GAC-MAC 2011 - Austman Et Al - Origin, Geology, and Composition of Fraser Lakes Zone B U-Th-REE mineralization

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Talk given at GAC-MAC 2011 in Ottawa, ON, on the geology, composition, and origin of the Fraser Lakes Zone B pegmatite-hosted U-Th-REE mineralization.

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  • Polyphase folding – defined by lithological units and EM conductor Superimposed ductile-brittle (E-W) and brittle structures (NNE and NNW) Pink is Archean, grey, yellow and blue metasediments, red – pegmatites
  • Point out E-W brittle fault Point out where map on next slide is
  • Explain colors – point to them NE, NNW brittle faults, E-W shears Approximate locations of first 3 drill holes, all hit mineralization. Pegmatites intrude sub parallel to dominant regional gneissosity
  • Unmineralized pegmatites tend to be later, but not always the case Some pegmatites folded!
  • Emphasize they are granitic Complex variable bt-rich to qtz-rich to k-sp rich; mineralization greatest within biotite rich quartz rich pegmatites Complexly zoned because of AFC processes Subdivided into two groups U-enriched vs. Th + REEs
  • Make axes test larger, move pegmatites in legend to top, bold pegmatites, space between Talk about pegmatites first then pelitic gneiss
  • Predominantly peraluminous Classified as s-type granitoids
  • Digress to talk about the host rocks to the granitic pegmatites since their metamorphic grade is important NO prograde metamorphic muscovite
  • Bottom photo shows a uranium mineralized pegmatite from WYL-08-524 intruding into migmatitic gneisses
  • Introduce title and that it is a cross-section Melt Transfer zone Bottom part gt rich Mid crd + gt Upper crd Gt in pegmatites – coming from deeper, gt-sill-crd host rock, middle to upper zone
  • Basement relationships very similar, point out structures Similar to Rössing (one of the largest open pit U mines) and Rössing South
  • GAC-MAC 2011 - Austman Et Al - Origin, Geology, and Composition of Fraser Lakes Zone B U-Th-REE mineralization

    1. 1. The geological setting, composition, and origin of the Fraser Lakes Zone B granitic pegmatite-hosted U-Th-REE mineralization, Wollaston Domain, northern Saskatchewan, Canada Austman, Christine L. 1, 3 Annesley, Irvine R. 1, 2 , and Ansdell, Kevin M. 1 1 Department of Geological Sciences, University of Saskatchewan 2 JNR Resources Inc., Saskatoon, SK 3 CanAlaska Uranium Ltd., Saskatoon, SK GAC-MAC 2011 May 2011
    2. 2. Outline <ul><li>Purpose </li></ul><ul><li>Regional Geological Setting </li></ul><ul><li>Fraser Lakes Geology </li></ul><ul><li>Granitic Pegmatite Mineralogy and Geochemistry </li></ul><ul><li>Metamorphism and Migmatization </li></ul><ul><li>Model for Pegmatite Generation </li></ul>
    3. 4. Purpose of this study <ul><li>Describe the granitic pegmatite-hosted U-Th-REE mineralization at Fraser Lakes Zone B </li></ul><ul><li>Develop a metallogenetic model for pegmatite-hosted U-Th-REE mineralization in the Fraser Lakes area </li></ul><ul><li>Build upon previous work done on pegmatite-hosted uranium mineralization in northern Saskatchewan </li></ul>
    4. 5. Regional Geology <ul><li>The Wollaston Domain consists of: </li></ul><ul><ul><li>Archean orthogneisses (predominantly granitic gneisses) </li></ul></ul><ul><ul><li>Paleoproterozoic Wollaston Supergroup metasedimentary and metavolcanic rocks </li></ul></ul><ul><ul><li>Hudsonian granites, amphibolites, leucogranites , migmatites , and granitic pegmatites </li></ul></ul><ul><li>Complexly deformed during the 1.8 Ga Trans-Hudson Orogen </li></ul>
