quartz-latitic lava domes or subvolcanic intrusions. Similar dacitic, trachyandesitic, and quartz latitic compositions may also be found in the Arvidsjaur Suite granitoids, probably as a result of magma mixing of coeval gabbroic and granitic magmas. The mafic volcanic rocks of the Arvidsjaur Group are of two principal types: coarse plagioclase phyric andesites–dacites and basalts–andesites with variable phenocryst populations. The latter type may occur as both lavas and volcaniclastic rocks. The coarse plagioclase porphyries occur in large complexes as lavas and subvolcanic intrusions with minor clastic components. The plagioclase phenocrysts are up to 2–3 cm in size, and rocks with a high phenocryst content may look almost like anorthosites. The mafic volcanic rocks probably occur at several stratigraphic positions in the volumetrically more important felsic volcanic rocks. Geochemistry Data sets A number of data sets on the geochemistry of the different rock types have been included in this study. The majority of the samples were collected and analyzed during the Geological Survey (SGU) mapping programme in northern Västerbotten County during the 1990ies. These analyses are mainly high quality data with major and trace elements including REE, analyzed by ICP-MS, with some older samples analyzed with ICP-AES. Other modern geochemical data from the Skellefte Project area include samples from a number of research projects in the 1980ies and 90ies (Claesson 1985, Vivallo 1987, Vivallo & Claesson 1987, Vivallo & Willden 1988, Wasström 1990, Allen et al. 1996, Bergman Weihed et al. 1996, Bergström 1997). The various older data has been included into the reference database only if major and trace elements have been analyzed and the quality was regarded as good. Some of these sample sets have been analyzed by XRF with additional INAA on selected trace elements. The aim has been directed towards quality rather than quantity, and several analyses where alteration, weathering, laboratory misfunction etc. are indicated, have been omitted. Cross correlation with good precision of methods and different laboratories have been achieved for a number of samples, including re-analyzing of some samples. References to all data sets are given below. Geochemical description Bothnian Group The Bothnian Group data include samples from the two principal assemblages: the homogeneous basalt lavas-volcaniclastic rocks and the fractionated basalts-andesitesdacites-rhyolites. The samples are mainly from the Knaften area and from various parts of the Storuman area. Generally, the Bothnian Group samples have low Na2O+K2O, but some high K2O samples exist, probably due to alteration (Fig. 3c). The volcanic rocks mapped as homogeneous basalts (HBA) cluster in the basaltic and picritic fields, whereas the FBRA fractionated assemblage forms a continouos trend from basaltic andesite to rhyolite. The latter group is generally peraluminous. The HBA basalts generally have flat REE patterns (LaN/YbN=1), and the majority of them are LREE depleted (Fig. 4a), although some are HREE depleted (Fig. 4b). The latter samples are mainly from south of Storuman and have high Mg-Ni content indicating accumulation of olivine. For the FBRA samples, the REE patterns are fractionated (LaN/YbN=4–7). The basaltic andesites (Fig. 4c) do not show any negative Eu anomaly, whereas dacitic and rhyolitic samples show an increasingly more negative Eu anomaly in the more felsic rocks (Fig. 4d). Skellefte Group The Skellefte Group includes samples from basalts to rhyolites from most parts of the district. As the volcanic rocks of the Skellefte Group have been subject to widespread alteration processes, only the least altered samples have been used in this study. The samples show a low-K trend on a SiO2–Na2O+K2O plot (Le Maitre 1989) and a limited number of samples have SiO2 contents between 57 and GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 77 a) b) 15 15 Na2O+K2O (wt-%) Ph Ph U3 10 F U2 U1 F T U2 S3 R S2 5 U3 10 T S1 S3 S2 S1 U1 5 O3 O2 R O3 O2 O1 Pc B Pc 0 35 45 55 65 SiO2 (wt-%) 75 0 35 c) O1 B 45 55 SiO2 (wt-%) 15 Ph Na2O+K2O (wt-%) 75 d) 15 Ph U3 10 65 U3 F 10 T U2 5 T S3 U2 S3 R S2 U1 F S2 S1 5 U1 S1 R O3 O2 O1 O1 0 35 Pc B 45 55 SiO2 (wt-%) 65 75 0 35 O2 O3 B Pc 45 55 SiO2 (wt-%) 65 75 Fig. 3. Le Maitre plot (1989) for samples of a) the Skellefte Group, b) the Arvidsjaur Group, c) the Bothnian Group, d) the Vargfors Group. Fields are: F=foidite, Pc=picrobasalt, B=basalt, O1=basaltic andesite, O2=andesite, O3=dacite, R=rhyolite, S1=trachybasalt, S2=basaltic trachyandesite, S3=trachyandesite, T=trachyte and trachydacite, U1=tephrite and basanite, U2=phonotephrite, U3=tephriphonolite, Ph=phonolite. Symbols: open circles=rhyolites, Skellefte Group, half-filled circles=dacites, Skellefte Group, filled circles=basalts– andesites, Skellefte Group, open rombs=dacites, Tjamstan Formation, filled rombs=basalts–andesites, Tjamstan Formation, open squares=rhyolites, Arvidsjaur Group, half-filled squares=dacites–trachy-andesites/quartz-latites, Arvidsjaur Group, filled squares=basalts– andesites–dacites, Arvidsjaur Group, open triangles with sharp apex down=FBRA assemblage, Bothnian Group, filled triangles with sharp apex down=HBA assemblage, Bothnian Group, open triangles=Gallejaur Formation, Vargfors Group, filled triangles=Varuträsk Formation, Vargfors Group, stars=Bjurås Formation, Vargfors Group. 63 wt. % (Fig. 3a). Vivallo & Claesson (1987) suggested this to be evidence of a weak bimodality in the Skellefte Group. Many rhyolite samples are extremely high in SiO2, indicated by the quartz porphyritic texture. The dacites are metaluminous–peraluminous, whereas the rhyolites are mainly peraluminous. The REE patterns of the basalts and the basaltic andesites of the Skellefte Group are generally weakly fractionated (LaN/YbN=3). The REE plot of the dacites normally form a concave upward shape with no Eu anomaly (Fig. 5c), whereas the rhyolites are enriched in LREE and have a negative Eu anomaly (Fig. 5e). Both dacites and rhyolites have LaN/YbN=5–7. A limited number of highly fractionated quartz-feldspar-porphyritic subvolcanic in78 U. BERGSTRÖM trusions show a flat REE pattern with a more distinct negative Eu anomaly (Fig. 5f ). Tjamstan Formation Two principal compositional groups are found within the Tjamstan Formation, one with basalts–andesites and one with volumetrically subordinate dacites (Fig. 3a). All the samples form a low Na2O+K2O trend in a SiO2– Na2O+K2O diagram (Le Maitre 1989), similar to the Skellefte Group. The total REE content of the basalts–andesites is generally very low (ΣREE<100 ppm) and the REE patterns are flat (LaN/YbN=1–2, Fig. 5b). The dacite samples have more fractionated patterns (Fig. 5d), with a negative Eu a) b) Rock/Chondrite 1000 1000 100 100 10 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1 d) c) Rock/Chondrite 1000 1000 100 100 10 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Fig. 4. REE patterns for different representative volcanic rocks of the Bothnian Group. Normalized REE abundance in rock/primitive mantle (Sun, 1982). a) Basalt lavas of the HBA homogeneous basalt assemblage from the Knaften area. b) Basalt lavas of the HBA homogeneous basalt assemblage from north of Storuman. c) Basalts and andesites of the FBRA fractionated basalt–rhyolite assemblage. d) Dacites and rhyolites of the FBRA fractionated basalt–rhyolite assemblage. anomaly, which is different from volcanic rocks of similar compositions in the Skellefte Group. Vargfors Group The heterogeneous character of the volcanic rocks in the Vargfors Group is evident in a SiO2–Na2O+K2O diagram (Le Maitre 1989). The basalts of the Varuträsk Formation are similar to the Bothnian Group basalts (Fig. 3d). The Bjurås Formation basalts are Mg-Cr-Ni-enriched komatiitic basalts to basalts and plot within the basalt field of the Le Maitre (1989) plot (Fig. 3d), but trend with fractionation into more alkali-rich compositions. The Gallejaur Formation consists of both basalt samples and a number of samples forming a trend from andesite to dacite (Fig. 3d). The Varuträsk Formation basaltic rocks show two principal types of REE pattern (Fig. 6a): flat REE patterns and LREE-enriched patterns. The LREE-enriched pattern correponds to Ti-rich samples with higher contents of to- tal REE. The Bjurås Formation generally has flat to mildly LREE-enriched patterns with LaN/YbN=1–3 (Fig. 6b). This is common for more or less all strongly Mg-Cr-Nirich ultramafites to basalts. Basalts from the Gallejaur Formation have a fractionated pattern without a negative Eu anomaly (Fig. 6c), whereas the dacites show a small but distinct Eu anomaly (Fig. 6d). Arvidsjaur Group The Arvidsjaur Group samples have been collected from the entire Arvidsjaur district and include volcanic rocks of all compositions, with sample locations concentrated to the type areas around Arvidsjaur. The Arvidsjaur Group shows a high-K trend on the SiO2–Na2O+K2O diagram (Le Maitre, 1989) and the large data set comprising volcanic rocks mapped as rhyolites clearly plot clustered in the rhyolite field (Fig. 3b), whereas the dacites include many samples which plot as trachydacite (T field in the TAS diagram) and quartz-latite (field S3). A K-enriched GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 79 Rock/chondrite 1000 a) 100 100 10 10 1 Rock/chondrite 1000 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu c) 1000 100 10 10 1000 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu e) 1000 100 10 10 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu d) 1 100 1 b) 1 100 1 Rock/chondrite 1000 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu f) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Fig. 5. REE patterns for different representative volcanic rocks of the Skellefte Group including the Tjamstan Formation. Normalized REE abundance in rock/primitive mantle (Sun 1982). a) Basalts and basaltic andesites from the Långdal-Boliden and Granbergsliden areas. b) Basalts and basaltic andesites of the Tjamstan Formation. c) Dacites (lava domes/subvolcanic intrusions) from the Boliden area. d) Dacites (lavas, intrusions, and dykes) of the Tjamstan Formation. e) Rhyolites from the Boliden-Renström area. f) Evolved rhyolites from the Storliden and Östra Högkulla areas. signature is evident also for the mafic volcanic rocks, mainly plotting in the trachyandesitic S2 and S3 fields. A majority of the rhyolites are peraluminous and mildly peralkaline. Most basalts and andesites have weakly fractionated REE patterns (LaN/YbN=3) with a small or non-existant negative Eu anomaly (Fig. 7a). The plagioclase phyric andesites-dacites are more fractionated. The dacites show 80 U. BERGSTRÖM small negative Eu anomalies, while the majority of the rhyolites have a more pronounced negative anomaly (Figs. 7b, 7c). The total REE content for the felsic rocks is relatively high compared to similar rocks of the Skellefte and Bothnian Groups. Samples with a quartz-latitic composition do not show an Eu anomaly, but show the wavy pattern (Fig. 7b), similar to the andesites and dacites. a) b) Rock/Chondrite 1000 1000 100 100 10 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1 c) d) Rock/Chondrite 1000 1000 100 100 10 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Fig. 6. REE patterns for different representative volcanic rocks of the Vargfors Group. Normalized REE abundance in rock/primitive mantle (Sun 1982). a) Basalts of the Varuträsk Formation. b) Mg-basalts of the Bjurås Formation. c) Basalt–andesite of the Gallejaur Formation. d) Dacite from the Gallejaur Formation. Tectonic discrimination The mafic volcanic rocks of the Bothnian, Skellefte, Vargfors, and Arvidsjaur Groups have been plotted in different discrimination diagrams in order to determine the tectonic settings for the respective volcanic group. Generally, it is necessary to use several different diagrams together in order to discriminate between the different groups, as just one or two diagrams for different reasons might show ambivalent results. Ideally the diagrams are designed for unaltered rocks reflecting melt compositions, especially the basaltic rocks. This is not very easily obtained in the Bothnian, Skellefte, Vargfors, and Arvidsjaur Groups, where phenocrysts are common (especially in the Arvidsjaur Group) and low-intensity alteration patterns, which mainly disturb LIL element patterns, frequently occur. Diagrams used in this paper are: Zr–Ti, Zr–Ti/100–Y*3 and Zr–Ti/ 100–Sr/2 (Pearce & Cann 1973), Ti–Cr, (Pearce 1975), Al2O3–FeO+TiO2–MgO (Jensen 1976), Zr/Y–Zr (Pearce & Norry 1979), Th–Hf/3–Ta (Wood 1980), MnO*10– Ti/100–P2O5*10 (Mullen 1983), and Zr/4–Nb*2–Y (Me- schede 1986). The felsic rocks of the Bothnian, Skellefte, Vargfors and Arvidsjaur Groups are plotted in the Rb– Y+Nb (Pearce et al. 1984), Zr+Nb+Ce+Y–FeO*/MgO (Whalen et al. 1987), and R1–R2 diagram (De La Roche 1980, Batchelor & Bowden 1985). Bothnian Group In the Al2O3–FeO*+TiO2–MgO-plot (Jensen 1976) the HBA homogeneous, basaltic lavas and related volcaniclastic rocks plot in the high-Fe field, typical for tholeiitic rocks (Fig. 8a). Some samples trend towards the MgO apex, reflecting a more primitive composition or, more likely, indicates cumulate processes. The FBRA rocks typically plot towards the Al2O3 apex and show a calc-alkaline trend, starting in the HMT field. A Mullen (1983) plot (Fig. 9a) gives a clear discrimination for the basaltic rocks of the two assemblages. The HBA basaltic rocks plot within or close to the MORB or ocean floor fields in most diagrams (Figs. 10a, 11a, 12a). Some samples, mainly from the Skarvsjö area GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 81 volcanic arc field of the Rb–Y+Nb plot (Pearce et al. 1984), where the rhyolites are more fractionated (higher Y+Nb) than the dacites and plot closer to the WPG field (Fig. 13b). a) Rock/Chondrite 1000 100 Skellefte Group 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu b) Rock/Chondrite 1000 100 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu c) Rock/Chondrite 1000 Vargfors Group 100 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Fig. 7. REE patterns for different representative volcanic rocks of the Arvidsjaur Group. Normalized REE abundance in rock/primitive mantle (Sun 1982). a) Basalts and andesites. b). Dacite/quartzlatite/trachyandesites. c) Rhyolites. south of Storuman, plot within or close to the within-plate field in a Zr–Ti/100–Y*3-plot (Pearce & Cann 1973) as seen in Figure 11a. These are possibly cumulate rocks. The FBRA basalts and andesites have a calc-alkaline basalt signature. The dacites and rhyolites plot in the 82 The basalts and andesites of the Skellefte Group plot in the island arc or calc-alkaline basalt fields in the different discrimination plots. The Zr/Y ratio discriminates between oceanic and continental arcs (Pearce & Norry 1979) and the low ratio, 2–4 for the Skellefte Group, suggests the former setting. In the Zr–Ti/100–Y*3-plot (Pearce & Cann 1973), the Skellefte Group mafic volcanic rocks plot all over the A, B, and C fields (Fig. 11b), with one cluster in the low-K tholeiite field and another cluster on the line separating the ocean-floor and calcalkaline fields. This suggests several magma sources within the Skellefte Group volcanic rocks. The low-K tholeiite samples are from the Långdal area (Vivallo 1987) and represent a stratigraphically high unit in the easternmost part of the Skellefte District, possibly reflecting a late extensional event and influx of new primitive magma. In the Zr– Ti/100–Sr/2-diagram a number of samples plot in the OFB field (Fig. 12b). These samples are mainly from the Granbergsliden area and exhibit Sr depletion due to alteration processes (Nicolson 1993). The felsic volcanic rocks plot in the volcanic arc field of the Rb–Y+Nb diagram (Fig. 13b). The Tjamstan Formation samples plot generally as volcanic arc basalts–andesites. The low Zr/Y value suggests an oceanic island arc setting. U. BERGSTRÖM Few samples (n=3) from the Varuträsk Formation are available and the results must be reviewed with some caution. The Varuträsk Formation basalts are generally similar to the Bothnian Group, HBA homogeneous basalts and plot within or close to the MORB/ocean floor fields in most discrimination diagrams. The Varuträsk Formation samples have high Fe and Ti content (Fig. 8c). The Varuträsk Formation basalts plot as low-K tholeiites and within-plate basalts in the Zr–Ti/100–Y*3 diagram (Pearce & Cann 1973, Fig. 11c). The Bjurås Formation Mg-basalts are strongly Mgand Cr-enriched, which is clearly seen in the Al2O3– FeO+TiO2–MgO (Jensen 1976, Fig. 8c) and a Ti-Cr-plot (Pearce 1975) not shown here. The tectonic setting of the Bjurås Formation Mg-basalts suggested from most discrimination diagrams (Figs. 9c, 10c, 11c, 12c), is a calcalkaline volcanic arc setting, where the Mg-basalts represent juvenile, primitive melts. The Gallejaur Formation basalts are calc-alkaline vol- FeO*+TiO2 a) TA HFT TA TD BK TD TR CB CA CR PK CD FeO*+TiO2 TA HFT TD TR Al2O3 CR CD MgO c) CD CA CB HFT BK TR HMT Al2O3 CR FeO*+TiO2 b) CA CB HMT PK Al2O3 MgO FeO*+TiO2 d) TA BK TD HFT BK TR HMT PK CR MgO Al2O3 CD CA CB HMT PK MgO Fig. 8. Jensen plot (Jensen, 1976) for samples from a) the Bothnian Group, b) the Skellefte Group, c) the Vargfors Group, d) the Arvidsjaur Group. Fields are: PK=peridotitic komatiite, BK=basaltic komatiite, HFT=high-Fe tholeiite basalt, HMT=high-Mg tholeiite basalt, CB=calcalkaline basalt, CA=calc-alkaline andesite, CD=calc-alkaline dacite, CR=calc-alkaline rhyolite, TA=tholeiitic andesite, TD=tholeiiitic dacite, TR=tholeiitic rhyolite. Symbols as in Figure 3. canic arc basalts according to most diagrams (Figs. 9c, 10c, 11c, 12c), similar to the Bjurås Formation high-Mg basalts. Andesites and dacites from the Gallejaur Formation form a calc-alkaline trend in the volcanic arc field in the Rb–Y+Nb-plot of Pearce et al. (1984), similar to the Skellefte Group (Fig. 13c). Arvidsjaur Group The subdivision of the mafic volcanic rocks from the Arvidsjaur Group in more primitive basalts–andesites and evolved plagioclase phyric andesites–dacites is seen in most discrimination diagrams. The basalts–andesites plot in the HMT field in the Jensen plot (Jensen 1976), whereas the plagioclase phyric andesites–dacites cluster in the CA-TD fields. The low Mg and Ca (MgO+CaO = 8–12 %) and high SiO2 content of the andesites–dacites make them unsuitable for many of the plots, and the results are to be considered as indications on magma composition during fractionation. The Zr/Y ratio above 4 for most samples indicates a continental margin setting (Pearce & Norry 1979). The basalts–andesites generally plot in the calc-alkaline basalt fields in most diagrams. In the Zr– Ti/100–Y*3-plot the andesites–dacites mainly plot within and partly outside the calc-alkaline C field, whereas the basalts are restricted to the ocean floor/volcanic arc B field. The felsic volcanic rocks of the Arvidsjaur group show a volcanic arc signature in the Rb–Y+Nb-plot (Pearce et al. 1984). A strong crustal influence is indicated for the rhyolite samples, which trend into the within-plate field. GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 83 TiO2 a) TiO2 b) OIT OIT MORB MORB IAT IAT OIA OIA CAB CAB MnO*10 P2O5*10 TiO2 c) MnO*10 P2O5*10 TiO2 d) OIT OIT MORB MORB IAT IAT OIA OIA CAB CAB MnO*10 P2O5*10 MnO*10 P2O5*10 Fig. 9. Mn*10–TiO2–P2O5*10 tectonic discrimination-plot for basaltic rocks (SiO2=45–54 wt. %) according to Mullen et al. (1983) for samples from a) the Bothnian Group b) the Skellefte Group, c) the Vargfors Group, and d) the Arvidsjaur Group. Fields are: OIT=ocean island tholeiite basalt, OIA=ocean island alkali basalt, MORB=mid ocean ridge basalt, IAT=island arc tholeiite basalt, CAB=calc-alkaline basalt. Symbols as in Figure 3. Discussion Tectonic setting The HBA homogeneous basalts of the Bothnian Group are interpreted as MORB basalts formed on the ocean floor, based on their flat REE to mildly LREE depleted pattern, and their behaviour in most discrimination plots. The FBRA assemblage is interpreted as volcanic arc type rocks. The interpreted tectonic setting of the Bothnian Group is speculative, but the overall setting with mixed MORB-type and arc-type volcanic rocks and sedimentary rocks is interpreted as an arc setting, where the HBA rocks formed on the ocean floor in marginal basins, surrounded by arc crust. The FBRA blocks constitute younger arc segments. The Skellefte Group basalts to rhyolites are interpreted as calc-alkaline rocks formed in a marine volcanic arc. The mafic volcanic rocks have both island arc tholeiite 84 U. BERGSTRÖM and calc-alkaline components. The felsic volcanic rocks include dacites and rhyolites, which are quartz-enriched and K-depleted. The most fractionated end members are coarse quartz-porphyritic subvolcanic stocks with flat REE pattern and a negative Eu anomaly. They are mildly bimodal, possibly reflecting an arc under extension. As felsic compositions predominate, one would suspect that a significant proportion of continental crust has been present in the source area and that AFC (Assimilation-Fractionation-Crystallization, DePaolo 1981) was the main process that generated the more felsic rocks. Allen et al. (1996) suggested an extensional continental margin arc setting rather than an oceanic arc for the Skellefte Group, based on the physical volcanology of the Skellefte Group volcanic rocks. This is in accordance with the geochemical data, with the mixed, but predominantly felsic compositions, the subordinate but present primitive island arc magmas, and the mild bimodality. The Tjamstan Formation mafic Ti (ppm) a) b) 18000 18000 15000 15000 12000 12000 9000 9000 D 6000 3000 C 0 25 C 3000 A 50 75 100 125 150 175 200 225 250 0 c) Ti (ppm) B 6000 B 0 D A 0 25 18000 15000 15000 12000 12000 9000 9000 D 6000 6000 C A 0 100 125 150 175 200 225 250 125 150 175 200 225 250 D B B 0 75 d) 18000 3000 50 25 50 75 100 C 3000 125 150 175 200 225 250 0 A 0 25 50 75 100 Fig. 10. Tectonic discrimination Zr–Ti-plot for basaltic rocks according to Pearce and Cann (1973) for basalts–andesites from a) the Bothnian Group, b) the Skellefte Group, c) the Vargfors Group, and d) the Arvidsjaur Group. Ocean floor basalts plot in fields D and B, low-K tholeiite basalts plot in fields A and B, and calc-alkali basalts plot in fields A and C. Symbols as in Figure 3. volcanic rocks are similar to the mafic volcanic rocks of the Skellefte Group, indicating a new generation of rather primitive island arc magmas in the arc environment. The Vargfors Group includes three principal units of mafic volcanic rocks, each with a distinct tectonic setting, but on the same principal stratigraphical level. The Varuträsk Formation consists of MORB-type basalts similar to the Bothnian Group basalts, maybe with a somewhat stronger crustal affinity, which is interpreted from the higher LREE content, the increasing levels of titanomagnetite crystallization, and the tendency to plot in withinplate fields in many discrimination diagrams. The interpreted tectonic setting for these rocks is a rift basin, possibly a back-arc marginal basin. The Mg-basalts of the Bjurås Formation are strongly Mg-Cr-Ni-rich, highly primitive volcanic arc rocks, indicated from several dis- crimination diagrams. The Gallejaur Formation volcanic rocks are calc-alkaline and intermediate between the Skellefte and Arvidsjaur Groups. The Arvidsjaur Group is a heterogeneous, strongly fractionated volcanic unit with a substantial crustal component, emplaced in a continental volcanic arc environment. The volcanic rocks are medium- to high-K in character, also evident from abundant microcline phenocrysts. The geochemical signature suggests significant arc maturity. Perdahl (1993, 1994, 1996) emphasized that the Arvidsjaur Group rocks from the the western part of the Arvidsjaur District, the Arjeplog volcanics, are bimodal, suggesting emplacement in a continental