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Potential for Rare-Earth Element (REE) Deposits in Northern Labrador and Québec: Lessons from Strange Lake and even stranger places Andrew Kerr1, Steve Amor2, Derek Wilton1 1Dept. of Earth Sciences, Memorial University 2Geological Survey of Newfoundland-Labrador St. John’s, NL, Canada Some Grateful Acknowledgements Merci de l’invitation de présenter ici. Je voudrais remercier aussi……. Red Wine Mountains, August 2010 Randy Miller (once with GSNL, now with Search Minerals), Tyson Birkett and Steve Zajac (originally with IOC in the 1980s). Pat Collins and Jeanette Walsh (Quest Rare Metals), Anthony Williams-Jones (McGill University), Robert Banville (Midland Exploration), and the for support TheNunatsiavut spectacular southGovernment coast of Newfoundland (photo by here. Andy Kerr) Strange Lake - Essential Facts the “B-Zone” Deposit (approximate location) The Strange Lake area contains world-class deposits of the REE, highly enriched in heavy (critical) REE. They are in many respects unique, and other potential REE deposits also occur in this part of Labrador and Quebec. Our purpose is to discuss geology and exploration methods. High-grade region of the “Main Zone” deposit QC LB Bulk sample site, Zone 1 Lens, Strange Lake Main Zone Deposit. The B-Zone (Quest Minerals) is located in the background. Coarse-grained eudialyte (Eu), nepheline (Ne) and pyroxene (Px) from the Red Wine Mountains area, central Labrador. Deposits also rich in HREE. Eu Px Ne Strange Lake is the best known – but not the only one. These deposits are diverse in character, mineralogy and potential. Eudialyte: Na4(Ca, light REE)2(FeII, Mn, Y, heavy REE) ZrSi8O22(OH, Cl)2 Presentation Outline • Some Regional Context: General geology and Mesoproterozoic “anorogenic” magmatism in northern Labrador, Québec and related regions. • Strange Lake: The discovery and wider context, and characteristics of the the REE resource. Summary of key geological and geochemical attributes, and the contrasting (but not contradictory?) models. • Other REE Deposit Types: A brief listing of other areas and deposit types in this region – with emphasis on the diversity of styles and chemistry. • Exploration Methodology: The roles of regional to local surficial geochemistry, geophysics and “new” methods using indicator minerals. Regional Context SL – Strange Lake ML- Misery Lake FR- Flowers River RW- Red Wine PHS – Port Hope Simpson SL ML FR • The Churchill Province is RW PHS REE • Much of the region of interest is within the Churchill Province, with some deposits in adjacent blocks such as the Nain. underlain by reworked Archean crust, and it has a long and complex Paleoproterozoic history. • All REE Mineralization is linked to younger Mesoproterozoic igneous suites (from 1460 to 1240 Ma) GREENLAND CONNECTIONS • Prior to the opening of the Labrador Sea in the Eocene, Labrador was joined to SW Greenland. •Something to illustrate •the Gardar This region includes the Gardar Province – A well •Connections to Greenland GREENLAND u Ch il rch lP (Nain) Anorogenic Magmatic Suites of Labrador v. ro Ketilidian SL Grenville Makkovik known region of alkaline igneous activity with many potential REE deposits. These rocks are younger than North American examples. • The Gardar region and the Mesoproterozoic igneous rocks of Labrador are likely part of the same plume event. Alkaline Intrusive rocks of the Gardar Province http://sp.lyellcollection.org/content/318/1/193/F19.large.jpg Strange Lake – An Abbreviated History • The deposit was found through a uranium exploration program – during an unplanned field ‘rest stop’. • Exploration (1979-84) proved a Zr-Y-Nb resource, but development plans failed due to the recession. • After Voisey’s Bay discovery, claimed as Inuit Land. • Interest in uranium (2008) grew in adjacent Quebec…. Then the REE suddenly become more strategic. • A ‘new’ deposit was defined a few km inside Québec (the B-zone) and is now in feasibility assessment. • Strange Lake is notable for high relative contents of the heavy REE – it contains some unique rocks, and is of much interest for research work. Plus, it is a world class resource of