ANATEXIS AND URANIUM PROTORE INTHE WOLLASTON DOMAIN,SASKATCHEWAN McKechnie, Christine L. 1 Annesley, Irvine R. 1, 2, and A...
Outline • Geological Setting • Pegmatite Mineralogy and Geochemistry • Model for Granitic Pegmatite/Leucogranite   Generat...
Regional Geology•   Hearne Province•   Deformed and metamorphosed    during the Paleoproterozoic    (ca. 1.9-1.8 Ga) Trans...
Fraser Lakes Geology•   NE-SW regional    fabric•   Zone A is in a NNE-                                                   ...
Fraser Lakes Geology After Ko, 1971
Granitic pegmatites and    leucogranites•   Granitic pegmatites and    leucogranites with    variable amounts of quartz,  ...
Mineralogy     Highly Variable! * Magmatic and/or peritectic minerals
Group A and Group B Granitic Pegmatites/Leucogranites   Group A Intrusives                 Group B Intrusives• Contain abu...
Major element geochemistry• Group A intrusives tend to  be more Si-rich than  Group B intrusives, with  significant overla...
Trace element geochemistry• The two groups also have dissimilar trace element geochemistry related to their accessory mine...
REE Geochemistry   Group A Intrusives            Group B Intrusives• Generally flat or slightly   • Generally show LREE HR...
Metamorphic Mineral Assemblages    in host migmatitic pelitic gneisses• Garnet• Biotite• Cordierite• Sillimanite• Spinel• ...
Granitic Pegmatites / Leucogranites – Partial melting at depth vs. in- situ?• Migmatites in close association with  the ra...
Model for Fraser Lakes Zone B granitic    pegmatites/leucogranite-hosted mineralization    schematic mid-crustal cross-sec...
Granitoid-hosted U mineralizationAfter Parslow and Thomas, 1982   after Cuney, 2005
Alteration of graniticpegmatites/leucogranites andremobilization of U, Th, PbPost-CrystallizationAlteration (during coolin...
U protore?• Chlorite, clay (including illite), and    hematite alteration found drill core;    similar to that of basement...
Unconformity-type uranium deposits: possiblemodel  Evaporated Sea Water: high salinity fluids [Cl]                        ...
Conclusions•   Structurally controlled, basement-hosted magmatic U and Th mineralization (+/-    REE mineralization)•   Ho...
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McKechnie et al. 2012 Goldschmidt talk

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McKechnie et al. 2012 Goldschmidt talk

