Fraser Lakes Zone B pegmatite-hosted U-Th-REE mineralization - chemistry, petrography, and origin of the mineralization.

1. Mineralogy, geochemistry and economic potential of granitic pegmatite- and leucogranite-hosted a) b) c)
a) b)
a) b)
uranium & thorium mineralization adjacent to the Athabasca Basin
AUSTMAN, Christine L.1, ANNESLEY, Irvine R.1,2, and ANSDELL, Kevin M.1
(1) Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK Canada S7N 5E2 (E-mail: christine.austman@usask.ca);
(2) JNR Resources Inc., Saskatoon, SK, Canada S7K 0G6
Introduction Location of the study area Mineralogy
Fig. 9. a) U vs. P2O5; b) Th vs. P2O5; b) Ce vs. P2O5 diagrams showing the evolution of the granitic pegmatite’s U, Th, Fig. 10. a) U vs. TiO2 and b) Th vs. TiO2 diagrams showing that the “U Fig. 11. a) MgO vs. TiO2 and b) Fe2O3t vs. TiO2 diagrams show fractionation
The Fraser Lakes Zone B uranium-thorium- Fig.1  Pegmatites are granitic in composition, with quartz, feldspar, and biotite being the main minerals in almost every pegmatite and LREE contents away from pelitic gneiss values. Trends represent the fractionation of different U-Th-REE pegmatites” are generally more depleted in TiO2 (i.e. are more trends of the pegmatites away from pelitic gneiss and orthogneiss compositions.
rare earth element (REE) mineralization is  Other minerals that may or may not be present include garnet, magnetite, ilmenite, titanite, muscovite, apatite, fluorite, sulphides, and minerals, which include uraninite ± zircon for the “U pegmatite. For the “Th pegmatites, two trends are apparent - fractionated) than the “Th pegmatites” and contain greater amounts of U. Note the trend of the magnetite- and ilmenite-bearing granitic pegmatites
the low P2O5-high U and Th trend is interpreted to be caused by uranothorite-thorite fractionation, while the trend The “Th pegmatites” tend to have TiO2 values comparable to and/or (intrusive into the Archean orthogneisses) away from the granitic orthogneiss
hosted in highly fractionated peraluminous to U-Th-REE-bearing accessory minerals (see below) towards higher P2O5 with increasing Th and Ce is thought to be due to monazite fractionation. greater than the pelitic gneisses. compositions on the MgO vs. TiO2 diagram, indicating a possible compositional
metaluminous granitic pegmatites and  U-Th-REE mineral assemblage is dependent on the uranium, thorium, LREE, and phosphate concentrations of the melt, and varies relationship between these pegmatites and the granitic Archean orthogneisses.
Fig. 13. a) FeOt/(FeOt+MgO) vs. SiO2 plot
leucogranites, formed by partial melting and depending on location in the fold nose Fig. 12. a) Al2O3 vs.
SiO2 and b) TiO2 vs. (Frost et al. 2001). “Th pegmatites” are
subsequent fractional crystallization during  Pegmatites intruded into the Archean orthogneisses contain magnetite and ilmenite intergrowths SiO2 diagrams
a) b) ferroan to magnesian while “U a) b) c)
thermal peak conditions of the Trans-Hudson  Chlorite, hematite, fluorite, clay, silica, sericite, and carbonate alteration is present in some pegmatites showing fractionation pegmatites” are magnesian and appear to
trends of the granitic be fractionated away from the “Th
Orogen (THO). The mineralization is similar pegmatites. “U pegmatites”. The magnetite- and ilmenite-
to that in pegmatite-hosted uranium deposits U– and Th-enriched pegmatites (“U pegmatites”) Th– and REE-enriched pegmatites (“Th pegmatites”) pegmatites” tend to bearing pegmatites plot in the ferroan field
as their own separate group. b) Modified
of the Grenville Province and the Rössing  U-Th-REE minerals: zircon, uraninite, and allanite  U-Th-REE minerals: monazite, members of the uranothorite- be more fractionated
away from pelitic alkali lime index (Na2O+K2O-CaO) vs.
deposit in Namibia, but also shares some thorite solid solution series, zircon, and allanite SiO2 diagram (Frost et al. 2001) showing
 Mineralogy is indicative of Černý and Ercit’s (2005) Abyssal-U gneiss compositions to
characteristics with basement-hosted  Mineralogy is indicative of Černý and Ercit’s (2005) Abyssal- high SiO2 values the pegmatites trending from alkalic to
subclass calcic. c) Shand (1943) plot showing the
LREE subclass whereas “Th
unconformity-type (U/C-type) uranium  Confined to the western part of the fold nose pegmatites” are only peraluminous to weakly metaluminous
 Most are in the eastern part of the fold nose, but a few are in the weakly fractionated. character of the pegmatites.