rift, whereas the central part (which dominates the data set in this study) are more arc like. GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 85 Ti / 100 a) A D Ti / 100 b) D B A B C C Zr Y *3 Ti / 100 c) Zr A D B B C Zr Ti / 100 d) A D Y *3 C Y *3 Zr Y *3 Fig. 11. Tectonic discrimination Zr–Ti/100–Y*3-plot for basaltic rocks according to Pearce and Cann (1973) for basalts–andesites from a) the Bothnian Group, b) the Skellefte Group, c) the Vargfors Group, and d) the Arvidsjaur Group. Within-plate basalts plot in field D, ocean floor basalts plot in field B, low-K tholeiite basalts in fields A and B, and calc-alkali basalts in fields B and C. Symbols as in Figure 3. Discrimination The Skellefte and Arvidsjaur Groups probably reflect two discrete episodes within the same destructive plate margin setting, separated by 5–10 million years (Billström & Weihed 1996). The Skellefte Group was deposited in a marine, extensional environment with influx of primitive island arc melts, whereas the Arvidsjaur Group was formed in a subaerial, compressional, continental margin arc. The geochemical differences between the two groups are mainly related to the much higher degree of crustally derived magmas in the Arvidsjaur Group, with higher K, Rb, and U-Th contents and a REE pattern with a negative Eu anomaly, especially in the more felsic rocks. This is readily seen in spectrometric surveys, where the K-U-Th components are much higher in the Arvidsjaur Group volcanic rocks compared to Skellefte Group volcanic rocks. The felsic components of the Skellefte Group normally lack microcline phenocrysts and fractionate towards a SiO2-rich quartz porphyritic end member. Samples from the Skellefte Group plotted in a R1–R2 dia86 U. BERGSTRÖM gram (Fig. 16) suggest a strong mantle component for the Skellefte Group, whereas the Arvidsjaur Group samples have a late-orogenic signature. The mafic rocks in the Skellefte Group include island arc tholeiites, contrary to corresponding Arvidsjaur Group volcanic rocks, which are typically calc-alkaline. In Figure 14b, the Skellefte Group mafic volcanic rocks plot close to the TiO2 apex and the oceanic arc field and grade towards the Arvidsjaur Group volcanic rocks, which are restricted to the continental arc field and consequently plot close to the K2O apex. The Tjamstan Formation volcanic rocks are compositionally similar to the Skellefte Group volcanic rocks and is included as the uppermost unit in the Skellefte Group. The time interval between the development of the Skellefte and Arvidsjaur arcs is dominated by the deposition of greywackes, now exposed in the eastern and western margins of the Skellefte District. Mafic volcanic rocks intercalated with the sedimentary rocks exist in both areas, but the chemical compositions are different. The Mg-basalts of the western Skellefte District are highly TiO / 100 a) b) OFB TiO / 100 OFB IAB IAB CAB CAB Zr c) Sr / 2 TiO / 100 Zr d) Sr / 2 TiO / 100 OFB OFB IAB IAB CAB CAB Zr Sr / 2 Zr Sr / 2 Fig. 12. Zr–Ti/100–Sr/2 plot for basaltic rocks according to Pearce & Cann 1973 for basalts-andesites of a) the Bothnian Group, b) the Skellefte Group, c) the Vargfors Group, and d) the Arvidsjaur Group. Fields are: OFB=ocean floor basalts, IAB=island arc tholeiite basalts and CAB=calc-alkali basalts. Symbols as in Figure 3. primitive volcanic arc rocks, whereas the Varuträsk Formation basalts in the eastern district have MORB and within-plate characteristics, probably reflecting a rift environment. The coeval Gallejaur Formation volcanic rocks erupted around the Gallejaur intrusive complex in the central Skellefte District and were deposited on the basement of the older Skellefte Group volcanic rocks. The volcanic rocks of the Gallejaur Formation are similar to the Skellefte and Arvidsjaur Group rocks, and may be regarded as a variety of Arvidsjaur arc volcanism on top of the Skellefte Arc. The Skellefte, Vargfors, and Arvidsjaur Groups represent different tectonic facies within the same destructive plate margin setting. The Skellefte Group was deposited in an early, mainly marine, extensional arc which was followed by the subaerial, compressional, mature Arvidsjaur arc. The Vargfors Group reflects the dominantly sedimentary stages between the two volcanic arc episodes. To the west, an intra-arc basin formed as a deep-water delta, succeded by primitive, Mg-rich, mafic volcanism, which may correspond to the initial stage of the Arvidsjaur volcanism. To the east, a rift basin was formed including new oceanic crust. This basin partly separates the Skellefte arc from poorly known felsic and mafic volcanic rocks in the Burträsk area, that possibly form an arc remnant. The fractionated basalt to rhyolite assemblage (FBRA) of the Bothnian Group south of the Skellefte District is geochemically similar to the volcanic rocks of the Skellefte Group. The FBRA volcanic rocks probably represent remnants of old volcanic arcs. The limited exposures of this unit prevent stratigraphic correlations, but age determinations clearly indicate that this unit is at least 50 millions years older than the Skellefte Group volcanic rocks. The boundary between similar greywackes of the Bothnian and the Vargfors Groups south of the Skellefte District is somewhat arbitrary since the subdivision between the Bothnian and Vargfors Groups is geographical as well as stratigraphical. The boundary which is outlined in Figure 1, is one interpretation. Critical areas for possible contact relations are the Bure, Pauliden, Njuggträskliden, and Burträsk GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 87 a) b) 1000 1000 WPG syn-COLG 100 Rb (ppm) Rb (ppm) syn-COLG 10 100 10 VAG 1 1 ORG 10 100 VAG 1 1000 1 ORG 10 Y+Nb (ppm) 1000 d) 1000 1000 syn-COLG WPG syn-COLG 100 Rb (ppm) Rb (ppm) 100 Y+Nb (ppm) c) 10 WPG 100 10 VAG 1 WPG 1 ORG 10 100 VAG 1000 Y+Nb (ppm) 1 1 ORG 10 100 1000 Y+Nb (ppm) Fig. 13. Tectonic discrimination Rb–Y+Nb-plot (Pearce et al. 1984) for felsic volcanic rocks from a) the fractionated basalt–rhyolite assemblage (FBRA) of the Bothnian Group, b) the Skellefte Group, c) the Gallejaur Formation of the Vargfors Group, and d) the Arvidsjaur Group. Fields are: VAG=volcanic arc granitoids, ORG=ocean ridge granitoids, syn-COLG=syn-collision granitoids and WPG=within-plate granitoids. Symbols as in Figure 3. areas (Fig. 1). In the two latter areas, the contact relations are probably strongly overprinted by both deformation and processes related to Ni mineralization. In Figure 14a, basaltic–andesitic volcanic rocks from the FBRA of the Bothnian Group and the Skellefte Group have been plotted in a La/Yb–Sc/Ni-plot of Bailey (1981). The rocks may be discriminated mainly due to the low Ni content of the Skellefte Group rocks, which is a general feature of island-arc basalts (Wilson 1989) and suggests important olivine fractionation in the evolution of the Skellefte Group magmas. The MORB type basalts of the homogeneous basalt assemblage (HBA) of the Bothnian Group 88 U. BERGSTRÖM is easy to discrimate from the Skellefte Group (Figs. 15a and b), mainly due to the strong Fe-enriched tholeiitic character of the rocks. The HBA basalts of the Bothnian Group are very similar to the basalts of the Varuträsk Formation in the Vargfors Group, and the units cannot be discriminated from each other with the available database in the Whalen plot (Whalen et al. 1987), where they plot close to the A-granite field, contrary to the Skellefte Group rhyolites (Fig. 16b). Figure 16c shows that a large part of the Arvidsjaur Group felsic volcanic rocks tend to plot in the A-granite field, contrary to the corresponding Gallejaur volcanic rocks which plot in the OGT field. a) a) 20 100000 Andean arc Ti (ppm) La/Yb 15 Continental island-arc 10 10000 OFB Other oceanic arc 5 Low-K oceanic arc 0 0 2 4 Sc/Ni LKT 6 1000 10 8 100 1000 Cr (ppm) TiO2 b) b) 22 Oceanic Fe2O3+FeO (wt-%) 19 Continental 16 13 10 7 K2O P 2O5 14. Discrimination plots. a) Basalts and andesites of the fractionated basalt–rhyolite assemblage (FBRA) of the Bothnian Group versus basalt–andesites of the Skellefte Group in a La/Yb–Sc/Ni-plot (Bailey 1981). b) Basalt–andesites of the Skellefte and Arvidsjaur Groups in a K2O–TiO2–P2O5-plot of Pearce et al. (1975). Symbols as in Figure 3. Conclusions The Skellefte District and surrounding areas include a number of litostratigraphic units which are geochemically distinguishable. The Bothnian Group, exposed south of the Skellefte District, includes two volcanic units: one older homogeneous basalt lava–volcaniclastic rock assemblage with MORB signature, and one younger (c. 1.95 Ga) fractionated basalt to rhyolite assemblage, formed in a volcanic arc setting. The Skellefte Group is a heterogeneous unit of basalt to rhyolite, deposited in an extensional continental mar- 4 6 9 12 15 18 21 24 Al2O3 (wt-%) Fig. 15. Discrimination plots. a) Basalts of the HBA homogeneous basalt assemblage of the Bothnian Group and basalts–andesites of the Skellefte Group in a Cr–Ti-plot according to Pearce (1975). Fields are: LKT=low-K tholeiite basalt, OFB=ocean floor basalt. b) Discrimination between basalts of the HBA homogeneous basalt assemblage of the Bothnian Group and basalts–andesites of the Skellefte Group in a Fe2O3+FeO–Al2O3-plot. Symbols as in Figure 3. gin arc at c. 1.90–1.88 Ga. The stratigraphically uppermost unit is composed of primitive basalts and andesites of the Tjamstan Formation and mudstones, reflecting the extensional environment. The Vargfors Group succeeds the Skellefte Group and indicates varying depositional environments at c. 1.88–1.87 Ga. The western part is dominated by greywackes, overlain by primitive Mg-basalts, which are the first sign of a renewed volcanic activity. The Vargfors Group in the eastern part also started with greywacke deposition, succeeded by evolved MORB-type volcanic rocks of the Varuträsk Formation. The latter probably re- GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 89 flects the initiation of a rift basin east of the Skellefte District. Subaerial environments and erosion of the uplifted Skellefte Group rocks characterize the central part of the Vargfors Group. The Arvidsjaur Group is deposited in the Arvidsjaur district north of the Skellefte District and may, at least partly be stratigraphically equivalent to the Vargfors Group rocks. The Arvidsjaur Group is a heterogeneous unit of subaerial basaltic to rhyolitic volcanic rocks, formed in a mature, compressional, continental margin arc. a) 2500 R2 = 6Ca + 2Mg + Al 2000 1 1500 2 1000 3 4 500 6 5 0 7 0 500 1000 1500 2000 2500 3000 R1 = 4Si – 11(Na + K) – 2(Fe + Ti) b) FeO* / MgO 100 10 FG OGT 1 100 1000 5000 Zr + Nb + Ce + Y (ppm) c) FeO* / MgO 100 10 1 FG OGT 100 1000 Zr + Nb + Ce + Y (ppm) 90 U. BERGSTRÖM 5000 Fig. 16. Discrimination plots for felsic volcanic rocks. a) R1–R2plot (De la Roche 1980, Batchelor & Bowden 1985) for felsic volcanic rocks of the Skellefte and Arvidsjaur Groups. Fields are: 1=mantle fractionates, 2=pre-plate collision, 3=post-collision uplift, 4=late orogenic, 5=anorogenic, 6=syn-collision, 7=post-orogenic. b) Tectonic discrimination for granitic rocks according to Whalen et al. (1987) for samples of the Skellefte Group and the fractionated basalt–rhyolite assemblage of the Bothnian Group. c) Tectonic discrimination for granitic rocks according to Whalen et al. (1987) for felsic volcanic samples of the Gallejaur Formation and Arvidsjaur Group. Symbols as in Figure 3. References Allen, R., Weihed, P., & Svenson, S.-Å, 1996: Setting of Zn-CuAu-Ag massive sulphide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc, Skellefte district, Sweden. Economic Geology 91, 1022–1053. Bailey, J.C., 1981: Geochemical criteria for a refined tectonic discrimination of orogenic andesites. Geochemical Geology 32, 139–154. Batchelor, R.A. & Bowden, P., 1985: Petrogenetic interpretation of granitoid rock series using multicationic parameters. Chemical Geology 48, 43–55. Bergman Weihed, J., Bergström, U., Billström, K. & Weihed, P., 1996: Geology and tectonic evolution of the Paleoproterozoic Boliden Au-Cu-As deposit, Skellefte district, northern Sweden. Economic Geology 91, 1073–1097. Bergström, U., 1997: Marginal basin magmatism in an ancient volcanic arc: Petrology of the Paleoproterozoic Malå group basalts, Skellefte district, northern Sweden. Geologiska Föreningens i Stockholms Förhandlingar 119, 151–157. Bergström, U., Billström, K. & Sträng, T., 1998: Age of the Kristineberg Pluton, western Skellefte district, northern Sweden. In S. Bergman (ed.): Radiometeric dating results 4. Sveriges geologiska undersökning C 831, 7–19. Billström, K. & Weihed, P., 1996: Age and provenance of host rocks and ores in the Paleoproterozoic Skellefte District, northern Sweden. Economic Geology 91, 1054–1072. Bergström, U. & Sträng, T., 1999: Berggrundskartan 23I Malå. Sveriges geologiska undersökning Ai 114–117. Bergström, U. & Triumf, C.-A., in press: Berggrundskartan 24I Storavan. Sveriges geologiska undersökning Ai 156–159. Björk, L., 1995: Berggrunden på kartbladen 22G Vilhelmina NO och SO, 22H Järvsjö och 22I Lycksele. In Wahlgren, C.-H. (ed.): Regional Berggrundsgeologisk undersökning – Sammanfattning av pågående undersökningar 1994. Sveriges geologisk undersökning Rapporter och meddelanden 79, 63–66. Björk, L. & Kero, L., 2001: Berggrundskartan 22H Järvsjö. Sveriges geologiska undersökning Ai 144–147. Brown, G.C., Thorpe, R.S. & Webb, P.C., 1984: The geochemical characteristics of granitoids in contrasting arcs and comments on magma sources. Journal of the Geological Society of London 141, 411–426. Claesson, L.-Å., 1985: The geochemistry of early Proterozoic metavolcanic rocks hosting massive sulphide deposits of the Skellefte Distrct, northern Sweden. Journal of Geological Society of London 42, 899–909. De la Roche, H., Leterrier, J., Grandclaude, P. & Marchal, M., 1980: A classification of volcanic and plutonic rocks using R1R2-diagram and major element analyses – its relationships with current nomenclature. Chemical Geology 29, 183–210. DePaolo, D.J., 1981: Trace element and isotopic effects of combined wallrock assimilation and fractional crystallization. Earth and Planetary Science Letters 53,189–202. Dumas, H., 1985: Lithofacies of the metasedimentary formations in the central part of the Skellefte district. Research report TULEA 1986:05. Luleå University. Ehnmark, T. & Nisca, D., 1983: The Gallejaur intrusion in northern Sweden – a geophysical study. Geologiska Föreningens i Stockholms Förhandlingar 105, 287–300. Eliasson, T. & Sträng, T., 1998: Kartbladen 23 H Stensele. In C.-H. Wahlgren (ed.): Regional Berggrundsgeologisk undersökning – Sammanfattning av pågående undersökningar 1997. Sveriges geologisk undersökning Rapporter och meddelanden 97, 55–59. Eliasson, T., Greiling, R.O., Sträng, T. & Triumf, C.-A., in press: Berggrundskartan 23H Stensele. Sveriges geologiska undersökning Ai 126–129. Gavelin, S., 1948: Adakområdet, översikt av berggrund och malmer. Sveriges geologiska undersökning C 490. Hietanen, A., 1975: Generation of potassium-poor magmas in the northern Sierra Nevada and the Svecofennian of Finland. Journal of Research U.S Geological Survey 3:6, 631–645. Jensen, L.S., 1976: A new cation plot for classifying subalkalic volcanic rocks. Ontario Department of Mines Miscellaneous Paper 66. Kathol, B. & Persson, P.-O., 1997: U-Pb zircon dating of the Antak granite, northeastern Västerbotten County, northern Sweden. In T. Lundqvist (ed): Radiometric dating results 3. Sveriges geologiska undersökning C 830, 6–13. Kathol, B. & Triumf, C.-A., in press: Berggrundskartan 24J Arvidsjaur. Sveriges geologiska undersökning Ai 148–151. Le Maitre, R.W. (ed.), 1989: A Classification of Igneous Rocks and Glossary of Terms. Blackwell, Oxford, 193 pp. Lilljeqvist, R. & Svenson, S.-Å., 1975: Exceptionally well preserved Precambrian ignimbrites and basic lavas. Geologiska Föreningens i Stockholm Förhandlingar 96, 221–229. Lundqvist, T., 1987: Early Svecofennian stratigraphy of southern and central Norrland, Sweden, and the possible existance of an Archaean basement west of the Svecokarelides. Precambrian Research 35, 343–352. Maniar, P.D. & Piccoli, P.M., 1989: Tectonic discrimination of granitoids. Geological Society of America Bulletin 101, 635–643. Meschede, M., 1986: A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram. Chemical Geology 56, 207–218. Mullen, E.D., 1983: MnO/TiO2/P2O5: a minor element discriminant for basaltic rocks of oceanic environments and its implications for petrogenesis. Earth and Planetary Science Letters 62, 53–62. Muller, J.-P., 1980: Geochemical and petrophysical study of the Arvidsjaur granitic intrusion, swedish Lapland. Ph. D. thesis, University of Genève, 189 pp. Nicolson, D., 1993: The paleoenvironmental setting and Au genesis of the early Proterozoic Holmtjärn volcanogenic massive sulphide deposit, Skellefte district, northern Sweden. Ph.D. thesis. University of Wales, College of Cardiff. Nilsson, G. & Kero, L., 1986: Berggrundskartan 21J Vindeln NO. Sveriges geologiska undersökning Ai 10. Pearce, J.A., Harris, N.B.W. & Tindle, A.G., 1985: Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 95, 437–450. Pearce, J.A. & Cann, J.R., 1973: Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth and Planetary Science Letters 19, 290–300. Pearce, J.A. & Norry, M.J., 1979: Petrogenetic Implications of Ti, Zr, Y, and Nb Variations in Volcanic Rocks. Contributions to Mineralogy and Petrology 69, 33–47. Perdahl, J.-A., 1993: Geological diversities within the Kiruna- GEOCHEMISTRY AND TECTONIC SETTING OF VOLCANIC UNITS IN THE NORTHERN VÄSTERBOTTEN COUNTY, NORTHERN SWEDEN 91 Arvidsjaur Porphyry groups. Lic. thesis 1993:07, Luleå University of Technology. Perdahl, J.-A., 1995: Svecofennian volcanism in northernmost Sweden. Doc. Thesis 1995:169, Luleå University of Technology. Skiöld, T., 1988: Implication of new U-Pb zircon chronology to early Proterozoic crustal accretion in northern Sweden. Precambrian Research 38, 147–164. Skiöld, T., Öhlander, B., Markkula, H., Widenfalk, L. & Claesson, L.-Å., 1993: Chronology of Proterozoic orogenic processes at the Archaean continental margin in northern Sweden. Precambrian Research 64, 225–238. Sun, S.S., 1982: Chemical composition and origin of the Earth’s primitive mantle. Geochim. Cosmochim. Acta, 46, 179–192. Vivallo, W., 1987: Early Proterozoic bimodal volcanism, hydrothermal activity, and massive sulphide deposition in the Boliden–Långdal area, Skellefte District, Sweden. Economic Geology 82, 440–456. Vivallo, W. & Claesson, L.-Å., 1987: Intra-arc rifting and massive sulphide mineralization in an early Proterozoic volcanic arc, Skellefte district, northern Sweden. In T.C. Pharaoh, R.D. Beckinsale & D. Rickard (eds.): Geochemistry and mineralization of Proterozoic volcanic suites. Geological Society Special Publication 33, 69–80. Wasström, A., 1990: Knaftenområdet – en primitiv Tidigproterozoisk vulkanisk öbåge söder om Skelleftefältet, norra Sverige. Pro Gradu avhandling, Åbo Akademi. Wasström, A., 1993: The Knaften granitoids of Västerbotten County, northern Sweden. In T. Lundqvist (ed.): Radiometric dating results. Sveriges geologiska undersökning C 823, 60–64. Wasström, A., 1996: U-Pb zircon dating of a quartz-feldspar porphyritic dyke in the Knaften area, Västerbotten County, northern Sweden. In T. Lundqvist (ed.): Radiometric dating results 2. Sveriges geologiska undersökning C 828, 34–40. 92 U. BERGSTRÖM Weihed, P. & Antal, I., 1998: Berggrundskartan 22 J Kalvträsk, skala 1:50 000. Sveriges geologiska undersökning Ai 92–95. Weihed, P., Bergman, J. & Bergström, U., 1992: Metallogeny and tectonic evolution of the Early Proterozoic Skellefte District, northern Sweden. Precambrian Research 58, 143–167. Weihed, P. & Schöberg, H., 1991: Age of porphyry-type deposits in the Skellefte District, northern Sweden. Geologiska Föreningens i Stockholm Förhandlingar 113, 289–294. Welin, E., 1987: The depositional evolution of the Svecofennian supracrustal sequence in Finland and Sweden. Precambrian Research 35, 95–113. Whalen, J.B., Currie, K.L. & Chappell, B.W, 1987: A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions in Mineralogy and Petrology 95, 407–419. Wilson, M., 1989: Igneous petrogenesis. HarperCollins Academic. 468 pp. Wilson, M.R., Claesson, L.-Å., Sehlstedt, S., Smellie, J.A.T., Aftalion, M., Hamilton, P.J. & Fallick, A.E., 1987: Jörn: An early Proterozoic intrusive complex in a volcanic arc environment. Precambrian Research 36, 201–225. Winchester, J.A. & Floyd, P.A., 1977: Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology 20, 325–343. Wood, D.A., 1980: The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province. Earth and Planetary Science Letters 50, 11–30. Rock classification, magmatic affinity, and hydrothermal alteration at Boliden, Skellefte district, Sweden – a desk-top approach to whole rock geochemistry Anders Hallberg Hallberg, A., 2001: Rock classification, magmatic affinity, and hydrothermal alteration at Boliden, Skellefte district, Sweden – a desk-top approach to whole rock geochemistry. In Weihed, P. (ed.): Economic geology research. Vol. 1, 1999–2000. Uppsala 2001. Sveriges geologiska undersökning C 833, pp. 93–131. ISBN 91-7158-665-2. Unambiguous mapping of rocks, geological contacts, and alteration patterns is vital in geological surveys as well as in the exploration for mineral deposits. In many Precambrian ore-bearing regions in Sweden and other parts of the world, hydrothermal alteration, penetrative deformation, and overprinting regional metamorphism have destroyed all diagnostic features in the rock. Correct identification of precursor rocks and characterisation of alteration in such areas are extremely difficult. Modern lithogeochemical techniques then provide a powerful and cost effective tool to decipher origin and history of the rock. The main aim with this paper is to explore the use of lithogeochemical techniques on the rocks that make up host and wall rocks to the Boliden massive sulphide deposit, both strongly altered and least altered rocks have been studied. The results of the study are only valid for the rocks in the studied area and direct application of the results on rocks from other areas might be misleading. More important, however, is the approach to whole rock geochemistry presented in this paper, an approach that can be used to identify alteration and indicate reliable less mobile elements from any rock and from any geological environment. Anders Hallberg, Geological Survey of Sweden, Mineral Resources Information Office, Skolgatan 4, SE-930 70 Malå, Sweden. E-mail: [email protected] The Boliden deposit The Boliden Cu-Au-As massive sulphide deposit is situated in the most gold-rich area in Europe – the eastern Skellefte district, northern Sweden (Fig. 1). Within a distance of less than 26 km from Boliden, two gold deposits and eleven gold-rich massive sulphide deposits have been mined. The combined gold production from these mines is in excess of 220 metric tons of gold. Around sixty percent, or 128 metric tons, of the gold came from the Boliden deposit. The Boliden deposit has been the subject of numerous studies since the discovery of the deposit in 1924, e.g. Ödman (1941), Gavelin (1955), Nilsson (1968), Grip & Wirstam (1970), Isaksson (1973), Rickard & Zweifel (1975), Vivallo (1987), and most recently by Bergman Weihed et al. (1996). The following is a brief summary of the main characteristics of the deposit. Base metal and gold mineralization at Boliden consists of massive arsenopyrite ore, massive pyrite + pyrrhotite ore, and veins and disseminations below the massive sulphides. The total tonnage of the deposit was 8.4 Mt with an average grade of 15.5 g/t Au, 1.43 % Cu, and 6.8 % As. The deposit is hosted by a large zone of strongly altered rocks including chlorite schists, quartz-sericite schists, and rutile-bearing andalusite-sericite rocks. The rocks outside the altered area consist of volcanic rocks of intermediate to felsic composition. About the data Almost 90 whole rock geochemical analyses from the Boliden area are available from publications (Ödman 1941, Nilsson 1968, Grip & Ödman 1942, Bergman Weihed et al. 1996). In addition, more than 200 analyses come from unpublished research reports (Hallberg 1994, Bergström 1994) and from other unpublished sources. A lot of the unpublished data have been published as averages or as diagrams without primary analyses in e.g. Vivallo (1987) and Allen et al. (1996). For several of the analyses there are very little information on sampling method, sample preparation method, analytical method, or precision in analyses. All available data are found in Appendix A–C. Information on analytical procedures, analytical methods, and laboratories are, when available, also given in Appendix A–C. The effect of crushing and milling methods are discussed in the text. In order to avoid any obstacles due to uncertainties in location, analytical quality, or sampling procedure, only modern analyses with sufficient control of the analytical procedures are used in this study. In practise this means that analyses done before 1985 are not used. Thus, most of the data used come from two unpublished research studies on the Boliden Cu-Au-As deposit made by the author and by U. Bergström in 1993–1994 (Hallberg 1994, Bergström 1994). Some of the data have been published in Bergman Weihed et al. (1996), all other data are given in Appendix A and B. Most of the samples in series B (B001–B205, Hallberg ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 93 1700000 Åkerberg Kedträsk Björkdal Petiknäs Åsen Kankberg Renström Åkulla Boliden Långsele 7200000 Långdal Younger granits 5 km Mafic metavolcanic rocks Early orogenic mafic intrusions Felsic metavolcanic rocks Early orogenic granitoid intrusions Metasedimentary rocks Fig. 1. Geological map of map sheet 23K Boliden SV (Lundström & Antal 2000) with airborne magnetics (200 m line distance, 30 m ground clearance, data from the Geological Survey of Sweden) in the background. Large red and yellow dots show the position of sulphide and gold mines, respectively. Small black dots show the position of sulphide and gold prospects. Data from the Geological Survey of Sweden, Mineral deposit database. 