GeoCanada 2010 - Austman et al - Fraser Lakes Zone B
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GeoCanada 2010 - Austman et al - Fraser Lakes Zone B

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Poster presented at GeoCanada 2010 on the Fraser Lakes Zone B U-Th-REE mineralization

Poster presented at GeoCanada 2010 on the Fraser Lakes Zone B U-Th-REE mineralization

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GeoCanada 2010 - Austman et al - Fraser Lakes Zone B GeoCanada 2010 - Austman et al - Fraser Lakes Zone B Presentation Transcript

  • PETROGRAPHY AND GEOCHEMISTRY OF GRANITIC PEGMATITE AND LEUCOGRANITE- HOSTED URANIUM & Other Pegmatites (U– and Th– enriched plus non-enriched samples) Geochemistry Highly Th– and LREE-enriched pegmatites (high Th/U) THORIUM MINERALIZATION: FRASER LAKES ZONE B, NORTHERN SASKATCHEWAN, CANADA Fig. 20 Major element (TiO2, Al2O3, FeOt, MgO, CaO, Na2O, K2O and P2O5; all in wt. %) and trace Fig. 22 Major and trace element Harker diagrams for the Th– and LREE-rich pegmatites. These 1 1 1,2 AUSTMAN, Christine L. , ANSDELL, Kevin M. , and ANNESLEY, Irvine R. element (Ba, Rb, Sr, Zr, Th/U, and Y; all in ppm) pegmatites show strong P2O5 enrichment due to (1) Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E2 (E-mail: christine.austman@usask.ca); Harker diagrams. Some of the elements (Al2O3, CaO, monazite; Th enrichment due to monazite, (2) JNR Resources Inc., Saskatoon, SK, Canada S7K 0G6 Na2O, K2O, and Sr) show weak trends likely related uranothorite-thorite, and allanite; Zr enrichment to igneous assimilation-fractional crystallization processes. The Zr content is mainly controlled by zir- due to zircon; and strong Y anomalies due to allanite and/or garnet. These pegmatites have lower Abstract Mineralogy con, while Y is mostly related to the presence of al- lanite and/or garnet. These pegmatites have higher SiO2 contents than the other pegmatites (with the Located just outside of the Athabasca Basin, the Fraser Lakes uranium- and thorium- bearing granitic pegmatites and  The radioactive granitic pegmatites, leucogranites and migmatitic leucosomes intrude the highly SiO2 contents than the Th-rich pegmatites and have lowest SiO2 contents being in samples containing deformed contact between Archean orthogneisses and the overlying Wollaston Group (Fig. 6, 11) variable chemistry suggesting that the data could be abundant garnet). Weak trends in the K2O and Ba leucogranites are one example of igneous-hosted uranium and thorium occurrences in the Wollaston Domain of northern from multiple groups of pegmatites. The spread in Saskatchewan. The mineralized granitic pegmatites and leucogranites intrude the highly deformed contact zone between  Zoning (Fig. 5) is common, due to igneous assimilation-fractional crystallization (AFC) processes the data also could be due to chemical zonation data are suggestive of igneous assimilation- fractional crystallization processes. Wollaston Group metasedimentary rocks and underlying Archean orthogneisses. Whole rock geochemical analyses of  Variable primary mineralogy, including quartz, feldspar, biotite, ± garnet, ± magnetite, within individual pegmatites. drill core samples from Zone B indicates the presence of multiple groups of granitic pegmatites that underwent igneous ± ilmenite, ± titanite, ± muscovite, ± apatite, ± fluorite, ± sulphides, ± zircon, ± U-Th-REE-bearing assimilation-fractional crystallization (AFC) processes. The granitic pegmatites generally fall within Černý and Ercit’s accessory minerals which vary depending on the composition of the pegmatite (See below for the Fig. 21 Classification Fig. 23 (2005) Abyssal-U and Abyssal-LREE pegmatite subclasses, and include syn-tectonic and post-tectonic varieties. The plots after Frost et al. All pegmatites (mineralized and unmineralized) Classification plots different kinds of pegmatites; also Fig. 7-10, 12-15, 17-19) granitic pegmatites are generally S-type and A-type granitoids that formed by partial melting of the intrusive hosts. Al- (2001) and Shand Fig. 24 U (ppm) vs. SiO2 (wt. Fig. 25 Chondrite-normalized (Boynton 1984) after Frost et al. teration of these pegmatites may have led to the remobilization of uranium and the development of unconformity-type  Accessory mineral assemblage is dependent on host rocks (example: magnetite is found only in (1943) showing that %) and Th (ppm) vs. SiO2 REE plot showing the differences in REE contents (2001) and Shand uranium mineralization in the Fraser Lakes area. pegmatites intruded into the Archean orthogneisses) and the melt composition (see below) these pegmatites are (wt. %) plots of mineralized of the different pegmatites. The Th– and LREE- (1943) showing that The pegmatites in the western part of the fold nose tend to be enriched in both U and Th (Fig. 6- more magnesian and unmineralized rich pegmatites show strong enrichment in the the Th-rich Introduction  Fig. 5 Drill core from WYL-09-50 showing fractionation from quartz-rich to feldspar-rich relative to the Th-rich pegmatites are more 10) with low Th/U ratio, while the pegmatites in the eastern part of the fold nose tend to have high pegmatites. The pegmatites. The uranium and LREEs and weak enrichment of most of the iron-rich than the in the core of this radioactive granitic pegmatite(158.7 - 62.7m). thorium mineralization in the HREEs relative to the other pegmatites. The  Fraser Lakes Zones A and B are located in JNR Resources Inc.’s Th/U ratios, and show Th– and LREE-enrichment (Fig. 11-15) pegmatites are also Fraser Lakes pegmatites is strong negative Eu-anomaly of the Th– and LREE majority of the other Way Lake Property, ~ 55 km from the Key Lake uranium mine in weakly metaluminous characteristic of Černý and -rich pegmatites is likely due to plagioclase frac- pegmatites and are the Athabasca Basin and ~25 km from the basin’s SE edge (Fig. 1) U– and Th-enriched pegmatites (western part of the fold nose) Th– and REE-rich granitic pegmatites (eastern part of fold nose) to peraluminous in Ercit’s (2005) Abyssal-U class tionation. The LREE enrichment in the Th– and peraluminous in composition. composition.  Paleoproterozoic Wollaston Group metasedimentary rocks and of granitic pegmatites. LREE-rich pegmatites is indicative of Černý and Fig. 6. Cross-section from the Fig. 11 Cross-section from Ercit’s (2005) Abyssal-LREE subclass. Archean orthogneisses underlie the study area, which was complexly western limb of the fold nose at the northern limb of the deformed, intruded, and metamorphosed during the Trans-Hudson Zone B. Drill holes include fold nose at Zone B. Drill Origin of the granitic pegmatites and primary mineralization Orogen (~ 1.8 Ga) WYL-09-41, -42, -49, and -50. holes include WYL-09-  Zone A is in a NE-plunging synformal fold nose and Zone B is in an Note the increase in 43a, -43, -44, -45, and -46.  Garnet, cordierite, sillimanite, pyroxenes, hornblende, and spinel in the surrounding metamorphic Fig. 26 Drill core from antiformal fold nose adjacent to a 65km long folded electromagnetic radioactivity (blue line – gamma Note the increase in rocks indicate that the regional metamorphism was of upper amphibolite to granulite facies WYL-09-524 (~15.6-19.8 (EM) conductor (Fig. 2, 4) probe results) in the granitic radioactivity in the  Abundant migmatites in drill core (Fig. 26) indicate that these metamorphic rocks underwent m) with boudinaged pegmatites (red units) with local granitic pegmatites with crustal melt pods and partial melting, consistent with melt micro-textures seen in thin section (Fig. 27, 28) radioactive granitic increases