deposits of the eastern Athabasca Basin western part of the fold nose
(Cuney, 2009). This study is being undertaken a) b)
to document the geological and structural  Fraser Lakes Zones A and B are located in JNR Resource’s
a) Economic Potential
controls on the Fraser Lakes mineralization Way Lake Property (Fig. 1 - modified map from JNR b) Origin of the Mineralization
and to determine the relationship (s) between Resources Inc., 2010) in northern Saskatchewan, Canada  Geochemical trends (Figs. 9-12) of the  U, Th, and LREE mineralization has been found in outcrop at the surface and within drill core to a depth of 250 m
pegmatite-hosted and U/C-type uranium  ~ 25 km from the SE edge of the Athabasca Basin pegmatites away from pelitic and migmatitic in a 500 m by 1.5 km area (Austman et al. 2009, 2010a)
deposits.  ~ 55 km from the Key Lake Uranium Mine pelitic gneiss compositions and their  Grades of up to 0.242% U3O8 with 0.254% ThO2 (over 0.5 m) in drill core from the west wide of the fold nose; up to
peraluminous to metaluminous chemistry (Fig. 0.109% ThO2 with 0.013% U3O8 (JNR Resources Inc., 2010) and significantly elevated LREE contents (up to 7000
13 c) are evidence that the pegmatite melt was ppm Ce in some samples) in the eastern part of the fold nose
Geologic Setting sourced from pelitic rocks in the lower to  Similar to pegmatite-hosted uranium deposits in the Grenville province (Lentz, 1998) and in Namibia (Rössing U
c) d) Fig. 14. Garnetiferous deposit, Berning et al., 1976)
 Area is underlain by Archean orthogneisses, Wollaston Group middle crust of the Fraser Lakes area, with
pelitic gneiss
metasedimentary rocks (pelitic gneisses ± graphite, psammopelitic c) some contribution from Archean orthogneisses (WYL-09-44-61.4) with  Radioactive granitic pegmatites are common in the Wollaston Domain, including underlying/hosting Athabasca Ba-
d)
gneisses, and calc-silicate gneisses), and Hudsonian intrusives  Migmatitic textures in the host pelitic gneisses, melt micro-textures at the sin U/C-type uranium deposits; these are thought to be a major source of uranium for U/C-type deposits (Annesley
(Annesley et al., 2009, Austman et al., 2009, 2010) melt reaction micro-textures (Fig. 14) and high contact between garnet and Madore, 1999; Annesley et al., 2000, 2005, 2010b; Hecht and Cuney, 2000; Madore et al., 2000; Mercadier et al.,
and biotite. Biotite is being
 Complexly deformed, intruded and metamorphosed (upper regional metamorphic grade, indicate that consumed in the melt- 2009; Portella and Annesley, 2000a, b; Richard et al., 2010)
amphibolite to lower granulite facies) during the Trans-Hudson significant partial melting occurred in the generating reaction.  Hydrothermal alteration of the Fraser Lakes granitic pegmatites and surrounding host rocks is similar in style and
Orogen ~1.8 Ga (Annesley et al., 2009; Austman et al., 2009, 2010) Fraser Lakes area (Austman et al. 2009, 2010a) composition to that of basement-hosted U/C-type uranium deposits; is related to basinal brine circulation in the
 Two mineralized zones, A and B, are hosted by NE-plunging  Primary mineralization ages are consistent with melting during high- basement rocks and remobilization of uranium and other metals (Austman et al. 2009, 2010; Mercadier et al., 2009)
regional fold structures adjacent to a 65km long folded grade THO metamorphism (Annesley et al., 2010a)  High potential for discovering U/C-type mineralization in the Fraser Lakes area
Fig. 4. Typical “U pegmatites” a) Granitic pegmatite from WYL-09-50 (~191.6 m) with
electromagnetic (EM) conductor (Annesley et al., 2009) Fig. 2 Total field aeromagnetic image of the Fraser abundant zoned zircon (Zrn), apatite (Ap), and monazite (Mnz) in a cluster of biotite (Bt).
