PETROGRAPHY AND GEOCHEMISTRY OF GRANITIC PEGMATITE AND LEUCOGRANITE- HOSTED URANIUM &

THORIUM MINERALIZATION: FRASER LAKES ZONE B, NORTHERN SASKATCHEWAN, CANADA

AUSTMAN, Christine L.1, ANSDELL, Kevin M.1, and ANNESLEY, Irvine R.1,2

(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

Abstract

References

Acknowledgements

Analytical Methods

Garnet, cordierite, sillimanite, pyroxenes, hornblende, and spinel in the surrounding metamorphic

rocks indicate that the regional metamorphism was of upper amphibolite to granulite facies

Abundant migmatites in drill core (Fig. 26) indicate that these metamorphic rocks underwent

partial melting, consistent with melt micro-textures seen in thin section (Fig. 27, 28)

Significant-sized granitoids of similar age and appropriate geochemistry in the area are not

common (i.e. typical of the middle crust)

Peraluminous to weakly metaluminous composition (Fig. 21, 23), plus the mineralogy of the granitic

pegmatites and leucogranites (quartz-feldspar-biotite-garnet) is consistent with an origin by partial melting of

metasedimentary rocks at variable depths within the middle to lower crust

Difference in U and Th contents of the granitic pegmatites could be due to a combination of factors, including

igneous assimilation and fractional crystallization (AFC) processes, interaction with magmatic fluids (B, F, Cl,

CO2, H2O), different melt-generating reactions, and variable source rock chemistry in the middle to lower crust

Fraser Lakes Zones A and B are located in JNR Resources Inc.’s

Way Lake Property, ~ 55 km from the Key Lake uranium mine in

the Athabasca Basin and ~25 km from the basin’s SE edge (Fig. 1)

Paleoproterozoic Wollaston Group metasedimentary rocks and

Archean orthogneisses underlie the study area, which was complexly

deformed, intruded, and metamorphosed during the Trans-Hudson

Orogen (~ 1.8 Ga)

Zone A is in a NE-plunging synformal fold nose and Zone B is in an

antiformal fold nose adjacent to a 65km long folded electromagnetic

(EM) conductor (Fig. 2, 4)

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

~500 m x 1500 m area northwest of the Fraser Lakes (Fig. 2, 4)

Multiple generations of pegmatites including syn-tectonic

(subcordant to gneissosity, often radioactive) and post-tectonic

(discordant, non-mineralized) pegmatites (Austman et al. 2009)

E-W ductile-brittle and NNW– and NNE-trending brittle structures cross-cut Zone B (Annesley et al., 2009)

Preliminary 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 which can be correlated to U-mineralization

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

Radioactive granitoids similar to the Fraser Lakes granitic pegmatites underlie several unconformity

uranium deposits of the eastern Athabasca Basin, including P-Patch, McArthur River Zone 2, Eagle

Point, Sue C, and Roughrider (Annesley et al., 2000a, 2000b, 2005, 2009, 2010b; Annesley and Madore,

1999; Madore et al., 2000; Portella and Annesley, 2000)

Radioactive granitoids are one of the potential sources of the uranium for the unconformity U deposits

Prior to erosion, the Athabasca sandstone/basement unconformity was ~ 200-250 m above the present

outcrop surface, indicating the potential for unconformity U mineralization in the area (Annesley et al., 2009)

Located just outside of the Athabasca Basin, the Fraser Lakes uranium- and thorium- bearing granitic pegmatites and

leucogranites are one example of igneous-hosted uranium and thorium occurrences in the Wollaston Domain of northern

Saskatchewan. The mineralized granitic pegmatites and leucogranites intrude the highly deformed contact zone between

Wollaston Group metasedimentary rocks and underlying Archean orthogneisses. Whole rock geochemical analyses of

drill core samples from Zone B indicates the presence of multiple groups of granitic pegmatites that underwent igneous

assimilation-fractional crystallization (AFC) processes. The granitic pegmatites generally fall within Černý and Ercit’s

(2005) Abyssal-U and Abyssal-LREE pegmatite subclasses, and include syn-tectonic and post-tectonic varieties. The

granitic pegmatites are generally S-type and A-type granitoids that formed by partial melting of the intrusive hosts. Al-

teration of these pegmatites may have led to the remobilization of uranium and the development of unconformity-type

uranium mineralization in the Fraser Lakes area.

The purpose of this M.Sc. study is to develop a metallogenetic model for the Fraser Lakes deposits,

and clarify their relationship with the rich uranium deposits in the Athabasca Basin.

Fig. 1 Location of JNR’s properties in northern

Saskatchewan, including the Way Lake Property

(modified from map on JNR Resources Inc.

website).