the REE (+ Zr, Nb, Hf…). Aplite-pegmatite-rich zones contain the high-grade material “exotic-rich granite” Inclusion-rich “exotic granite” The “exotic-rich granite” may itself constitute low-grade ore The “ore” at the Strange Lake Deposit is a physical mixture of variably-enriched granite and highly enriched aplite-pegmatite zones. NW-SE Cross-section from part of the new B-Zone deposit in Québec, TRANSVERSE CROSS-SECTION drawn from Rare Minerals. The geology is essentially the same. Source: QuestQuest Rare Minerals ) iched r n e ( te gmati e p y l Large Inclusion-rich “exotic granite” (with variable Hematite alteration ) After Quest Minerals, 2010 • Like the original discovery in Labrador, the ”B-Zone” is a mixture of highgrade pegmatite zones, and lower-grade host granite; the bulk grade is largely a function of pegmatite density and thickness. Latest B-Zone Indicated Resource Estimates (2013) 278 Mt at 0.93% TREO*, 1.92% ZrO2, 0.18% Nb2O5 (includes 20 Mt at 1.44% TREO* for actual mining resource) An additional 214 Mt at 0.85% TREO* is inferred at depth in “granite” The original Strange Lake discovery from the 1980s has a non-compliant resource of some 58 Mt at ~0.9% TREO*, but the drilling is very shallow. The Exploration Camp at Lac Brisson, Québec The REE, Zr and Nb are preferentially hosted in pegmatitic and aplitic zones that cut the host granite. These contain unusual Zr- and REE-bearing minerals, also found in disseminated form in many granites. 2 cm (approx) ` Strange Lake – Bulk Rare Earth Distributions Note consistent patterns and negative Eu anomalies: extensive fractionation Source: GSNL analyses • REE Patterns from within the Strange Lake Deposit and its host rocks are very consistent, although the individual units overlap. • The most enriched granites are of interest as REE sources, with average grades of ~ 0.6% TREO*. This material was generally not included in any historical resource estimates. Important Mineralogical Factors Gittinsite • Strange Lake is a “treasure trove”house of unusual minerals, and it is likely that many new species remain to be described. • Unusual alkali and calcium zirconosilicates such as elpidite and narsarsukite are present as early ‘phenocryst’ phases in some of the granites and melanocratic inclusions. The most important Zr source is gittinsite – named for Ernest Gittins (U of Toronto petrologist). Kainosite Galena Elpidite? • Important Ca (Na) – Y – REE silicates include gerenite, kainosite and gadolinite. Importantly, these are amenable to acid leaching extraction. • Lots of fluorite and other mineral species; some common, some still to be documented. REE/chondrite • The REE patterns of the various units at Strange Lake show systematic variation that is best explained through igneous fractionation processes. • The country rocks have steeper REE patterns and are lower in total REE. (Country rocks} (Country rocks} • Granites show increasing HREE content that could record removal of LREE by minerals or by loss of LREE to hydrothermal fluids as the magmas crystallized. • REE patterns of high-grade zones are very distinctive and HREE- enriched. Strange Lake Main Zone – Relative HREE Contents Pegmatites/Aplites 1.71% TREO* Y 43% Source: GSNL analyses • The heavy REE are relatively enriched, representing some 17% to 24% of the total REE budget. • Pegmatite and aplite units (high-grade) generally have higher heavy REE and Y proportions – notably the latter. • The B-Zone mineralization has essentially the same features and chemistry, although the relative HREE contents are somewhat lower. Strange Lake – Other Key Attributes • The ring complex is surrounded by a fluorite-rich magmatic breccia zone likely representing an arcuate fault – but this has no REE enrichment. • Many (but not all) granites contain dark inclusions with relict zirconosilicate phenocrysts; textures are very like those attributed to mafic-felsic mixing. • Nd isotope data do not match country rocks or likely Archean basement – a significant proportion of the REE were sourced in the mantle ~ 1240 Ma. • Mixed mantle-crust heritage is most likely origin. • A wide range of incompatible elements other than REE are strongly enriched – e.g., U, Th, Be, Rb, Pb, Sn. Negative correlations between these and Ca. B-Zone Main Zone • • • Model partly after R. R. Miller, 1986 1. Emplacement of latest, most evolved granite magma along contact between older units. 