Lakes area. The EM conductor (red dots)
 At Zone B, the uranium and thorium mineralization is located in a b) Disseminated fine grained uraninite (Urn) in a pleochroic halo around an altered Fig. 5. Typical “Th pegmatites” a) WYL-09-46-42; b) WYL-09-46-36.1; c) WYL-09-46-42
~500 m x 1500 m area northwest of the Fraser Lakes in a
corresponds to an aeromagnetic low (blue to green
colors). The black dashed lines are basement allanite (Aln) grain in a granitic pegmatite from WYL-09-50 (~ 232.9 m) intrusive into containing quartz, (Qtz), feldspar (Kfs), biotite, altered monazite, zircon, and altered Conclusions
lineaments/structures. Archean orthogneisses and containing ilmenite (Ilm) and magnetite (Mgt) c) and d) Hem- uranothorite-thorite (Thr) with pyrite (Py) inclusions). Monazite is being altered to
antiformal fold nose (Fig. 2, 3; Austman et al., 2009, 2010) atite (Hem), fluorite (Fl), chlorite (Chl), carbonate (Cal), sericite (Ser) and epidote (Ep) hematite (Hem), chlorite (Chl), and clay. d) “Th Pegmatite” (WYL-09-46-83.0) intrusive  Structurally controlled, basement-hosted U-Th-LREE mineralization within Hudsonian leucogranites and granitic pegmatites
 Multiple generations of pegmatites including syn-tectonic
alteration of uranium-mineralized granitic pegmatites. Abbreviations after Kretz into Archean orthogneiss containing quartz, ilmenite, magnetite, titanite (Ttn), and  Granitic pegmatites intruded the highly deformed Archean/Paleoproterozoic contact which may represent a pre-existing redox front
(1983). monazite is being altered to chlorite and hematite.
subcordant to gneissosity, often radioactive) and post-tectonic  Pegmatites on the east side of the fold nose are Th– and LREE-enriched and U-depleted, whereas those on the west side are highly fractionated, U– and Th-rich pegmatites
(discordant, non-mineralized) pegmatites intrude the contact  Formed by partial melting and subsequent fractional crystallization during the THO, similar to the formation of the Grenville Province and Namibian pegmatite-hosted uranium deposits
between the Archean orthogneisses and Wollaston Group (Austman  Pegmatites and host rocks are similar to the basement rocks underlying and/or hosting many U/C-type uranium deposits of the eastern Athabasca Basin, thought to be the main source of uranium
et al., 2009, 2010) Geochemistry for the deposits (U-protore)
 E-W ductile-brittle and NNW- and NNE-trending brittle
 Post-crystallization alteration of the pegmatites with variable U-loss indicates the potential for uranium remobilization and formation of U/C-type uranium mineralization in the Fraser Lakes area
structures cross-cut Zone B (Annesley et al., 2009)
Legend for all References Acknowledgements
 U-Th-Pb chemical age dating of uraninite from one of the
geochemical Annesley, I.R. & Madore, C., 1999, Leucogranites and pegmatites of the sub-Athabasca basement, Saskatchewan: U protore?: In: Stanley, C.J. et al., (eds.) Mineral Deposits: Processes to Processing, Balkema 1: 297-300. The authors acknowledge
Fraser Lakes pegmatites yielded a crystallization age of 1770 ±90 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, Vol. 2, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 2000-4.2. p. 201-211. the financial support of JNR
diagrams 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. Resources Inc., NSERC
Ma, plus younger age clusters correlated to U-mineralization 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: Proceedings of the 24th International Applied Geochemistry Symposium
(IAGS), Fredericton, NB. Conference Abstract Vol.1. p. 409-414.
(Discovery Grant to Ansdell)
and the University of
Fig. 3. Aerial photograph of the Fraser Lakes Zone
events in the Athabasca Basin (Annesley et al., 2010a) B area looking northeast.
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, Extended Abstract.
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.
Saskatchewan (Department
Heads Research Grant to
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. Ansdell and Graduate
Austman, C.L., Ansdell, K.M., and Annesley, I.R., 2010, Petrography and geochemistry of granitic pegmatite and leucogranite- hosted uranium & thorium mineralization: Fraser Lakes Zone B, northern Saskatchewan, Canada: GeoCanada 2010, Calgary, Canada, May 2010, Extended Abstract. Scholarship to Austman).
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JNR Resources Inc., 2010, —Home Page—July 30, 2010: JNR Resources Inc., Saskatoon, SK Canada, 07/30/2010, http://www.jnrresources.com. and the Saskatchewan
Analytical Methods Fig. 6. Chondrite-normalized (Sun and McDonough, 1989) Fig. 7. Chondrite-normalized (Boynton, 1984) REE spider Fig. 8. Feldspar diagram showing the
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Research Council for the
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holes and outcrops for petrographic study. Whole rock geochemical analysis (by ICP-MS, ICP-OES, and XRF) of Th, and U between the “Th pegmatites” and “U the enrichment in REEs and in particular LREE in the pegmatites based on CIPW norm values. 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).
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