Austman - Departmental Seminar - Fraser Lakes Zone B Mineralization


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Departmental seminar that I gave on my research on the Fraser Lakes Zone B U-Th-REE mineralization.

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  • Indicate geology of u deposits from east Athabasca generally associated w/ Wollaston DomainFraser Lakes Zone B is also in the Wollaston DomainControversy – source rocks?
  • Study to provide additional constraints on the origin of Athabasca unconformity-related U deposits as well as characterize the pegmatites as their own unique target for U mineralization
  • Area Multiply deformed and metamorphosed about 1.8 Ga during the THOAthabasca Basin unconformably overlies the metamorphosed rocksTHO source of sediment for Athabasca BasinArea Square larger and brighter color!!! More contrast (Drk red)
  • Refolded fold structure – polyphase folding – defined by lithological units and EM conductorSuperimposed ductile-brittle (E-W) and brittle structures (NNE and NNW)
  • Point out E-W brittle fault
  • NE, NNW brittle faults, E-W shearsApproximate locations of first 3 drill holes, all hit mineralization.
  • Late tectonic to post tectonic pegmatitesUnmineralized pegmatites tend to be later, but not always the case
  • Emphasize they are graniticComplex variable bt-rich to qtz-rich to k-sp rich; mineralization greatest within biotite rich quartz rich pegmatitesComplexly zoned because of AFC processesSubdivided into two groups U-enriched vs. Th + REEs
  • Stack photos
  • Stack Have arrows to pel gn, u rich peg, th rich pegm, non rad pegmatite. Two diagrm
  • Shand diagram
  • Log U vs. SiO2Log Th vs. SiO2Log La vs. P2O5Th vs. U
  • Digress to talk about the host rocks to the granitic pegmatites since their metamorphic grade is importantNO prograde metamorphic muscovite
  • Scale bar and Kretz symbols
  • Melt Transfer zoneBottom part gt richMid crd + gtUpper crdGt in pegmatites – coming from deeper, gt-sill-crd host rock, middle to upper zone
  • Basement relationships very similar, Similar to Rössing (one of the largest open pit U mines) and Rössing South, also similar occurrences in Grenville
  • Top figure shows what it may have looked like when the Athabasca was overtop.Bottom figure shows the location of basement and sandstone hosted uranium deposits, alteration zones, etc.
  • Austman - Departmental Seminar - Fraser Lakes Zone B Mineralization

    1. 1. Fraser Lakes Zone BPegmatite-hosted U-Th-REE mineralization: Geology, geochemistry, and origin<br />Christine Austman<br />Department of Geological Sciences<br />University of Saskatchewan<br />
    2. 2. <ul><li>Purpose
    3. 3. Regional Geological Setting
    4. 4. Fraser Lakes Geology
    5. 5. Granitic Pegmatite Mineralogy and Geochemistry
    6. 6. Alteration and Remobilization of U-Th-Pb-REE
    7. 7. Metamorphism and Migmatization
    8. 8. Metallogenetic Model
    9. 9. Similarities to other uranium deposits
    10. 10. Conclusions</li></ul>Outline<br />
    11. 11.