1994) come from altered rocks within the Boliden alteration zone and are sampled with the purpose to investigate internal zoning patterns. The sampling, with the exception for outcrops and archive hand specimen samples, was done by picking rock chips from drill core in order to get a representative sample. Sectioning has in most cases been guided by geological logging of the drill core. Outcrop and archive samples were cut by diamond saw and analysed. All samples were analysed at XRAL, Canada, using XRF, ICP, and INAA on crushed and milled powder. The first batch of samples (B001–B073) was pulverised using a tungsten carbide ring mill whereas the second batch (B151–B205) was milled in a Cr-steel ring mill. The Cocontamination from tungsten carbide and the Cr-contamination from the Cr-steel ring mill is estimated at 60–80 ppm for each element, and can be seen in Appendix A. Samples 91125 to 951517 (Bergström 1994) come 94 A. HALLBERG from less altered rocks from the vicinity of the Boliden deposit. Sampling procedures, sample preparation, and analytical work differ somewhat between the samples. In most cases these samples consist of hand specimen samples from outcrops and approximately 15 cm drill core sections from underground samples. The samples have been analysed at XRAL using XRF and NA and at SGAB, Luleå using ICP, see Appendix B. The approach The data treatment reported in this paper chiefly follows the technique described by MacLean & Barrett (1993) and references therein. Most of the chemical data used in this study relate to rocks that have been mapped as altered or strongly altered. It has not been possible to determine the precursor to these rocks in hand specimen with a few exceptions. Even among rocks mapped as least altered, and thus considered to have a primary composition, a more detailed analysis reveals evidence of alteration. For example, only four out of the eight analyses of ”least altered rocks near Boliden” presented in Bergman Weihed et al. (1996) plot within the igneous spectrum of Hughes (1973), which means that they have been affected by alkali alteration. The initial steps in the procedure described by MacLean and Barrett (1993), e.g. mapping and core logging, have turned out to be difficult and equivocal. Therefore the techniques presented by MacLean and Barrett (1993) have been used in a somewhat different order and some modifications of the methods have been done. The modified work plan for single precursor and multiple precursor systems are outlined in Table 1. Altered rocks that host the Boliden deposit consist of andalusite schist, sericite schist, chlorite schist, and mixtures between two or more types. The occurrence of andalusite rocks and locally also rutile rocks indicates that alteration at Boliden was more intense than elsewhere in the Skellefte district. Due to pervasive alteration and penetrative deformation, the precursor rocks within the alteration zone are impossible to identify, with one important exception, the quartz porphyritic rock that makes up a significant part of the north-western wallrock. Table 1. Work plan for single and multiple precursor systems. Single precursor system 1. If possible, identify a single precursor system, that is a single rock unit that can be followed from the least altered state into strongly altered states. 2. Check the single precursor chemical data for immobile and incompatible elements. 3. Identify precursor composition of single rock and calculate mass change during alteration. Multiple precursor system 4. Search the database for least altered rocks. 5. Search the chemical data of all rocks for immobile and incompatible elements. 6. Construct a fractionation curve using immobile incompatiblecompatible element pair. 7. Use fractionation curve and least altered rock compositions to calculate mass changes during alteration. Single precursor system – the quartz porphyries around Boliden The rock Quartz porphyritic rocks (qz-p) in the Boliden area occur as two major stocks, the Boliden stock and the northern stock, and several narrow quartz porphyritic dykes (Bergman Weihed et al. 1996). The major characteristic of the rock type, already indicated by its name, is bluish, opalescent quartz phenocrysts that make up a significant part of the rock. In less altered rocks, the phenocrysts are host- ed by a fine-grained, greyish matrix of quartz, feldspar, and mica, mainly biotite (Nilsson 1968). What makes the qz-p so unique and so useful for geochemical studies is the fact that the quartz phenocrysts remained unaffected during hydrothermal alteration. Even in strongly altered quartz-sericite schist the qz-p precursor can be identified by the quartz phenocrysts. This was recognised more than 50 years ago (Ödman 1941) and quartz phenocrysts in strongly altered rocks have since then been used to map the Boliden qz-p stock in underground exposures and in drill cores down to 600 m depth. The Boliden qz-p stock makes up a significant part of the northern wall rock to the Boliden Cu-Au-As ore. At the surface, the rock occurs in a weakly altered state (Bergman Weihed et al. 1996) while at depth, and within the alteration zone, it consists of chlorite-sericite schist, sericite-quartz schist, and locally andalusite-bearing sericite schist (Nilsson 1968). By extrapolating the southern contact of the qz-p stock from mine maps (Ödman 1941) towards the surface, it can be shown that surface exposures of qz-p occurring immediately north of the Boliden mine are part of the same stock. Outcrops of the northern stock, on the other hand, show no visual evidence of alteration (Bergman Weihed et al. 1996). The fact that qz-p rocks in different states of alteration are exposed and available for sampling makes it highly suitable for alteration studies. Based on visual examination of the qz-p rocks in outcrop and in drill core, they have been divided into least altered, altered, chlorite±sericite altered, and sericite±andalusite altered. The chemistry of the 22 quartz porphyry rock samples is shown in Table 2. Least altered rocks are the well preserved rocks from the northern stock, altered rocks are found in outcrops of the Boliden stock, whereas chlorite±sericite and sericite±andalusite altered rocks occur at depth. Alteration Figure 2 shows all qz-p data plotted in Hughes igneous spectrum (Hughes 1973). This graph is used here to recognise samples with an anomalous alkali distribution, i.e. altered samples. All samples that plot to the right of the igneous spectrum by Hughes are considered to be altered in some way whereas the samples that plot within the spectrum are classified as least altered samples. As can be seen from the diagram in Figure 2, only one (sample 92026, Table 2) of the samples from the northern stock falls within the igneous spectrum. The other sample from the northern stock (sample 92027, Table 2) shows a weak K-alteration. In the altered samples from outcrops of the Boliden qz-p stock, most of the Na has been leached and the K is enriched. Total alkali is, however, nearly the same ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 95 Table 2. Whole rock geochemistry of the quartz porphyries in the Boliden area. Data from Hallberg (1994) and Bergström (1994). More information on analytical methods and laboratories used in Appendix A–B. sample # B016 B022 B033 B034 B035 B036 B038 B039 B049 B050 B051 B052 B053 B054 bh core (m) level (m) N (RT90) E (RT90) 75 99 100 100 100 100 100 320 322 322 322 322 322 322 47,0–51,3 0,0–15,0 0,0–15,7 15,7–34,0 34,0–50,9 50,9–66,5 68,7–87,4 410 410 410 410 0,0–15,7 0,0–18,3 7204331 1716531 7204297 1716552 7204318 1716551 7204335 1716550 7204353 1716549 7204369 1716549 7204388 1716548 7204282 1716585 SiO2 79,9 80,7 77,5 82,4 77,4 74,0 76,2 Al2O3 11,5 15,2 16,8 13,9 11,1 11,9 12,2 CaO 0,1 0,1 0,1 0,0 0,6 0,1 MgO 0,3 0,2 0,2 0,1 2,1 Na2O 0,50 0,29 0,38 0,26 K2O 2,77 1,43 1,31 Fe2O3 2,3 <0,01 <0,01 MnO <0,01 <0,01 <0,01 TiO2 0,23 0,32 P2O5 0,05 0,07 330 410 410 570 570 B075 B157 outcrop outcrop 18,7–33,8 33,8–41,7 41,7–44,2 44,2–50,1 50,1–54,4 91124 30 92028 92026 outcrop outcrop 573,6–574,0 91125 30 92027 951504 outcrop 585,1–585,4 424 97 69,9–70,1 570 570 570 570 570 429 90 7204303 1716584 7204320 1716583 7204332 1716583 7204337 1716582 7204341 1716582 7204346 1716582 7204650 1716200 7204650 1716200 7204337 1716523 7204650 1716330 7205140 1715670 7204344 1716516 7205150 1715730 - 81,2 78,5 80,8 78,7 84,2 77,5 75,5 74,9 72,7 72,7 75,3 73,0 73,6 71,9 70.8 14,8 17,6 13,4 13,0 11,1 12,5 11,9 12,3 12,4 11,7 11,4 12,7 12,8 13,0 12.3 0,4 0,0 0,1 0,1 0,1 0,1 0,1 0,1 2,6 3,2 0,1 3,0 2,4 0,2 2,6 0.1 2,8 1,7 0,2 0,2 0,3 1,6 0,2 1,6 2,8 1,8 1,7 3,7 1,7 1,8 2,7 1,8 5,4 0,18 0,24 0,33 0,17 0,07 0,31 0,29 0,25 0,23 0,18 0,22 0,29 0,16 0,24 2,80 0,23 1,85 0.21 0,96 2,04 2,08 2,73 0,96 0,31 2,14 2,88 2,83 2,81 2,07 4,05 4,09 1,69 3,15 2,12 2,24 2,75 1.66 <0,01 4,0 4,8 3,8 <0,01 <0,01 0,1 1,5 0,2 2,0 5,0 3,0 3,4 6,2 2,9 3,7 5,0 3,4 5,0 <0,01 0,04 0,02 0,02 <0,01 <0,01 <0,01 0,01 <0,01 0,01 0,04 0,06 0,07 0,06 0,11 0,08 0,05 0,12 0.13 0,37 0,26 0,24 0,30 0,27 0,34 0,32 0,28 0,23 0,21 0,26 0,24 0,22 0,24 0,22 0,25 0,28 0,26 0,30 0,25 0,08 0,04 0,05 0,05 0,06 0,06 0,05 0,07 0,06 0,04 0,06 0,06 0,05 0,06 0,10 0,06 0,07 0,09 0,07 LOI 2,50 1,90 3,45 2,30 2,60 2,60 2,75 2,40 2,95 2,50 0,47 1,40 1,75 2,35 0,85 0,95 3,42 1,30 1,20 2,99 1,15 3.4 SUM 100,2 100,1 100,2 100,2 100,4 99,0 100,4 100,1 100,1 100,0 98,9 100,5 98,8 100,3 100,0 99,0 100,0 99,4 100,1 100,2 99,0 99,2 Cu 142 3,2 1,1 1,0 1,4 4,8 76,5 1,2 1,3 0,5 16,2 0,6 2,4 3,3 8,4 12,1 Zn 78,2 7,1 6,7 6,2 30,2 58,4 274 6,3 4,2 4,3 36,2 3,1 13,7 21,8 48,5 32,7 32 149 68 31 58 134 Pb 21 <2 <2 <2 <2 <2 32 <2 <2 <2 <2 <2 <2 <2 <2 3 Cd <1 <1 <1 <1 <1 <1 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 Au 22 23 23 16 <5 <5 <5 150 <5 <5 7 <5 6 5 11 14 Ag 1,6 0,3 0,6 <0,1 0,3 0,6 0,6 0,6 0,8 0,6 0,7 0,6 0,3 1,0 0,6 0,1 1 11 19 6 12 As 31 2 11 340 3 3 11 <2 <2 2 2 3 <2 2 7 6 Sb 0,7 0,3 0,2 0,5 0,2 0,5 0,8 0,2 0,2 0,3 0,3 <0,2 0,3 <0,2 0,6 0,7 Bi 6 <3 4 <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 5 <3 <3 Br <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 1 <1 Co 38 37 28 53 29 25 17 34 30 36 35 31 30 26 24 <5 Ni <1 1 3 1 <1 <1 3 <1 5 1 1 <1 2 1 1 5 7 15 Cr 8 2 <1 <1 4 3 4 1 3 1 1 <1 1 3 2 116 5 11 Mo 1 <1 <1 <1 2 <1 <1 2 <1 <1 <1 <1 <1 <1 <1 1 V 11 19 18 6 6 23 14 20 14 19 8 6 7 7 8 8 5 Ba 402 92 128 111 557 506 606 70 <50 250 550 599 662 597 796 845 554 Cs <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 <3 5 385 4 387 5 831 506 442 29 Rb 49 30 28 17 32 27 44 22 21 36 40 48 43 29 53 32 11 30 36 20 43 Sc 12,2 11,2 12,0 13,8 9,1 12,5 11,9 12,9 10,5 16,4 14,8 14,2 13,2 11,4 10,9 10,3 8,3 9,3 11,0 8,6 11,0 Sr 26,3 18,8 30,6 19,4 15,1 14,5 29,8 17,7 11,1 24,7 16,6 15,6 16,4 11,7 133,0 143,0 11 65 65 19 79 Be 1,0 <0,5 <0,5 <0,5 0,9 1,0 1,1 <0,5 <0,5 <0,5 0,6 <0,5 0,7 1,1 1,2 0,9 5,0 5,0 Hf 4 5 5 4 4 4 4 5 6 3 4 3 4 4 4 4 Sn <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 13 5,0 Ta <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 Nb <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 10 12 11 Th 4,3 5,5 5,9 4,1 3,5 3,8 4,2 5,2 5,3 4,4 4,2 3,9 4,5 4,1 4,9 4,5 3,3 4,1 4,1 U 2,8 3,5 3,0 2,6 2,1 2,2 2,9 3,0 3,0 2,6 2,6 2,1 2,4 2,4 2,4 2,6 2,3 2,0 Y 6,5 5,6 7,3 7,2 7,9 6,9 7,3 7,1 6,7 7,4 8,9 6,9 6,4 6,5 18,3 20,1 26 21 24 34 19 27 Zr 165 197 211 189 154 156 164 202 230 189 174 159 176 158 162 159 148 158 171 159 178 170 La 23 38 39 27 21 24 26 34 35 31 29 23 32 23 26 26 21 24,0 26 19,8 28,0 Ce 47 76 80 54 45 50 52 70 73 64 61 50 66 52 54 54 50 52 46 53 Nd 20 30 30 20 20 20 20 30 30 30 30 20 30 20 30 20 25 26 29 27 Sm 4,1 6,1 7,4 4,9 4,1 4,5 5,1 6,4 6,6 5,8 5,9 4,7 5,8 4,7 5,0 5,0 4,4 4,9 6,67 4,9 Eu 0,9 1,0 1,8 0,9 0,6 0,7 0,5 1,1 1,3 1,2 1,4 1,1 1,1 0,7 1,5 1,1 1,4 0,8 0,95 1,1 Tb <0,5 0,7 0,7 0,5 0,5 0,5 0,6 0,7 0,8 0,6 0,9 0,7 0,7 0,5 0,7 0,5 0,6 0,6 Yb 2,4 1,8 2,3 2,6 2,6 2,3 2,6 2,4 2,3 2,0 4,0 3,7 3,3 2,6 2,6 2,7 2,3 2,9 Lu 0,34 0,26 0,34 0,38 0,37 0,33 0,36 0,34 0,34 0,32 0,51 0,47 0,44 0,37 0,40 0,42 0,34 0,35 stock BS BS BS BS BS BS BS BS BS BS BS BS BS BS BS BS BS BS NS NS NS BS Alt. SA SA SA SA CS CS CS SA SA SA CS SA CS CS A A CS A LA CS LA CS 3,2 2,2 0,8 3,72 2,7 0,34 BS: Boliden stock, NS: Northern stock, SA: sericite±andalusite altered, NS: chlorite±sericite altered, A: altered, LA: least altered as in the least altered sample. The alteration could be due to a replacement of Na by K in the fine-grained matrix of the qz-p rock – a K-feldspar alteration. At least some of the K-enrichment is, however, due to sericite alteration 96 A. HALLBERG since sericite-filled veins can be seen in the rock. Whether this K-alteration is related to the hydrothermal alteration beneath the Boliden deposit is not known. For a distance of about 500 m from outcropping Boli- 10 Na-altered Na2O+K2O (wt%) 8 unaltered K-altered 6 4 2 0 Northern qz-p stock least altered weakly altered 0 Boliden qz-p stock altered (outcrop) chlorite±sericite altered sericite±andalusite altered 20 40 Fig. 2. Data for quartz-porphyries from the Boliden area plotted in the igneous spectrum, Hughes (1973). 60 80 100 K2O/(Na2O+K2O)x100 den qz-p to the closest underground drill core sample of qz-p rock, sample B038 from the 410 m level, there is a large area from which there are no data. The samples from underground drill cores differ significantly from the relatively weakly altered surface exposures. They consist of chlorite rocks, chlorite-sericite rocks and sericite rocks, locally andalusite-bearing. Since these rocks are part of the alteration zone under the Boliden deposit, they have most likely been formed by an ore-related alteration. The K/Na ratio is broadly the same as for the less altered outcrops but the total alkali has decreased significantly. This means that also K is leached from the rock which suggests that there is a tendency towards total destabilisation of K-bearing silicates and a total removal of alkali from the system. In the most altered qz-p sample in this study, sample B049 from the central parts of the alteration zone, the K2O content is as low as 0,3 % and Na2O is close to the detection limit. This confirms previ- ous observations of strong hydrothermal leaching in the more central parts of the alteration zone (Nilsson 1968, Bergman Weihed et al. 1996). The effect of alteration on the other major elements is shown in the spider diagram in Figure 3. Data for altered samples have been normalised to the least altered sample (sample 92026, Table 2). Both chlorite±sericite schist and sericite±andalusite schist show a strong depletion in Ca and a higher loss of ignition (LOI). The chlorite±sericite schist is strongly enriched in Mg and Fe due to the high chlorite content whereas the relatively chlorite-poor sericite±andalusite schist shows a strong depletion in those elements. Fe and Mg vary with the chlorite content in the samples indicating that chlorite is the major host mineral for these elements. The strong correlation between Mg and Fe (Table 3) is also due to the strong affinity to chlorite. With increasing chlorite content the Fe and Mg increases proportionally. Evident- log10 (altered /least altered) 0,5 Fig. 3. Spider diagram showing the major element composition of altered quartz-porphyry rocks normalised to the least altered quartz-porphyry (sample 92026, Table 2). Same colours as for the dots in Figure 2. 0,0 -0,5 -1,0 -1,5 -2,0 SiO2 Al2O3 CaO MgO Na2O K2O Fe2O3 MnO TiO2 P2O5 LOI ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 97 ly, chlorite was not a stable mineral in the more central parts of the alteration zone. Note also the small but significant Al-increase for sericite±andalusite altered samples (Fig. 3). Al2O3 10 % 1% Less mobile and mobile elements K2O TiO2 MgO 1000 ppm Zr 100 ppm La 10 ppm Y Th Yb B049 B039 B034 B033 B022 B052 B050 B016 B053 B051 B038 #91125 B054 B036 B035 #951504 #91124 B157 B075 #92028 #92027 #92026 Of particular interest is the strong correlation between a class of elements often referred to as immobile or less mobile, e.g. Al2O3, TiO2, V, Th, U, LREE, and Zr shown in Table 3. Most of these elements are high field strength (HFS) elements and their resistance to hydrothermal alteration has been well documented (MacLean & Barrett 1993 and references therein). Al and Ti are often reported as enriched or depleted in hydrothermally altered rocks (e.g. Nilsson 1968), but these changes are almost always due to residual enrichment or dilution. It is noteworthy that some HFS elements are strongly affected by hydrothermal alteration at Boliden. The content of Nb, for example, drops below the detection limit (10 ppm) and the Y content is reduced by 70 percent in the most altered qz-p samples from Boliden. The HREE seem also to have been affected by the alteration. Thus, there is no reliable ”rule of thumb” to identify immobile elements. This must be carefully checked for every new set of data. For the qz-p at Boliden it seems, however, that the relative proportion of Al2O3, TiO2, V, Th, U, LREE, and Zr remains constant during alteration. The content of selected less mobile and mobile elements in least altered to strongly altered qz-p is shown in Figure 4. Al2O3 and Zr show a nearly identical pattern independent of the degree of alteration, in agreement with the high correlation coefficient of 0,95 between the elements (Table 3). Th, TiO2 and some LREE show a similar pattern, and a good correlation with Al2O3 and Zr. The behaviour of more mobile elements is illustrated by K, Mg, and the HFS-elements Y and HREE, exemplified by Yb (Fig. 4). The fact that some elements are unaffected by hydrothermal alteration make them suitable for rock classification and mass change calculation. Fig. 4. Spider diagram showing the content of less mobile elements in least altered and altered quartz-porphyries. K2O and MgO are included to illustrate the behaviour of typically mobile elements. Note the mobile behaviour for Y in most of the chlorite+/-sericite samples and all of the sericite+/-andalusite samples. Colour bar at the base of the diagram indicates type of alteration and uses the same colours as in Figure 2 and 3. Mass changes during alteration Among the demonstrated less mobile or immobile elements, Al, Ti, and Zr are most useful for mass change calculations, mainly because the content of each of these elements is well above the detection limit. In the Al2O3 vs. Zr diagram (Fig. 5) the variation in Al and Zr content in different qz-p samples is illustrated. All samples plot along a line with the least altered samples in the middle of the population. Together, the plotted data form an alteration line (MacLean & Barrett 1993) with a nearly constant Al2O3/Zr-ratio at around 745±60. Samples with higher Table 3. Matrix of correlation coefficient for the quartz porphyries. Calculated from the data in Table 2. n=22 SiO2 Al2O3 MgO Na2O Fe2O3 MnO TiO2 V Nb Th Y Zr La Ce Sm 98 SiO2 0.27 -0.80 -0.33 -0.83 -0.82 0.09 0.11 -0.53 0.21 -0.74 0.42 0.36 0.34 0.15 A. HALLBERG Al2O3 MgO Na2O Fe2O3 MnO TiO2 V Nb Th Y Zr La Ce Sm -0.49 -0.05 -0.63 -0.39 0.81 0.50 -0.17 0.84 -0.27 0.95 0.85 0.86 0.82 0.01 0.88 0.70 -0.37 -0.33 0.26 -0.55 0.63 -0.59 -0.65 -0.59 -0.34 0.13 0.40 0.17 0.17 0.81 -0.15 0.29 -0.02 -0.03 -0.17 -0.18 0.64 -0.44 -0.32 0.30 -0.59 0.62 -0.77 -0.75 -0.73 -0.48 -0.24 -0.46 0.81 -0.45 0.78 -0.43 -0.44 -0.48 -0.38 0.81 0.07 0.66 -0.26 0.78 0.77 0.73 0.66 o 0.46 -0.41 0.49 0.58 0.51 0.46 -0.36 0.78 -0.15 -0.18 -0.27 -0.26 -0.27 0.78 0.88 0.88 0.86 -0.41 -0.47 -0.42 0.01 0.88 0.87 0.73 0.98 0.72 0.79 - Mass change=RC – precursor composition Al2O3 (%) 20 least altered 16 12 ain ss g ma oss ss l ma 0 0 150 Zr (ppm) 200 250 Fig. 5. Al2O3 vs. Zr diagram to illustrate the positive correlation between these elements. Equation for the line is Al2O3 (%)=0.0788 Zr (ppm) - 0.7318 and R=0.95. The largest mass loss is experienced by sericite±andalusite samples while most of the chlorite±sericite is affected by mass gain. Same symbols as in Figure 1. Al and Zr contents than the least altered samples have been affected by residual enrichment of immobile elements when several of the mobile major elements have been leached from the rock. The rock has been affected by net mass loss. In other samples, the Al and Zr contents have decreased due to dilution by added elements. Here the rock has experienced a net mass gain. The purpose with mass change calculations on the chemical data is to quantify the net mass gain or loss and to determine the magnitude of change for each mobile element. The mass change is the change in content of a mobile element, expressed in %-units, in an altered sample relative to the unaltered precursor. Since the precursor composition of the altered samples is not known, the composition of the least altered sample is used. The first step in mass change calculations is to determine the reconstructed compositions (RC). The reconstructed compositions for each altered sample is the composition where the immobile element content in the altered sample is the same as in the least altered sample (MacLean 1990). The reconstructed compositions should not be confused with a chemical analysis of the rock samples. It is simply a mathematical construction that can, depending on degree of alteration, deviate considerably from 100 %. The reconstructed composition is here reported as %-units in order not to be mixed-up with the common way of reporting chemical data. RC= Xalt.rock. (IMMleast alt./IMMalt) RC is the reconstructed composition, Xalt.rock is the content of an element in the altered rock, and (IMMleast alt./IMMalt ) is the ratio between less mobile element content in least altered and altered rock respectively Mass changes during alteration are the differences between the reconstructed