Download Economic geology research, volume 1 1999-2000

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It is our ambition to continue to publish compilations and novel research based on the vast unpublished archives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
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A REVIEW OF PALAEOPROTEROZOIC INTRUSIVE HOSTED CU-AU-FE-OXIDE DEPOSITS IN NORTHERN SWEDEN
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Hedin, J.-O., 1985b: Preliminär geologisk modell över Sijsjka
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P. WEIHED
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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.
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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.
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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.
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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
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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.
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Magnusson, N.H., 1936: The evolution of the lower Archean
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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
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Ohlsson, L.G., 1979: Tungsten occurrences in central Swden.
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Ripa, M., 1988: Geochemistry of wall-rock alteration and of
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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.
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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
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Uppsala 2001
ISSN 1103-3371
ISBN 91-7158-665-2
Print: Elanders Tofters AB