in pelitic gneiss (green) local increases in pelitic  At Zone B, the uranium and thorium mineralization is located in a Fig. 1 Location of JNR’s properties in northern and Archean orthogneiss and gneiss, granite gneiss, and  Significant-sized granitoids of similar age and appropriate geochemistry in the area are not pegmatites. ~500 m x 1500 m area northwest of the Fraser Lakes (Fig. 2, 4) Saskatchewan, including the Way Lake Property granitic gneiss (orange and orthogneiss intervals. See common (i.e. typical of the middle crust) (modified from map on JNR Resources Inc. Peraluminous to weakly metaluminous composition (Fig. 21, 23), plus the mineralogy of the granitic Fig. 27, 28 Garnetiferous  Multiple generations of pegmatites including syn-tectonic pink) intervals. See Fig. 4 for Fig. 4 for the location of  website). the location of the cross-section. the cross-section. pelitic gneiss (WYL-09-44- (subcordant to gneissosity, often radioactive) and post-tectonic pegmatites and leucogranites (quartz-feldspar-biotite-garnet) is consistent with an origin by partial melting of 61.4) with melt micro-textures (discordant, non-mineralized) pegmatites (Austman et al. 2009) metasedimentary rocks at variable depths within the middle to lower crust at the contact between garnet  E-W ductile-brittle and NNW– and NNE-trending brittle structures cross-cut Zone B (Annesley et al., 2009)  U-Th-REE minerals: monazite, zircon, allanite, and members of the  Difference in U and Th contents of the granitic pegmatites could be due to a combination of factors, including and biotite. Biotite is being  U-Th-REE minerals: zircon, allanite, and uraninite uranothorite-thorite solid solution series igneous assimilation and fractional crystallization (AFC) processes, interaction with magmatic fluids (B, F, Cl, consumed in the melt-  Preliminary U-Th-Pb chemical age dating of uraninite from one of the Fraser Lakes pegmatites yielded a  Mineralogy is indicative of Černý and Ercit’s (2005) Abyssal-U subclass  Mineralogy is indicative of Černý and Ercit’s (2005) Abyssal-LREE subclass CO2, H2O), different melt-generating reactions, and variable source rock chemistry in the middle to lower crust generating reaction. crystallization age of 1770 ±90 Ma, plus younger age clusters which can be correlated to U-mineralization events in the Athabasca Basin (Annesley et al. 2010a) Fig. 7 (PPL), 8 Fig. 12, 13. Biotite- Conclusions (XPL); Granitic rich section of a  Radioactive granitoids similar to the Fraser Lakes granitic pegmatites underlie several unconformity pegmatite from  Structurally controlled, basement-hosted U, Th, and LREE mineralization in Hudsonian-aged leucogranites and granitic pegmatites intruded into the highly deformed contact granitic pegmatite uranium deposits of the eastern Athabasca Basin, including P-Patch, McArthur River Zone 2, Eagle WYL-09-50 (~191.6 (WYL-09-46-36.1) between Paleoproterozoic graphitic pelitic gneisses and Archean orthogneisses Point, Sue C, and Roughrider (Annesley et al., 2000a, 2000b, 2005, 2009, 2010b; Annesley and Madore, m) with abundant with hematized  The pegmatites on the northern limb of the fold nose are Th– and LREE-enriched, becoming U– and HREE-enriched on the western side of the fold nose 1999; Madore et al., 2000; Portella and Annesley, 2000) zoned zircon (Zrn), monazite (Mnz),  Granitic pegmatites are of Černý and Ercit’s (2005) Abyssal-U and Abyssal-LREE subclasses, and formed by partial melting of the Wollaston Group Radioactive granitoids are one of the potential sources of the uranium for the unconformity U deposits apatite (Ap), and uranothorite-thorite  monazite (Mnz) in a (Thr) containing  Post-crystallization alteration and fluid flow through the rocks raises the possibility of remobilization of U, Th, and REE’s  Prior to