composition and the composition of the precursor. The composition of the least altered qz-p sample represents the precursor composition. Mass change is also reported as %-units for the same reasons as for the reconstructed composition. Figure 6a shows the major element chemistry for the least altered sample from the Northern stock, for the mildly altered sample from the same stock, from the outcropping Boliden qz-p, and for chlorite±sericite and sericite±andalusite rocks at depth. The reconstructed composition is shown in Figure 6b. In the calculation, Al has been used as immobile element but the use of Zr or Ti as immobile element does not result in any significant differences. Finally, the calculated mass changes are shown in Figure 6c. For the majority of the samples, it is the SiO2-content that controls the total mass changes during alteration. The net mass change of Si, expressed as SiO2 %-units, varies between –16 %-units and +23 %-units in sericite ±andalusite altered rocks. It is also obvious from the diagram in Figure 6c that the samples mapped as sericite± andalusite altered could be subdivided into samples with a net gain and a net loss of Si. Samples with a net addition of Si are also enriched in K. Mass changes of Si seem thus to be related to changes in K. It should be noted here that Nilsson (1968), by measuring the amount of quartz phenocrysts in variously altered qz-p, argued that there had been no major change of volume during alteration. MacLean and Barrett (1993) also noted that a large mass change not necessarily results in any drastic change in volume. Classification diagrams A useful feature concerning less mobile or immobile elements is that they are used to classify rocks. Classification diagrams by Winchester and Floyd (1977) utilise the ratios between Zr, Y, Nb, and TiO2. Other rock classification diagrams are partly or fully based on major elements, several of them known to be mobile during hydrothermal alteration, e.g. diagrams by LeMaitre et al. (1989), Jensen (1976), and De la Roche et al. (1980). All of these diagrams are frequently used for rock classification. For further geochemical discussion it is useful to investigate how the qz-p rocks, least altered to strongly altered, plot in various classification diagrams. For this purpose the qz-p samples are plotted in five different classification diagrams in Figure 7a–e. The igneous spectrum by Hughes (1973), also a form of rock classification diagram, has been discussed previously. It should be noted, however, that these diagrams are designed for unaltered and non-porphyritic igneous rocks. The results gained from plotting data for qz-p rocks, most of them strongly altered, should be interpreted with uttermost precaution. It can, nevertheless, be informative to see how altered and ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 99 a) Original composition (%) b) Reconstructed composition (%-units) 100 90 mass gain mass loss 100 80 90 70 80 60 B049 B039 B034 B033 B022 B052 B050 B016 B053 B051 B038 #91125 B054 B036 B035 #951504 #91124 B157 B075 #92028 #92027 #92026 70 60 c) Mass change (%-units) 50 15 B049 B039 B034 B033 B022 B052 B050 B016 B053 B051 B038 #91125 B054 B036 B035 #951504 #91124 B157 B075 #92028 #92027 #92026 25 5 MgO CaO Al2O3 SiO2 -5 MnO Fe2O3 K2O Na2O LOI -15 -25 B049 B039 B034 B033 B022 B052 B050 B016 B053 B051 B038 #91125 B054 B036 B035 #951504 #91124 B157 B075 #92028 #92027 #92026 Fig. 6. Columnar diagrams to illustrate the mass change calculations discussed in the text. a) Original whole rock geochemistry of the 22 qz-p samples. Average sum of major element oxides is 99.8+0.6/-1.0. The samples have not been normalised to 100 % before mass change calculations. b) Reconstructed composition (RC) of qz-p samples. To calculate the RC, the whole rock geochemical data for all altered samples have been multiplied with a factor so that the immobile element content is the same as for the least altered sample. For the calculations, Al has been used as immobile element. This is shown in the diagram as an identical Al2O3 content of all samples. Samples with a RC larger than 100 %-units have experienced mass gain whereas samples with RC less than 100 %-units show mass loss, compare Figure 5. Note that the RC is expressed in %-units in order to avoid confusion with ordinary whole rock geochemical data. c) Mass change during alteration. The mass change is the difference between the RC and the composition of the precursor rock. Here the least altered qz-p is used to represent precursor composition. The mass changes for the least altered samples are, by definition, zero. Note that several samples showing total mass gain have experienced a large mass loss of Na and Ca. less altered samples behave in these frequently used diagrams. The name quartz porphyry simply indicates that the rock contains quartz phenocrysts, it does not say anything about the rock composition, except that it is a fairly felsic rock since it contains free quartz. When plotted in diagrams using SiO2 as a variable, the least altered qz-p sample plots close to or inside the rhyolite field. Graphs not using SiO2 as a variable rather suggest that the qz-p has a dacitic to rhyodacitic composition. Apparently, the quartz phenocrysts give the rock a higher SiO2-content than would be expected if the rock was non-porphyritic and illustrates why porphyritic rocks easily give erratic 100 A. HALLBERG results when plotted in classification diagrams (see i.e. Hughes 1973). In the diagrams not using SiO2 the rock has consistently a dacitic to rhyodacitic composition. The altered samples show a large scatter when plotted in the classification diagrams. Beside the disturbance due to quartz phenocrysts, also residual enrichment of Si, dilution of the Si-content, or a net addition or removal of Si strongly affects graphs with SiO2 as variable. In most cases, the altered samples will appear to be more felsic in composition. Absence or presence of chlorite, with net removal or addition of Mg and Fe, will indicate a too felsic or too mafic composition, respectively, in the AFM diagram (Jensen 1976). The Mg and Fe contents seem also a) b) 1,00 n=22 n=3 80 rhyolite rhyodacite dacite 70 0,10 trachyte 60 trachyandesite andesite trachyte Zr/TiO2 SiO2 (wt.%) rhyolite rhyodacite dacite trachyandesite andesite 50 0,01 subalkaline basalt alkalibasalt andesitebasalt subalkaline basalt 0,01 0,10 Zr/TiO2 0,1 c) d) Nb/Y 1,0 10 Fetot+Ti 14 10 8 rhyolite 6 2 0 40 50 andesite basalt 4 basaltic andesite Na2O+K2O (wt.%) 12 O TH dacite L -A LE KA IIT E L IN E KO MA TII TE C and bas AL e s i a lt rh y C dac te o lit it e e 60 70 Al 80 Mg SiO2 (wt.%) e) 2000 R1=4Si–11(Na+K)–2(Fe+Ti) R2=6Ca+2Mg+Al R2 basalt trachyandesite 1000 lati latite andesite andesite dacite rhyodacite rhyolite alkali rhyolite 0 0 1000 2000 3000 R1 Fig. 7. Data for the qz-p rocks at Boliden plotted in different rock classification diagrams. Same symbols as in Figure 2. a) SiO2 vs. Zr/TiO2 (Winchester and Floyd 1977). b) Zr/TiO2 vs. Y/Nb (Winchester and Floyd 1977). c) The total alkali vs. SiO2 (TAS) (LeMaitre et al. 1989). d) AFM ternary diagram (Jensen 1976) and modified by Rickwood (1989). e) R1R2 diagram in which R1=4Si-11(Na+K)2(Fe+Ti), and R2=6Ca+2Mg+Al, all elements as cation proportion (De la Roche et al. 1980). ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 101 to affect how the rock plots in an R1–R2 diagram (De la Roche et al. 1980). Notable is that even the weakly altered samples can result in false rock classifications. This is important to consider for anyone using classification diagrams. The fact that altered samples, also weakly altered ones, result in false rock classification makes it possible to use classification diagrams to distinguish least altered samples. Altered samples usually give different results depending on which classification diagrams that are used, whereas the least altered sample should, with the exception of phenocryst-bearing rocks, result in identical rock classifications. Multiple precursor systems – rocks from the Boliden area The first part of the study was focused on one well-defined rock type, the quartz porphyries around Boliden. Due to the occurrence of quartz phenocrysts in the rock, a mineral that remains stable despite strong hydrothermal alteration, the precursor rock can be easily identified even in strongly altered rocks. The element changes that take place during alteration were determined, qualitatively as well as quantitatively, but also immobility for some elements were demonstrated. Various rock classification diagrams indicate that the qz-p has a dacitic to rhyodacitic composition. Altered qz-p samples plotted in the diagrams yield varying rock compositions, an effect that can be used to discriminate altered samples and to identify the least altered samples. For the other country rocks and rocks in the alteration zone around the Boliden deposit, no simple trace mineral like quartz-phenocrysts exists. However, with the knowledge gained from the qz-p data it is possible to expand the study to other rocks in the Boliden area, rocks for which the precursor is unknown. Least altered rocks In this study, most of the samples come from the alteration zone beneath the Boliden ore. None of these samples, mapped as mineralised rocks, sericite rocks, quartz rocks, chlorite-bearing rocks, andalusite-bearing rocks etc., can be considered as least altered samples. Several of the sampled country-rocks around the Boliden deposit have been mapped as altered (Bergman Weihed et al. 1996) and these samples must also be excluded in the search for least altered samples. Among the 267 analysed samples in the database (Appendix A–C), about 135 show visible evidence of alteration, according to the descriptions. Additionally c. 20 samples are excluded on geological reasons. These rocks include the so-called lamprophyre dykes, 102 A. HALLBERG which are younger mafic dykes that intrude ores and rocks at Boliden. The age of these dykes and the genetic relationship to mineralization and alteration at Boliden is unclear. In addition, they do not make up any significant portion of the rocks at Boliden. Metasedimentary rocks, chemical sediments, tourmaline veins, and ore samples cannot be used since they do not follow igneous fractionation trends on which the discussion below is based. A second step in the search for least altered rocks is to exclude all samples that show chemical evidence of alteration. For that purpose, the remaining samples have been plotted in Hughes igneous spectrum (Hughes 1973). There are 52 samples that show K-alteration and 16 samples that are Na-enriched. This procedure thus eliminates another 68 samples from the database and leaves 44 samples as possibly least altered samples. There is no simple way, like the Hughes igneous plot, to identify disturbances among the other major elements. However, by plotting the data in the different rock classification diagrams and comparing the result from the diagrams it is possible to distinguish samples with disturbed major element contents, i.e. altered samples. It turns out that only eight samples give a reasonably similar result independent of classification diagram used. These samples, shown in Table 4, are considered to be the least altered rocks in the Boliden area. They will be used to define fractionation curves and precursor rocks, and to calculate mass changes in the altered rocks. Note that the least altered qz-p samples are not included in these eight samples due to the occurrence of quartz phenocrysts in the rock. Fractionation curve and precursor rocks A large part of the rocks in this investigation are altered in such a way that precursor rocks cannot be visually identified. Lithogeochemistry provides a tool to circumvent these obstacles, but before applying geochemical techniques, the immobility of used elements must be investigated. It has already been shown, for the qz-p rocks, that several elements are immobile during alteration and it is assumed that these elements behave in a similar way also when hosted in other rock types around Boliden. A matrix of correlation coefficients for all igneous rock, felsic to mafic, around Boliden is shown in Table 5. The matrix does not, however, show the same good correlations as the matrix for the qz-p rocks (Table 3). The most likely reason for the weak correlation between for example Zr and Ti is that these elements, beside being less mobile, also behave differently in fractionation processes. Due to the highly incompatible behavior for some trace elements, e.g. Zr, Th, and REE, they are strongly enriched in the melt during igneous fractionation and are thus enriched in late stage fractionation rocks, i.e. felsic rocks. Other elements, Table 4. Whole rock geochemistry of the least altered samples found from the Boliden area. See text for explanation. sample # 91101 91103 91104 92022 92033 931008 bh 686 686 686 92005 30 Giller 428 core 262,5- 262,9 352,6- 353,0 217,0 129,0- Bo39 vattnet 2 253,9-254,2 390,3- 390,7 129,4 local n -154 -5096 local e 66 -1634 -235 7 z 188 188 170 N (RT90) 7204892 7204914 7204923 7203950 7204144 7204893 7204103 7209260 E (RT90) 1717035 1716999 1716984 1715270 1716615 1714480 1716543 1718200 SiO2 56,1 55,2 56,6 59,7 61,1 68,7 69,4 73,2 Al2O3 17,0 17,3 17,6 15,1 15,4 13,6 14,6 13,2 CaO 5,2 7,2 6,7 6,8 6,6 2,5 3,6 3,1 MgO 5,2 5,0 4,4 2,4 3,4 1,2 1,2 0,8 Na2O 3,31 2,64 2,78 2,87 2,14 3,86 4,47 3,81 K2O 0,73 1,10 1,03 1,39 1,43 1,86 1,77 1,25 Fe2O3 9,7 10,3 9,7 8,0 8,5 4,1 4,2 3,1 MnO 0,09 0,16 0,14 0,16 0,10 0,12 0,10 0,09 TiO2 1,07 1,12 1,04 0,79 0,72 0,45 0,48 0,19 P2O5 0,28 0,12 0,17 0,23 0,28 0,09 0,15 0,05 LOI 2,75 2,02 1,85 2,70 0,75 1,30 0,50 1,25 SUM 101,5 102,2 102,0 100,1 100,5 97,9 100,4 100,0 Cu 75 190 47 29 31 1 17 <2 Zn 1125 115 123 87 96 92 60 71 Pb 10 3 8 <2 6 <10 As <3 7 2 12 Co 19 23 6 10 11 5 5 150 180 10 82 Ni 9 176 9 Cr 42 6 12 V 302 345 311 Ba 151 283 202 543 344 508 365 310 Rb 43 27 40 26 25 32 28 25 Sc 27,0 32,0 30,0 25,5 24,5 16,0 16,5 Sr 341 328 390 555 414 81 176 2,0 2,0 3,0 3,2 Hf <2 116 Nb 9 10 11 9 10 Th 1,4 1,9 4,1 3,9 18 <2 U 1,4 0,7 1,6 2,9 Y 17 11 11 19 18 24 25 31 Zr 75 64 67 109 122 136 150 174 La 11,7 9,7 19 18,0 22,0 32,7 Ce 26 23 40 39 44 64 Nd 17,3 15,1 20 20 21 29 Sm 3,65 3,92 4,0 4,0 4,5 5,4 Eu 1,90 1,49 1,7 1,6 1,4 1,1 0,6 0,5 0,6 0,5 2,3 2,1 2,4 0,35 0,30 Tb Yb 2,36 1,85 Lu method-lab. ICP-Lul Rock Alter., struct., mineralisation Andesite ICP-Lul Andesite ICP-Lul XRAL-92/XRF/NA Andesite Dacite, feldspar akt Dacite porphyritic actinolite 2,1 0,35 XRF/NA Dacite porphyry XRF/NA XRF/NAXRAL-93-95/XRF Dacite volcaniclastic Preserved Rhyolite, porphyry feldspar porphyritic e.g. Ti, behave in a more compatible manner during fractionation and will be enriched in the solid phase and depleted in the melt, i.e. in felsic rocks. Therefore, for a multiple precursor system like the one at Boliden, which includes mafic to felsic rocks, a good correlation between incompatible and less incompatible elements is not expected. Of importance, however, is that Zr shows a rather good correlation with other highly incompatible, HFS elements, e.g. Th and LREE. This indicates that the elements used to calculate mass changes etc. for the qz-p can be used also for other rocks around Boliden. In Figure 8, the contents of Zr and TiO2 in all igneous samples from the Boliden area are plotted. The previously discussed qz-p rocks show a distinct trend with high Zr contents and low TiO2 contents but with a Zr/ TiO2 ratio at 0.065±0.013. The qz-p rocks around Boliden can thus be identified on their unique Zr/ TiO2. In the diagram (Fig. 8), the eight least altered samples, together with variously altered samples, have been plotted. The least altered samples make up a trend that resembles a fractionation trend for igneous rocks. Basaltic andesites, with high TiO2 content and low Zr content, plot in the upper left part of the fractionation trend, more intermediate samples further down along the trend towards the most felsic end member, the qz-p. It should be noted that this does not necessarily mean that the rocks share magmatic affinity or that they are part of the same fractionation series. It simply indicates that they are following fractionation trends. Altered samples have been divided into three groups: weakly altered samples (with no visible signs of alteration and that plot within the igneous spectrum of Hughes 1973), samples that are K- or Na-altered according to Hughes (1973), and samples that are mapped as altered. In the diagram, the altered samples together with the least altered samples form trends or clusters, similar to the qz-p trend, but at different Zr/ TiO2 ratios. It is suggested that the Zr/ TiO2 ratio is unique for every igneous rock type in the Boliden area, in analogy with the qz-p samples. This is corroborated by the fact that each of the least altered samples has a unique Zr/ TiO2 ratio, low ratios for mafic rocks and high ratios for felsic rocks. From this it is possible to determine the composition of the precursor rock for every altered sample in the data set. The compositions of the least altered samples can then be used to approximate the primary compositions in mass change calculations. Note that the sampling from strongly altered rocks in most cases has been guided by degree of alteration. Therefore the samples might contain a mixture of more than one precursor rock composition. Chemical mapping Different rock types, deduced from their Zr/TiO2 ratio, have been plotted on the geological map in Figure 9 and the geological profile in Figure 10. The division according to the Zr/TiO2 ratio is found in Table 6. The geology deduced from whole rock geochemistry broadly agrees with the geological map and profile presented in Bergman Weihed et al. (1996, Figs. 3 and 4) and apparently the method of using the Zr/TiO2 ratio to classify rocks works well in this area. ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 103 2,5 basaltic andesite basalt 2,0 andesite TiO2 (%) 1,5 dacite 1,0 rhyolite 0,5 qz-p rocks 0,0 0 100 200 300 400 Zr (ppm) least altered K/Na altered weak alteration visible alteration Fig. 8. TiO2 vs. Zr diagram with all igneous samples from the Boliden area. Altered rocks divided according to the stepwise elimination of altered rocks discussed in the text. 500 Open red ellipses: samples mapped as altered Filled red ellipses: samples identified as altered in Hughes (1973) igneous spectrum.Filled blue ellipses: samples identified as altered by comparing different classification diagrams. Black ellipses: least altered samples. The basalt to rhyolite sectors defined from the least altered samples. Qz-p samples within hatched line. The least altered samples define a trend resembling a fractionation trend. Table 5. Matrix of correlation coefficient for all igneous rocks from the Boliden area. Chemical data from Appendix A–C. n=239 Al2O3 TiO2 V Sc Th Zr La Ce Nd Sm Tb Yb Lu Al2O3 0,81 0,38 0,39 0,36 0,55 0,58 0,60 0,65 0,65 0,46 0,11 0,19 TiO2 V Sc Th Zr La Ce Nd Sm Tb Yb Lu 0,69 0,68 0,10 0,22 0,34 0,37 0,45 0,49 0,44 0,01 0,08 0,82 -0,27 -0,24 -0,06 -0,05 -0,03 -0,03 0,08 -0,21 -0,20 -0,25 -0,14 -0,05 -0,04 -0,01 0,01 0,18 -0,05 -0,01 0,79 0,68 0,71 0,74 0,76 0,69 0,34 0,42 0,60 0,64 0,69 0,72 0,71 0,37 0,45 1,00 0,95 0,90 0,54 0,25 0,31 0,97 0,93 0,59 0,27 0,34 0,98 0,68 0,29 0,36 0,78 0,35 0,43 0,59 0,66 0,97 - The dacite unit in the uppermost part of the volcanic sequence on the southern side of the ore (Fig. 11) seems to be thinner compared to the geological profile in Bergman Weihed et al. (1996). The chemistry also indicates an andesitic unit within the dacites. A c. 250 m thick sequence dominated by andesite with some basaltic andesite rocks occurs stratigraphically below the dacites. The chemistry shows a rather heterogeneous composition varying from dacite to basaltic andesite, with an andesitic average composition. The chemistry thus suggests that this unit is somewhat more intermediate in composition compared to Bergman Weihed et al. (1996) who mapped the unit as basaltic andesite. The lowest exposed unit on the 104 A. HALLBERG Table 6. Rock classification according to Zr/TiO2-ratio. Rock classification log10(Zr/TiO2) Zr/ TiO2 rhyolite (incl. rhyodacite) (quartz porphyry) dacite andesite basaltic andesite basalt >-1,40 (-1,12 to -1,24) -1,41 to -1,59 -1,60 to -1,94 -1,95 to -2,24 <-2,34 >0,040 (0,075 to 0,057) 0,039 to 0,026 0,025-0,011 0,011 to 0,006 <0,005 southern side of the Boliden ore is a thick sequence of dacitic rocks with some andesitic intercalations. According to the chemistry, this sequence is thicker than suggested in Bergman Weihed et al. (1996). This stratigraph- 7206000 Northern quartzporphyry rhyolitic–dacitic lavas, breccias etc. basaltandesite 7205000 she ar z Boliden alteration zone one Boliden quartzporphyry ddh 686 Profile Boliden ore 7204000 metasedimentary rocks dacitic porphyritic lavas and domes ddh 678 7203000 1714000 1715000 1716000 rhyolite andesite quartz porphyry basaltic andesite dacite sediment 1717000 1718000 Fig. 9. Geological map of the Boliden area from Bergman Weihed et al. (1996). Position of ore and alteration zone from Nilsson (1968) and Ödman (1941). Dots show sample location and the chemical rock classification. The surface geology has not been reinterpreted on the basis of the lithogeochemistry due to the low amount of analysed rock samples. For details see text. Coordinate system is Swedish National Grid (RT 90). ic unit can be correlated with rocks in a drill hole about 5 km southwest of the deposit. The stratigraphical column C in Allen et al. (1996) is partly based on that drill hole. The rocks on the northern side of the deposit are more mafic in character, with the exception of the intrusive quartz-porphyry, which has a dacitic to rhyodacitic composition. The uppermost part of the observed stratigraphy consists of andesites. These overlie a nearly 100 m thick sequence of basaltic andesites. The mapped dyke-like basalt-andesite that occurs north of the deposit (Bergman Weihed et al. 1996, Fig. 4 and Ödman 1941) cannot be distinguished by geochemistry. Evidently the rock is some kind of dyke but isochemical with its country rocks. Below the basaltic andesite, the few samples in the database indicate a unit with dacites and andesites. This unit can be traced into the alteration zone. Further down in the stratigraphy the chemistry indicates an andesitic basalt composition of the rocks. A stratigraphy nearly identical to the one observed immediately north of the Boliden deposit is found in a drill core about 1 km northwest of the deposit. The 16 samples previously identified as Na-altered by plotting in Hughes igneous spectrum (Hughes 1973) all seem to occur in the upper part of the volcanic sequence at Boliden, about 60–80 meters below the contact to the overlying metasedimentary rocks. Na-altered samples at this stratigraphic position are found in a drill core (ddh 686) about 900 m from the Boliden deposit and in an outcrop a further 1100 m to the north-east. South-west of the deposit, Na-altered samples are found in drill core about 1 km from the deposit (ddh 678), in another drill ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 105 North South Boliden ore l t ic e s a s it ba nde a ddh 678 1.4 km south-west of the Boliden mine an ddh 686 700 m north-east of the Boliden mine me de sit mi Z ne n-P ra b ed lis i ro m e ati ck n on s ta ry ta s e da cit an de si e ddh 679 2.5 km south-west of the Boliden mine te Na-alt da c it e an Na-alt Boliden alteration zone de s it e Na-alt zone with most intense alteration q po ua r p r tz hy ry da c it Na-alt quartz porphyry dacite andesite basaltic andesite metasediments e Na-altered 100 m Fig. 10. Geological profile of the Boliden deposit. Modified and reinterpreted from Bergman Weihed et al. (1996) and Ödman (1941). Coloured bars and dot show position and classified rock composition from chemistry for whole rock samples. Areas with light blue stripes indicate position of rock samples that show Na-alteration. Light grey area below and south of the Boliden ore indicates the zone of most intense alteration. Position of profile and ddh 686 and 678 are shown in Figure 9. core about 1.4 km from the deposit (ddh 679), and in an outcrop nearly 5 km away. In the mine area, Na-altered samples are found within the upper dacite unit south of the deposit and in andesitic basalt north of the deposit. Towards the alteration zone beneath the Boliden ore, the Na-anomalous character of the rocks disappears, and close to the alteration zone the rocks become K-altered instead. This is best seen among the samples from the basaltic andesite in the northern hanging wall (Fig. 10). A set of samples that shows the transition of a basaltic andesite from Na-altered to a near normal alkali distribution, to K-altered, and to strongly altered sericite±andalusite schist can be found in appendix A (samples B011, B176, B186–B187, B189–B194). The three samples with a normal alkali distribution occur between the Na-altered rock to the north and the K-altered rock to the south. Most likely these samples have been affected by a weak K-alteration that erases the Na-alteration and gives the rocks an apparent least altered composition. The Na-alteration is thus overprinted by the alteration system that envelops the Boliden deposit indicating that the Na-alteration is 106 A. HALLBERG older. The Na-anomalous rocks are outlined in the geological profile in Figure 10. The trace element chemistry shows that the host rocks to all Na-altered samples are dacites to basaltic andesites. The alteration is thus not confined to any particular rock type. Possibly the Na-alteration represents a spilitized sequence, but it could also be remnants of an earlier hydrothermal event responsible for the syn-volcanic sulphide deposits in the region. The apparent offset of Na-altered rocks at Boliden (Fig. 10) is most likely caused by the east–west striking sinistral, north-side-up, shear zone that cuts the ore and alteration zone (Bergman Weihed et al. 1996). Vivallo (1987) used the Alteration Index (A.I.