2. Crystallization causes accumulation of residual melt and volatiles near the roof of the unit, forming pegmatite and aplite units. The latter cross-cut the contacts of granite units. 3. Main Zone and B-Zone may represent deeper and shallower levels of a magmatic-hydrothermal system. Strange Lake – Genetic Mysteries • The deposit and associated granitic rocks are to a large extent unique – the relative HREE-Y enrichment particularly unusual. How did this happen? • Initial ideas (1980s) invoked largely magmatic processes to enrich REE, but an alternative ‘hydrothermal’ explanation was favoured by others; fluid mixing proposed as mechanism for REE deposition. • This debate is not over – new models for the B-Zone propose mixing of magmatic and meteoric fluids. • The two deposits are similar, although there is more hematite alteration in the B-Zone, and perhaps a dominance of pegmatite over aplite. • Different levels of a common magmatic system? 2 cm Fine-grained “exotic-rich” peralkaline granite unit • Highly-enriched inclusion-free unit associated with Labrador mineralization • Less-enriched inclusion-bearing unit that is the dominant host at the B-Zone. “Exotic”granite unit with fine-grained inclusions • Mineralized pegmatite with gittinsite and other Zr and REE minerals – this is where much of the grade resides. Some pegmatites have zonation suggesting igneous processes. • <<<<<<<<<<< Homogeneous, highlyenriched granite that was encountered in the deepest holes beneath the B-Zone. This resembles the host granite seen in Labrador – possibly beneath deposit? >>>>>>>>>>>>>> How can we make a Strange Lake magma? • Evolved granites are considered by some as crustal melts, but this cannot come from known basement. • Crustal melting gives steep REE patterns – not seen! • Isotopic data suggest that a mantle component or a crustal precursor with a very short residence time – Could a two stage process be involved? • One possibility lies within a little-known group of evolved intermediate rocks associated with anorthosite-granite suites – ‘ferrodiorites’ • Protracted fractionation seems to have formed the most enriched magmas, but there has been some hydrothermal compositional disturbance also. But magmatic processes are way more important. Exploration from 2009 to 2012 was focused mostly in north-central Labrador, and adjacent regions of Québec. The area to the north along the border saw less activity, largely because no major Mesoproterozoic igneous suites were identified through earlier mapping. Misery Lake These are the main areas of recent exploration, but other smaller prospects have been identified in both provinces, and partially explored. Other Areas of REE Interest in the Area • Flowers River Complex: Closest analogue to the Strange Lake host rocks, partly volcanic, ~ 1290 Ma • Letitia Lake: Distinctive LREE-Be rich zones associated with ~ 1330 Ma peralkaline volcanic rocks on the northern edge of the Grenville Prov. • Red Wine Mountains: Undersaturated ~ 1330 Ma metaplutonic suite noted for the presence of eudialyte – a mineral enriched in HREE but no U,Th • Misery Lake (QC): Well-defined ca. 1410 Ma ringcomplex with known REE zones; now also of current interest for scandium (Sc) – rare but valuable. • Ytterby: Magmatic LREE concentrations in late (~1420 Ma) granites in the Mistastin Batholith. Critical REE Abundances in Labrador/Québec Mineralization UZ LZ Lower Zone Upper Zone Nechelacho After V. Sederin et al. • It has proven useful to classify REE mineralization using the relationships between ”Critical”, ”Surplus” and ”Total” REE. On this basis, areas in the top right of the charts are the most economically encouraging. • Enrichment is clear for Strange Lake, Red Wine and Flowers River – note that these have higher critical REE values than Nechelacho (NWT) area. Exploration Methods for REE Deposits • In many cases, peralkaline igneous suites are small, and may not be well exposed; Strange Lake is a good