erosion, the Athabasca sandstone/basement unconformity was ~ 200-250 m above the present cluster of biotite pyrite (Py) inclusions,  Fraser Lakes U-deposits are similar to several basement-hosted U-deposits in the Athabasca Basin, and to the pegmatite-hosted U deposits in the Grenville Province outcrop surface, indicating the potential for unconformity U mineralization in the area (Annesley et al., 2009) (Bt). Abbreviations and zoned zircon  The potential exists for finding basement-hosted unconformity-type mineralization in the Fraser Lakes area after Kretz (1983). (Zrn). The purpose of this M.Sc. study is to develop a metallogenetic model for the Fraser Lakes deposits,  Future work to include: additional petrography, electron microprobe work, further whole-rock geochemical analysis, Pb-isotope studies, XRF analysis, and U-Pb chemical age and clarify their relationship with the rich uranium deposits in the Athabasca Basin. Fig. 9 (PPL), 10 Fig. 14 (WYL-09-46- dating of the mineralization to aid in the development of a metallogenetic model and examination of the potential for future discoveries (RL); Disseminated fine grained 83.0), 15 (WYL-09-46- 42.8) Pegmatites with References uraninite (Urn) in a monazite (Mnz), zir- Annesley, I.R. & Madore, C., 1999, Leucogranites and pegmatites of the sub-Athabasca basement, Saskatchewan: U protore? Mineral Deposits: Processes to Processing (Stanley, C.J. et al., eds.), Balkema 1: 297-300. Annesley, I., Madore, C., Kusmirski, R., and Bonli, T., 2000, Uraninite-bearing granitic pegmatite, Moore Lakes, Saskatchewan: Petrology and U-Th-Pb chemical ages. In: Summary of Investigations 2000, Volume 2, Saskatchewan Geological Survey, Saskatchewan Energy and pleochroic halo con (Zrn), ilmenite Mines, Miscellaneous Report 2000-4.2. p. 201-211. around an altered (Ilm), magnetite (Mgt), Annesley, I.R., Madore, C. and Portella, P., 2005, Geology and thermotectonic evolution of the western margin of the Trans-Hudson Orogen: evidence from the eastern sub-Athabasca basement, Saskatchewan, Canadian Journal of Earth Sciences, 42, 573-597. allanite (Aln) grain and titanite (Ttn). Annesley, I., Cutford, C., Billard, D., Kusmirski, R., Wasyliuk, K., Bogdan, T., Sweet, K., and Ludwig, C., 2009, Fraser Lakes Zones A and B, Way Lake Project, Saskatchewan: Geological, geophysical, and geochemical characteristics of basement-hosted mineralization. in a granitic Monazite is being Proceedings of the 24th International Applied Geochemistry Symposium (IAGS), Fredericton, NB. Conference Abstract Volume 1. p. 409-414. pegmatite from altered to hematite Annesley, I.R., Creighton, S., Mercadier, J., Bonli, T., and Austman, C.L., 2010a, Composition and U-Th-Pb chemical ages of uranium and thorium mineralization at Fraser Lakes, northern Saskatchewan, Canada. GeoCanada 2010, Calgary, Canada, May 2010. WYL-09-50 (~ (Hem), chlorite (Chl), Annesley, I.R., Wheatley, K., and Cuney, M., 2010b, The Role of S-Type Granite Emplacement and Structural Control in the Genesis of the Athabasca Uranium Deposits. GeoCanada 2010, Calgary, Canada, May 2010, Extended Abstract. 232.9 m). and clay. Austman, C.L., Ansdell, K.M., and Annesley, I.R., 2009, Granitic pegmatite- and leucogranite-hosted uranium mineralization adjacent to the Athabasca basin, Saskatchewan, Canada: A different target for uranium exploration. Geological Society of America Abstracts with Programs, Vol. 41, No. 7, p. 83. Boynton, W.V., 1984. Cosmochemistry of the rare earth elements: meteorite studies. In: Henderson, P. (Ed.), Rare Earth Element Geochemistry. Elsevier, Amsterdam, pp. 63–114. Fig. 2 Topographic map showing the Fig. 3 Aerial photograph (looking to the Fig. 4 Total field aeromagnetic image of the Alteration Černý, P., and Ercit, T. 2005, The classification of granitic pegmatites