=(K2O +MgO)/(CaO+MgO+Na2O+K2O)x100, Hashighusi et al. 1983) to distinguish Na- and K-altered samples from least altered samples. He found that a large part of the rocks in the Boliden area showed Na-enrichment. However, the results from using the A.I. in defining Na-alteration are not compatible with the results from the Hughes igneous spectrum (Hughes 1973). The reason for the differences is that Vivallo (1987) considered all samples with an A.I. of less than 50 to be Na-enriched. An A.I. smaller than 50 can, however, also be caused by other element changes, e.g. increase in Ca. Several of the samples used by Vivallo (1987) show anomalous Ca values, a feature that will result in a low A.I. Thus, the A.I. is less reliable than Hughes igneous spectrum to identify Na- and K-altered samples. An important advantage with geochemical mapping is that it is independent of hydrothermal alteration, at least in this case. Geological units can, thus, be followed into the alteration zone. The east–west striking shear zone that cuts the area (Bergman Weihed et al. 1996) and the Naenriched rocks on both sides of the deposit suggest that the basaltic andesites on the northern side correlate with the thin, but eastward thickening, and more mafic andesite unit within the dacites. In the geological profile in Figure 10 this results in an apparent offset of nearly 200 m. Mass changes Knowledge of the precursor to altered rocks and the possibility to estimate the unaltered composition of that rock makes it possible to calculate mass changes during alteration. Firstly, the composition of the unaltered precursor to the altered rock is calculated. This is achieved by calculating the regression equations on the element content and immobile element ratio in the least altered rocks. Here equations of the second order are used with the Zr/Tiratio defining the rock type (Table 7). Table 7. Regression equations for major element compositions. Based on data from Table 4. SiO2 Al2O3 CaO MgO Na2O K2O Fe2O3 = = = = = = = -2,3235x2 + 8,4064x + 85,273 2,2768x2 + 3,8501x + 14,743 0,2276x2 - 2,7972x - 0,5438 2,7419x2 + 5,2542x + 3,1736 -0,0381x2 + 1,001x + 5,1494 0,8272x2 + 4,3131x + 6,4602 1,6737x2 - 0,9906x - 0,1558 Where x=log10(Zr/TiO2) From the resulting equations, the composition of the unaltered precursor of every sample is calculated. Then the calculated precursor composition is adjusted to the same Al, Ti, and/or Zr content as the analysed sample. The difference between the adjusted composition and the actual composition of the rock sample is the mass change, or ∆-value, and is expressed in %-units. The ∆-value can be either negative, for mass loss, or positive, for mass gain. The procedure described here is the same as for the single precursor system, the qz-p rocks, with the exception that the precursor composition is represented by a regression equation of several least altered samples and not a single chemical analysis of a least altered sample. Since the method is based on igneous fractionation and associated element changes of the volcanic sequence around Boliden, non-igneous rocks and rocks of a different magmatic affinity cannot be treated. Mass change calculation in the way described above is a fast method to treat large amounts of geochemical data. It gives, however, crude results due to uncertainties in the Zr, Ti, and Al determinations. Also the composition of the least altered rocks is based on very few samples. Furthermore, the method is not independent of precursor rock type since one type of rock can lose several tens of percents of an element that only occurs in minor amount in another rock. Compare, for example, the Mg content in least altered basalt and quartz porphyry in this study. Nevertheless, the calculated mass changes give reasonable results. In Figure 11, plots for Si, Mg, K, and Y show the mass changes among those elements on a profile across the ore and alteration zone. It can be noted that silicification is not common among the altered rocks at Boliden. There are very few samples that display a positive mass change for Si. Desilicification, on the other hand, is very common and it seems that almost every altered rock has lost a significant portion of its Si. The most intense desilification occurs below the sulphide ore. The mass changes of K follow the opposite pattern compared to Si: where Si is strongly depleted, K is strongly enriched. At surfac,e the mass change calculations reveal both K-enriched and K-depleted areas (Fig. 12). Whether these element changes have any relevance for exploration remains to be checked. The changes in Mg show a more complex pattern. There is a large depletion beneath the sulphide ore, but outside this depleted area, Mg shows both enrichment and depletion. Mass change calculations can also be applied to minor or trace elements as shown for Y in Figure 11d. In fact, Y is the best element to outline the alteration zone. None of the samples from outside of the mapped alteration zone show any significant mass changes for Y. Figure 11d also illustrates the mobile nature of Y. For the rock classification and mass change calculations, only Zr and Ti have been used. Al has been avoided despite the positive correlation between all three elements. The reason for this is that Al sometimes acts in a mobile manner during hydrothermal alteration in the Boliden area. ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 107 a) 0 0 100 North South b) 0 0 -100 -100 -200 -200 -300 -300 100 Si c) -100 %-units 0 mass change -400 +50 %-units -500 -500 -600 -600 0 0 100 North South d) 0 0 -100 -100 -200 -200 -300 -300 Mg –9 %-units 0 +12 %-units -5 %-units 100 0 +6 %-units North South Y mass change -400 South K mass change -400 North mass change -400 -500 -500 -600 -600 –40 ppm-units 0 Fig. 11 a–d. The calculated mass change for Si, K, Mg, and Y plotted on a black and white version of the geological profile found in Figure 10. 108 A. HALLBERG rhyolitic-dacitic lavas, breccias etc Northern quartzporphyry basaltandesite ddh 686 Boliden quartzporphyry +5 %-units metasediments K mass change dacitic porphyritic lavas and domes ddh 678 –2 %-units Fig. 12. The calculated mass change for K in surface samples plotted on a black and white version of the geological map of the Boliden area found in Figure 9. Conclusions A single rock type that occurs in different states of alteration and contains some kind of alteration-resistant marker is highly appreciated by anyone investigating the lithogeochemistry of hydrothermal systems. The quartz porphyritic rocks, with alteration resistant quartz phenocrysts, that occur as stocks and dykes around and beneath the Boliden deposit fulfil all of these criteria. In the database of 22 high-quality whole-rock analyses from less altered to strongly altered samples, several immobile elements can be identified, i.e. Al2O3, TiO2, V, Th, U, LREE, and Zr. Most of the major, minor, and trace elements are, however, mobile during alteration, even some elements that were expected to behave less mobile, i.e. Y and HREE. A plot in different rock classification diagrams helped to identify one least altered sample. By multiplying the element content of each altered sample with the immobile element ratio of the least altered and the altered sample and then comparing the result with the composition of the least altered sample, the mass change for every sample and every mobile element could be calculated. Other rocks around the Boliden deposit lack alteration-resistant markers. However, by assuming that the elements shown to be immobile during alteration of the quartz porphyries also behave in an immobile manner during alteration of other rocks, and by confirming this assumption on some incompatible trace elements, e.g. Zr, Th, and LREE, it is possible to apply mass change calculation to the whole set of igneous rocks around Boliden. By excluding altered samples on geological and/or chemical grounds a set of least altered samples were identified. The least altered samples, plotted in a TiO2 vs. Zr diagram, define a trend that resembles a fractionation trend for igneous rocks. Data for altered samples deviate considerably from the trend of least altered samples due to mass changes during alteration and residual enrichment or depletion of immobile elements caused by the mass change. However, since the immobile element ratios are believed to be constant during alteration, it is possible to identify precur- ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 109 sor rocks to every igneous sample in the database. This has been used to lithogeochemically map the wall rock types in the Boliden deposit and to trace geological contacts into the alteration zone. The results are generally in agreement with previous results based on core logging. The mass change during alteration has been calculated in the same way as for the quartz porphyries, with the exception that the composition of least altered rocks has been replaced by a regression equation describing the composition at different immobile element ratios, e.g. Zr/TiO2. Acknowledgements Critical comments from Magnus Ripa, Pär Weihed, and Jan-Anders Perdahl improved the manuscript and forced me to strengthen my arguments. Two anonymous reviewers further contributed to the manuscript. Boliden Mineral AB are thanked for providing access to drill cores. Financial support from the Swedish National Board for Industrial and Technical Development (NUTEK) and the Geological Survey of Sweden (SGU) is acknowledged. References Allen, L.R., Weihed, P. & Svenson, S-.Å., 1996: Setting of ZnCu-Au-Ag massive sulfide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc, Skellefte district, Sweden. Economic Geology 91, 1022–1053. Bergman Weihed, J., Bergström, U., Billström, K. & Weihed, P., 1996: Geology, tectonic setting, and origin of the Paleoproterozoic Boliden Au-Cu-As deposit, Skellefte district, northern Sweden. Economic Geology 91, 1073–1097. Bergström, U., 1994: Boliden – a multidisciplinary study. Geological modelling of rocks and ores in the Boliden deposit, Northern Sweden. NUTEK 931 207 (unpublished). De la Roche, H., Leterrier, J., Grande Claude, P. & Marchal, M., 1980: A classification of volcanic and plutonic rocks using R1-R2 diagrams and major element analyses – its relationships and current nomenclature. Chemical Geology 29, 183–210. Gavelin, S., 1955: Beskrivning till berggrundskarta över Västerbottens län. 1. Urbergsområdet inom Västerbottens län. Sveriges geologiska undersökning Ca 37, 88–99. Grip, E. & Ödman, O.H., 1942: The telluride-bearing andalusite-sericite rocks of Mångfallberget at Boliden, N. Sweden. Sveriges geologiska undersökning C 447, 21 pp. 110 A. HALLBERG Hallberg, A., 1994: A multidisciplinary study of the Boliden ore. Part 2: Hydrothermal fluids and alteration, a key to metallogenesis in the Boliden deposit. NUTEK 931 282 (unpublished). Hashiguchi, H., Yamada, R. & Inoue, T., 1983: Practical application of low Na2O anomalies in footwall acid lava for delimiting promising areas around the Kosaka and Fukozawa Kuroko deposits, Akita prefekture, Japan. Economic Geology Monograph 5, 387–394. Hughes, C.J., 1973: Spilites, keratophyres and the igneous spectrum. Geological magazine 109, 513–527. Isaksson, I., 1973: Vismut-antimonrika mineraliseringar i Bolidenmalmen. Lic. Thesis, Stockholm University (unpublished). Jensen, L.S., 1976: A new cation plot for classifying subalcalic volcanic rocks. Ontario Division of Mines Miscellaneous Papers 66. Le Maitre, R.W., Bateman, P., Dudek, A., Keller, J., Lameyre Le Bas, M.J., Sabine, P.A., Schmid, R., Sirensen, H., Streckeisen, A., Wooley, A.R. & Zanettin, B., 1989: A classification of igneous rocks and glossary of terms. Blackwell, Oxford Lundström, I. & Antal, I., 2000: Bedrock map 23K Boliden SV, scale 1:50 000. Sveriges geologiska undersökning Ai 112. MacLean, W.H., 1990: Mass change calculations in altered rock series. Mineralium Deposita 25, 44–49. MacLean, W.H. & Barrett, T.J., 1993: Lithogeochemical techniques using immobile elements. Journal of Geochemical Exploration 48, 109–133. Nilsson, C.A., 1968: Wall rock alteration at the Boliden deposit, Sweden. Economic Geology 63, 472–494. Ödman, O.H., 1941: Geology and ores of the Boliden deposit, Sweden. Sveriges geologiska undersökning C 438, 190 pp. Rickard, D.T. & Zweifel, H., 1975: Genesis of precambrian sulfide ores, Skellefte district, Sweden. Economic Geology 70, 255–274. Rickwood, P.C., 1989: Boundary lines within petrologic diagrams which use oxides of major and minor elements. Lithos 22, 247–263. Vivallo, W., 1987: Early Proterozoic bimodal volcanism, hydrothermal activity, and massive sulfide deposition in the Boliden-Långdal area, Skellefte district, Sweden. Economic Geology 82, 440–456. Winchester, J.A. & Floyd P.A., 1977: Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology 20, 325–343. Appendix A sample # bh B001 6 B002 6 B003 11 B004 11 B005 10 B006 11 B007 11 B008 52 B009 52 B010 52 B011 52 B012 52 B013 75 core 32,6-32,9 60,5-60,7 111,5-111,6 56,1-56,3 59,1-59,3 64,9-65,1 109,8-110,1 19,8-20,6 0,0-10,0 10,2-13,3 13,3-19,5 20,6-32,0 1,2-7,1 local n local e z N (RT90) E (RT90) SiO2 Al2O3 CaO MgO Na2O K2O Fe2O3 MnO TiO2 P2O5 LOI SUM Cu Zn Pb Cd Au Ag As Sb Bi Br Co Ni Cr Mo V Ba Cs Rb Sc Sr Be Hf Sn Ta Nb Th U Y Zr La Ce Nd Sm Eu Tb Yb Lu Ref. -82 2 28 7204256 1716538 44,4 8,0 10,4 13,4 0,26 0,05 9,7 0,33 0,38 0,12 1,80 88,9 4840 406 13800 2 2800 59 2000 8300 inf <1 54 157 1220 <1 113 76 <3 140 23,0 86,7 1,8 10 <10 <1 15 1,2 9,1 12,4 148 7 14 <10 1,9 4,0 <0,5 3,0 0,36 1 -65 -3 49 7204272 1716533 67,0 11,3 0,8 0,9 1,34 1,75 9,9 <0,01 0,49 0,11 6,50 100,1 79,3 1640 227 10 67 1,8 130 110 87 <1 52 2 16 <1 82 267 <3 30 17,7 121,0 1,6 <1 <10 <1 14 1,4 1,0 6,5 89 19 40 20 3,5 1,8 <0,5 1,7 0,26 1 -71 18 100 7204267 1716554 67,8 21,6 0,7 0,5 1,86 3,69 0,3 <0,01 1,04 0,24 2,75 100,4 27,4 33,9 84 <1 47 1,2 13 19 133 <1 43 2 8 <1 115 324 4 54 20,7 178,0 0,6 <1 <10 <1 <10 7,7 2,4 13,6 213 68 140 60 12,8 2,9 1,4 2,3 0,34 1 -98 25 52 7204241 1716563 67,1 15,0 0,5 3,4 0,40 3,20 5,0 0,02 0,68 0,16 3,60 99,0 46,3 322 186 <1 38 2,7 46 14 7 <1 36 8 17 <1 116 189 <3 64 22,1 34,5 1,5 2 <10 <1 <10 2,3 1,5 9,4 124 18 36 20 4,0 1,0 0,5 1,6 0,26 1 -48 243 51 7204302 1716777 50,7 14,9 8,1 6,1 0,90 1,63 13,9 0,20 0,88 0,09 2,15 99,6 116 171 24 <1 <5 1,7 3 2,5 25 <1 37 3 15 <1 363 279 8 40 42,6 188,0 2,5 <1 <10 <1 <10 1,0 0,6 9,8 30 6 14 <10 1,8 1,4 <0,5 1,0 0,14 1 -94 24 60 7204245 1716561 79,6 13,6 0,1 0,3 0,55 3,34 0,2 <0,01 0,51 0,02 1,90 100,1 14,8 15,4 15 <1 550 1,4 15 6,5 13 <1 33 <1 5 1 76 256 <3 59 15,5 82,4 <0,5 <1 <10 <1 <10 2,0 2,3 10,0 124 12 30 10 3,8 0,5 0,8 2,6 0,38 1 -72 18 99 7204267 1716554 62,8 23,7 1,7 1,0 2,25 3,76 0,5 <0,01 1,04 0,27 2,75 99,7 16,5 34,8 48 <1 79 0,5 20 2,8 115 <1 42 9 6 1 113 509 <3 59 19,9 180,0 1,8 <1 <10 <1 <10 5,9 3,2 12,2 206 39 80 30 7,1 2,1 0,9 2,2 0,33 1 -111 -25 250 7204225 1716513 42,8 32,8 1,0 6,1 1,49 2,26 2,6 <0,01 1,62 0,52 2,90 94,1 9,5 32,3 80 <1 370 6,9 290 1,8 619 <1 130 102 35 <1 150 250 <3 42 18,5 54,0 1,1 2 <10 <1 <10 1,7 1,5 25,4 220 8 18 10 3,3 0,4 0,6 1,5 0,22 1 -96 -25 250 7204241 1716512 63,6 24,8 0,4 0,5 0,93 5,63 0,1 <0,01 0,99 0,25 3,35 100,5 2,5 13,1 5 <1 80 1,1 12 1,6 20 <1 18 2 8 1 142 412 <3 85 23,1 56,2 <0,5 7 <10 <1 <10 5,4 2,9 8,9 201 35 71 30 7,8 1,1 1,0 1,8 0,37 1 -103 -25 250 7204234 1716513 44,9 39,0 0,2 0,3 1,27 7,75 0,0 <0,01 1,27 0,14 5,10 99,9 1,8 9,7 <2 <1 240 1,2 2 2,5 38 <1 11 <1 5 12 116 519 <3 107 25,8 90,6 0,5 13 <10 <1 <10 12 6,5 16,5 298 326 580 210 38,6 5,4 1,9 4,7 0,71 1 -107 -25 250 7204229 1716513 54,4 30,7 0,3 0,4 1,03 7,22 0,2 <0,01 1,80 0,16 3,95 100,2 3,2 6,9 5 <1 600 2,2 30 4,0 527 <1 30 <1 4 2 263 491 <3 102 37,7 102,0 0,7 6 <10 <1 <10 4,8 2,5 8,1 186 39 85 40 11,2 1,4 1,1 1,8 0,32 1 -117 -25 250 7204219 1716513 47,6 17,0 0,9 15,5 0,36 0,49 9,8 0,06 1,00 0,23 7,20 100,2 44,4 187 5 <1 21 1,5 11 2,0 28 <1 25 <1 6 <1 112 70 3 15 29,9 27,8 2,0 3 <10 <1 11 2,1 1,1 8,7 126 18 37 20 4,2 0,9 0,5 2,0 0,33 1 38 -2 330 7204376 1716528 53,2 24,7 0,4 0,8 0,89 6,29 6,0 <0,01 1,54 0,22 4,65 98,7 75,6 2560 54 21 14 0,7 40 2,9 25 <1 31 5 6 1 324 1210 3 81 57,6 61,7 1,8 <1 <10 <1 <10 1,9 1,3 6,0 113 9 18 10 2,5 0,9 <0,5 3,0 0,39 1 Lab.-year XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 method XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA Lampro- Sericite- Sericite- Sericite- dark fine- Sericite Sericite- Tourma- Sericite- Sericite- Sericite- Chlorite- Chloritee- phyre quartz quartz chlorite grained schist quartz line vein quartz quartz quartz sericite sericite schist rock rock rock schist schist schist schist schist Alter., struct. minerali sericite- sericite sericite pyrrhotite sericite sericite sericite chlorite chlorite sation pyrite sericite sericite Rock chlorite schist sericite sericite quartz Cr-mica porphyrite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 111 Appendix A, cont. B014 75 112 B015 75 B016 75 B017 75 B018 75 B019 75 B020 75 B021 75 B022 99 B023 99 B024 99 B025 99 B026 99 B027 99 13,0-19,6 41,5-47,0 47,0-51,3 51,3-58,9 59,0-61,9 69,2-80,5 80,5-84,6 85,6-99,2 0,0-15,0 15,0-17,6 17,6-25,0 25,0-27,2 27,4-29,7 29,4-40,9 26 -2 330 7204363 1716529 46,5 19,8 0,3 11,0 0,26 1,75 13,3 0,10 0,71 0,15 6,27 100,1 419 550 25 <1 52 2,9 6 2,0 19 <1 17 1 7 <1 56 346 <3 32 18,6 14,8 2,5 5 <10 <1 13 5,7 3,8 8,5 187 8 17 <10 1,7 0,5 <0,5 2,4 0,38 1 -2 -2 330 7204336 1716531 67,6 14,3 0,5 2,2 0,73 2,97 7,1 0,04 0,53 0,10 3,15 99,2 3420 10500 65 218 1100 13,3 3 0,7 inf <1 59 5 6 27 76 531 <3 50 17,6 20,7 1,4 5 <10 <1 <10 3,8 1,8 7,0 144 24 50 20 4,8 0,9 <0,5 2,3 0,29 1 -7 -2 330 7204331 1716531 79,9 11,5 0,1 0,3 0,50 2,77 2,3 <0,01 0,23 0,05 2,50 100,2 142 78,2 21 <1 22 1,6 31 0,7 6 <1 38 <1 8 1 11 402 <3 49 12,2 26,3 1,0 4 <10 <1 <10 4,3 2,8 6,5 165 23 47 20 4,1 0,9 <0,5 2,4 0,34 1 -13 -2 330 7204325 1716531 78,6 10,3 <0,01 1,1 0,42 1,65 5,5 0,02 0,39 0,05 2,20 100,3 1270 884 488 6 1400 44,2 6200 23 996 <1 4500 112 7 <1 56 262 <3 46 17,0 19,2 1,3 -33 -2 330 7204305 1716532 72,2 17,5 0,4 0,3 1,11 2,83 0,2 <0,01 0,94 0,22 2,90 98,6 4,0 7,3 9 <1 140 1,1 8 0,9 18 <1 35 1 4 <1 154 280 <3 39 20,7 79,8 0,6 <1 <10 <1 <10 4,9 2,0 8,2 154 25 51 20 4,8 1,1 0,5 2,2 0,36 1 -40 -2 330 7204297 1716533 47,0 18,6 0,4 10,0 0,38 2,18 13,9 0,06 0,99 0,18 6,80 100,4 255 260 11 <1 27 0,6 6 1,2 17 1 120 4 9 <1 231 344 <3 31 29,4 29,0 2,3 4 <10 <1 <10 1,2 0,9 5,5 88 10 22 10 2,6 1,1 <0,5 1,2 0,27 1 -50 -2 330 7204288 1716533 67,3 11,4 0,4 5,1 0,38 1,45 8,1 0,02 0,54 0,14 5,20 100,0 72,2 74,9 9 <1 23 0,6 20 1,9 4 <1 19 8 4 2 50 236 <3 31 12,2 20,3 1,4 <1 <10 1 <10 1,2 1,1 7,3 106 11 25 10 2,7 1,1 <0,5 1,4 0,18 1 -41 18 410 7204297 1716552 80,7 15,2 0,1 0,2 0,29 1,43 <0,01 <0,01 0,32 0,07 1,90 100,1 3,2 7,1 <2 <1 23 0,3 2 0,3 <3 <1 37 1 2 <1 19 92 <3 30 11,2 18,8 <0,5 2 <10 <1 <10 5,5 3,5 5,6 197 38 76 30 6,1 1,0 0,7 1,8 0,26 1 -50 18 410 7204289 1716553 74,4 18,9 0,1 0,2 0,48 2,83 <0,01 <0,01 0,65 0,10 2,50 100,1 0,9 7,1 <2 <1 33 0,4 2 0,3 6 <1 29 2 2 1 64 295 <3 45 10,9 28,1 <0,5 5 <10 <1 <10 5,8 3,6 6,4 215 35 71 30 6,9 1,6 0,8 1,9 0,30 1 -55 18 410 <10 <1 42 3,4 2,6 20,7 130 23 54 30 7,7 4,6 2,0 17,8 2,03 1 -18 -2 330 7204319 1716531 60,2 25,9 0,3 0,5 1,32 4,80 2,3 <0,01 1,24 0,13 3,40 100,1 261 20,6 18 <1 110 2,0 90 1,8 36 <1 97 8 5 1 171 657 <3 68 32,3 80,3 0,9 <1 <10 <1 <10 5,6 3,1 10,7 194 43 90 50 10,9 3,7 1,2 3,5 0,51 1 60,5 21,5 0,4 5,6 1,29 0,03 2,4 0,00 0,40 0,10 2,60 94,8 11,4 24,5 <2 <1 <5 1,0 <2 0,3 <3 <1 19 4 3 <1 23 57 <3 <10 5,5 21,8 0,5 5 <10 <1 <10 1,5 0,9 12,2 118 7 15 10 1,8 0,3 <0,5 0,7 0,09 1 -60 18 410 7204279 1716553 73,9 17,3 0,4 0,3 0,63 4,11 0,0 <0,01 0,86 0,31 2,25 100,1 8,3 7,2 <2 <1 <5 0,5 4 0,9 5 <1 28 1 1 <1 51 451 <3 50 14,8 36,1 0,5 <1 <10 <1 <10 3,5 1,9 7,5 168 24 54 30 6,5 1,3 0,8 2,8 0,50 1 -62 18 410 7204276 1716554 65,3 15,4 0,4 4,5 0,33 2,30 7,2 0,02 0,70 0,22 3,95 100,3 176 41,5 <2 <1 <5 0,8 3 0,8 <3 <1 27 2 4 <1 49 287 <3 34 19,4 19,0 1,1 4 <10 <1 <10 2,4 1,8 7,2 137 23 50 20 5,2 1,5 0,7 2,3 0,36 1 -69 18 410 7204270 1716554 83,6 11,2 0,1 0,2 0,34 2,49 0,0 <0,01 0,42 0,12 1,55 100,1 5,3 5,6 <2 <1 <5 0,5 2 0,6 7 <1 30 5 4 <1 31 259 <3 43 11,6 20,4 <0,5 4 4 <10 <1 <10 3,0 1,8 4,0 120 17 37 20 3,8 1,1 0,5 1,6 0,27 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA NA Chlorite schist Chloritesericite schist Sericite schist Sericitechloritequartz Sericitequartz schist Sericitequartz schist Chloritesericite schist Chloritesericite schist Sericitequartz rock Sericitequartz schist Tourmaline vein Sericitequartz schist Chloritesericite schist Sericitequartz schist chlorite chloritesericite sericite sericitechlorite sericite sericitechlorite chloritesericite chloritesericite sericite sericite quartz brecciated sericite chloritesericite sericite A. HALLBERG Appendix A, cont. B028 99 B029 99 B030 99 B031 99 B032 99 B033 100 B034 100 B035 100 B036 100 B037 100 B038 100 B039 320 B040 320 B041 320 40,9-49,1 49,1-61,5 61,5-70,0 70,0-89,4 89,4-92,4 0,0-15,7 15,7-34,0 34,0-50,9 50,9-66,5 66,5-68,7 68,7-87,4 0,0-15,7 15,7-27,3 27,3-28,2 -79 18 410 7204260 1716554 75,4 17,2 0,1 0,2 0,44 2,89 0,0 <0,01 0,59 0,07 3,35 100,3 1,5 3,3 <2 <1 54 0,4 4 0,5 <3 <1 26 1 <1 1 47 228 <3 44 14,7 24,5 <0,5 4 <10 <1 <10 5,5 4,6 7,2 191 32 68 30 6,8 0,9 0,9 2,9 0,38 1 -89 18 410 7204250 1716555 52,1 36,6 0,1 0,2 0,65 4,55 0,3 <0,01 1,32 0,04 4,60 100,4 2,0 9,3 <2 <1 390 0,7 2 1,4 111 <1 13 1 3 2 122 358 <3 61 20,2 47,0 <0,5 6 <10 <1 <10 8,1 4,8 8,0 270 63 127 60 12,1 1,9 1,3 2,1 0,34 1 -100 18 410 7204239 1716555 53,9 32,8 0,2 0,3 0,76 7,17 0,1 <0,01 1,18 0,15 4,25 100,7 2,5 10,4 <2 <1 42 0,5 <2 0,5 5 <1 9 1 3 <1 134 421 <3 87 23,3 57,8 <0,5 6 <10 <1 <10 5,9 3,5 8,9 253 47 100 40 9,6 2,1 1,3 2,1 0,37 1 -113 18 410 7204225 1716556 64,1 13,7 0,3 9,6 0,12 1,53 4,8 0,03 0,50 0,11 4,70 99,4 32,3 114 <2 <1 21 0,5 <2 0,5 <3 <1 21 4 3 <1 44 152 <3 20 12,6 11,9 0,9 3 <10 <1 <10 2,9 2,1 8,3 130 19 41 20 3,9 0,9 <0,5 1,9 0,31 1 -125 18 410 