GeoCanada 2010 - Austman et al - Fraser Lakes Zone B
PETROGRAPHY AND GEOCHEMISTRY OF GRANITIC PEGMATITE AND LEUCOGRANITE- HOSTED URANIUM & Other Pegmatites (U– and Th– enriched plus non-enriched samples)
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: firstname.lastname@example.org); 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
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
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
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
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
83.0), 15 (WYL-09-46-
42.8) Pegmatites with
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.