    12. 12. Unresolved issues still exist in understanding uranium source, fluid flow, and the nature of the reductant involved in the formation of unconformity- related (U/C) uranium deposits<br />Determine if uraniferous pegmatites are related to high-grade unconformity-related uranium deposits of the Athabasca Basin (U protore?)<br />Determine whether granitic pegmatites represent a distinct target for uranium exploration in Saskatchewan <br />Purpose of this study<br />
    13. 13. <ul><li>The Wollaston Domain </li></ul> consists of:<br /><ul><li>Archean orthogneisses (predominantly granitic gneisses)
    14. 14. Paleoproterozoic Wollaston Group metasedimentary rocks
    15. 15. Hudsoniangranites, amphibolites, leucogranites, migmatites, and granitic pegmatites</li></ul>Regional Geology<br />
    16. 16. Fraser Lakes Geology<br /><ul><li>NE-SW regional fabric
    17. 17. Two mineralized zones: A and B
    18. 18. Zone A is in a NNE-plunging synformal and Zone B is in an NNE-plunging antiformal fold nose
    19. 19. 5 km section of a complexly folded electromagnetic (EM) conductor (i.e. graphitic pelitic gneisses) is adjacent to Zones A and B</li></ul>Wollaston Group metasedimentary gneisses<br />Wollaston Group metasedimentary gneisses<br />Johnson River<br />Granite Inlier<br />Fraser Lakes Granite Inlier<br />Fraser Lakes Zone B<br />Needle Falls Shear Zone<br />Wathaman <br />Batholith<br />Fraser Lakes <br />Zone A<br />After Ray, 1979<br />
    20. 20. Fraser Lakes Zone B<br /><ul><li>The surface expression of the EM conductor adjacent to Fraser Lakes Zone B isa swampy, low-lying area
    21. 21. Zone B mineralization outcrops at surface on the eastern edge of the swamp
    22. 22. Fold nose is visible from the air</li></li></ul><li>Fraser Lakes Zone B geology<br />WYL-08-526<br />WYL-08-524<br />WYL-08-526<br />Modified from Ko, 1971<br />
    23. 23. Granitic pegmatites<br /><ul><li>Granitic pegmatites with variable amounts of quartz, feldspar, biotite, and other minerals
    24. 24. Overall coarse grained to pegmatitic
    25. 25. Variable size (cm to several m scale)
    26. 26. Complexly zoned (igneous AFC processes)
    27. 27. Multiple generations of granitic pegmatites
    28. 28. 1810-1790 Ma uraninite U-Pb chemical ages in mineralized pegmatites</li></li></ul><li>Mineralogy <br />Highly Variable!<br />U-Th-REE Minerals<br /><ul><li>Zircon (Zrn)
    29. 29. Uraninite (Urn)
    30. 30. Uranothorite – Thorite (Uth)
    31. 31. Monazite (Mz)
    32. 32. Allanite (Aln)
    33. 33. Xenotime (Xen)</li></ul>Primary Minerals<br /><ul><li>Quartz (Qtz)
    34. 34. Feldspar (Fsp)
    35. 35. Biotite (Bt)
    36. 36. Magnetite (Mgt)
    37. 37. Ilmenite (Ilm)
    38. 38. Pyrite (Py)
    39. 39. Fluorite (Fl)
    40. 40. Sphalerite
    41. 41. Molybdenite
    42. 42. Apatite (Ap)
    43. 43. Titanite
    44. 44. Rutile
    45. 45. Garnet
    46. 46. Chalcopyrite
    47. 47. Pyrrhotite
    48. 48. Graphite
    49. 49. Nb-oxide?</li></li></ul><li>Uraninite- and uranothorite-bearing<br />Also contain zircon and minor allanite<br />Monazite is very rare<br />Intrude the western part of the fold nose<br />Uraniferous pegmatites<br />
    50. 50. <ul><li>Monazite-rich
    51. 51. Also contain zircon, uranothorite-thorite, altered allanite, and xenotime as the main </li></ul> U-Th-REE hosts<br /><ul><li>Generally confined to eastern portions of the fold nose</li></ul>Th- and LREE Pegmatites <br />
    52. 52. Alteration of granitic pegmatites<br />Retrograde Alteration<br /><ul><li>Chlorite (Chl)
    53. 53. Epidote (Ep)
    54. 54. Sericite (Ser)
    55. 55. Hematite (Hem)
    56. 56. Quartz (Qtz)</li></ul>Hydrothermal Alteration<br /><ul><li>Fluorite (Fl)
    57. 57. Chlorite (Chl)
    58. 58. Hematite (Hem)
    59. 59. Clay minerals
    60. 60. Sausserite
    61. 61. Carbonate(Cal)
    62. 62. Quartz (Qtz)</li></li></ul><li><ul><li>Uranothorite - evidence for reaction (i.e. elevated Zr) where in contact with zircon
    63. 63. Radiogenically produced galena inclusions in U-Th-REE minerals
    64. 64. Uraninite and secondary uranium minerals in fractures with galena and pyrite
    65. 65. Monazite -commonly altered to hematite, chlorite, and clay</li></ul>Alteration of U-Th-REE phases and remobilization of U, Th, Pb<br />
