Mineralogy, geochemistry and economic potential of granitic pegmatite- and leucogranite-hosted

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

Fig. 2 Total field aeromagnetic image of the Fraser

Lakes area. The EM conductor (red dots)

corresponds to an aeromagnetic low (blue to green

colors). The black dashed lines are basement

lineaments/structures.

Fig. 4. Typical “U pegmatites” a) Granitic pegmatite from WYL-09-50 (~191.6 m) with

abundant zoned zircon (Zrn), apatite (Ap), and monazite (Mnz) in a cluster of biotite (Bt).

b) Disseminated fine grained uraninite (Urn) in a pleochroic halo around an altered

allanite (Aln) grain in a granitic pegmatite from WYL-09-50 (~ 232.9 m) intrusive into

Archean orthogneisses and containing ilmenite (Ilm) and magnetite (Mgt) c) and d) Hem-

atite (Hem), fluorite (Fl), chlorite (Chl), carbonate (Cal), sericite (Ser) and epidote (Ep)

alteration of uranium-mineralized granitic pegmatites. Abbreviations after Kretz

(1983).

Origin of the Mineralization Geochemical trends (Figs. 9-12) of the

pegmatites away from pelitic and migmatitic

pelitic gneiss compositions and their

peraluminous to metaluminous chemistry (Fig.

13 c) are evidence that the pegmatite melt was

sourced from pelitic rocks in the lower to

middle crust of the Fraser Lakes area, with

some contribution from Archean orthogneisses

Migmatitic textures in the host pelitic gneisses,

melt reaction micro-textures (Fig. 14) and high

regional metamorphic grade, indicate that

significant partial melting occurred in the

Fraser Lakes area (Austman et al. 2009, 2010a)

Primary mineralization ages are consistent with melting during high-

grade THO metamorphism (Annesley et al., 2010a)

Fig. 5. Typical “Th pegmatites” a) WYL-09-46-42; b) WYL-09-46-36.1; c) WYL-09-46-42

containing quartz, (Qtz), feldspar (Kfs), biotite, altered monazite, zircon, and altered

uranothorite-thorite (Thr) with pyrite (Py) inclusions). Monazite is being altered to

hematite (Hem), chlorite (Chl), and clay. d) “Th Pegmatite” (WYL-09-46-83.0) intrusive

into Archean orthogneiss containing quartz, ilmenite, magnetite, titanite (Ttn), and

monazite is being altered to chlorite and hematite.

Th– and REE-enriched pegmatites (“Th pegmatites”) U-Th-REE minerals: monazite, members of the uranothorite-

thorite solid solution series, zircon, and allanite

Mineralogy is indicative of Černý and Ercit’s (2005) Abyssal-

LREE subclass

Most are in the eastern part of the fold nose, but a few are in the

western part of the fold nose

U– and Th-enriched pegmatites (“U pegmatites”)

U-Th-REE minerals: zircon, uraninite, and allanite

Mineralogy is indicative of Černý and Ercit’s (2005) Abyssal-U

subclass

Confined to the western part of the fold nose

References 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.

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.

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.

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.

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.

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.

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.

Berning, J., Cook, R., Hiemstra, S.A., and Hoffman, U., 1976, The Rössing uranium deposit, South-West Africa: Economic Geology, v. 71, p. 351-368.

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.

Černý, P., and Ercit, T., 2005, The classification of granitic pegmatites revisited: Canadian Mineralogist, 43, 2005-2026.

Cuney, M., 2005, The extreme diversity of uranium deposits: Mineralium Deposita, v. 44, p. 3–9.

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.

Hecht, L., and Cuney, M., 2000, Hydrothermal alteration of monazite in the Precambrian crystalline basement of the Athabasca Basin (Saskatchewan, Canada): implications for the formation of unconformity-related uranium deposits: Mineralium Deposita, v. 35, p. 791–795.

Kretz, R., 1983, Symbols for rock-forming minerals: American Mineralogist, 68, 277-279.

JNR Resources Inc., 2010, —Home Page—July 30, 2010: JNR Resources Inc., Saskatoon, SK Canada, 07/30/2010, http://www.jnrresources.com.

Lentz, D., 1996, U, Mo, and REE mineralization in late-tectonic granitic pegmatites, south-western Grenville Province, Canada: Ore Geology Reviews, 11, 197-22 .

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 1041 (Conference CD).

Mercadier, J., Richard, A., Boiron, M.C., Cathelineau, M., and Cuney, M., 2010, Migration of brines in the basement rocks of the Athabasca Basin through microfracture networks (P-Patch U deposit, Canada): Lithos, v. 115, p. 121–136.

O’Connor, J.T., 1965, A classification for Quartz-rich igneous rocks based on feldspar ratios: U. S. Geological Survey Professional Paper 525-B, B79-B84.

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, Vol. 2, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 2000-4.2, 191-200.

Shand, S., 1943, The Eruptive Rocks, 2nd ed., New York: John Wiley, 444 pp.