revisited. The Canadian Mineralogist, 43, 2005-2026. location of Fraser Lakes Zones A and B, the northeast) of the Fraser Lakes Zone B area, Fraser Lakes area. The EM conductor Frost, B.R., Arculus, R.J., Barnes, C.G., Collins, W.J., Ellis, D.J., Frost, C.D., 2001, A geochemical classification of granitic rocks. Journal of Petrology, 42, 2033–2048. folded EM conductor (red dots), drill hole showing the swamp corresponding to the corresponds to an aeromagnetic low (blue  Secondary pyrite is commonly found in Kretz, R., 1983, Symbols for rock-forming minerals. American Mineralogist, 68, 277-279. collars (black dots), swamps (light green), surface trace of the EM conductor. to green colors). The black dashed lines are altered uranium and thorium minerals JNR Resources Inc., 2009, —Home Page—Oct. 10, 2009, Saskatoon, 10/10/2009, http://www.jnrresources.com. and lakes and rivers (blue). basement lineaments/structures. Note the location of Fig. 6 and Fig. 11.  Hematite, chlorite, clay, fluorite, silica, and Lentz, D., 1991, U-, Mo-, and REE-bearing pegmatites, skarns and veins of the Grenville Province, Ontario and Quebec. Can. Journal of Earth Sciences, 28, 1-12. Madore, C., Annesley, I. and Wheatley, K., 2000, Petrogenesis, age, and uranium fertility of peraluminous leucogranites and pegmatites of the McClean Lake / Sue and Key Lake / P-Patch deposit areas, Saskatchewan. GeoCanada 2000, Calgary, Alta., May 2000, Extended Abstract calcite alteration associated with weak to 1041 (Conference CD). Analytical Methods locally strong brittle fracturing (Fig. 16-19) Portella, P. and Annesley, I.R., 2000a, Paleoproterozoic tectonic evolution of the eastern sub-Athabasca basement, northern Saskatchewan: Integrated magnetic, gravity, and geological data. GeoCanada 2000, Calgary, Alta., May 2000, Extended Abstract 647 (Conference CD). Portella, P. and Annesley, I.R., 2000b, Paleoproterozoic thermotectonic evolution of the eastern sub-Athabasca basement, northern Saskatchewan: Integrated geophysical and geological data. in Summary of Investigations 2000, Volume 2: Saskatchewan Geological Survey, Drill core from the Fraser Lakes Zone B deposit was examined for this study, with samples taken from  Alteration indicates that there was post- Saskatchewan Energy and Mines, Miscellaneous Report 2000-4.2, 191-200. several drill holes for petrographic study. After drilling, each hole was probed using a gamma-ray probe to crystallization hydrothermal fluid flow Fig. 16 Granitic pegmatite (96.8 m) in WYL-09- Fig. 17 Moderate to strongly Fig. 18 Granitic pegmatite from Fig. 19 Granitic pegmatite (WYL- Shand, S., 1943, The Eruptive Rocks, 2nd ed., New York: John Wiley, 444 pp. through the rocks, which may have caused 41 with hematite alteration, fracture controlled altered granitic pegmatite (WYL- WYL-09-50 (215.8 m) with calcite- 09-50-166.2) with hematite, test for radioactivity. Whole rock geochemical analysis (by ICP-MS and ICP-OES) of selected samples from pyrite and chlorite, and up to 2100 cps 09-50-215.8) containing zircon, fluorite-quartz veining and altered fluorite, calcite, and epidote Acknowledgements WYL-09-50, WYL-09-49, WYL-09-46, and WYL-09-525 was completed by the Saskatchewan remobilization of the U, Th, and REEs radioactivity. and possibly allanite. feldspar. alteration in fractures. The authors acknowledge the financial support of JNR Resources Inc., NSERC (Discovery Grant to Ansdell) and the University of Saskatchewan (Graduate Scholarship to Austman). Thanks to Blaine Novakovski for preparing the thin sections, to Kimberly Bradley from JNR Research Council Geoanalytical Laboratories in Saskatoon.  Possibly related to Athabasca basinal brines Resources Inc. for her assistance with petrography, and the Saskatchewan Research Council for the geochemical results.