  1. 1. ANATEXIS AND URANIUM PROTORE INTHE WOLLASTON DOMAIN,SASKATCHEWAN McKechnie, Christine L. 1 Annesley, Irvine R. 1, 2, and Ansdell, Kevin M.1 1 Department of Geological Sciences, University of Goldschmidt 2012 Saskatchewan June 2012 2 JNR Resources Inc., Saskatoon, SK
  2. 2. Outline • Geological Setting • Pegmatite Mineralogy and Geochemistry • Model for Granitic Pegmatite/Leucogranite Generation • U protore?The aim of this project was to determine whether these [granitic pegmatites and leucogranites]represent a distinct target for uranium exploration in Saskatchewan and/or if the mineralization is somehow related to unconformity-type uranium deposits
  3. 3. Regional Geology• Hearne Province• Deformed and metamorphosed during the Paleoproterozoic (ca. 1.9-1.8 Ga) Trans-Hudson Orogeny (THO)• ~ 25 km SE of the Mesoproterozoic Athabasca Basin• In the Eastern Wollaston Domain, which consists of: • Archean orthogneisses (mostly granitic) • Paleoproterozoic Wollaston Group metasedimentary rocks • Hudsonian granites, amphibolites, migmatites, leucogranites, and granitic pegmatites• Study area shown in red box
  4. 4. Fraser Lakes Geology• NE-SW regional fabric• Zone A is in a NNE- es up s s ro nei G g plunging synformal on ary st t and Zone B is in an o lla en W dim NNE-plunging ta se e antiformal fold nose m se nta p e is e o u ry• 5 km section of a r er iv r gn edim Gr li e R ie In on I nl as o n complexly folded s te ns te ni et st a oh a ni m olla electromagnetic Gr J r G es W k (EM) conductor (i.e. rL a as e o ne graphitic pelitic Fr rZ a gneisses) is Fraser Lakes She ai n Zone B lls om adjacent to Zones A Fa eD ak le rL and B Fraser Lakes Zone A ed e Ne t Pe After Ray, 1979
  5. 5. Fraser Lakes Geology After Ko, 1971
  6. 6. Granitic pegmatites and leucogranites• Granitic pegmatites and leucogranites with variable amounts of quartz, feldspar, biotite, and other minerals• Overall coarse grained to pegmatitic• Variable width (cm to dm scale)• Complexly zoned (igneous AFC processes)• Multiple generations of granitic pegmatites• 1850-1780 Ma U-Pb chemical ages (CHIME) for magmatic uraninite
  7. 7. Mineralogy Highly Variable! * Magmatic and/or peritectic minerals
  8. 8. Group A and Group B Granitic Pegmatites/Leucogranites Group A Intrusives Group B Intrusives• Contain abundant uraninite, • Monazite-rich w/ zircon, thorite, thorite, and zircon and minor allanite, and xenotime allanite • Intrude the central part of the• Intrude the western part of the antiformal fold nose antiformal fold nose
  9. 9. Major element geochemistry• Group A intrusives tend to be more Si-rich than Group B intrusives, with significant overlap• Group B intrusives overlap with pelitic gneisses• Controlled by sample mineralogy • (i.e. high SiO2 = quartz-rich; low SiO2= higher mafics/oxide content)• Controlled by host rock composition • Archean granitic orthogneisses vs. Wollaston Group metasedimentary gneisses
  10. 10. Trace element geochemistry• The two groups also have dissimilar trace element geochemistry related to their accessory mineral contents • U- plus Th- rich (Group A) • Th- and LREE-rich (Group B)
  11. 11. REE Geochemistry Group A Intrusives Group B Intrusives• Generally flat or slightly • Generally show LREE HREE-enriched patterns, enriched patterns, higher low total REE content, total REE content, and variable Eu anomalies strong –Eu anomalies
  12. 12. Metamorphic Mineral Assemblages in host migmatitic pelitic gneisses• Garnet• Biotite• Cordierite• Sillimanite• Spinel• Quartz• Plagioclase• K-feldspar• Rutile• Myrmekite• NO prograde muscoviteUpper amphiboliteto granulite facies peak thermal metamorphism during THO
  13. 13. Granitic Pegmatites / Leucogranites – Partial melting at depth vs. in- situ?• Migmatites in close association with the radioactive intrusives• Leucosomes tend to be boudinaged, but also form small pegmatitic veins• Crystallized melt occasionally forms thin rims around minerals, and locally larger blobs• Biotite frequently shows degradation due to partial melting
  14. 14. Model for Fraser Lakes Zone B granitic pegmatites/leucogranite-hosted mineralization schematic mid-crustal cross-sections• Primary magmatic U (+/-Th, REE) mineralization within late-tectonic granitic pegmatites and leucogranites; 1850-1780 Ma (related to THO)• Partial melting of metasedimentary gneisses (i.e. Wollaston Group equivalent) at depth during peak thermal metamorphism (THO)• Melt migrated upwards along the structural discontinuity/contact between Archean and Wollaston Group, undergoing igneous assimilation-fractional crystallization (cross-section A)• Melts concentrated preferentially in antiformal fold noses• Similarities to Rössing and Husab (formerly Rössing South) uranium deposits in Namibia (cross-section B)A) Modified from Ray, 1979 B) Extract Resources, 2009
  15. 15. Granitoid-hosted U mineralizationAfter Parslow and Thomas, 1982 after Cuney, 2005
  16. 16. Alteration of graniticpegmatites/leucogranites andremobilization of U, Th, PbPost-CrystallizationAlteration (during cooling)•Chlorite (Chl)•Epidote (Ep)•Sericite (Ser)•Quartz (Qtz)Hydrothermal Alteration•Fluorite (Fl)•Chlorite (Chl)•Hematite (Hem)•Clay minerals•Sausserite•Carbonate (Cal)•Quartz (Qtz)•With secondary hydrothermalU-Th-REE minerals
  17. 17. U protore?• Chlorite, clay (including illite), and hematite alteration found drill core; similar to that of basement-hosted unconformity-type U deposits• Erosion to an estimated depth of 150-200 m below the Athabasca/ basement unconformity• Brittle faulting cross-cuts the mineralized zone • Conduit for fluid and heat flow?• Uranium (and other metals) remobilized along fractures away from primary magmatic uraninite• Alteration of monazite may have also led to uranium remobilization• Drilling has yet to intersect a basement-hosted unconformity- type U deposit in the area – does not mean it does not exist Modified from Ray, 1979
  18. 18. Unconformity-type uranium deposits: possiblemodel Evaporated Sea Water: high salinity fluids [Cl] Richard et al. (2011) Geochim. Comsochim. Acta 75, 2792-2810 Mercadier et al., (2012) Geology Sea Basin 1.75-1.5 Ga typercolation into the mi 1.4–1.1 Ga UO2 n forbasement with leaching coMercadier et al. (2010) +/- REEs, Au, Cu, UnLithos 115, 121-136 Co, Ni, As… Basement 2.8 - 1.7 Ga ore [U]crust ~ 1.7 ppm × 105 !!! [U]ore ~ 20% UO2 > 20% Abundant U source(e.g. monazites, uraninites) Up to 200.000 t U at Hecht & Cuney (2000) Fraser Lakes approx. 20%: Giant Mineral. Deposita 35, 791-795 Zone B uranium deposits of Salinity [U]: 10-6 to 10-2 mol/L, pH:3-4.5 high grade Richard et al. (2012), Nature Geoscience cf. presentations of Michel Cathelineau, 2011 and Mercadier et al., 2012
  19. 19. Conclusions• Structurally controlled, basement-hosted magmatic U and Th mineralization (+/- REE mineralization)• Hosted by Hudsonian granitic pegmatites and leucogranites intruding at/near the highly deformed contact between Wollaston Group metasediments and Archean orthogneisses• Formed by partial melting of metasedimentary rocks in the middle to lower crust followed by transport and assimilation-fractional crystallization• Similarities to Rössing and Husab (Rössing South) granitoid-hosted U deposits• Granitic pegmatites experienced post-crystallization alteration and remobilization of U and Th and other metals• The magmatic U mineralization is potential protore for basement-hosted unconformity-type uranium deposits in the Fraser Lakes area (yet-to-be discovered) and elsewhere in the Wollaston Domain and Athabasca Basin• Magmatic U mineralization may represent a new type of economic uranium deposit in northern Saskatchewan
  20. 20. Questions?

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