Richard, A., Pettke, T., Cathelineau, M., Boiron, M.C., Mercadier, J., Cuney, M., and Derome, D., 2010, Brine–rock interaction in the Athabasca basement (McArthur River U deposit, Canada): consequences for fluid chemistry and uranium uptake: Terra Nova, doi: 10.1111/j.1365-3121.2010.00947.x

Sun, S.S., and McDonough, W.F., 1989, Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes: In: Saunders, A.D., Norry, M. (eds.) Magmatism in Ocean Basins: Geological Society of London Special Publication 42, p. 313-345.

Acknowledgements The authors acknowledge

the financial support of JNR

Resources Inc., NSERC

(Discovery Grant to Ansdell)

and the University of

Saskatchewan (Department

Heads Research Grant to

Ansdell and Graduate

Scholarship to Austman).

Thanks to Blaine

Novakovski for preparing

the thin sections, to

Kimberly Bradley from JNR

Resources Inc. for her

assistance with petrography,

and the Saskatchewan

Research Council for the

geochemical results.

Purpose: to develop a metallogenetic model for the Fraser Lakes U-Th-REE mineralization,

and clarify its relationship to unconformity uranium deposits in the Athabasca Basin

Economic Potential U, Th, and LREE mineralization has been found in outcrop at the surface and within drill core to a depth of 250 m

in a 500 m by 1.5 km area (Austman et al. 2009, 2010a)

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

0.109% ThO2 with 0.013% U3O8 (JNR Resources Inc., 2010) and significantly elevated LREE contents (up to 7000

ppm Ce in some samples) in the eastern part of the fold nose

Similar to pegmatite-hosted uranium deposits in the Grenville province (Lentz, 1998) and in Namibia (Rössing U

deposit, Berning et al., 1976)

Radioactive granitic pegmatites are common in the Wollaston Domain, including underlying/hosting Athabasca Ba-

sin U/C-type uranium deposits; these are thought to be a major source of uranium for U/C-type deposits (Annesley

and Madore, 1999; Annesley et al., 2000, 2005, 2010b; Hecht and Cuney, 2000; Madore et al., 2000; Mercadier et al.,

2009; Portella and Annesley, 2000a, b; Richard et al., 2010)

Hydrothermal alteration of the Fraser Lakes granitic pegmatites and surrounding host rocks is similar in style and

composition to that of basement-hosted U/C-type uranium deposits; is related to basinal brine circulation in the

basement rocks and remobilization of uranium and other metals (Austman et al. 2009, 2010; Mercadier et al., 2009)

High potential for discovering U/C-type mineralization in the Fraser Lakes area

Conclusions Structurally controlled, basement-hosted U-Th-LREE mineralization within Hudsonian leucogranites and granitic pegmatites

Granitic pegmatites intruded the highly deformed Archean/Paleoproterozoic contact which may represent a pre-existing redox front

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

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

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

for the deposits (U-protore)

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

Location of the study area

Geologic Setting Area is underlain by Archean orthogneisses, Wollaston Group

metasedimentary rocks (pelitic gneisses ± graphite, psammopelitic

gneisses, and calc-silicate gneisses), and Hudsonian intrusives

(Annesley et al., 2009, Austman et al., 2009, 2010)

Complexly deformed, intruded and metamorphosed (upper

amphibolite to lower granulite facies) during the Trans-Hudson

Orogen ~1.8 Ga (Annesley et al., 2009; Austman et al., 2009, 2010)

Two mineralized zones, A and B, are hosted by NE-plunging

regional fold structures adjacent to a 65km long folded

electromagnetic (EM) conductor (Annesley et al., 2009)

At Zone B, the uranium and thorium mineralization is located in a

~500 m x 1500 m area northwest of the Fraser Lakes in a

antiformal fold nose (Fig. 2, 3; Austman et al., 2009, 2010)

Multiple generations of pegmatites including syn-tectonic

subcordant to gneissosity, often radioactive) and post-tectonic

(discordant, non-mineralized) pegmatites intrude the contact

between the Archean orthogneisses and Wollaston Group (Austman

et al., 2009, 2010)

E-W ductile-brittle and NNW- and NNE-trending brittle

structures cross-cut Zone B (Annesley et al., 2009)

U-Th-Pb chemical age dating of uraninite from one of the

Fraser Lakes pegmatites yielded a crystallization age of 1770 ±90

Ma, plus younger age clusters correlated to U-mineralization

events in the Athabasca Basin (Annesley et al., 2010a)

Analytical Methods Drill core from the Fraser Lakes Zone B deposit was examined for this study, with samples taken from several drill

holes and outcrops for petrographic study. Whole rock geochemical analysis (by ICP-MS, ICP-OES, and XRF) of

drill core and outcrop samples was completed by the Saskatchewan Research Council Geoanalytical Laboratories in

Saskatoon.