    5. 6. Fraser Lakes Geology <ul><li>NE-SW regional fabric </li></ul><ul><li>Two mineralized zones: A and B </li></ul><ul><li>Zone A is in a NNE-plunging synformal and Zone B is in an NNE-plunging antiformal fold nose </li></ul><ul><li>5 km section of a complexly folded electromagnetic (EM) conductor (i.e. graphitic pelitic gneisses) is adjacent to Zones A and B </li></ul>After Ray, 1979 Fraser Lakes Granite Inlier (Archean) Johnson River Granite Inlier (Archean) Wollaston Group metasedimentary gneisses Wollaston Group metasedimentary gneisses Fraser Lakes Zone B Fraser Lakes Zone A Needle Falls Shear Zone Peter Lake Domain and Wathaman Batholith
    6. 7. Fraser Lakes Zone B <ul><li>The surface expression of the EM conductor adjacent to Fraser Lakes Zone B is a swampy, low-lying area </li></ul><ul><li>Zone B mineralization outcrops at surface on the eastern edge of the swamp </li></ul><ul><li>Fold nose is visible from the air </li></ul>
    7. 8. Fraser Lakes Zone B geology Modified from Ko, 1971 WYL-08-526 WYL-08-524 WYL-08-525
    8. 9. Granitic pegmatites <ul><li>Granitic pegmatites with variable amounts of quartz, feldspar, biotite , and other minerals </li></ul><ul><li>Overall coarse grained to pegmatitic </li></ul><ul><li>Variable size (cm to several m scale) </li></ul><ul><li>Complexly zoned (igneous AFC processes) </li></ul><ul><li>Multiple generations of granitic pegmatites (late-tectonic </li></ul><ul><li>to post-tectonic) </li></ul><ul><li>1810-1790 Ma uraninite </li></ul><ul><li>U-Pb chemical ages in </li></ul><ul><li>mineralized pegmatites </li></ul>
    9. 10. Mineralogy <ul><li>Quartz (Qtz) </li></ul><ul><li>Feldspar (Fsp) </li></ul><ul><li>Biotite (Bt) </li></ul><ul><li>Magnetite (Mgt) </li></ul><ul><li>Ilmenite (Ilm) </li></ul><ul><li>Pyrite (Py) </li></ul><ul><li>Fluorite (Fl) </li></ul><ul><li>Sphalerite </li></ul>Highly Variable! <ul><li>Uraninite (Urn) </li></ul><ul><li>Uranothorite (Uth) </li></ul><ul><li>Monazite (Mz) </li></ul><ul><li>Zircon (Zrn) </li></ul><ul><li>Allanite (Aln) </li></ul><ul><li>Xenotime (Xen) </li></ul>U-Th-REE Minerals <ul><li>Molybdenite </li></ul><ul><li>Apatite (Ap) </li></ul><ul><li>Titanite </li></ul><ul><li>Garnet </li></ul><ul><li>Rutile </li></ul><ul><li>Chalcopyrite </li></ul><ul><li>Pyrrhotite </li></ul><ul><li>Nb oxide </li></ul><ul><li>Graphite </li></ul>Primary Minerals
    10. 11. Uraniferous pegmatites <ul><li>Uraninite- and uranothorite- bearing </li></ul><ul><ul><li>Also contain zircon and minor allanite </li></ul></ul><ul><ul><li>Monazite is very rare </li></ul></ul><ul><li>Typically intrude the western part of the fold nose </li></ul>
    11. 12. Th- and LREE Pegmatites <ul><li>Monazite-rich </li></ul><ul><ul><li>Also contain zircon , uranothorite-thorite , altered allanite , and xenotime as the main U-Th-REE hosts </li></ul></ul><ul><ul><li>Rare Nb oxide </li></ul></ul><ul><li>Generally confined to eastern portions of the fold nose </li></ul>
    12. 13. Major element geochemistry Legend
    13. 14. Alumina saturation index <ul><li>Samples range from strongly peraluminous (off the chart) to slightly metaluminous </li></ul><ul><li>No distinct difference between U and Th mineralized pegmatites </li></ul><ul><li>S-type granitoids </li></ul>