example, as there are very few outcrops. • Regional radiometric surveys have proved useful, and this is how many were first detected. High Th/U ratios are typical. Radiometry is also useful for prospecting – as REE minerals are often cryptic. • Aeromagnetic surveys may reveal patterns of ringcomplexes, but not all deposits will reveal these. • Surficial geochemical methods have great potential, especially if linked with indicator mineral studies. The latter can also tell us something about the mineralogy of a target – this is very important! STRANGE LAKE Radiometric (Th) anomaly over the Strange Lake Intrusion- highest zones are seen over the Main Zone 1 Lens in Labrador. (GSC data, figure from Zajac et al., in press, Canadian Mineralogist) B-Zone Main Zone Note that the B-Zone has little response – due to a blanket of material derived from the west. MISTASTIN BATHOLITH AREA Radiometric data also give a good indication of the inner red granite at Y2. These are data for Th-related radioactivity – reflecting the Thenriched nature of such rocks and related mineralization. (from Midland Exploration) The clear definition of intrusive bodies by high-resolution aeromagnetics is truly remarkable – This survey in 2009 in part led to definition of the Misery Lake Complex within the Mistastin Batholith. This is now an active exploration Project. Diabase dykes (Harp dykes? (GSC total field; assistance by G. Kilfoil at GSNL) Misery Lake Complex and REE prospects QUEBEC Intrusive “edge” of the Mistastin Batholith Diabase dykes (Harp dykes? 25 km LABRADOR ??? Ytterby 3 p ??? H ar D yk e ML1 p ML2 ??? H ar ~ 12 km D yk e Mistastin Batholith (S) Ring-complexes and other intrusions (?) defined by new aeromagnetic (1vd) data ML3 GSC Data, assisted by G. Kilfoil, GSNL A border area located to the northwest of the Mistastin Batholith: Can you find the expression of Strange Lake? GSC Data, assistance by G. Kilfoil, GSNL First vertical derivative (1vd) Labrador Québec Napeu Kainut Intrusion (age unknown) Mistastin Batholith The use of surficial geochemistry as an exploration tool on various scales “North River Anomalies” Strange Lake Image: Fluoride in lake waters, Northern Labrador (Fluoride in lake waters seems to be one of the most effective regional indicator elements….) Regional Surficial Geochemistry – Summary • Most of the known REE deposits have expression in surficial geochemistry, and not only from REE. • Strange Lake has a well-developed dispersion train. • Extensive lake sediment database for both sides of the border, but the element suites vary, with limited REE analyses in Québec. Recent reanalysis work under GEM-2 now allows easier merging of these data. • This is a valuable database, although some aspects remain puzzling. There are challenges in separating mineralization signatures from the other factors which can create regional zones of enrichment. • These new data give enhanced definition of the dispersion train from Strange Lake….and much more. Thorium (Th) Incompatible elements such as Th and Cs do provide some definition for known REE prospects, but these are not easily discriminated from wider regional patterns. Th is associated with wider granitic areas, with lows on areas of anorthosites. Cs is not a clear pattern. REE Deposit Strange Lake Flowers River Red Wine / Letitia Lake Cesium (Cs) INAA Data; NGR samples (GSNL) Samarium (Sm) The REE form more useful surficial indicators of known mineralization, but in general the light REE are more widely dispersed than the heavy REE, which work better. Note the marked unexplained area of enrichment NE of Strange Lake, and also SL train. REE Deposit Strange Lake Flowers River Red Wine / Letitia Lake Ytterbium (Yb) INAA Data; NGR samples (GSNL) “NORTH RIVER” The geochemical anomaly known as North River still has not been fully explored. It is very interesting that regional magnetic data reveal some ring-like patterns in here…… • SYMBOLS Fluoride in Water (scaled for value) Yttrium (Y) (smoothed) MERGED LB/QC DATA • Y and La are the only REE available. Y is a good proxy for the heavy REE, but the regional pattern is once again diffuse. • Interestingly, it seems to define other areas in