7204214 1716557 66,8 13,2 2,0 5,3 0,27 2,32 4,9 0,07 0,43 0,11 3,15 98,6 8,9 70,3 <2 <1 <5 0,6 2 0,5 <3 <1 15 3 3 <1 36 253 <3 51 12,5 48,0 1,3 3 <10 <1 <10 3,7 2,2 10,9 127 19 41 20 3,6 1,2 <0,5 2,0 0,26 1 -20 18 410 7204318 1716551 77,5 16,8 0,1 0,2 0,38 1,31 <0,01 <0,01 0,37 0,08 3,45 100,2 1,1 6,7 <2 <1 23 0,6 11 0,2 4 <1 28 3 <1 <1 18 128 <3 28 12,0 30,6 <0,5 5 <10 <1 <10 5,9 3,0 7,3 211 39 80 30 7,4 1,8 0,7 2,3 0,34 1 -3 18 410 7204335 1716550 82,4 13,9 0,0 0,1 0,26 0,96 <0,01 <0,01 0,26 0,04 2,30 100,2 1,0 6,2 <2 <1 16 <0,1 340 0,5 <3 <1 53 1 <1 <1 6 111 <3 17 13,8 19,4 <0,5 4 <10 <1 <10 4,1 2,6 7,2 189 27 54 20 4,9 0,9 0,5 2,6 0,38 1 14 18 410 7204353 1716549 77,4 11,1 0,6 2,1 0,18 2,04 4,0 0,04 0,24 0,05 2,60 100,4 1,4 30,2 <2 <1 <5 0,3 3 0,2 <3 <1 29 <1 4 2 6 557 <3 32 9,1 15,1 0,9 4 <10 <1 <10 3,5 2,1 7,9 154 21 45 20 4,1 0,6 0,5 2,6 0,37 1 30 18 410 7204369 1716549 74,0 11,9 0,1 2,8 0,24 2,08 4,8 0,02 0,30 0,05 2,60 99,0 4,8 58,4 <2 <1 <5 0,6 3 0,5 <3 <1 25 <1 3 <1 23 506 <3 27 12,5 14,5 1,0 4 <10 <1 <10 3,8 2,2 6,9 156 24 50 20 4,5 0,7 0,5 2,3 0,33 1 39 18 410 7204378 1716548 53,5 16,3 0,5 9,0 0,21 1,20 12,4 0,09 0,75 0,30 5,30 99,5 53,7 185 <2 <1 <5 0,8 <2 3,0 5 <1 20 1 4 <1 90 301 <3 26 23,4 10,2 1,6 4 <10 <1 14 2,9 1,8 7,0 146 32 66 30 6,7 1,1 1,0 1,8 0,32 1 50 18 410 7204388 1716548 76,2 12,2 0,4 1,7 0,33 2,73 3,8 0,02 0,27 0,06 2,75 100,4 76,5 274 32 1 <5 0,6 11 0,8 <3 <1 17 3 4 <1 14 606 <3 44 11,9 29,8 1,1 4 <10 <1 <10 4,2 2,9 7,3 164 26 52 20 5,1 0,5 0,6 2,6 0,36 1 -59 50 570 7204282 1716585 81,2 14,8 0,0 0,2 0,17 0,96 <0,01 <0,01 0,34 0,06 2,40 100,1 1,2 6,3 <2 <1 150 0,6 <2 0,2 <3 <1 34 <1 1 2 20 70 <3 22 12,9 17,7 <0,5 5 <10 <1 <10 5,2 3,0 7,1 202 34 70 30 6,4 1,1 0,7 2,4 0,34 1 -72 49 570 7204268 1716585 66,9 23,1 0,1 0,4 0,45 2,80 0,4 <0,01 0,75 0,10 5,05 100,1 10,7 4,5 <2 <1 <5 0,5 2 0,3 <3 1 13 1 2 2 52 223 <3 35 12,7 33,9 <0,5 7 <10 <1 10 2,8 3,3 8,4 238 9 18 10 2,3 0,6 <0,5 2,5 0,36 1, 3 -79 49 570 7204262 1716585 67,6 15,1 0,3 2,9 0,41 3,04 5,2 0,01 0,83 0,21 3,35 99,0 213 18,5 <2 <1 7 0,9 19 1,7 <3 <1 30 5 5 <1 74 264 <3 44 21,4 30,0 0,8 4 <10 <1 <10 2,5 1,8 6,0 125 24 52 20 5,4 1,0 0,6 2,5 0,35 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA NA Sericitequartz schist Sericitequartz schist Sericitequartz schist Chlorite schist Chlorite schist Sericitequartz schist Sericitequartz rock Chlorite schist Chloritesericite schist Chloritesericite schist Chloritesericite schist Sericitequartz rock Sericitequartz rock Chloritesericite schist sericite sericiteandalusite sericite chlorite chlorite sericiteandalusite sericite chlorite chloritesericite chloritesericite chloritesericite sericite sericite chloritesericite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 113 Appendix A, cont. B042 320 B043 320 B044 320 B045 320 B046 320 B047 320 B048 320 B049 322 B050 322 B051 322 B052 322 B053 322 B054 322 B055 394 28,2-31,2 31,2-52,7 52,7-62,9 62,9-66,3 66,3-72,3 72,3-88,5 88,5-94,2 0,0-18,3 18,7-33,8 33,8-41,7 41,7-44,2 44,2-50,1 50,1-54,4 0,0-5,0 -81 49 570 7204260 1716585 71,9 18,0 0,6 0,3 0,60 4,49 0,3 <0,01 0,91 0,40 2,55 100,0 449 5,3 <2 <1 88 2,6 16 0,8 16 1 25 1 3 <1 62 459 <3 66 25,1 56,6 0,7 4 <10 <1 <10 2,9 2,4 8,2 172 25 54 20 5,9 1,8 1,0 3,8 0,50 1 -93 49 570 7204248 1716586 54,4 15,8 0,3 14,4 0,09 0,68 7,1 0,08 0,66 0,13 6,45 100,0 21,4 82,6 <2 <1 9 0,4 130 0,7 <3 <1 37 73 182 <1 113 145 <3 21 23,6 8,8 1,0 3 <10 <1 <10 3,1 2,0 6,6 120 17 36 20 3,6 1,2 0,5 1,8 0,29 1 -109 48 570 7204232 1716586 53,9 29,6 0,1 0,4 0,77 7,37 0,1 <0,01 1,63 0,07 4,00 98,0 1,0 4,2 <2 <1 340 1,2 11 1,9 362 <1 9 6 4 <1 120 398 <3 91 22,4 70,0 <0,5 8 <10 <1 <10 14 6,0 11,8 326 91 190 80 16,4 2,3 1,2 2,9 0,43 1 -116 48 570 7204225 1716586 56,8 16,8 0,3 12,3 0,13 1,49 5,8 0,04 0,62 0,15 5,65 100,1 76,1 124 <2 <1 10 0,8 <2 0,3 7 <1 28 7 4 2 62 192 <3 23 17,8 15,7 0,8 4 <10 <1 10 4,2 2,6 9,2 162 23 50 20 5,2 0,9 0,6 2,7 0,41 1 -120 48 570 7204220 1716586 65,8 14,3 4,3 3,9 0,53 2,95 4,5 0,07 0,55 0,14 1,40 98,3 15,1 68,8 <2 <1 <5 0,7 <2 0,2 4 1 22 2 3 2 49 437 <3 47 16,4 77,4 1,5 4 <10 <1 <10 3,6 2,3 16,2 137 22 44 20 4,3 0,9 <0,5 2,5 0,39 1 -131 47 570 7204209 1716586 70,1 13,7 5,0 2,4 0,89 3,03 4,3 0,07 0,47 0,12 0,35 100,5 22,6 74,6 <2 <1 <5 0,6 2 0,4 <3 <1 30 2 5 <1 50 425 <3 52 15,2 148,0 1,4 3 <10 <1 <10 3,8 2,1 17,5 132 21 44 20 4,0 1,2 <0,5 2,2 0,33 1 -142 47 570 7204198 1716587 48,4 5,8 11,5 17,4 0,17 1,16 9,1 0,27 0,30 0,05 3,80 97,9 18,3 143 <2 2 15 0,5 17 0,6 3 <1 54 375 739 1 135 140 <3 35 32,0 48,6 1,1 <1 <10 <1 <10 1,3 0,8 8,2 43 5 13 <10 1,4 0,6 <0,5 1,1 0,10 1 -37 50 570 7204303 1716584 78,5 17,6 0,1 0,2 0,07 0,31 <0,01 <0,01 0,32 0,05 2,95 100,1 1,3 4,2 <2 <1 <5 0,8 <2 0,2 <3 <1 30 5 3 <1 14 <50 <3 21 10,5 11,1 <0,5 6 <10 <1 <10 5,3 3,0 6,7 230 35 73 30 6,6 1,3 0,8 2,3 0,34 1 -20 50 570 7204320 1716583 80,8 13,4 0,1 0,3 0,31 2,14 0,1 <0,01 0,28 0,07 2,50 100,0 0,5 4,3 <2 <1 <5 0,6 2 0,3 <3 <1 36 1 1 <1 19 250 <3 36 16,4 24,7 <0,5 3 <10 <1 <10 4,4 2,6 7,4 189 31 64 30 5,8 1,2 0,6 2,0 0,32 1 -9 50 570 7204332 1716583 78,7 13,0 0,1 1,6 0,29 2,88 1,5 0,01 0,23 0,06 0,47 98,9 16,2 36,2 <2 <1 7 0,7 2 0,3 <3 <1 35 1 1 <1 8 550 <3 40 14,8 16,6 0,6 4 <10 <1 <10 4,2 2,6 8,9 174 29 61 30 5,9 1,4 0,9 4,0 0,51 1 -4 50 570 7204337 1716582 84,2 11,1 0,1 0,2 0,25 2,83 0,2 <0,01 0,21 0,04 1,40 100,5 0,6 3,1 <2 <1 <5 0,6 3 <0,2 <3 <1 31 <1 <1 <1 6 599 <3 48 14,2 15,6 <0,5 3 <10 <1 <10 3,9 2,1 6,9 159 23 50 20 4,7 1,1 0,7 3,7 0,47 1, 3 1 50 570 7204341 1716582 77,5 12,5 0,1 1,6 0,23 2,81 2,0 0,01 0,26 0,06 1,75 98,8 2,4 13,7 <2 <1 6 0,3 <2 0,3 <3 <1 30 2 1 <1 7 662 <3 43 13,2 16,4 0,7 4 <10 <1 <10 4,5 2,4 6,4 176 32 66 30 5,8 1,1 0,7 3,3 0,44 1 6 50 570 7204346 1716582 75,5 11,9 0,1 2,8 0,18 2,07 5,0 0,04 0,24 0,06 2,35 100,3 3,3 21,8 <2 <1 5 1,0 2 <0,2 5 <1 26 1 3 <1 7 597 <3 29 11,4 11,7 1,1 4 <10 <1 <10 4,1 2,4 6,5 158 23 52 20 4,7 0,7 0,5 2,6 0,37 1 -71 -4 270 7204267 1716532 72,7 18,8 <0,01 0,4 0,69 4,60 0,1 <0,01 1,09 0,05 0,60 99,0 <0,5 3,5 <2 <1 31 <0,1 9 1,3 <3 <1 20 1 <1 <1 206 450 <3 64 16,9 37,9 <0,5 3 <10 1 <10 3,1 1,6 5,1 125 34 70 30 7,3 1,2 0,7 2,0 0,31 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA Mafic dike Sericitequartz rock Sericitequartz schist Seicite/ chlorite sericite schist Sericite schist Seicite/ chlorite sericite schist Chloritesericite schist Sericitequartz rock sericite sericiteandalusite chloritesericite sericite chloritesericite chlorite sericite sericite NA 114 Sericitequartz schist Chloritesericite schist Sericite schist Chloritesericite schist black fine grained rock black fine grained rock sericite, quartz vein chloritesericite sericite chloritesericite pyrrhotite sericite A. HALLBERG Appendix A, cont. B056 394 B057 394 B058 394 B059 394 B060 394 B061 394 B062 395 B063 395 B064 395 B065 395 B066 395 B067 395 B068 395 B069 395 5,0-8,0 8,1-10,6 13,4-23,3 24,6-34,1 36,2-41,9 43,4-45,2 0,0-6,2 6,2-15,3 16,0-17,1 17,1-23,5 23,5-28,7 30,2-38,0 38,0-39,7 39,7-41,6 -67 -4 270 7204271 1716532 46,5 35,8 0,1 0,5 1,23 8,83 0,3 <0,01 1,94 0,07 4,40 99,7 <0,5 4,2 <2 <1 <5 <0,1 2 1,9 10 <1 7 <1 1 2 371 946 <3 130 35,4 69,8 <0,5 5 <10 2 <10 3,1 2,3 5,6 169 36 76 40 8,1 1,5 0,9 1,6 0,23 1 -64 -4 270 7204273 1716532 38,3 28,1 0,3 10,1 0,63 4,53 9,3 0,03 1,79 0,20 6,40 99,7 14,5 104 <2 <1 <5 <0,1 2300 2,7 9 <1 27 3 4 1 362 527 <3 63 63,1 39,7 1,2 4 <10 <1 <10 1,7 <0,9 7,2 140 13 27 10 3,5 1,0 0,6 2,0 0,28 1 -55 -4 270 7204282 1716531 60,4 17,3 0,3 6,0 0,42 2,87 6,1 0,02 1,02 0,14 4,30 98,9 12,0 119 55 <1 <5 0,5 36 2,0 3 <1 25 5 2 <1 153 359 <3 48 33,4 22,3 0,9 4 <10 <1 <10 1,3 0,7 5,9 124 11 24 10 2,9 0,9 <0,5 1,6 0,32 1 -44 -4 270 7204293 1716531 57,6 14,2 0,4 9,9 0,27 0,95 10,1 0,06 0,75 0,17 5,70 100,1 334 164 15 2 36 1,8 17 2,2 <3 <1 32 2 5 <1 99 181 <3 20 23,4 13,5 1,3 2 <10 <1 <10 1,6 1,2 6,1 107 17 34 20 3,9 1,5 <0,5 1,6 0,31 1 -34 -4 270 7204303 1716530 72,4 19,0 0,5 0,3 2,46 1,67 0,1 <0,01 0,86 0,24 2,10 99,7 4,2 4,0 46 <1 2000 2,5 <2 0,8 11 <1 18 1 4 1 84 99 <3 26 12,3 121,0 <0,5 4 <10 <1 <10 5,3 2,8 6,5 184 44 82 30 5,8 2,3 0,5 1,1 0,16 1 -29 -4 270 7204308 1716530 52,6 16,7 0,6 3,6 1,17 2,66 13,7 0,02 1,10 0,14 7,85 100,1 107 42,4 33 1 87 1,4 50 2,2 9 <1 43 1 3 <1 252 298 <3 43 30,2 51,4 1,5 <1 <10 <1 <10 1,8 0,9 5,3 91 9 20 <10 1,8 0,6 <0,5 1,3 0,13 1 -81 -4 270 7204257 1716533 48,9 34,2 0,1 0,4 1,33 8,32 0,1 <0,01 1,31 0,06 4,00 98,8 <0,5 2,8 <2 <1 120 0,8 3 1,6 23 <1 6 1 4 <1 107 747 <3 117 25,1 55,4 <0,5 6 <10 <1 <10 7,7 5,4 8,6 280 56 121 60 14,5 1,9 1,6 4,6 0,65 1 -88 -4 270 7204249 1716533 49,6 33,3 0,1 0,3 1,33 7,86 0,1 <0,01 2,24 0,03 4,00 98,8 0,8 5,6 <2 <1 48 <0,1 4 1,4 19 <1 <5 2 2 2 320 490 <3 108 26,7 79,5 <0,5 6 <10 <1 <10 4,0 3,1 6,6 218 38 79 30 7,6 1,4 0,9 2,4 0,43 1 -94 -4 270 7204244 1716533 44,8 37,5 0,1 0,4 1,50 8,69 0,2 <0,01 2,03 0,05 4,30 99,5 <0,5 7,9 4 <1 97 0,6 2 2,3 104 <1 <5 1 4 4 203 582 4 114 26,0 93,8 <0,5 6 <10 <1 <10 4,1 4,2 7,6 219 106 208 100 19,3 2,6 1,0 2,7 0,42 1 -98 -4 270 7204240 1716533 37,6 50,7 0,0 0,3 0,84 4,66 <0,01 <0,01 2,00 0,06 4,05 100,2 <0,5 5,4 <2 <1 150 0,6 5 1,8 44 <1 8 1 3 4 88 307 <3 59 17,7 64,3 <0,5 5 <10 <1 <10 4,6 4,2 6,8 214 98 203 110 22,4 3,1 0,8 2,4 0,39 1, 3 -104 -4 270 7204234 1716534 56,4 28,3 0,2 0,4 1,08 6,81 0,1 <0,01 1,72 0,13 3,15 98,3 1,4 3,9 <2 <1 260 0,7 <2 3,2 202 <1 14 1 1 13 258 379 3 105 28,1 60,5 <0,5 5 <10 <1 <10 3,4 2,9 5,7 195 74 140 50 9,2 2,5 0,6 2,4 0,34 1, 3 -112 -4 270 7204226 1716534 67,4 21,0 0,4 0,6 0,68 5,27 0,3 <0,01 0,89 0,27 2,10 98,9 12,7 9,9 <2 <1 39 0,2 3 0,6 4 <1 18 2 2 2 120 408 <3 81 27,8 58,8 <0,5 2 <10 <1 <10 1,5 1,6 5,8 127 11 25 10 3,4 1,3 0,6 2,3 0,30 1 -116 -4 270 7204221 1716534 54,6 23,8 0,2 7,4 0,45 4,48 4,6 0,01 1,21 0,20 2,50 99,4 13,4 144 25 <1 <5 0,4 4 1,5 5 <1 20 3 3 <1 155 368 <3 69 41,9 50,0 1,0 4 <10 <1 <10 2,1 1,6 6,5 152 12 26 10 3,4 1,7 0,7 2,7 0,42 1 -118 -4 270 7204220 1716535 44,7 24,5 0,4 11,3 0,33 3,98 6,4 0,03 1,35 0,28 6,45 99,8 20,2 276 23 <1 <5 0,3 <2 1,7 8 <1 17 2 4 <1 172 273 <3 62 53,0 52,3 1,4 6 <10 <1 13 3,1 2,8 9,8 178 28 61 30 6,4 1,9 1,0 3,5 0,45 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA NA Sericitequartz schist Chloritesericite schist dark grey rock dark grey rock Sericite schist dark grey rock Sericite schist Sericite schist Sericite schist Andalusite rock Sericite schist Sericitequartz schist Chloritesericite schist Chlorite schist sericite chloritesericite chlorite, foliated chlorite, foliated sericiteandalusite, foliated chloritechalcopyrite sericiteandalusite sericite sericite andalusite sericite sericite chloritesericite chlorite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 115 Appendix A, cont. 116 B070 395 B071 395 B072 395 B073 428 B074 428 41,6-46,8 46,8-48,6 48,6-50,0 1,8-2,0 -122 -4 270 7204216 1716535 46,7 17,7 1,3 11,0 0,32 2,41 11,0 0,08 0,94 0,18 8,35 100,0 58,7 300 73 2 58 1,3 54 4,2 4 <1 29 3 6 2 213 269 <3 40 35,7 35,7 1,8 2 <10 <1 <10 2,4 0,9 8,1 103 15 29 10 3,6 1,6 0,5 1,5 0,26 1, 3 -125 -4 270 7204213 1716535 53,6 14,8 2,2 9,4 0,52 1,42 10,1 0,14 0,83 0,14 6,65 99,7 14,7 134 18 1 340 1,7 44 3,0 3 <1 53 8 9 <1 172 122 <3 48 26,1 58,8 1,9 2 <10 <1 <10 2,2 1,3 7,2 88 11 25 10 2,5 1,1 <0,5 1,3 0,24 1 -127 -4 270 7204211 1716535 70,6 14,6 0,3 1,0 0,27 4,11 4,9 <0,01 0,60 0,15 3,60 100,1 29,8 56,1 15 1 43 0,6 46 1,9 <3 <1 25 4 8 <1 97 397 <3 65 20,9 36,2 1,1 3 <10 <1 <10 3,5 1,8 6,9 125 17 38 20 3,8 1,1 <0,5 1,7 0,28 1 -108 7 170 7204230 1716544 63,9 22,7 0,2 0,3 1,00 5,25 0,2 <0,01 2,13 0,11 2,65 98,4 2,5 18,6 <2 <1 96 1,6 9 7,2 159 <1 20 1 5 2 132 269 <3 71 33,6 268,0 <0,5 14 <10 2 <10 14 10,9 23,4 448 85 199 120 32,5 5,0 3,4 5,9 0,95 1 XRAL-94 XRAL-94 B075 Gruvstugan B076 11 B077 11 10,8-11,0 71,0-71,2 -117 7 170 7204221 1716545 54,9 18,1 0,3 11,0 0,24 2,20 5,7 0,03 0,75 0,19 5,05 98,5 5,0 336 5 <1 <5 0,6 13 1,1 5 <1 17 2 7 <1 85 182 <3 34 25,9 34,1 1,0 4 <10 <1 <10 3,6 2,2 9,8 150 21 47 20 4,4 1,5 0,5 2,1 0,32 1 -91 23 65 7204248 1716560 inf inf inf inf inf inf inf inf inf inf inf 7204650 1716200 74,9 12,3 2,6 1,8 0,22 4,05 3,0 0,06 0,22 0,05 0,85 100,0 8,4 48,5 <2 <1 11 0,6 7 0,6 <3 1 24 1 2 <1 8 796 <3 53 10,9 133,0 1,2 4 <10 <1 <10 4,9 2,4 18,3 162 26 54 30 5,0 1,5 0,7 2,6 0,40 1 B078 stuff 270 B079 stuff 760 B151 576 B152 576 B153 577 B154 577 93,9-94,2 1,7-4,7 13,4-18,1 34,5-39,3 45,3-47,2 inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf inf 1 -80 20 85 7204259 1716557 10,6 0,0 2,4 0,4 1,03 <0,01 58,3 0,17 0,02 0,10 27,60 100,6 inf inf inf inf 1300 inf 5700 250 inf <1 92 inf inf inf inf 715 <3 44 0,8 inf inf <2 inf <1 326 <0,5 <0,5 nd 12 <1 <3 <10 <0,5 1,6 <0,5 0,6 0,05 1 8,0 0,2 0,3 0,2 0,12 <0,01 72,2 nd 1,26 0,12 29,90 112,4 nd nd nd nd inf nd inf inf nd inf inf nd nd nd nd 147 inf 37 inf nd nd inf nd inf 19 inf inf nd 74 inf inf inf inf inf inf inf inf 1 -57 35 250 7204283 1716570 69,7 17,1 0,6 1,3 0,85 3,45 2,2 <0,01 0,92 0,42 2,98 99,6 46,2 27,0 20 <1 140 0,3 110 0,8 165 <1 91 4 48 1 92 441 <3 52 24,0 44,8 <0,5 3 <10 <1 10 2,4 1,5 6,0 120 24 51 20 5,9 1,9 0,6 1,9 0,29 1 -44 36 250 7204295 1716570 49,0 14,1 1,1 3,1 1,46 1,40 18,0 0,05 0,94 0,16 11,00 100,3 108 104 49 <1 140 1,0 100 2,6 21 <1 33 2 162 <1 179 287 <3 26 28,7 93,6 0,5 2 <10 <1 <10 1,2 0,5 3,9 86 9 20 10 2,5 1,4 <0,5 1,3 0,19 1 -26 54 250 7204314 1716588 51,6 14,9 4,9 8,1 1,08 1,38 12,4 0,10 0,99 0,14 3,85 99,4 18,3 119 2 <1 <5 0,4 6 2,5 <3 <1 11 2 107 <1 190 168 <3 17 32,3 106,0 0,6 1 <10 <1 <10 1,2 0,9 8,5 71 7 14 10 1,8 0,7 <0,5 1,0 0,18 1 -17 54 250 7204324 1716587 54,3 15,3 7,9 6,5 1,15 1,27 9,0 0,12 1,03 0,18 2,00 98,8 23,1 107 4 <1 <5 0,7 3 1,2 4 <1 12 3 73 <1 199 231 4 13 33,3 193,0 0,9 2 <10 <1 <10 0,9 0,6 9,9 74 9 20 10 2,2 0,7 <0,5 1,1 0,19 1 13,4 9,5 3,4 0,2 0,41 2,51 32,0 nd 5,25 2,24 31,80 100,7 nd nd nd nd inf nd inf inf nd inf inf nd nd nd nd 338 inf 26 inf nd nd inf nd inf 31 inf inf nd 633 inf inf inf inf inf inf inf inf 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA NA Chlorite schist Sericitequartz schist Chloritesericite schist Sericite schist Chloritesericite schist, quartz vein Quartz porphyry Arsonopyrite ore Pyrite ore Arsonopyrite ore Arsonopyrite ore Sericitequartz schist Sericitequartz schist dark grey rock dark grey rock chlorite sericite chloritesericite, chalcopyrite sericite chloritesericite pyrite chalcopyrite sericite sericitepyrite pyrite veinlets A. HALLBERG Appendix A, cont. B155 577 B156 577 49,7-49,8 B157 Gruvstugan B158 464 B159 464 B160 464 B161 464 B162 464 B163 464 B164 464 B165 464 B166 464 B167 464 B168 600 58,9-65,4 4,2-8,7 8,7-13,0 13,0-23,3 23,3-30,7 30,7-37,2 37,2-42,9 42,9-52,9 52,9-62,0 62,0-66,5 66,5-70,1 12,5-15,6 -13 54 250 7204327 1716587 49,4 11,2 10,9 9,3 0,56 0,53 14,1 0,22 0,55 0,13 1,35 98,2 99,7 161 <2 <1 12 0,8 15 1,0 <3 <1 71 482 1060 3 171 118 <3 16 30,0 64,8 <0,5 2 <10 <1 <10 2,1 1,8 12,9 60 8 17 10 1,9 0,9 <0,5 1,3 0,19 1 -1 54 250 7204340 1716586 58,3 14,1 6,5 5,2 1,27 0,98 9,7 0,12 0,74 0,17 1,85 98,9 56,8 82,2 <2 <1 <5 0,4 5 1,2 <3 1 11 7 137 <1 93 232 <3 13 23,6 217,0 0,9 2 <10 <1 <10 1,5 1,0 16,3 99 21 43 20 4,3 1,5 0,5 2,0 0,35 1 -78 -26 330 7204258 1716511 41,8 20,1 0,3 14,3 0,22 1,17 13,7 0,09 1,06 0,15 7,60 100,5 108 152 <2 <1 8 0,1 3 1,7 5 <1 37 24 84 <1 352 164 <3 16 41,6 12,2 <0,5 2 <10 <1 <10 1,4 0,7 4,4 75 11 26 10 3,0 1,1 <0,5 1,3 0,20 1 -83 -25 330 7204254 1716511 72,0 16,2 0,5 1,3 0,56 3,71 1,4 <0,01 0,82 0,19 2,50 99,2 32,3 14,4 16 <1 88 <0,1 6 0,6 <3 <1 7 8 44 <1 201 310 <3 59 26,3 32,1 <0,5 1 <10 <1 <10 1,8 0,7 4,0 86 13 28 10 3,4 1,5 <0,5 1,3 0,24 1 -90 -25 330 7204246 1716512 53,9 31,4 0,3 0,3 0,75 4,72 0,4 <0,01 2,28 0,10 5,10 99,3 3,6 2,6 <2 <1 82 <0,1 3 1,7 83 <1 <5 1 33 3 121 245 <3 73 20,6 36,8 <0,5 7 <10 <1 14 8,6 5,7 7,2 271 87 183 90 19,8 3,1 1,0 3,0 0,44 1 -99 -24 330 7204238 1716513 53,3 34,7 0,3 0,2 0,29 1,67 0,2 <0,01 1,67 0,19 6,30 98,9 3,1 2,7 <2 <1 24 0,1 2 0,7 28 <1 <5 2 25 3 100 163 <3 26 17,0 19,6 <0,5 5 <10 <1 12 4,9 3,6 6,0 220 48 104 50 10,8 2,0 0,9 2,3 0,33 1 -106 -24 330 7204231 1716514 53,6 30,9 0,2 0,4 0,98 7,20 0,2 <0,01 1,57 0,15 4,15 99,4 3,0 0,8 <2 <1 81 0,1 19 0,8 27 <1 5 10 15 1 172 452 <3 113 23,3 46,5 <0,5 7 <10 <1 14 5,8 3,0 6,9 228 50 102 50 9,6 2,0 1,0 3,3 0,47 1 -112 -23 330 7204225 1716515 59,0 20,9 0,3 4,4 0,55 4,50 3,4 0,01 1,02 0,15 4,45 98,7 23,3 52,7 <2 <1 6 <0,1 <2 0,6 6 <1 12 5 50 2 226 404 <3 69 31,4 31,1 <0,5 2 <10 <1 136 2,1 1,2 3,9 112 17 36 20 4,0 0,8 0,6 1,6 0,31 1 -120 -23 330 7204217 1716516 65,6 15,1 0,3 5,2 0,35 2,57 5,7 0,03 0,59 0,14 4,35 100,0 39,6 149 2 <1 19 <0,1 4 0,6 <3 <1 10 7 67 <1 74 244 <3 32 18,3 26,2 <0,5 3 <10 <1 <10 2,7 2,3 6,5 128 21 44 20 4,3 1,2 0,5 1,9 0,29 1 -129 -22 330 7204207 1716517 60,8 13,9 1,4 7,7 0,35 2,43 7,7 0,08 0,55 0,14 4,25 99,3 37,4 120 5 <1 16 0,4 8 0,9 <3 <1 20 24 152 3 103 305 <3 48 17,8 36,4 0,8 3 <10 <1 <10 2,4 1,8 9,8 112 14 31 10 3,1 0,8 <0,5 1,8 0,27 1 -136 -22 330 7204201 1716518 58,0 15,2 4,1 6,5 0,30 3,16 8,4 0,10 0,75 0,18 2,05 98,7 14,2 127 <2 <1 <5 <0,1 2 0,2 <3 <1 14 4 137 <1 150 384 3 48 23,7 76,2 0,9 2 <10 <1 <10 1,1 0,7 10,9 91 12 28 10 3,1 1,2 0,5 1,5 0,21 1 -140 -21 330 7204197 1716518 59,3 14,7 4,6 5,0 0,31 3,53 8,2 0,12 0,75 0,21 1,55 98,3 15,8 138 7 <1 <5 <0,1 4 0,4 <3 <1 12 4 146 <1 93 438 4 51 21,8 92,5 0,9 2 <10 <1 <10 1,5 1,4 13,6 106 14 31 10 3,5 1,3 <0,5 1,9 0,27 1 -117 -17 210 7204220 1716521 58,3 15,9 0,9 8,8 0,42 1,80 7,1 0,05 0,84 0,24 5,30 99,7 53,9 172 10 <1 15 0,3 2 1,4 9 1 13 4 43 <1 77 227 <3 32 24,4 37,3 0,7 3 <10 <1 <10 1,9 1,3 9,7 118 17 37 20 3,9 1,3 0,5 2,4 0,32 1 XRAL-94 XRAL-94 7204650 1716200 72,7 12,4 3,2 1,7 0,29 4,09 3,4 0,07 0,24 0,06 0,95 99,0 12,1 32,7 3 <1 14 0,1 6 0,7 <3 <1 <5 5 116 1 8 845 <3 32 10,3 143,0 0,9 4 <10 <1 <10 4,5 2,6 20,1 159 26 54 20 5,0 1,1 0,5 2,7 0,42 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA NA dark grey rock dark grey rock Quartz porphyry dark grey ser-qz schist Sericitequartz schist Sericitequartz rock Sericitequartz rock Sericitequartz rock Sericitequartz schist Sericitequartz schist Sericitequartz schist dark grey fine-grained rock grey finegrained rock grey finegrained rock sericite sericite sericite sericite sericite sericite sericite sericite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 117 Appendix A, cont. B169 600 B170 11 B171 11 B172 428 B173 428 B174 428 B175 428 15,6-20,6 23,0-46,7 46,7-55,0 0,0-20,0 20,0-50,0 60,0-90,0 90,0-119,0 -120 -19 210 7204217 1716519 59,2 14,9 0,6 8,8 0,37 1,92 8,0 0,05 0,79 0,21 5,45 100,2 26,2 128 8 <1 28 <0,1 12 1,4 5 <1 12 3 45 <1 97 178 <3 28 23,6 25,2 0,7 3 <10 <1 <10 2,1 1,1 8,3 103 15 32 10 3,6 1,2 0,5 1,7 0,26 1 -108 28 34 7204231 1716566 63,3 15,6 5,5 2,4 3,17 1,63 4,7 0,08 0,63 0,18 0,95 98,2 39,8 74,8 3 <1 <5 <0,1 14 0,7 <3 <1 18 9 72 <1 97 330 <3 31 24,2 256,0 1,1 3 <10 <1 <10 3,6 2,2 16,6 125 19 39 20 4,3 1,5 0,6 2,3 0,34 1 -100 26 48 7204239 1716564 57,8 16,5 6,4 4,8 0,86 2,66 6,5 0,12 0,70 0,19 1,45 98,0 74,7 113 10 <1 7 0,1 30 3,2 <3 <1 18 10 69 <1 119 274 3 68 27,7 144,0 1,0 3 <10 <1 <10 3,0 1,3 14,0 128 18 39 20 4,1 1,3 0,5 2,3 0,33 1 -116 7 170 7204222 1716545 58,4 20,1 0,8 5,6 0,67 4,06 4,3 0,03 0,93 0,16 4,45 99,5 42,5 116 18 <1 130 0,7 550 9,8 13 <1 18 10 49 3 115 283 <3 69 24,6 65,0 0,6 4 <10 <1 10 4,3 3,6 9,8 148 29 62 30 6,8 1,1 0,9 2,9 0,41 1 -141 7 170 7204197 1716546 54,9 15,0 6,2 5,8 3,08 1,13 9,9 0,14 0,88 0,20 1,55 98,7 51,4 113 6 <1 14 0,5 6 0,5 <3 <1 22 3 47 <1 150 225 <3 20 30,0 238,0 0,9 2 <10 <1 <10 2,1 0,7 16,0 90 15 32 10 3,7 1,5 0,5 2,2 0,32 1 -181 7 170 7204157 1716548 62,8 16,3 5,5 2,0 3,18 1,50 5,3 0,10 0,65 0,18 0,95 98,4 34,0 80,9 <2 <1 <5 <0,1 9 0,4 <3 <1 15 8 150 <1 100 297 <3 50 23,6 402,0 1,2 4 <10 <1 <10 3,5 1,6 13,0 133 20 41 20 4,5 1,2 0,6 2,2 0,35 1 XRAL-94 B177 stuff 296 B178 stuff 297 B179 stuff 428 B180 stuff 436 B181 stuff 462 B182 stuff 505 -211 7 170 7204128 1716550 65,9 13,5 6,6 1,5 2,94 1,55 4,1 0,13 0,53 0,15 1,50 98,4 41,3 70,9 <2 <1 13 0,2 45 0,5 <3 <1 13 7 91 <1 64 272 <3 37 18,7 199,0 0,9 3 <10 <1 <10 2,5 1,4 13,8 112 21 44 20 4,3 1,8 <0,5 1,8 0,28 1 -60 -36 210 7204276 1716499 69,0 12,4 0,4 5,8 0,48 1,54 5,6 0,03 0,83 0,15 3,85 100,1 31,0 92,9 7 <1 12 <0,1 3 3,9 4 1 8 7 100 <1 154 211 <3 21 24,3 22,3 <0,5 2 <10 <1 <10 1,2 1,1 4,2 77 3 6 <10 1,3 0,7 <0,5 0,9 0,19 1 30 -1 250 7204368 1716529 61,2 15,3 0,5 4,8 0,50 2,48 9,2 0,12 0,81 0,19 4,80 99,9 108 343 12 <1 51 0,4 25 3,5 3 <1 18 3 71 <1 128 511 <3 41 29,5 28,3 0,7 2 <10 <1 <10 1,3 0,7 6,2 96 29 61 30 6,3 2,3 0,8 1,4 0,25 1 12 -1 250 7204349 1716531 44,5 16,4 0,7 3,2 0,95 2,64 19,6 0,05 0,89 0,11 11,30 100,3 50,3 154 94 <1 120 2,4 170 8,4 11 <1 36 10 149 <1 191 362 <3 28 24,2 88,7 1,0 1 <10 <1 <10 0,6 0,7 1,7 66 2 6 <10 0,7 1,1 <0,5 0,8 0,15 1 -52 1 -103 14 7204286 1716536 46,1 22,2 2,3 2,8 1,20 1,28 15,9 0,01 0,96 <,01 5,55 98,2 2520 440 150 <1 47 1,8 160 17 inf <1 17 12 204 2 148 281 <3 27 25,2 193,0 1,1 2 17 <1 10 1,4 2,0 7,9 132 3 8 <10 2,0 1,0 0,8 2,2 0,33 1 7204236 1716551 63,7 14,1 4,9 4,5 0,65 2,50 5,9 0,11 0,62 0,17 1,40 98,5 61,4 95,3 7 <1 8 <0,1 29 2,8 <3 <1 20 11 90 <1 116 236 3 62 25,9 118,0 0,8 3 <10 <1 <10 2,0 1,9 12,6 104 14 31 10 3,6 1,3 0,6 1,8 0,27 1 96 9 170 7204434 1716536 65,6 15,2 6,0 1,4 1,61 1,01 4,0 0,12 0,97 0,19 1,90 98,1 40,0 53,9 6 <1 31 <0,1 12 2,0 <3 <1 21 12 113 1 219 308 <3 22 29,8 345,0 1,1 2 <10 <1 <10 2,5 1,0 14,6 91 23 52 20 6,1 2,2 0,7 2,0 0,31 1 -52 33 90 7204287 1716568 40,0 24,0 0,5 8,9 0,65 3,28 14,6 0,06 1,06 0,26 6,70 99,9 135 660 72 <1 48 0,4 2300 11 6 <1 13 9 121 2 169 202 <3 60 32,8 50,4 0,7 4 <10 <1 <10 3,5 <0,9 8,4 181 24 51 20 5,3 2,4 0,6 3,1 0,48 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA NA NA NA NA grey finegrained rock dark grey fine-grained rock dark grey fine-grained rock Sericitequartz schist grey finegrained rock grey finegrained rock dark grey fine-grained rock black schist dark grey siliceous rock black rock Dacite finegrained black rock light grey siliceous rock black finegrained rock pyrite filled amygdules pyrite pyrite sericite 118 B176 stuff 138 A. HALLBERG Appendix A, cont. B183 stuff 506 B184 stuff 509 B185 stuff 511 B186 stuff 615 B187 stuff 616 B188 stuff 626 B189 stuff 676 B190 stuff 677 B191 stuff 678 B192 stuff 687 B193 stuff 688 B194 stuff 689 B195 stuff 1109 B196 30 144,0-160,0 127 1 90 7204465 1716526 57,6 13,7 6,3 4,9 1,67 1,05 10,9 0,20 0,70 0,13 1,55 98,7 71,3 138 3 <1 30 0,1 22 1,3 <3 <1 23 6 191 <1 176 200 3 23 29,1 178,0 <0,5 2 <10 <1 <10 1,4 0,8 13,9 67 11 24 10 2,9 1,3 <0,5 2,0 0,31 1 118 -33 90 7204453 1716493 57,7 21,3 3,6 1,3 6,54 1,77 2,4 0,03 1,42 0,23 2,50 98,8 79,4 148 8 <1 17 <0,1 12 0,9 <3 2 14 5 65 <1 423 325 <3 29 44,4 416,0 0,9 2 <10 <1 <10 2,9 1,9 6,9 105 15 34 20 4,3 1,5 0,6 1,1 0,25 1 112 -23 90 7204448 1716503 74,2 13,0 3,8 1,0 2,86 0,79 2,3 0,03 0,40 0,10 0,70 99,2 12,6 35,1 6 <1 <5 <0,1 5 0,6 <3 <1 10 5 72 3 57 137 <3 10 16,7 470,0 1,2 5 <10 <1 <10 4,6 1,8 10,3 143 23 50 20 5,0 2,0 0,6 2,0 0,35 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP NA NA NA NA black schist dark grey rock light grey finegrained rock dark grey finegrained rock pyrite -26 -7 170 7204311 1716527 59,2 17,3 5,3 3,9 2,59 0,78 6,1 0,09 1,09 0,24 2,10 98,8 19,1 109 5 <1 <5 <0,1 3 0,7 <3 1 18 2 67 <1 257 201 <3 14 40,2 396,0 1,1 3 <10 <1 <10 2,2 1,1 15,6 99 18 41 20 5,2 1,9 0,8 2,4 0,43 1 -17 -3 170 7204321 1716530 53,8 17,3 6,9 3,2 6,04 0,12 9,0 0,12 1,13 0,25 0,30 98,1 54,9 110 8 <1 <5 0,1 10 1,3 <3 3 50 2 68 <1 276 <50 4 <10 40,3 271,0 0,9 3 <10 <1 <10 0,8 <0,7 18,0 101 18 38 20 4,7 2,1 0,7 2,1 0,38 1 38 -2 170 7204376 1716528 55,3 17,3 12,7 2,7 0,89 0,18 6,3 0,15 0,77 0,24 1,85 98,4 5,1 78,4 15 <1 <5 <0,1 25 2,4 <3 <1 12 3 74 <1 147 <50 <3 <10 32,7 350,0 0,8 3 <10 <1 <10 2,5 1,4 19,1 104 16 39 20 4,5 1,8 0,6 3,4 0,50 1 -41 8 130 7204297 1716542 58,9 17,2 6,1 2,8 2,42 0,88 7,7 0,07 1,07 0,19 2,10 99,5 46,3 71,8 13 <1 11 0,5 13 1,9 4 <1 20 4 88 <1 196 211 <3 29 33,8 313,0 1,0 1 <10 <1 <10 0,9 0,6 8,5 96 8 18 <10 2,0 1,6 <0,5 2,1 0,30 1 17 2 130 7204354 1716533 61,0 13,7 6,4 3,4 3,01 0,37 9,2 0,14 0,78 0,14 0,80 98,9 15,7 94,2 <2 <1 8 <0,1 4 1,4 <3 <1 21 4 165 <1 182 148 <3 <10 25,3 263,0 0,9 2 <10 <1 <10 1,5 0,7 12,7 72 12 26 10 2,7 1,4 <0,5 1,4 0,22 1 29 -20 130 7204365 1716511 55,2 16,6 5,0 4,8 3,81 0,24 10,4 0,11 1,00 0,11 1,70 99,0 48,8 