    66. 66. Major element geochemistry<br />Legend<br />
    67. 67. Samples range from strongly peraluminous (off the chart) to slightly metaluminous<br />S-type granitoids<br />Alumina saturation index<br />
    68. 68. Two major compositional subdivisions of pegmatites; correspond to mineralogical subdivisions<br />U- plus Th-rich<br />Th- and LREE-rich<br />Trace element geochemistry<br />
    69. 69. Garnet<br />Biotite<br />Cordierite<br />Sillimanite<br />Spinel<br />K-feldspar<br />Quartz<br />Plagioclase<br />Rutile<br />Myrmekite<br />NO prograde <br /> muscovite<br />Metamorphic Mineral Assemblages – Pelitic gneisses<br />Upper amphibolite to lower granulite facies metamorphism<br />
    70. 70. Clinopyroxene<br />Orthopyroxene<br />Hornblende<br />Biotite<br />Spinel<br />Myrmekite<br />Quartz<br />K-feldspar<br />Plagioclase<br />Metamorphic Mineral Assemblages –Orthogneisses<br />Upper amphibolite to lower granulite facies metamorphism<br />
    71. 71. Pegmatites – Partial melting at depth vs. in situ melting ?<br />Migmatitesassociated with the granitic pegmatites<br />Leucosomes tend to be boudinaged<br />Locally small pegmatitic veins of leucosome<br />
    72. 72. Melt occasionally forms thin rims around minerals, and locally larger blobs<br />Common near the contact between biotite and garnet and within K-feldspar<br />Biotite frequently shows degradation due to partial melting<br />Migmatites and melt-textures in the pelitic gneisses<br />
    73. 73. Metallogenetic model – Fraser Lakes Zone B<br /><ul><li>Melts generated at depth (a)
    74. 74. Transported upwards along the structural discontinuity/contact between Archean and Wollaston Group (b)
    75. 75. Underwent igneous assimilation-fractional crystallization during transport and crystallization
    76. 76. Melts were concentrated in antiformal fold noses (c)
    77. 77. Peraluminous to weakly metaluminous chemistry agrees with the pegmatites forming due to partial melting of pelitic gneisses</li></ul>c<br />b<br />a<br />
    78. 78. Similarities to Rössing/Rössing South, among other deposits<br /><ul><li>Uranium mineralization within late-tectonic to post-tectonic granitoids
    79. 79. Structurally controlled: mineralization concentrated in antiformal fold noses
    80. 80. Concentrated in areas of highest metamorphic grade
    81. 81. Formed from melts generated by partial melting of metasedimentary gneisses</li></ul>Modified from Ray, 1979<br />Extract Resources, 2009<br />
    82. 82. Similarities to Athabasca unconformity-type uranium deposits<br /><ul><li>Radioactive leucogranites and granitic pegmatites are in the basement rocks under several Athabasca Basin unconformity uranium deposits (ex: McArthur River Zone 2, Millenium, Roughrider, and others)
    83. 83. Chlorite, clay, and hematite alteration with drusy quartz found in Zone B drill core is similar in appearance to that of basement-hosted unconformity uranium deposits</li></ul>~150 – <br />200 m<br />Modified from Ray, 1979<br />Jefferson et al. 2007<br />
    84. 84. Conclusions<br /><ul><li>Structurally controlled, basement-hosted U and Th mineralization (+/- REE mineralization)
    85. 85. Hosted by Hudsonian granitic pegmatites intruding at/near the contact between Wollaston Group metasediments and Archean orthogneisses
    86. 86. Granitic pegmatites formed by partial melting of metasedimentary rocks in the middle to lower crust followed by transport and assimilation-fractional crystallization
    87. 87. Regional metamorphism up to lower granulite facies
    88. 88. Granitic pegmatites experienced post-crystallization alteration and remobilization of U and Th
    89. 89. Similarities to Rossing and U/C-related basement-hosted uranium deposits</li></li></ul><li>Acknowledgements<br />Thesis co-supervisors: Dr. Irvine Annesley and Dr. Kevin Ansdell<br />JNR Resources Inc. – access to drill core, geological and geophysical datasets, logistical support, and financial assistance<br />NSERC - Discovery Grant (Kevin)<br />University of Saskatchewan Graduate Scholarship<br />Saskatchewan Research Council – geochemical analysis<br />Blaine Novakovski – thin section preparation<br />Kimberly Bradley – assistance with petrography<br />Steven Creighton and Tom Bonli – assistance with electron microprobe analyses<br />