northern Labrador not revealed by LREE data. Data from NGR (GSC) and MRNF samples, ICP-MS Merged, and smoothed. Amor et al., 2016, In “Explore” • The representation of data and scaling are of great importance if the objective is to highlight smaller areas of the strongest enrichment. • What you get out of data depends on treatment. Yttrium (Y) (rescaled, Smoothed) MERGED LB/QC DATA • These are the same data as in the previous slide, but rescaled to show only the highest values, and leave most other variation unseen. • This gives much clearer definition of the Strange Lake dispersion train, and other areas of possible interest in both provinces, but mostly in Labrador. Data from NGR (GSC) and MRNF samples, ICP-MS Merged, and smoothed. Amor et al., 2016, “Explore” • A good illustration of the potential of these data given further manipulation and processing. Tin (Sn) (smoothed) SL Train Data from NGR (GSC) and MRNF samples, ICP-MS Merged, and smoothed. Amor et al., 2016, “Explore” MERGED LB/QC DATA • One of the interesting results was the very good definition of the Strange Lake dispersal train by Sn – This is also enriched in the rocks at Strange Lake. • Sn also highlights the areas in northern Labrador noted for the heavy REE, and also the Letitia and Red Wine areas in Labrador. • Broad anomalies west of the border do not have obvious causes – but they may vanish with scale adjustment. Gittinsite – located about 140 km from its source! Strange Lake Voisey’s Bay Area • Investigations into MLA-SEM methods by Derek Wilton and Altius Minerals led to the discovery of gittinsite in tills on the Labrador coast. This must have come all the way from Strange Lake – there is no other known source closer than Kipawa, W. Québec. SEM/MLA Photos from Derek Wilton A Role for Indicator Mineral Surveys? • Looking for distinctive indicator minerals is a promising method, and also a way to distinguish true anomalies from broad regional patterns. • A new project using Mineral Liberation Analyzer (MLA) and Scanning Electron Microscope (SEM) is under way at Memorial, initially for Strange Lake. • What questions might this project answer? • How far do minerals survive transportation? • Can they be detected even where bulk geochemical anomalies are absent or extremely subtle? • Can a reference library for these minerals be assembled for application to other project areas? CREAIT Labs, MUN Photos – D. Wilton • SEM/MLA – ”Scanning Electron Microscope / Mineral Liberation Analyzer ” is a method of investigating rock samples or mineral separates using automatic imaging and analysis. It is a variant of the QEMSCAN technique used in geometallurgy. • Reference libraries are used for spectral identification – so the first step is to develop these libraries. • The method can be used to screen processed till samples, looking for rare grains of indicator minerals – which also give an indication of what the undiscovered target might be. Mineralized “aplite” containing poikilitic gittinsite (CaZrSi2O7) High-grade pegmatite, with fluorite and “exotics” • Information from MLA-SEM work will also help to understand the myriad complexities of the rocks at Strange Lake. • Information from mineralized rocks will provide material for reference libraries. So this is very much a two-way street. • Typical scenery in the area of the Strange Lake dispersion train. I think you can see why surficial techniques would be a valuable method for prospecting! • <<<<<<<<<<< Sampling tills down-ice from Strange Lake, summer of 2016. The project involves funding from RDC, and also the Nunatsiavut Government (photos from Derek Wilton). >>>>>>>>>>>> LB QC LB QC Thank You. Merci beaucoup. Nakkumek. Is this the shape of things to come? Source: Financial Post, business section, Nov 21, 2016 (website www.business.financialpost.com) • The recent article about the use of ‘blimps’ for development of Strange Lake (and possibly concentrate transportation) underlines an important point – the remoteness of the region and lack of infrastructure raises the economic threshold for any discovery. Should something like this ultimately prove feasible, it has implications for other types of projects, notably gold.