    14. 15. Trace element geochemistry <ul><li>Two major compositional subdivisions of pegmatites; correspond to mineralogical subdivisions </li></ul><ul><ul><li>U- plus Th-rich </li></ul></ul><ul><ul><li>Th- and LREE-rich </li></ul></ul>
    15. 16. Metamorphic Mineral Assemblages in host pelitic gneiss <ul><ul><li>Garnet </li></ul></ul><ul><ul><li>Biotite </li></ul></ul><ul><ul><li>Cordierite </li></ul></ul><ul><ul><li>Sillimanite </li></ul></ul><ul><ul><li>Spinel </li></ul></ul><ul><ul><li>K-feldspar </li></ul></ul><ul><ul><li>Quartz </li></ul></ul><ul><ul><li>Plagioclase </li></ul></ul><ul><ul><li>Rutile </li></ul></ul><ul><ul><li>Myrmekite </li></ul></ul><ul><ul><li>NO prograde </li></ul></ul><ul><ul><li>muscovite </li></ul></ul>Upper amphibolite to granulite facies metamorphism
    16. 17. Pegmatites – Partial melting at depth vs. in-situ? <ul><li>Migmatites associated with the granitic pegmatites </li></ul><ul><li>Leucosomes tend to be boudinaged, but also form small pegmatitic veins </li></ul><ul><li>Melt occasionally forms thin rims around minerals, and locally </li></ul><ul><li>larger blobs </li></ul><ul><li>Biotite frequently shows </li></ul><ul><li>degradation due to partial </li></ul><ul><li>melting in thin section </li></ul>
    17. 18. Model for Fraser Lakes Zone B pegmatites schematic mid-crustal cross-section <ul><li>Melts generated at depth (a) </li></ul><ul><li>Transported upwards along the structural discontinuity/contact between Archean and Wollaston Group (b) </li></ul><ul><li>Underwent igneous assimilation-fractional crystallization during transport and crystallization </li></ul><ul><li>Melts were concentrated in antiformal fold noses (c) </li></ul><ul><li>Peraluminous chemistry agrees with the pegmatites forming due to partial melting of pelitic gneisses </li></ul>a b c
    18. 19. Similarities to Rössing/Rössing South <ul><li>Uranium mineralization is in late-tectonic to post-tectonic granitoids </li></ul><ul><li>Structurally controlled mineralization -concentrated in antiformal fold noses </li></ul><ul><li>Concentrated in areas of highest metamorphic grade </li></ul><ul><li>Melt generated by partial melting of metasedimentary gneisses </li></ul>Extract Resources, 2009 Modified from Ray, 1979
    19. 20. Conclusions <ul><li>Structurally controlled, granitic pegmatite-hosted U and Th mineralization (+/- REE mineralization) </li></ul><ul><li>Hosted by Hudsonian granitic pegmatites intruding at/near the contact between Wollaston Group metasediments and Archean orthogneisses </li></ul><ul><li>Regional metamorphism up to granulite facies </li></ul><ul><li>Granitic pegmatites formed by partial melting of metasedimentary rocks in the middle to lower crust followed by transport and assimilation-fractional crystallization </li></ul><ul><li>Similarities to Rössing and Rössing South granitoid-hosted U deposits </li></ul>
    20. 21. Acknowledgements <ul><li>JNR Resources Inc. – access to drill core, outcrops, geological and geophysical datasets, logistical support, and financial assistance </li></ul><ul><li>NSERC - Discovery Grant (Ansdell) </li></ul><ul><li>University of Saskatchewan Graduate Scholarship (Austman) </li></ul><ul><li>Saskatchewan Research Council – geochemical analysis </li></ul><ul><li>Blaine Novakovski – thin section preparation </li></ul><ul><li>Kimberly Bradley – assistance with petrography </li></ul><ul><li>Steven Creighton and Tom Bonli – assistance with electron microprobe analyses </li></ul>

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