Mineralogy Pegmatites are granitic in composition, with quartz, feldspar, and biotite being the main minerals in almost every pegmatite

Other minerals that may or may not be present include garnet, magnetite, ilmenite, titanite, muscovite, apatite, fluorite, sulphides, and

U-Th-REE-bearing accessory minerals (see below)

U-Th-REE mineral assemblage is dependent on the uranium, thorium, LREE, and phosphate concentrations of the melt, and varies

depending on location in the fold nose

Pegmatites intruded into the Archean orthogneisses contain magnetite and ilmenite intergrowths

Chlorite, hematite, fluorite, clay, silica, sericite, and carbonate alteration is present in some pegmatites

Fraser Lakes Zones A and B are located in JNR Resource’s

Way Lake Property (Fig. 1 - modified map from JNR

Resources Inc., 2010) in northern Saskatchewan, Canada

~ 25 km from the SE edge of the Athabasca Basin

~ 55 km from the Key Lake Uranium Mine

Fig. 3. Aerial photograph of the Fraser Lakes Zone

B area looking northeast.

Geochemistry

Introduction The Fraser Lakes Zone B uranium-thorium-

rare earth element (REE) mineralization is

hosted in highly fractionated peraluminous to

metaluminous granitic pegmatites and

leucogranites, formed by partial melting and

subsequent fractional crystallization during

thermal peak conditions of the Trans-Hudson

Orogen (THO). The mineralization is similar

to that in pegmatite-hosted uranium deposits

of the Grenville Province and the Rössing

deposit in Namibia, but also shares some

characteristics with basement-hosted

unconformity-type (U/C-type) uranium

deposits of the eastern Athabasca Basin

(Cuney, 2009). This study is being undertaken

to document the geological and structural

controls on the Fraser Lakes mineralization

and to determine the relationship (s) between

pegmatite-hosted and U/C-type uranium

deposits.

Fig.1

Fig. 14. Garnetiferous

pelitic gneiss

(WYL-09-44-61.4) with

melt micro-textures at the

contact between garnet

and biotite. Biotite is being

consumed in the melt-

generating reaction.

Legend for all

geochemical

diagrams

Fig. 6. Chondrite-normalized (Sun and McDonough, 1989)

spider diagram showing the differences in REE contents,

Th, and U between the “Th pegmatites” and “U

pegmatites”.

Fig. 7. Chondrite-normalized (Boynton, 1984) REE spider

plot for the “Th pegmatites” and “U pegmatites” showing

the enrichment in REEs and in particular LREE in the

“Th pegmatites” relative to the “U pegmatites”.

Fig. 8. Feldspar diagram showing the

compositional variation of the granitic

pegmatites based on CIPW norm values.

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,

and LREE contents away from pelitic gneiss values. Trends represent the fractionation of different U-Th-REE

minerals, which include uraninite ± zircon for the “U pegmatite. For the “Th pegmatites, two trends are apparent -

the low P2O5-high U and Th trend is interpreted to be caused by uranothorite-thorite fractionation, while the trend

towards higher P2O5 with increasing Th and Ce is thought to be due to monazite fractionation.

Fig. 11. a) MgO vs. TiO2 and b) Fe2O3t vs. TiO2 diagrams show fractionation

trends of the pegmatites away from pelitic gneiss and orthogneiss compositions.

Note the trend of the magnetite- and ilmenite-bearing granitic pegmatites

(intrusive into the Archean orthogneisses) away from the granitic orthogneiss

compositions on the MgO vs. TiO2 diagram, indicating a possible compositional

relationship between these pegmatites and the granitic Archean orthogneisses.

Fig. 13. a) FeOt/(FeOt+MgO) vs. SiO2 plot

(Frost et al. 2001). “Th pegmatites” are

ferroan to magnesian while “U

pegmatites” are magnesian and appear to

be fractionated away from the “Th

pegmatites”. The magnetite- and ilmenite-

bearing pegmatites plot in the ferroan field

as their own separate group. b) Modified

alkali lime index (Na2O+K2O-CaO) vs.

SiO2 diagram (Frost et al. 2001) showing

the pegmatites trending from alkalic to

calcic. c) Shand (1943) plot showing the

peraluminous to weakly metaluminous

character of the pegmatites.

Fig. 12. a) Al2O3 vs.

SiO2 and b) TiO2 vs.

SiO2 diagrams

showing fractionation

trends of the granitic

pegmatites. “U

pegmatites” tend to

be more fractionated

away from pelitic

gneiss compositions to

high SiO2 values

whereas “Th

pegmatites” are only

weakly fractionated.

Fig. 10. a) U vs. TiO2 and b) Th vs. TiO2 diagrams showing that the “U

pegmatites” are generally more depleted in TiO2 (i.e. are more

fractionated) than the “Th pegmatites” and contain greater amounts of U.

The “Th pegmatites” tend to have TiO2 values comparable to and/or

greater than the pelitic gneisses.

a) b)

c) d)

a) b)

c) d)

a) b) c) a) b)

b) a)

a) b) a) b) c)