Fig. 2 Topographic map showing the

location of Fraser Lakes Zones A and B, the

folded EM conductor (red dots), drill hole

collars (black dots), swamps (light green),

and lakes and rivers (blue).

Fig. 4 Total field aeromagnetic image of the

Fraser Lakes area. The EM conductor

corresponds to an aeromagnetic low (blue

to green colors). The black dashed lines are

basement lineaments/structures. Note the

location of Fig. 6 and Fig. 11.

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

Resources Inc. for her assistance with petrography, and the Saskatchewan Research Council for the geochemical results.

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

several drill holes for petrographic study. After drilling, each hole was probed using a gamma-ray probe to

test for radioactivity. Whole rock geochemical analysis (by ICP-MS and ICP-OES) of selected samples from

WYL-09-50, WYL-09-49, WYL-09-46, and WYL-09-525 was completed by the Saskatchewan

Research Council Geoanalytical Laboratories in Saskatoon.

Introduction

The radioactive granitic pegmatites, leucogranites and migmatitic leucosomes intrude the highly deformed contact between Archean orthogneisses and the overlying Wollaston Group (Fig. 6, 11)

Zoning (Fig. 5) is common, due to igneous assimilation-fractional crystallization (AFC) processes

Variable primary mineralogy, including quartz, feldspar, biotite, ± garnet, ± magnetite,

± ilmenite, ± titanite, ± muscovite, ± apatite, ± fluorite, ± sulphides, ± zircon, ± U-Th-REE-bearing

accessory minerals which vary depending on the composition of the pegmatite (See below for the

different kinds of pegmatites; also Fig. 7-10, 12-15, 17-19)

Accessory mineral assemblage is dependent on host rocks (example: magnetite is found only in

pegmatites intruded into the Archean orthogneisses) and the melt composition (see below)

The pegmatites in the western part of the fold nose tend to be enriched in both U and Th (Fig. 6-

10) with low Th/U ratio, while the pegmatites in the eastern part of the fold nose tend to have high

Th/U ratios, and show Th– and LREE-enrichment (Fig. 11-15)

Fig. 5 Drill core from WYL-09-50 showing fractionation from quartz-rich to feldspar-rich

in the core of this radioactive granitic pegmatite(158.7 - 62.7m).

Secondary pyrite is commonly found in altered uranium and thorium minerals Hematite, chlorite, clay, fluorite, silica, and

calcite alteration associated with weak to locally strong brittle fracturing (Fig. 16-19) Alteration indicates that there was post-

crystallization hydrothermal fluid flow

through the rocks, which may have caused remobilization of the U, Th, and REEs Possibly related to Athabasca basinal brines

Mineralogy

Fig. 26 Drill core from

WYL-09-524 (~15.6-19.8

m) with boudinaged

crustal melt pods and

radioactive granitic

pegmatites.

Conclusions Structurally controlled, basement-hosted U, Th, and LREE mineralization in Hudsonian-aged leucogranites and granitic pegmatites intruded into the highly deformed contact

between Paleoproterozoic graphitic pelitic gneisses and Archean orthogneisses

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

Granitic pegmatites are of Černý and Ercit’s (2005) Abyssal-U and Abyssal-LREE subclasses, and formed by partial melting of the Wollaston Group

Post-crystallization alteration and fluid flow through the rocks raises the possibility of remobilization of U, Th, and REE’s

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

The potential exists for finding basement-hosted unconformity-type mineralization in the Fraser Lakes area

Future work to include: additional petrography, electron microprobe work, further whole-rock geochemical analysis, Pb-isotope studies, XRF analysis, and U-Pb chemical age

dating of the mineralization to aid in the development of a metallogenetic model and examination of the potential for future discoveries

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

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 Volume 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.

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.

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. The Canadian Mineralogist, 43, 2005-2026.

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.

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

JNR Resources Inc., 2009, —Home Page—Oct. 10, 2009, Saskatoon, 10/10/2009, http://www.jnrresources.com.

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

1041 (Conference CD).

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,

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. Fig. 16 Granitic pegmatite (96.8 m) in WYL-09-

41 with hematite alteration, fracture controlled

pyrite and chlorite, and up to 2100 cps

radioactivity.

Fig. 19 Granitic pegmatite (WYL-

09-50-166.2) with hematite,

fluorite, calcite, and epidote

alteration in fractures.

Fig. 17 Moderate to strongly

altered granitic pegmatite (WYL-

09-50-215.8) containing zircon,

and possibly allanite.

Fig. 18 Granitic pegmatite from

WYL-09-50 (215.8 m) with calcite-

fluorite-quartz veining and altered

feldspar.

Alteration

Fig. 7 (PPL), 8

(XPL); 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). Abbreviations

after Kretz (1983).

Fig. 9 (PPL), 10

(RL); 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).