131 2 <1 <5 0,1 3 1,4 <3 <1 26 3 125 <1 266 156 <3 <10 33,5 197,0 0,9 2 <10 <1 <10 1,4 1,6 14,7 87 16 33 10 3,2 1,4 <0,5 1,6 0,25 1 -27 -9 90 7204310 1716524 69,0 10,1 1,4 0,7 1,87 0,80 9,9 0,03 0,66 0,07 5,40 99,9 27,5 21,0 10 <1 40 <0,1 85 2,1 6 <1 20 3 118 <1 132 173 <3 <10 38,4 211,0 0,7 1 <10 <1 <10 0,8 1,1 2,9 64 3 7 <10 1,2 0,9 <0,5 1,0 0,15 1 29 -7 90 7204366 1716523 48,6 17,5 7,8 5,1 3,30 0,29 13,1 0,20 1,13 0,12 1,20 98,3 41,2 125 <2 <1 <5 <0,1 4 1,5 <3 <1 36 3 73 <1 334 140 <3 <10 38,7 367,0 0,8 2 <10 <1 <10 0,9 1,6 12,7 95 12 24 10 2,9 1,1 <0,5 1,5 0,27 1 54 2 90 7204391 1716531 57,2 15,7 6,4 3,8 3,91 0,29 9,8 0,17 0,95 0,26 0,60 99,1 22,5 100 <2 <1 12 <0,1 2 1,0 <3 <1 27 2 71 <1 222 188 <3 <10 28,2 351,0 0,7 1 <10 <1 <10 1,7 0,9 15,9 88 13 27 10 3,0 1,1 <0,5 1,5 0,24 1 17 -21 570 7204354 1716510 40,3 27,8 10,0 5,8 1,49 0,24 8,5 0,12 0,60 0,14 3,45 98,3 25,8 65,3 4 <1 55 1,7 15 0,5 16 <1 15 12 42 <1 69 79 <3 12 27,7 299,0 3,9 12 <10 <1 12 8,8 5,0 19,2 383 35 71 30 6,7 1,3 1,1 4,4 0,68 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA NA black finegrained rock light grey rock black rock dark grey siliceous rock black rock light grey siliceous rock black rock black rock coarsegrained rock light grey rock sulfides -207 93 96 7204103 1716649 65,2 15,4 2,7 2,2 2,07 3,18 5,0 0,04 0,55 0,13 2,30 98,8 33,7 91,3 3 <1 <5 0,5 17 2,3 3 <1 10 4 149 1 56 499 <3 44 15,9 126,0 1,1 3 <10 <1 <10 4,4 1,9 14,4 142 28 54 20 4,6 1,9 0,5 2,6 0,42 1 pyrite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 119 Appendix A, cont. 120 B197 30 B198 30 B199 30 B200 30 B201 30 B202 30 B203 30 B204 30 B205 30 210,0-240,0 265,0-295,0 320,0-336,0 336,0-357,0 357,0-384,0 400,0-420,0 420,0-440,0 450,0-474,0 474,0-498,0 -176 77 152 7204136 1716629 69,6 13,8 4,0 0,7 3,54 1,69 3,0 0,06 0,50 0,13 1,50 98,6 17,6 61,4 8 <1 <5 0,1 6 0,9 <3 <1 8 4 76 1 45 412 <3 23 13,0 221,0 1,1 3 <10 <1 <10 3,3 1,9 13,2 129 21 43 20 3,8 0,9 <0,5 2,0 0,30 1 -149 64 198 7204163 1716614 58,9 15,7 7,2 2,3 3,27 1,74 5,7 0,13 0,68 0,21 2,50 98,3 43,4 93,7 3 <1 <5 <0,1 5 0,6 <3 <1 25 9 66 <1 107 390 3 40 26,8 307,0 1,0 4 <10 <1 <10 2,6 2,2 14,1 118 26 52 20 4,8 3,0 0,5 2,6 0,42 1 -120 51 243 7204188 1716602 59,9 15,9 3,3 2,5 0,33 4,90 8,4 0,16 0,84 0,21 2,80 99,2 73,4 94,4 9 <1 24 0,3 33 1,0 <3 <1 19 2 127 <1 108 1240 3 76 29,8 73,4 0,9 3 <10 <1 <10 2,5 1,5 15,6 107 22 45 20 4,9 2,2 0,6 2,5 0,36 1 -111 48 256 7204199 1716598 62,8 13,6 0,9 3,2 0,32 4,78 8,7 0,37 0,74 0,21 2,85 98,5 114 1980 989 <1 82 2,6 52 5,1 <3 <1 19 4 90 3 104 1800 <3 80 27,7 34,0 0,5 4 <10 <1 <10 2,2 1,3 10,4 97 17 36 20 3,6 1,0 <0,5 1,9 0,27 1 -99 44 272 7204212 1716592 60,7 13,6 1,1 7,4 0,32 2,66 7,8 0,25 0,55 0,13 4,85 99,3 101 1080 695 <1 100 1,6 22 3,7 <3 <1 20 10 133 <1 97 503 3 51 20,9 21,5 0,7 3 <10 <1 <10 2,9 2,4 8,7 107 20 41 20 3,7 1,4 0,5 1,8 0,31 1 -73 35 306 7204236 1716583 73,4 17,0 0,2 0,5 0,57 4,33 0,9 <0,01 0,72 0,13 2,65 100,5 50,1 26,6 17 <1 320 0,1 5 1,1 5 <1 10 6 33 1 126 282 <3 68 21,5 28,4 <0,5 3 <10 <1 16 2,9 2,0 3,6 112 24 47 20 4,8 1,6 0,5 2,2 0,30 1 -61 31 322 7204248 1716578 69,7 20,7 0,2 0,3 0,65 4,00 0,3 <0,01 0,93 0,09 3,35 100,1 5,3 4,9 <2 <1 460 <0,1 2 0,8 14 1 <5 2 24 <1 148 220 <3 64 23,2 23,0 <0,5 6 <10 <1 13 5,6 3,4 3,6 155 46 95 40 8,8 2,2 <0,5 2,1 0,44 1 -42 24 344 7204268 1716570 63,3 22,9 0,2 0,6 0,70 4,52 2,2 <0,01 1,11 0,14 3,70 99,4 18,7 6,6 4 <1 100 <0,1 22 0,9 10 <1 14 7 56 1 144 388 <3 73 28,5 25,6 <0,5 5 <10 <1 <10 4,4 2,9 4,8 151 37 74 30 7,7 2,1 1,0 4,0 0,59 1 -26 18 362 7204283 1716562 75,9 13,8 0,2 1,1 0,49 3,14 1,6 <0,01 0,57 0,13 2,35 99,3 39,4 7,4 5 <1 44 0,1 16 0,5 8 1 12 4 52 <1 41 410 <3 38 17,8 19,3 <0,5 3 <10 <1 <10 2,7 2,8 4,1 118 21 42 20 4,2 0,9 0,6 2,5 0,36 1 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRAL-94 XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP XRF/ICP/ XRF/ICP/ XRF/ICP/ XRF/ICP/ NA NA NA NA NA NA NA NA NA light greybrown rock dark browngrey rock dark browngrey rock grey rock Sericitequartz rock Sericitechlorite rock Sericitequartz rock Sericitequartzandalusite schist Sericitequartz rock sericite sericitechlorite sericite- sericite andalusite sericite A. HALLBERG Appendix B sample # bh core local n local e z N (RT90) E (RT90) SiO2 Al2O3 CaO MgO Na2O K2O Fe2O3 MnO TiO2 P2O5 LOI SUM Cu Zn Pb As Sb Co Ni Cr V Ba Rb Sc Sr Hf Nb Th U Y Zr La Ce Nd Sm Eu Tb Yb Lu 91101 686 262,5-262,9 91102 686 296,0-296,3 91103 686 352,6-353,0 91104 686 390,3-390,7 91105 686 458,9-459,2 91106 686 492,7-493,0 7204948 1716943 74,5 13,7 3,2 0,5 3,94 1,09 1,3 0,05 0,45 0,14 0,75 99,6 8 28 91107 678 126,1-126,5 -6759 -248 109 7203148 1715763 61,1 19,5 7,2 2,0 3,70 0,78 5,0 0,08 0,43 0,10 1,12 101,0 37 89 91108 678 247,2-247,6 -6721 -295 214 7203190 1715719 72,3 12,9 3,3 1,3 1,32 2,17 4,7 0,08 0,53 0,12 1,48 100,2 34 10 91109 678 402,9-403,2 -6671 -354 349 7203243 1715662 51,0 24,7 7,5 2,8 3,76 2,83 5,8 0,07 0,87 0,06 1,27 100,5 5 82 91110 678 413,0-413,2 -6667 -358 358 7203247 1715659 50,8 19,3 9,4 6,1 1,74 1,57 9,4 0,20 0,66 0,13 1,94 101,2 54 102 91111 678 475,5-476,0 -6647 -382 412 7203268 1715636 68,4 15,2 4,1 0,6 5,99 1,08 1,3 0,05 0,56 0,20 1,99 99,5 8 109 91112 678 532,3-532,6 -6629 -404 461 7203288 1715615 64,2 13,9 6,4 1,9 1,44 3,51 4,8 0,09 0,52 0,17 2,77 99,8 9 75 91121 30 56,2-56,5 -247 107 19 7204051 1716657 63,1 16,0 3,9 2,6 3,12 1,46 8,0 0,08 0,73 0,17 1,78 100,8 27 112 7204892 1717035 56,1 17,0 5,2 5,2 3,31 0,73 9,7 0,09 1,07 0,28 2,75 101,5 75 1125 10 7204900 1717022 58,4 17,0 4,5 4,2 3,21 1,20 9,0 0,08 1,13 0,22 2,52 101,5 26 367 10 7204914 1716999 55,2 17,3 7,2 5,0 2,64 1,10 10,3 0,16 1,12 0,12 2,02 102,2 190 115 7204923 1716984 56,6 17,6 6,7 4,4 2,78 1,03 9,7 0,14 1,04 0,17 1,85 102,0 47 123 7204940 1716956 70,1 15,0 3,4 2,1 3,12 1,46 3,6 0,05 0,49 0,15 1,31 100,8 7 70 9 42 302 151 43 27,0 341 8 13 255 358 49 27,0 260 176 6 345 283 27 32,0 328 9 12 311 202 40 30,0 390 10 13 34 296 34 11,0 441 8 5 30 414 17 6,8 216 47 11 18 92 289 26 9,0 472 9 9 24 420 130 11,0 143 62 14 24 332 370 87 33,0 379 61 40 10 247 479 32 27,0 237 7 9 52 194 18 12,0 241 6 5 54 1136 64 12,0 164 12 10 66 230 45 18,0 338 18 133 13 29 7 24 18 119 17 89 16 21 122 14,0 30 18,3 3,59 1,53 2,1 2,44 method-lab. ICP-Lul ICP-Lul ICP-Lul ICP-Lul ICP-Lul ICP-Lul ICP-Lul ICP-Lul ICP ICP ICP-Lul ICP-Lul ICP-Lul Rock Andesite Andesite Andesite Andesite Dacite porphyry Dacite porphyry Volcanic flow in sediment Volcanic sandstone Siltstone Siltstone Dacite porphyry Dacite porphyry Volcanic sandstone actinolite actinolite 10 17 75 11,7 26 17,3 3,65 1,90 15 86 2,36 11 64 9,7 23 15,1 3,92 1,49 11 67 1,85 Alter., struct., minerali-sation 19 122 14,2 33 19,2 4,07 1,46 13 112 8 61 2,08 11 2,5 actinolite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 121 Appendix B, cont. 91122 30 70,7-71,7 -240 106 32 7204058 1716655 62,6 20,5 4,6 2,0 2,75 3,15 2,7 0,04 0,37 0,11 1,46 100,2 17 63 5 5 38 670 160 10,0 701 91123 30 118,3-118,6 -218 99 74 7204080 1716648 63,7 12,8 1,0 5,1 0,22 2,49 9,5 0,63 0,70 0,09 3,96 100,2 82 261 27 13 22 286 1249 34 28,0 48 91124 30 573,6-574,0 37 -21 424 7204337 1716523 72,7 11,7 0,1 3,7 0,16 1,69 6,2 0,06 0,22 0,10 3,42 100,0 91125 30 585,1-585,4 45 -28 429 7204344 1716516 73,6 12,8 0,2 2,7 0,23 2,24 5,0 0,05 0,26 0,09 2,99 100,2 32 31 7 5 5 554 11 8,3 11 15 11 831 20 8,6 19 10 9 91 10,7 24 14,5 2,85 1,44 26 148 21 34 159 19,8 46 29 6,67 0,95 91142 29 140,6-140,9 -191 -114 143 7204145 1716422 73,3 13,7 2,0 1,4 3,03 2,28 2,3 0,10 0,49 0,10 1,08 99,8 54 9 91143 29 187,8-188,0 -171 -115 186 7204165 1716420 57,2 15,6 5,0 4,0 0,72 2,80 11,2 0,15 0,98 0,16 1,87 99,7 69 120 10 7 60 173 982 22 1 20 53 362 24 1 21 244 499 33 362 155 233 10 4,0 5 4,0 18 177 11 135 4 6,0 2,0 13 77 34 11 92006 92007 92008 92009 92010 92011 7203950 1715270 59,7 15,1 6,8 2,4 2,87 1,39 8,0 0,16 0,79 0,23 2,70 100,1 29 87 <10 <3 7203990 1715180 67,0 14,9 4,6 1,2 2,11 2,50 5,9 0,10 0,62 0,18 1,20 100,4 7203780 1714290 64,7 14,4 6,4 1,4 1,99 2,08 6,3 0,13 0,74 0,25 2,25 100,6 31 75 7203620 1714050 57,6 17,0 5,4 3,3 2,38 2,69 9,4 0,16 0,82 0,24 1,10 100,0 12 98 7203280 1714260 55,0 18,7 3,2 4,2 3,40 3,06 9,9 0,12 0,73 0,18 1,85 100,4 8 114 19 2 7203290 1714190 66,8 15,0 2,8 2,1 2,67 2,28 5,3 0,08 0,56 0,15 1,20 99,0 7203570 1715460 68,3 16,4 3,3 0,8 4,37 2,09 2,2 0,06 0,62 0,16 1,45 99,8 74 12 69 19 11 12 10 12 72 4 11 8 16 150 3 10 543 26 25,5 555 2,0 9 1,4 1,4 19 109 19 40 20 4,0 1,7 0,6 2,3 0,35 741 36 16,6 307 2,0 9 2,6 1,5 12 134 19,0 38 19 3,9 1,4 0,5 1,8 0,24 803 29 19,1 281 3,0 9 1,9 1,4 16 131 17,0 36 18 4,0 1,3 0,6 2,0 0,28 803 43 23,5 414 3,0 9 2,6 1,2 22 124 21,0 42 20 4,4 1,3 0,6 2,3 501 40 20,2 285 5,0 10 4,4 2,1 24 179 26 53 27 4,9 1,3 0,7 2,6 579 49 14,7 296 3,0 11 2,6 1,5 13 153 21,0 41 20 3,9 1,2 0,5 2,1 603 27 17,0 307 4,0 11 3,3 1,9 19 159 21,0 41 20 4,0 1,1 0,5 2,0 0,27 3,2 ICP-Lul ICP-Lul ICP-Lul XRF-Not. XRF-Not. XRF-Not. XRAL92/XRF/NA A XRF/NA XRF/NA XRF/NA XRAL92/XRF/NA A XRF/NA XRF/NA Biotite siltstone Quartz porphyry Quartz porphyry Dacite porphyry Dacite porphyry Andesite Dacite, feldspar porphyritic Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry chl/garnet biotitechlorite biotitechlorite Preserved ”granite” texture biotite akt actinolite actinolite A. HALLBERG 3,72 92005 1,40 Volcanic flow in sediment 122 5 23 91141 29 80,1-80,4 -216 -113 89 7204119 1716424 56,5 23,4 3,9 1,2 6,34 2,58 3,3 0,11 1,06 0,24 1,16 99,8 18 59 23 Appendix B, cont. 92012 92013 92014 92015 92016 92017 92018 92019 7205750 1716800 70,6 13,6 4,2 0,6 2,33 2,06 3,7 0,11 0,46 0,12 1,60 99,4 12 44 7203050 1714550 79,7 10,2 1,2 0,3 4,87 0,77 1,7 0,04 0,35 0,07 1,30 100,5 7203040 1714570 70,9 11,8 6,3 0,7 2,74 1,37 2,1 0,10 0,30 0,07 3,75 100,1 27 43 7205630 1717520 71,0 15,4 1,6 0,8 5,57 1,54 2,3 0,04 0,55 0,14 1,10 100,1 7204740 1716420 69,5 13,3 4,1 1,2 3,31 1,51 3,8 0,09 0,72 0,19 1,65 99,4 12 72 7206500 1717600 61,7 19,8 3,3 1,5 3,89 2,95 5,3 0,13 0,59 0,14 1,30 100,6 7206120 1717500 68,6 14,3 2,5 1,1 2,40 4,36 4,6 0,14 0,49 0,13 0,75 99,3 13 72 7206720 1716990 71,2 13,0 3,0 1,4 1,96 3,74 4,1 0,18 0,37 0,06 1,30 100,4 5 105 11 6 1,0 5 5 10 46 55 5 11 5 73 7 9 8 6 8 8 190 436 32 11,6 266 3,0 12 3,3 1,9 13 127 20,0 41 20 3,6 0,9 0,5 1,9 0,25 302 12 7,7 161 3,0 11 2,7 1,8 17 164 24,0 46 22 3,7 0,6 0,5 2,2 0,36 XRF/NA XRF/NA Dacite porphyry Dacite porphyry silicified 617 26 8,6 305 3,0 9 3,8 1,7 18 137 27,0 48 22 3,7 1,4 0,5 1,9 0,28 Volcanic sandstone 245 33 16,2 182 3,0 10 3,8 2,1 13 137 22,0 44 21 3,9 1,3 0,5 1,9 0,28 456 26 18,4 195 2,0 9 1,7 1,1 12 105 13,0 27 13 3,3 0,7 0,6 1,4 0,15 1430 43 18,5 307 5,0 13 4,9 1,3 28 192 36,0 68 33 5,7 1,1 0,7 2,9 950 58 13,3 218 3,0 10 3,3 1,8 17 131 21,0 40 20 3,7 1,0 0,5 1,8 0,25 XRF/NA XRF/NA XRF/NA XRF/NA Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry 731 50 14,0 102 3,0 12 3,9 2,0 24 153 25,0 49 20 4,8 1,5 0,6 2,5 0,44 Ryolite 92020 30 176,3-176,7 -192 86 124 7204106 1716635 63,5 19,1 2,4 2,1 4,86 2,66 3,1 0,03 0,71 0,16 1,60 100,2 18 87 92021 30 192,8-193,0 -184 82 138 7204114 1716630 68,7 16,3 2,4 1,5 5,50 1,56 2,2 0,03 0,61 0,15 0,80 99,8 17 87 92022 30 253,9-254,2 -154 66 188 7204144 1716615 61,1 15,4 6,6 3,4 2,14 1,43 8,5 0,10 0,72 0,28 0,75 100,5 31 96 92023 30 289,9-290,1 -136 58 218 7204163 1716606 52,8 23,3 5,8 0,1 5,13 2,34 5,4 0,16 1,18 0,26 1,20 97,7 27 320 20 8 92024 30 244,9-245,2 -159 69 181 7204139 1716617 66,4 13,6 6,1 0,9 3,08 1,82 4,1 0,10 0,52 0,14 2,80 99,6 16 58 16 6 7 23 11 180 24 80 11 5 150 7205290 1715340 71,0 12,2 5,0 2,4 0,63 2,39 3,8 0,13 0,44 0,10 1,20 99,3 5 49 6 2 1,1 6 5 12 14 12 5 120 423 36 19,4 281 4,0 12 2,7 2,7 21 183 26,0 54 28 5,4 2,2 0,7 2,1 283 29 15,2 247 3,0 11 3,3 1,8 14 158 22,0 44 23 4,5 1,2 0,6 1,6 0,23 344 25 24,5 414 2,0 10 1,9 0,7 18 122 18,0 39 20 4,0 1,6 0,5 2,1 0,30 531 45 32,8 390 3,0 11 4,4 1,3 25 185 25,0 51 28 5,6 1,8 0,7 3,3 0,43 391 30 13,5 193 2,0 9 2,5 1,1 16 135 20,0 38 20 3,7 1,1 0,5 1,9 0,30 391 46 11,0 104 5,0 9 5,0 1,8 30 173 27,0 54 20 5,1 0,9 0,6 2,8 0,39 XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry actinolite biotiteactinolite 118 92025 Ryolite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 123 Appendix B, cont. 92026 92027 92028 92029 92033 Gillervattnet 2 217,0 -5096 -1634 188 7204893 1714480 68,7 13,6 2,5 1,2 3,86 1,86 4,1 0,12 0,45 0,09 1,30 97,9 1 92 3 2 92034 69 163,3 -431 35 250 7203906 1716576 71,9 14,6 2,1 1,3 6,48 0,58 2,2 0,04 0,54 0,15 0,85 100,7 1 82 5 12 93035 69 263,5 -531 39 250 7203806 1716581 57,1 21,3 6,1 1,9 4,17 1,74 5,2 0,08 0,44 0,10 1,00 99,1 8 74 11 30 931001 24 54,8-55,0 -103 90 66 7204233 1716624 46,5 14,6 8,0 13,5 0,40 0,56 11,9 0,20 0,84 0,18 3,65 100,4 1 119 3 7 931002 24 74,9-75,1 -95 87 84 7204241 1716621 53,7 17,8 0,5 9,3 0,69 2,17 9,2 0,07 1,21 0,25 5,80 100,6 4 375 47 35 931003 24 77,8-78,1 -94 87 87 7204242 1716621 41,4 16,0 0,6 8,3 0,84 1,76 19,4 0,09 1,12 0,22 10,20 99,9 269 301 59 130 931004 24 114,0-114,3 -79 83 119 7204257 1716616 54,0 12,5 1,5 14,2 0,12 1,43 9,9 0,20 0,50 0,23 4,95 99,6 328 518 84 240 931005 428 13,0-13,2 -119 7 170 7204219 1716541 64,9 14,2 0,2 8,9 0,19 1,97 4,7 0,05 0,48 0,15 4,55 100,3 1 117 13 1 931006 428 22,9-23,2 -129 7 170 7204209 1716541 66,4 13,9 4,1 3,6 0,52 2,75 6,1 0,08 0,74 0,22 1,70 100,2 23 69 9 3 931007 428 28,8-29,1 -135 7 170 7204203 1716541 54,6 15,9 6,9 5,5 2,27 2,54 10,4 0,17 0,88 0,22 0,65 100,0 17 96 2 2 7205140 1715670 73,0 12,7 2,4 1,8 2,80 2,12 3,7 0,08 0,28 0,07 1,20 100,1 7205150 1715730 71,9 13,0 2,6 1,8 1,85 2,75 3,4 0,12 0,30 0,07 1,15 99,0 7204650 1716330 75,3 11,4 3,0 1,7 0,24 3,15 2,9 0,11 0,25 0,06 1,30 99,4 68 58 149 11 6 7204550 1714800 63,3 14,3 2,9 3,6 2,23 2,37 8,3 0,08 0,82 0,25 1,70 99,8 10 96 5 1 4 5 5 16 6 5 10 12 5 20 10 10 20 26 3 26 22 4 26 41 1 33 22 86 700 12 7 54 10 5 70 22 3 43 387 36 11,0 65 5,0 12 4,1 2,0 24 171 26 52 26 4,9 0,8 0,6 2,9 0,35 506 43 11,0 79 5,0 11 4,1 2,2 19 178 28,0 53 27 4,9 1,1 0,8 2,7 0,34 385 30 9,3 65 5,0 10 3,3 2,3 21 158 24,0 50 25 4,4 1,4 0,6 2,3 0,34 664 30 21,0 82 1,0 10 2,0 0,9 14 124 18,0 39 20 4,0 1,2 0,5 1,8 0,41 508 32 16,0 81 3,0 11 4,1 1,6 24 136 22,0 44 21 4,5 1,4 0,6 2,4 153 13 14,0 214 3,0 10 3,4 1,9 21 136 17,0 38 21 5,1 1,4 0,8 2,5 0,35 393 43 15,0 544 2,0 9 3,4 1,4 15 122 16,0 31 16 2,9 0,9 0,4 1,3 0,23 199 17 31,8 66 1,6 6 1,5 5,8 19 83 16,7 36 19 4,3 1,2 0,5 1,6 0,24 256 32 39,9 45 2,7 8 2,0 2,1 25 103 0,38 23 13 2,9 1,0 0,5 1,7 0,24 253 29 30,2 56 2,1 7 1,8 2,0 10 95 14,5 32 19 4,3 1,5 0,6 1,6 0,23 187 25 25,8 1 2,5 10 4,4 3,8 10 87 14,5 32 16 3,5 1,5 0,4 0,6 0,09 214 29 19,3 15 3,2 9 3,6 3,2 21 127 20,1 42 21 4,1 1,2 0,5 2,0 0,32 582 49 21,3 90 2,2 6 2,1 1,7 19 107 17,1 36 19 4,1 1,3 0,5 1,8 0,27 947 52 31,1 248 2,5 3 1,7 2,1 19 102 14,5 31 16 3,5 1,1 0,5 1,8 0,26 XRAL92/XRF/NA A XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA Quartz porphyry Quartz porphyry Quartz porphyry Andesite dyke Dacite volcaniclastic Dacite porphyry Volcanic flow flow in sediment Andesite Andesite Andesite Ultramafic dyke in ore Biotite sand/ siltstone Biotite sand/ siltstone Biotite sand/ siltstone chlorite chloritepyrite altered biotitechlorite sulphides, fractures 124 A. HALLBERG Preserved actinolite Appendix B, cont. 931008 428 129,0-129,4 -235 7 170 7204103 1716543 69,4 14,6 3,6 1,2 4,47 1,77 4,2 0,10 0,48 0,15 0,50 100,4 17 60 8 12 931009 428 156,2-156,6 -262 7 170 7204075 1716544 71,2 14,9 2,6 0,8 5,40 1,77 2,6 0,05 0,50 0,16 0,60 100,5 5 75 18 23 931010 428 168,0-168,3 -274 7 170 7204064 1716544 47,5 23,6 6,2 5,3 1,43 4,97 7,4 0,13 1,28 0,35 2,30 100,5 33 111 17 60 931011 428 172,7-172,9 -279 7 170 7204059 1716544 72,0 14,5 1,1 1,2 0,65 4,29 3,7 0,03 0,68 0,24 2,20 100,6 12 134 13 1400 931012 428 194,6-194,8 -301 7 170 7204037 1716545 69,4 14,9 1,4 0,8 4,97 1,83 4,8 0,03 0,50 0,16 1,40 100,2 22 49 7 92 931013 428 200,0-200,3 -306 7 170 7204032 1716545 61,4 15,5 2,4 2,5 4,14 2,02 9,2 0,05 0,60 0,14 2,25 100,2 60 63 13 3 931014 428 204,9-205,2 -311 7 170 7204027 1716545 68,6 12,9 3,7 1,9 3,30 1,09 6,9 0,05 0,49 0,13 1,30 100,3 42 56 10 5 931015 428 224,0-224,3 -330 7 170 7204008 1716545 72,8 11,4 2,9 2,9 1,90 0,55 5,2 0,05 0,38 0,12 1,85 100,0 7 69 10 34 931016 320 64,4-64,7 -116 48 570 7204221 1716582 64,0 15,2 0,4 7,9 0,23 2,20 5,2 0,04 0,52 0,16 4,40 100,2 120 98 1 1 931017 320 76,3-76,5 -127 47 570 7204210 1716582 67,3 14,5 4,0 2,4 2,25 2,86 5,4 0,09 0,56 0,15 0,65 100,1 1 82 11 2 931018 320 91,2-91,4 -142 47 570 7204195 1716582 50,1 6,6 10,1 19,0 0,24 1,71 10,2 0,21 0,30 0,09 1,30 99,8 40 98 5 26 931019 30 397,9-398,0 -74 36 305 7204225 1716582 67,0 14,4 0,3 6,2 0,32 2,16 5,7 0,05 0,58 0,15 3,80 100,7 1 208 11 1 931020 583 114,6-114,9 -114 733 410 7204210 1717267 47,6 16,0 10,7 8,8 1,04 1,90 12,2 0,26 0,70 0,11 0,85 100,2 17 93 2 5 931021 583 120,4-120,7 -112 738 410 7204212 1717272 48,2 18,3 4,0 8,5 0,48 3,09 13,5 0,17 0,85 0,16 3,10 100,4 49 163 4 42 10 5 82 6 1 130 11 8 40 12 5 85 6 4 84 14 8 88 10 12 110 18 8 130 13 5 33 8 3 92 72 438 2000 11 10 64 29 3 30 36 9 36 365 28 16,5 176 3,2 9 3,9 2,9 25 150 32,7 64 29 5,4 1,1 0,5 2,1 0,35 395 23 19,7 193 3,9 7 3,4 5,2 21 158 24,1 50 25 4,9 2,0 0,6 2,0 0,30 778 81 41,6 177 4,5 7 3,2 3,0 31 168 42,1 80 36 6,7 2,8 0,7 2,9 0,45 598 48 15,3 57 3,1 6 1,9 1,9 23 105 12,2 26 15 3,7 1,9 0,5 1,6 0,23 609 21 13,8 186 3,5 9 4,0 5,2 21 153 22,5 48 22 4,9 1,2 0,6 1,9 0,27 677 30 19,3 294 4,2 11 3,6 24,2 11 156 25,5 53 23 4,7 1,4 0,4 1,2 441 19 15,1 333 3,1 8 3,8 10,9 18 140 23,9 50 25 5,0 1,6 0,5 1,3 0,19 144 6 14,5 285 3,1 7 2,9 4,2 16 134 18,6 39 19 3,8 1,2 0,5 1,7 0,25 309 27 16,6 20 4,7 10 3,6 4,1 24 152 21,2 44 21 4,4 1,0 0,6 2,1 0,32 555 38 15,8 147 3,7 10 3,9 3,1 21 151 23,1 46 22 4,2 1,1 0,5 2,1 0,35 102 32 33,9 22 0,6 4 1,6 1,4 7 45 6,6 16 7 1,8 0,8 0,3 0,7 0,12 269 27 19,1 23 2,6 8 3,7 3,7 28 127 23,6 50 24 4,8 1,1 0,7 2,5 0,36 589 26 46,5 168 0,5 2 0,4 12,4 10 45 6,9 16 10 2,6 1,0 0,4 1,5 0,23 868 47 48,2 143 1,0 5 0,5 1,2 11 48 7,6 20 10 2,4 0,9 0,3 0,9 0,13 XRAL92/XRF/NA A XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Volcanic sandstone Dacite Dacite Ultramafic dyke in dacite Andesite Biotite sandstone Biotite sandstone Preserved Preserved, bleached chloritepyrite sericitepyrite Preserved, bleached chloritepyrite Preserved, biotitechlorite akt biotitechlorite ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 125 Appendix B, cont. 126 931022 647 221,1-221,5 -239 634 618 7204086 1717170 67,4 14,1 4,0 2,1 1,41 2,88 4,5 0,09 0,40 0,13 0,90 98,0 9 71 7 2 931023 647 285,6-286,0 -255 649 679 7204071 1717186 68,4 14,4 5,7 1,6 0,75 2,66 5,5 0,16 0,47 0,12 0,55 100,2 7 85 4 1 931024 647 388,1-388,5 -279 674 775 7204045 1717211 60,8 11,8 1,5 2,6 0,24 1,46 18,6 0,12 0,52 0,11 2,40 100,1 77 88 1 170 931025 647 418,3-418,6 -287 681 803 7204038 1717219 59,9 16,0 0,4 2,6 0,16 3,39 13,6 0,26 0,60 0,14 3,05 100,1 145 519 54 810 931026 647 461,5-461,8 -297 692 844 7204027 1717230 62,6 13,7 6,2 2,1 0,42 4,84 7,4 0,86 0,42 0,11 1,45 100,1 5 79 14 17 941001 Strömfors 6 578,0 -4111 2600 501 7205934 1718766 70,4 15,4 4,4 1,6 3,08 1,09 2,6 0,04 0,63 0,19 0,55 99,9 8 4 81 8 7 130 17 7 66 12 4 60 8 8 65 5 61 69 600 2300 59 300 1800 73 600 2200 67 700 2000 767 41 14,1 188 3,7 7 4,1 4,3 17 136 23,2 48 21 4,3 1,0 0,6 2,0 0,31 578 46 19,2 108 3,7 10 3,5 3,3 20 128 23,1 47 21 4,4 1,6 0,5 2,2 0,36 204 52 16,6 20 3,3 6 2,9 2,7 25 101 15,2 33 17 3,6 1,1 0,6 2,4 0,37 384 59 22,5 16 3,1 9 2,9 3,1 23 110 18,4 38 20 4,0 0,7 0,5 2,1 0,32 1040 76 18,2 121 2,9 7 3,8 3,1 24 117 20,8 45 20 4,3 1,4 0,6 2,0 0,31 263 23 19,2 328 3,0 25,5 55 1,2 23,8 68 0,7 12,1 48 0,8 20,9 38 0,6 25,4 547 1,6 10 29,2 109 1,9 2,4 1,8 1,4 1,5 1,7 1,2 1,7 1,0 42 12,4 26 12 2,9 1,0 0,4 1,1 0,15 29 6,3 15 6 1,5 0,5 0,3 0,9 0,13 27 7,1 15 7 1,6 0,5 0,3 1,1 0,14 18 5,9 15 8 1,6 0,7 0,3 0,9 0,11 3,9 2,3 17 101 16,5 37 19 4,5 0,9 0,4 1,5 0,23 1,8 1,0 17 75 12,7 26 13 2,8 0,9 0,4 1,5 0,23 2,0 1,1 25 109 14,4 32 19 5,4 1,9 0,8 2,2 0,33 XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA XRF/NA Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Dacite porphyry Ultramafic dyke in sediment Ultramafic dyke in sediment Ultramafic dyke in dacite Andesite Andesite Andesite breccia? breccia? chloritegarnet chloritegarnet chloritegarnet A. HALLBERG 50 140 942251 30 334,0-334,7 -112 49 254 7204187 1716596 61,3 16,2 2,6 1,6 0,28 4,99 8,9 0,10 0,86 0,20 3,05 100,0 194 96 8 14 14 9 1640 85 314 82 55 103 3,2 2,0 23 122 17,2 38 18 4,3 1,3 0,6 2,5 0,39 941002 Strömfors 6 514,0 -4143 2600 445 7205902 1718764 45,8 9,2 9,3 19,8 0,30 0,02 11,2 0,17 0,52 0,13 3,25 99,6 941003 Strömfors 6 434,0 -4183 2600 376 7205862 1718762 47,4 8,3 8,4 21,1 0,23 0,03 10,6 0,23 0,38 0,10 3,35 100,1 941004 Strömfors 6 379,0 -4211 2600 328 7205835 1718760 46,2 8,3 8,2 21,8 0,14 0,12 10,8 0,20 0,34 0,11 3,75 99,9 941005 69 158,0 -426 35 250 7203911 1716576 48,1 7,5 9,9 21,0 0,22 0,03 9,6 0,20 0,30 0,13 2,70 99,8 941006 Strömfors 6 529,0 -4136 2600 458 7205910 1718765 49,7 12,9 10,2 13,2 1,37 0,10 9,7 0,16 0,67 0,20 1,75 99,9 37 300 1500 941007 24 58,3 -102 89 69 7204234 1716623 54,6 15,0 1,8 9,9 1,39 0,38 10,6 0,08 1,00 0,20 5,20 100,2 16 20 54 UM in volcanic/sediment contact UM in volcanic/sediment contact 942252 24 51,9 -105 90 63 7204232 1716624 49,8 16,3 6,9 9,3 0,53 3,35 10,2 0,11 1,01 0,20 1,50 99,2 15 112 19 94 biotite-actinolite Appendix B, cont. 942253 24 67,3 -98 88 77 7204238 1716622 56,8 14,7 0,4 6,8 0,43 2,19 10,9 0,04 0,94 0,21 6,80 100,2 37 287 942254 24 85,3 -91 86 93 7204245 1716620 83,5 6,0 0,2 0,3 0,41 1,52 5,0 0,01 0,23 0,11 2,60 99,8 1170 4240 942255 30 106,6 -224 101 64 7204074 1716650 55,8 11,4 10,2 4,1 0,16 2,87 9,5 1,03 0,57 0,07 2,30 98,0 95 121 942256 30 85,7 -233 104 46 7204065 1716654 41,9 20,8 2,4 10,9 0,51 3,77 10,5 0,38 1,02 0,14 5,80 98,1 1160 2090 95 6660 40 583 951501 99 23,1-23,3 -57 18 410 7204280 1716551 55,3 20,8 0,3 7,2 0,48 3,51 6,1 0,03 0,64 4,95 1 58 7 6 951502 69 42,4-42,6 -310 31 250 7204027 1716569 66,5 17,7 0,5 1,9 0,33 5,75 2,1 0,02 0,61 0,10 3,20 98,7 1 106 28 17 951503 23 44,1-44,3 951505 343 8,6-8,8 951504 97 69,85-70,00 90 72 14 1,61 1,89 2,31 2,57 3,34 0,02 0,411 0,01 1,55 99,711 16 66 6 5 51,9 15,9 0,28 12,5 0,16 0,73 10,5 0,06 0,776 0,14 5,95 98,896 1 75 12 24 1000 100 1400 70,8 12,3 0,1 5,38 0,21 1,66 4,98 0,13 0,251 3,4 99,211 1 134 19 12 951506 4 48,6-48,7 -170 -405 42 7204160 1716131 41,4 14,9 0,8 5,2 0,48 2,12 22,0 0,05 1,04 0,01 12,30 100,2 34 144 27 74 951507 4 56,8-57,0 -166 -406 49 7204164 1716130 36,7 22,6 1,2 1,1 0,91 4,87 19,4 0,01 1,54 0,27 11,70 100,3 16 47 45 69 951508 4 64,8-65,0 -162 -407 56 7204168 1716129 66,1 13,8 0,3 2,1 0,32 2,03 11,4 0,06 0,84 0,17 2,90 100,0 323 204 18 12 100 951509 4 80,0-80,2 -155 -409 69 7204175 1716126 66,5 14,4 0,3 3,3 0,32 2,38 7,8 0,07 0,72 0,20 3,35 99,4 41 59 6 5 951510 10 34,9-35,0 -61 243 35 7204272 1716776 65,8 15,2 0,6 3,9 1,11 2,05 6,6 0,04 0,59 0,15 3,90 99,9 38 130 47 25 100 219 40 171 43 1010 52 276 81 867 55 736 76 595 43 151 17 442 29 319 38 740 86 388 31 669 36 288 43 49 27 200 49 25 49 219 11 13 63 78 18 15 126 1,3 0,8 24 88 13,2 29 17 4,4 1,2 0,7 1,9 0,30 2 76 9 26 8 44 XRF/NA XRF/NA Andesite Quartz porphyry Biotite siltstone Biotite siltstone chlorite sericitepyrite chl/garnet chl/garnet 5,9 3,7 37 214 31,4 67 34 8,2 1,2 1,1 3,7 0,55 Mafic rock 24 167 Dacite 5,3 3 27 200 22 50,4 25,1 6,2 1,05 0,8 2,9 0,39 7 85 2,2 1,2 22 116 17,5 37 19 4,9 0,9 0,7 2,2 0,32 27 170 13 86 24 118 17 82 25 138 Dacite Mafic dyke volcaniclastic Quartz porphyry Sericitepyrite rock Sericitepyrite rock Sericitepyrite rock Volcaniclastic rock Andesite quartz phenocrysts biotitechlorite banded banded banded quartz phenocrysts altered ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 127 Appendix B, cont. 951511 10 53,5-53,7 -51 243 51 7204282 1716776 50,2 17,0 2,0 6,4 3,11 1,23 14,3 0,07 0,99 0,12 4,60 100,0 132 247 34 22 951512 18 50,0-51,0 -38 200 64 7204295 1716733 58,2 18,1 0,8 3,4 3,50 2,34 8,9 0,03 0,74 0,17 3,95 100,1 148 521 177 67 951513 20 93,8-94,0 -71 -103 101 7204265 1716431 48,4 16,2 6,4 9,1 1,03 0,39 12,1 0,12 1,05 0,15 3,20 98,1 54 111 1 8 951514 22 65,2-65,4 -58 -220 66 7204276 1716313 56,5 14,8 1,6 6,2 1,45 1,65 11,3 0,07 0,98 0,15 4,20 98,9 76 534 228 79 100 128 