U– and Th-enriched pegmatites (western part of the fold nose) Th– and REE-rich granitic pegmatites (eastern part of fold nose)

Fig. 11 Cross-section from

the northern limb of the

fold nose at Zone B. Drill

holes include WYL-09-

43a, -43, -44, -45, and -46.

Note the increase in

radioactivity in the

granitic pegmatites with

local increases in pelitic

gneiss, granite gneiss, and

orthogneiss intervals. See

Fig. 4 for the location of

the cross-section.

Fig. 6. Cross-section from the

western limb of the fold nose at

Zone B. Drill holes include

WYL-09-41, -42, -49, and -50.

Note the increase in

radioactivity (blue line – gamma

probe results) in the granitic

pegmatites (red units) with local

increases in pelitic gneiss (green)

and Archean orthogneiss and

granitic gneiss (orange and

pink) intervals. See Fig. 4 for

the location of the cross-section.

Fig. 12, 13. Biotite-

rich section of a

granitic pegmatite

(WYL-09-46-36.1)

with hematized

monazite (Mnz),

uranothorite-thorite

(Thr) containing

pyrite (Py) inclusions,

and zoned zircon

(Zrn).

Fig. 14 (WYL-09-46-

83.0), 15 (WYL-09-46-

42.8) Pegmatites with

monazite (Mnz), zir-

con (Zrn), ilmenite

(Ilm), magnetite (Mgt),

and titanite (Ttn).

Monazite is being

altered to hematite

(Hem), chlorite (Chl),

and clay.

Fig. 20 Major element (TiO2, Al2O3, FeOt, MgO,

CaO, Na2O, K2O and P2O5; all in wt. %) and trace

element (Ba, Rb, Sr, Zr, Th/U, and Y; all in ppm)

Harker diagrams. Some of the elements (Al2O3, CaO,

Na2O, K2O, and Sr) show weak trends likely related

to igneous assimilation-fractional crystallization

processes. The Zr content is mainly controlled by zir-

con, while Y is mostly related to the presence of al-

lanite and/or garnet. These pegmatites have higher

SiO2 contents than the Th-rich pegmatites and have

variable chemistry suggesting that the data could be

from multiple groups of pegmatites. The spread in

the data also could be due to chemical zonation

within individual pegmatites.

Fig. 21 Classification

plots after Frost et al.

(2001) and Shand

(1943) showing that

these pegmatites are

more magnesian

relative to the Th-rich

pegmatites. The

pegmatites are also

weakly metaluminous

to peraluminous in

composition.

Fig. 22 Major and trace element Harker diagrams

for the Th– and LREE-rich pegmatites. These

pegmatites show strong P2O5 enrichment due to

monazite; Th enrichment due to monazite,

uranothorite-thorite, and allanite; Zr enrichment

due to zircon; and strong Y anomalies due to

allanite and/or garnet. These pegmatites have lower

SiO2 contents than the other pegmatites (with the

lowest SiO2 contents being in samples containing

abundant garnet). Weak trends in the K2O and Ba

data are suggestive of igneous assimilation-

fractional crystallization processes.

Fig. 27, 28 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.

Fig. 3 Aerial photograph (looking to the

northeast) of the Fraser Lakes Zone B area,

showing the swamp corresponding to the

surface trace of the EM conductor.

U-Th-REE minerals: monazite, zircon, allanite, and members of the

uranothorite-thorite solid solution series

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

Fig. 25 Chondrite-normalized (Boynton 1984)

REE plot showing the differences in REE contents

of the different pegmatites. The Th– and LREE-

rich pegmatites show strong enrichment in the

LREEs and weak enrichment of most of the

HREEs relative to the other pegmatites. The

strong negative Eu-anomaly of the Th– and LREE

-rich pegmatites is likely due to plagioclase frac-

tionation. The LREE enrichment in the Th– and

LREE-rich pegmatites is indicative of Černý and

Ercit’s (2005) Abyssal-LREE subclass.

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

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

Fig. 23

Classification plots

after Frost et al.

(2001) and Shand

(1943) showing that

the Th-rich

pegmatites are more

iron-rich than the

majority of the other

pegmatites and are

peraluminous in

composition.

All pegmatites (mineralized and unmineralized)

Fig. 24 U (ppm) vs. SiO2 (wt.

%) and Th (ppm) vs. SiO2

(wt. %) plots of mineralized

and unmineralized

pegmatites. The uranium and

thorium mineralization in the

Fraser Lakes pegmatites is

characteristic of Černý and

Ercit’s (2005) Abyssal-U class

of granitic pegmatites.

Origin of the granitic pegmatites and primary mineralization

Geochemistry

Highly Th– and LREE-enriched pegmatites (high Th/U) Other Pegmatites (U– and Th– enriched plus non-enriched samples)