951515 679 484,0-484,2 -7344 -1435 419 7202636 1714542 71,1 14,5 2,2 1,9 0,88 4,38 3,0 0,02 0,43 0,09 1,25 99,7 18 61 1 7 951516 679 468,9-469,3 -7349 -1430 406 7202631 1714548 66,7 15,3 0,5 4,0 0,20 4,97 5,1 0,02 0,48 0,10 2,60 99,9 49 117 15 7 100 300 951517 196 156,8-157,0 -341 644 410 7203984 1717183 53,5 12,1 0,5 9,1 0,03 0,17 18,0 0,79 0,72 0,08 4,80 99,7 25 186 1 2540 341 28 243 35 169 8 473 37 871 66 666 93 125 7 168 301 139 63 110 33 7 21 193 3 33 Pumice tuff Pumice tuff Volcaniclastic rock quartz phenocrysts quartz phenocrysts garnetchlorite 11 42 23 169 Andesite Andesite altered altered A. HALLBERG 1,4 0,9 16 84 9,9 23 13 3,3 1,1 0,5 1,5 0,23 Andesite 5 90 Andesite 4,9 2,6 27 186 26,8 57 28 6,3 1,1 0,8 2,7 0,44 Appendix C sample # Bo161 Bo39 Bo686-436 Bo686-450 Bo686-483 Bol679 Bol679 Bol679 Bol679 bh core local n local e z N (RT90) E (RT90) SiO2 Al2O3 CaO MgO Na2O K2O Fe2O3 MnO TiO2 P2O5 LOI SUM Cu Zn Pb Cd Au Ag As Sb Bi Br Co Ni Cr Mo V Ba Cs Rb Sc Sr Be Hf Sn Ta Nb Th U Y Zr La Ce Nd Sm Eu Tb Yb Lu 161 27 164 <2 10 18 <2 31 174 Ref. ref 4 4 method-lab. XRFF,ICP,NA XRAL-93-95/XRF Rock Andesite, intrusive, feldspar porphyritic Rhyolite, feldspar porphyritic MHA930026 6 MHA930141 1 OIL940007 OIL971001A A 678 686 450,0 -4988 814 369 7204950 1716931 54,0 20,5 6,0 1,7 5,00 1,80 5,9 0,10 1,29 0,30 1,60 98,2 11 109 7 686 483,0 -4978 798 396 7204959 1716915 67,6 15,1 2,4 2,1 3,60 1,50 5,2 0,10 0,52 0,10 1,60 99,8 2 76 13 679 679 679 -7500 -1250 -7500 -1250 -7500 -1250 -7500 -1250 dagen 7209260 1718200 73,2 13,2 3,1 0,8 3,81 1,25 3,1 0,09 0,19 0,05 1,25 100,0 <2 71 <2 686 436,0 -4992 821 357 7204946 1716937 63,9 15,6 5,5 0,9 4,40 1,40 4,5 0,10 0,81 0,20 1,50 98,8 4 75 3 679 -99 85 250 7204237 1716619 65,3 15,5 5,2 2,3 2,30 2,16 5,8 0,11 0,52 0,15 1,00 100,3 7 74 26 7202469 1714718 66,4 15,0 2,8 2,2 4,24 0,92 6,4 0,06 0,60 0,14 1,30 100,0 15 165 35 7202469 1714718 70,6 13,9 3,3 2,7 2,42 2,10 4,3 0,08 0,51 0,13 0,55 100,5 4 79 <2 7202469 1714718 69,4 17,1 2,5 0,5 6,27 1,11 1,9 0,01 0,64 0,17 0,65 100,3 18 86 25 7202469 1714718 71,8 13,9 2,9 2,7 2,14 2,35 3,5 0,04 0,43 0,08 0,35 100,0 <2 66 4 7202420 1713250 65,3 15,5 5,2 2,3 2,30 2,16 5,8 0,11 0,52 0,15 1,00 100,3 7 74 26 7208370 1718420 63,4 15,7 3,4 1,7 3,36 1,90 6,6 0,08 0,67 0,17 1,20 98,2 7202300 1711850 56,0 16,6 7,0 3,9 3,40 0,23 10,5 0,14 0,91 0,17 1,20 100,0 130 <50 7203064 1715814 67,7 13,2 4,3 1,3 3,59 0,85 5,5 0,11 0,42 0,12 2,60 99,7 38 263 <3 6 41 6 79 14 3 <5 <5 <2 0,5 170 <5 <2 1,5 4 <2 3 <2 <1 22 <1 39 3 <2 10 <5 20 <5 735 <3 56 17,8 303 80 <3 12,0 31,3 287 5,0 <1 <1 9 2,3 1,3 29,0 147 13,0 31,0 10,0 3,1 1,3 <0,5 2,4 0,38 <1 3 <0,5 <0,5 15,0 80 7,0 12,0 <10 2 1 <0,5 1,5 0,25 13,7 20,1 237 <0,5 5,3 1,16 0,56 4 3,3 2,3 20,7 105 17,6 35,9 18,6 3,65 0,95 0,69 2,36 0,50 34 57 2 15,1 205 467 310 358 444 426 276 293 364 281 467 34 25 22 29 23 18 35 17 36 34 250 116 244 386 371 311 256 252 253 250 <2 10 5 <2 21 162 <2 10 5 <2 25 182 4 4 4 5 5 5 8 Alter., struct., minerali-sation 10 7 9 8 <1 121 7 109 4 138 19 126 <2 9 7 <2 22 139 4 4 4 4 4 Andesite basalt Andesitebasalt Dacite, feldspar porphyritic fine grained, fine grained, amygdules amygdules 8 27 164 XRF, ICP-ms XRF, ICP-ms XRF, ICP-ms XRF, ICP-ms XRAL-9395/XRF XRAL96/XRF+IN AA XRAL96/XRF+IN AA SGAB-97/ICPAES,MS Mafic mass flow Dacite porphyry Dacite porphyry Mass flow Dacite, intrusive, feldspar porphyritic Feldspar porphyritic lava Andesite Volcanic mass flow ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 129 Appendix C, cont. B-01 B-04 B-06 B-07 B-08 B-20 B-22 B-23 B-25 B-27 B-30 B-31 B-32 7206550 1717210 73,4 12,2 2,3 1,6 0,49 3,66 4,4 0,07 0,33 0,03 1,38 99,9 5 84 16 7207050 1716730 66,1 15,3 2,1 1,5 1,44 6,80 4,4 0,10 0,38 0,02 1,29 99,5 4 77 26 7207050 1716730 77,7 9,5 2,2 0,9 2,39 2,61 2,6 0,05 0,24 0,02 2,65 100,8 5 58 14 7207100 1716690 70,3 10,9 2,8 1,6 0,27 5,86 4,1 0,15 0,29 0,01 3,74 100,1 4 63 25 7207250 1716480 72,6 12,8 3,0 1,1 1,84 3,27 3,2 0,07 0,37 0,02 1,02 99,2 4 56 11 7205980 1716600 73,1 11,9 4,1 1,6 0,54 3,02 4,4 0,17 0,39 7206380 1715590 74,6 12,0 0,7 1,1 1,64 3,76 3,6 0,11 0,31 0,02 1,42 99,2 4 59 11 7205400 1717120 48,2 11,7 11,8 10,7 1,21 0,43 12,4 0,26 0,66 0,01 3,56 101,0 3 173 15 7205450 1717130 67,7 16,4 3,0 1,1 4,23 1,92 2,7 0,07 0,72 0,25 1,30 99,4 16 43 19 7204550 1714770 70,6 12,8 3,9 3,0 0,36 3,58 4,2 0,04 0,36 1,13 100,3 6 219 19 7206360 1716430 76,3 10,6 1,4 2,7 0,91 2,64 3,5 0,08 0,26 0,09 1,70 100,0 22 112 52 1,16 99,9 5 75 16 7204600 1714850 77,4 10,1 2,7 1,6 0,75 3,22 3,0 0,05 0,20 0,07 0,75 99,7 5 33 17 7204600 1714850 66,0 15,4 1,7 2,3 0,61 6,44 4,3 0,05 0,37 0,07 1,81 99,0 3 73 22 31 5 20 9 3 4 33 3 5 14 4 5 32 10 16 26 10 15 35 15 5 35 19 18 357 1679 6 10 15 6 14 12 6 16 12 6 77 641 51 803 15 322 35 890 76 437 75 1209 25 493 66 1551 260 121 64 353 8 224 18 357 29 541 78 16 140 80 19 100 36 13 90 80 14 135 43 16 102 36 15 134 10 13 79 65 14 60 5 35 137 8 19 261 67 14 91 12 95 79 12 78 14 15 11 12 12 10 11 29 148 26,21 47,64 24,81 5,35 1,09 32 182 27,59 56,73 27,22 6,12 1,23 21 112 27 133 22 127 22,26 47,14 21,11 4,68 1,10 22 107 20,98 40,54 19,35 4,43 1,14 13 125 26 152 17,84 38,61 18,44 4,39 0,98 13 56 9,44 22,55 12,31 3,27 0,87 20 124 19,97 41,44 20,24 4,48 1,24 19 116 15 88 22 134 2,72 3,10 2,20 2,21 2,62 1,11 0,19 1,83 6 6 6 6 6 ICP-Nan 6 6 6 ICP-Nan 6 ICP-Nan 6 ICP-Nan 6 ICP-Nan 6 ICP-Nan 6 Ryolite Ryolite Ryolite Ryolite Ryolite Dacite porphyry, Ryolite Ryolite Ultramafic dyke in dacite Dacite porphyry Volcaniclastic rock Volcaniclastic rock Volcaniclastic rock volcaniclastic 130 A. HALLBERG Appendix C, cont. B-33 B-34 B-35 7204620 1714900 62,5 15,5 3,6 2,5 2,25 3,07 8,6 0,09 0,66 0,20 2,11 101,0 11 97 11 7203950 1715130 58,2 14,8 7,7 2,4 3,89 1,49 8,1 0,15 0,65 0,16 3,73 101,1 28 100 15 7203550 1714620 67,1 12,9 2,8 2,4 3,70 0,96 8,0 0,11 0,73 0,23 1,30 100,2 22 110 12 22 21 5 11 34 12 11 59 384 132 344 58 148 21 23 110 25 27 310 8 28 324 20 114 18 92 27 129 18,26 40,91 21,68 5,18 1,63 2,43 6 ICP-Nan. 6 ICP-Nan 6 ICP-Nan Andesite dyke Dacite porphyry Dacite porphyry actinolite? actinolite References (6) Vivallo (1987) (4) Allen et al. (1996) (5) Lundström & Antal (2000) ROCK CLASSIFICATION, MAGMATIC AFFINITY, A HYDROTHERMAL ALTERATION AT BOLIDEN, SKELLEFTE DISTRICT, SWEDEN ... 131 A review of the Fe oxide deposits of Bergslagen, Sweden and their connection to Au mineralisation Magnus Ripa Ripa, M,. 2001: A review of the Fe oxide deposits of Bergslagen, Sweden and their connection to Au mineralisation. In Weihed, P. (ed.): Economic geology research. Vol. 1, 1999–2000. Uppsala 2001. Sveriges geologiska undersökning C 833, pp. 132–136. ISBN 91-7158-665-2. This presentation results from a review of a selection of prospecting reports and published papers on gold in the iron ores of Bergslagen, Sweden. It will describe the different types of iron ore deposits, their geological and volcanic setting, and their relation to gold mineralisation. The Bergslagen region has had a long history of mining base and precious metals (Cu, Zn, Ag), as well as iron. The country rocks to the ore deposits belong to a Palaeoproterozoic, metamorphosed volcano-sedimentary succession (the ”leptite formation”). Most mineral occurrences are hosted by skarn-altered carbonate rocks interlayered with volcanogenic ash-siltstone strata. There is a genetical relationship between more or less coeval subvolcanic intrusions emplaced into the host rocks and mineralisation. The supracrustals were also intruded by early-orogenic ultramafic to granitic plutons, mafic dykes, late-orogenic granites, post-orogenic plutons, and later dolerites. The supracrustal rocks, the early-orogenic plutonic rocks, and the mafic dykes were deformed and metamorphosed at varying grades during the Svecokarelian orogeny. In at least 39 iron ore deposits in the Bergslagen area gold occurrences have been noted. Gold occurs only in a few geographically restricted areas, which are spatially close to some of the younger plutonic rocks. From this preliminary study it seems certain that most, if not all, gold in the area formed in relation to regional Svecokarelian metamorphism and coeval plutonic activity. The connection to Fe mineralisation is coincidental, and is probably due to the fact that the host rocks were favourable horizons for both mineralising events. Magnus Ripa, Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden. e-mail [email protected] Introduction This presentation results from an initial study on the geologically interesting and genetically diversified iron ores of the intensely mineralised ore district of Bergslagen, south central Sweden. The study has this far involved reviewing of a selection of prospecting reports available at the SGU Mineral Information Office at Malå and published papers. The presentation will describe the different types of iron ore deposits, their geological and volcanic setting, and their relation to gold mineralisation. The Bergslagen region has had a long history, since medieval days, of mining base and precious metals (Cu, 132 M. RIPA Zn, Ag), as well as iron. During the last century, tungsten has also been mined intermittently. Today, three mines for base metals (mainly Zn) are in operation in the area. The total tonnage of the region is dominated by iron ore production, which amounts to more than 420 million tonnes of ore. Regional geology and volcanic setting of the Bergslagen iron ores The country rocks (Fig. 1) to the Bergslagen iron ore deposits belong to a Palaeoproterozoic, c. 1900 Ma old (Lundström et al. 1998), metamorphosed volcano-sedimentary succession, informally known as the ”leptite formation” (e.g. Magnusson 1936). The metasupracrustal rocks consist dominantly of rhyolitic volcanic, subvolcanic, and volcaniclastic rocks deposited in a submarine environment (Oen et al. 1982, Van der Welden et al. 1982, Lundström 1987, Allen et al. 1996). Subordinate intermediate and mafic volcanic rocks together with chemical, epiclastic, and organogenic sedimentary rocks occur at different stratigraphic levels of the volcanic pile. Most mineral occurrences are hosted by skarn-altered carbonate rocks interlayered with volcanogenic ash-siltstone strata interpreted to represent distal volcanic facies (Allen et al. 1996). There is, however, a spatial and probably genetical relationship between more or less coeval subvolcanic intrusions emplaced into the distal facies and mineralisation. In fact, one type (type c below) of iron ore is partly hosted by subvolcanic rocks. Thus, the ores are hosted by distal facies but are genetically related to this somewhat later phase of igneous activity (Allen et al. 1996). Overlying (and locally also underlying) the volcanic rocks are argillites, greywackes, quartzites, and conglomerates (Lundström 1995). The supracrustal rocks were intruded by early-orogenic ultramafic to granitic plutons, mafic dykes, late-orogenic granites, post-orogenic plutons, and later dolerites (Lundqvist 1979). The supracrustal rocks, the early-orogenic plutonic rocks, and the mafic dykes were deformed and metamorphosed at varying grades during the Svecokarelian orogeny (Lundqvist 1979). Mesoproterozoic and Phanerozoic sedimentary rocks overlay the metamorphic rocks in some areas. Falun Garpenberg Stollberg Grängesberg Yxsjöberg Stockholm Zinkgruvan 50 km Au-bearing Fe-oxide deposit Fe-oxide deposit ED EN Young sedimentary rocks SW Diabase Young plutonic rocks (c. 1.85–1.65 Ga and 1.5 Ga) Old plutonic rocks (c. 1.89–1.85 Ga) Svecofennian metasupracrustal rocks Fig. 1. Schematical geological map of the Bergslagen area. Fe oxide deposits (n=5955) and Au-bearing Fe oxide deposits (n=39) are shown. Classification and description of the iron ores Traditionally, the iron ores of the Bergslagen area have, for both geological and metallurgical reasons, been divided into two major groups (Geijer & Magnusson 1944). The discriminant factor in this primary division is the phosphorus (or apatite) content of the ores. One group con- tains (considerably) less than 0.2 wt-% P and the other 0.2 wt-% or more. Based on their style of occurrence, the ores are also subdivided (Geijer & Magnusson 1944): a) banded quartz-hematite(±magnetite) ore This type of deposit occurs as thin, mm to cm scale, alternating layers of quartz and hematite. The layers are parallel to bedding in the surrounding country rocks, and may amount to c. 20 m in thickness. The hematite is A REVIEW OF THE FE OXIDE DEPOSITS OF BERGSLAGEN, SWEDEN AND THEIR CONNECTION TO AU MINERALISATION 133 locally reduced to magnetite. Ore grades are c. 50 % Fe. b) skarn-limestone magnetite ore The gangue of the skarn-iron ores has given rise to the expression skarn, now in international usage in a slightly more restricted way than in the original sense. The ores occur as beds or massive to disseminated replacements in variably skarn-altered carbonate rocks. Iron mineralisation was locally accompanied by manganese and/or base metal enrichment. Ore grades are 43–62 % Fe and 0–5 % Mn. Ore grade base metals occur in several deposits. c) massive apatite-rich magnetite (±hematite) ore The apatite-rich magnetite ores occur as massive replacements in extrusive volcanic host rocks. They are also to some extent hosted by subvolcanic intrusions emplaced into the latter. As the subvolcanic rocks most likely are genetically related to mineralisation, this (Kiruna) type of iron ore can be considered to belong to the group of porphyry-style deposits. A deposit of this type, at Grängesberg (Fig. 1), was the single most productive in the region (c. 150 million tonnes). Grades are 56–63 % Fe and 0.9–1.3 % P. Locally, apatite contents were high enough (27–43 %) to be mined as a by-product. d) disseminated apatite-bearing magnetite ore The apatite-rich magnetite ores grade laterally and stratigraphically into disseminated deposits. Due to the more dispersed character of these, only a few were economic. Type a) and bedded varieties of type b) most likely formed as exhalites interbedded with the surrounding volcanic rocks (Geijer & Magnusson 1944). The other types are interpreted to have formed slightly later during the emplacement of subvolcanic intrusions into the volcanic rocks (Allen et al. 1996), or during the intrusion of syngenetic plutonic rocks (Geijer & Magnusson 1944). It is known that some iron mineralisation occurred in connection with the intrusions of late-orogenic magmas and contemporary deformational events (Bergman et al. 2001). Especially ores of types c) and d) may totally or in part have formed this way. Other types of deposits in the Bergslagen area Base metal and tungsten deposits are also found in the region. The former occur as volcanic-hosted massive sulphide ores or as disseminated to massive sulphide replacements, locally in association with some of the skarn-iron ores. The VHMS-type ores are exemplified by the famous Falun (Fig. 1) Cu-Zn deposit and the still producing Zinkgruvan (Fig. 1) Zn deposit (Zinkgruvan Mining AB). Some sulphide deposits occur in skarn or limestone associations, but without an immediate connection to iron 134 M. RIPA ore. Examples of this type are the two producing Garpenberg mines (Boliden AB; Fig. 1) of mainly zinc. A mined sulphide deposit associated with iron ore is the Stollberg (Fig. 1) Fe-Pb-Zn-Mn(-Ag) ores (Ripa 1988, 1994). The tungsten deposits are also hosted by limestone or skarnbearing rocks, locally overprinting iron ore formations. An example is the Yxsjöberg (Fig. 1) scheelite deposit (Lindroth 1922, Ohlsson 1979). The base metal mineralisation occurred at the same time as some of the skarn-iron ores formed; i.e. more or less coeval with the volcanic rocks (Ripa 1994), whereas the tungsten ores formed c. 100 million years later in relation to, but in a late stage of, Svecokarelian metamorphism (Ohlsson 1979, Romer & Öhlander 1994). Gold in the iron ores Gold occurrences in the Fennoscandian Shield and in the Bergslagen region have been reviewed by Gaal & Sundblad (1990), Bergman (1990), and Bergman & Sundblad (1991). According to those studies, gold may occur in all of the ore types noted above, and do so in at least five iron ore deposits. In these, a positive correlation between Au and Bi is noted. This study shows, that in at least 39 iron ore deposits in the Bergslagen area gold occurrences have been noted (Fig. 1). It must be remembered that in most of these cases the method of gold detection and the amount of gold have not been stated. Furthermore, in deposits where gold has not been noted, it is uncertain whether a proper investigation for gold has been undertaken or not. Gold grades as high as 45 g/ton are locally reported, but tonnage has not been evaluated (Geijer & Magnusson 1944). The gold mineralisation may have occurred at four different stages: 1) synsedimentary with the iron ore-types a) and partly b) above, 2) at the same time as the other iron ores and the sulphide ores, 3) during regional (Svecokarelian) metamorphism (as the tungsten deposits), or 4) during local (Sveconorvegian) deformation at c. 1.0 to 0.9 Ga. If gold mineralisation occurred at stage 1 or 2 (and possibly 3; see above), there should be a genetical connection between iron and gold (and base metal) precipitation, i.e. the ore-forming process was the same for both metals. If gold mineralisation occurred at stage 3 or 4, the connection between iron and gold may be that both formed in a favourable horizon, but the ore-forming processes were different. If valid, the latter implies that gold may be found laterally away from known iron deposits. 50 km Young plutonic rocks Gold occurrences All other rocks Fig. 2. Simplified geological map of the area shown in Figure 1. Younger plutonic rocks are high-lighted in red. Yellow dots indicate all known gold occurrences (n=145) in Bergslagen. According to Gaal & Sundblad (1990) and Bergman & Sundblad (1991) it is likely that gold mineralisation occurred at stages 2 and 3, because it is related to late quartz veins and skarn formations. In this preliminary investigation, a selection (n=59; those containing a thorough geologic description) from 109 available prospecting reports and papers on gold in Bergslagen at the SGU Mineral Information Office in Malå has been studied in order to try to evaluate the relation between gold and other metals. Judging from these reports and papers (including those cited above), it is fairly evident that Au in all cases formed, or at least could have formed, at stage 3 or 4 because it is related to quartz veins and skarn formations, which are at the oldest synmeta- morphic. Stage 4 gold is, however, this far, only known from rocks situated to the west of the area indicated in Figure 1. Thus, with a few possible exceptions (e.g. Bergman & Sundblad 1991), most Bergslagen gold apparently formed at stage 3. In Figure 2, the position of all known gold occurrences in Bergslagen are plotted on a simplified version of the map of Figure 1. In this version, the younger plutonic rocks are high-lighted (in red). It can be noted that gold only occurs in a few geographically restricted areas of Bergslagen, which are spatially close to, but never actually within, some of the younger plutonic rocks. A genetical connection between Au and younger granites have been suggested in some of the prospecting reports men- A REVIEW OF THE FE OXIDE DEPOSITS OF BERGSLAGEN, SWEDEN AND THEIR CONNECTION TO AU MINERALISATION 135 tioned above and by Gaal & Sundblad (1990) and Bergman (1994). Conclusions From this preliminary study it seems certain that most, if not all, gold in the Bergslagen area formed in relation to regional Svecokarelian metamorphism and coeval plutonic activity. The connection to iron mineralisation is coincidental, and is probably due to the fact that the host rocks were favourable horizons for both mineralising events. The magnetite-bearing, favourable horizons are easily followed by magnetic geophysical methods. Acknowledgements This paper and a preliminary version of it (the latter presented as a poster at the joint SGA-IAGOD meeting in London 1999; Ripa 1999) have benefited by reviews by K. Billström, D.J. Blundell, O. Martinsson, and P. Weihed. References Allen, R.L., Lundström, I., Ripa, M., Simeonov, A. & Christoffersson, H., 1996: Facies analysis of a 1.9 Ga, continental margin, back-arc, felsic caldera province with diverse Zn-PbAg-(Cu-Au) sulfide and Fe oxide deposits, Bergslagen region, Sweden. Economic Geology 91, 979–1008. Bergman, T., 1990: A preliminary overview of gold-bearing skarn mineralizations in Bergslagen, south-central Sweden. Geologiska Föreningens i Stockholm Förhandlingar 112, 173. Bergman, T., 1994: Geology and origin of Early Svecofennian gold-bearing base metal skarn ores of Bergslagen, Sweden. Unpubl. thesis, Stockholm University. Bergman, T. & Sundblad, K., 1991: Boviksgruvan, a Au-Bibearing sulphide deposit in the Bergslagen province, south central Sweden. Geologiska Föreningens i Stockholm Förhandlingar 113, 327–333. Bergman, S., Delin, H., Kübler, L., Ripa, M. & Söderman, J., 2001: Projekt Svealand. In H. Delin (ed.): Regional berggrundsgeologisk undersökning. Sammanfattning av pågående undersökningar 2000. Sveriges geologiska undersökning Rapporter och meddelanden 105, 16–28. Gaal, G. & Sundblad, K., 1990: Metallogeny of gold in the Fennoscandian Shield. Mineralium Deposita 25, S104–S114. Geijer, P. & Magnusson, N.H., 1944: De mellansvenska järnmalmernas geologi. Sveriges geologiska undersökning Ca 35, 654 pp. Lindroth, G.T., 1922: Studier över Yxsjöfältets geologi och petrografi. Geologiska Föreningens i Stockholm Förhandlingar 44, 19–123. Lundqvist. T., 1979: The Precambrian of Sweden. Sveriges geologiska undersökning C 768, 87pp. 136 M. RIPA Lundström, I., 1987: Lateral variations in supracrustal geology within the Swedish part of the Southern Svecokarelian Volcanic Belt. Precambrian Research 35, 353–365. Lundström, I., 1995: Beskrivning till berggrundskartorna Filipstad SO och NO. Sveriges geologiska undersökning Af 177, 185. With an English summary, 218 pp. Lundström, I., Allen, R.L., Persson, P.O. & Ripa, M., 1998: Stratigraphies and depositional ages of Svecofennian, Palaeoproterozoic metavolcanic rocks in E. Svealand and Bergslagen, south central Sweden. GFF 120, 315–320. Magnusson, N.H., 1936: The evolution of the lower Archean rocks in central Sweden and their iron, manganese, and sulphide ores. Quaterly Journal of the Geological Society of London 367, 332–359. Oen, I.S., Helmers, H., Verschure, R.H. & Wiklander, U., 1982: Ore deposition in a Proterozoic incipient rift zone environment: a tentative model for the Filipstad-GrythyttanHjulsjö region, Bergslagen, Sweden. Geologische Rundschau 71, 182–194. Ohlsson, L.G., 1979: Tungsten occurrences in central Swden. Economic Geology 74, 1012–1034. Ripa, M., 1988: Geochemistry of wall-rock alteration and of mixed volcanic-exhalative facies at the Proterozoic Stollberg Fe-Pb-Zn-Mn(-Ag) deposit, Bergslagen, Sweden. Geologie en Mijnbouw 67, 443–457. Ripa, M., 1994: The mineral chemistry of hydrothermally altered and metamorphosed wall-rocks at the Stollberg Fe-PbZn-Mn(-Ag) deposit, Bergslagen, Sweden. Mineralium Deposita 29, 180–188. Ripa, M., 1999: A review of the Fe-oxide deposits of Bergslagen, Sweden and their connection to Au mineralisation. In C.J. Stanley et al. (eds.): Mineral deposits: Processes to Processing. Proceedings of the fifth biennial SGA meeting and the tenth quadrennial IAGOD meeting, 1349–1352. Romer, R.L. & Öhlander, B., 1994: U-Pb age of the Yxsjöberg tungsten-skarn deposit, Sweden. GFF 116, 161–166. Van der Welden, W., Baker, J.H., De Measschalk, S. & Van Meerten, T., 1982: Bimodal early Proterozoic volcanism in the Grythytte field and associated volcano-plutonic complexes, Bergslagen, Sweden. Geologische Rundschau 71, 171–181. SGU Research Paper C 833 Economic geology research, Volume1 1999–2000 Geological Survey of Sweden Box 670 SE-751 28 Uppsala Phone: +46 18 17 90 00 Fax: +46 18 17 92 10 www.sgu.se Uppsala 2001 ISSN 1103-3371 ISBN 91-7158-665-2 Print: Elanders Tofters AB