Uraninite-bearing Granitic Pegmatite, Moore Lakes, : Petrology and U-Th-Pb Chemical Ages

1 1 1 3 Irvine R. Annesley , Catherine Madore , Richard T Kusmirski , and Tom Bonli

Anm:slcv. l.R .. Madore. C .. Kusmirski, R.T.. and Bonli. T. (2000): lJraninite-bearing granitic pegmat1tc, Moore Lakes, . Saskatcl1ewan: Petrology and l!-Th-Pb chcmic,tl ages: in Summary of Investigations 2000, Volume 2. Saskatchewan Gcolog1cal Survey. Sask. Energy Mines, Misc. Rep. 2000-4.2.

attribute their genesis to some variation of the Abstract diagenctic-hydrothermal model proposed by Hoeve This paper documents the.fir.1·t results ofa detailed and Sibbald ( 1978), which invokes the mixing of study of -bearing granitic pegmatite, which highly saline oxidized basinal fluids with variably occurs near unconj(Jrmity-lJpe uranium mineralizalion reduced basement fluids. More recent research shows in the Moore Lakes area in the southeastern part ofthe that the transport and precipitation of uranium is Athabasca Basin. Drilling has revealed that wanitic controlled by basin paleohydrology, basement pegmatites comprise <5 to 10% ofthe basement topography, large-scale reactivated basement cornplex with hallestimated being radioactive. structures, fluid flow, heat flow, and physiochemical Relatively fresh, radioactive granitic pegmatite, the traps (Hoeve and Quirt, 1984, 1987; Wilson and Kyser, subject of this investigation, was intersected in drill 1987; Kotzcr and Kyser, l 991, 1992. 1995; Fayek and hole ML00-08. The pegmatite is JO m thick and occurs Kyser, 1997; Quirt. 1997). There are several 55 m he/ow the unconformity with sandstones olthe hypotheses as to the source of the uranium. Pagel et al. overlving Athabasca Group. ( 1980) and Dah lkamp ( 1993 ). amongst others, speculated that uranium is derived from the basement. The pegmatite is/ine to coarse grainecl, sheared and The regolith in the Archean/Palcoproterozoic basement foliated, and essentially unaltered It is composed has been proposed by Pagel ( 1991) as a major source mainly olquartz. greyfeldspar. and biotite. with of uranium. In contrast, Hoeve and Sibbald ( 1978) subordinate amounts olapatite, ::ircon, uraninite, and suggested that uranium was derived from sandstones of ilmenite. Uraninite and U-rich ::irr.:on are the dominant the Athabasca Group. Recent work by Fayek and uranium-hearing accessory . Some uraninite Kyser ( 1997) favored this option and suggested that grains are zoned. SEM and mtcroprobe results showed most of the uranium was leached from detrital zircons that uraninite alteratwn is greatest along grain in the sandstones of the Athabasca Group. More recent boundaries andfractures, ivith significant U loss and research by Annesley and Madore ( I 999c) in the Ph gain/loss. southeastern part of the Athabasca Basin and by Hecht and Cuney (2000, in press) in the western part of the The pristine parts olthe uraninite grains are composed Athabasca Basin advocated that granitic rocks (i.e.

mostly of U (66.-12 ~UOJ U/)8 ~72.40 wt%), Th (3.24 monazite-bearing leucogranites, granitic pegmatites, -5,ThO, -:;,884 wt %), and Ph (12. 92 -:;,PbO and potassic orthogneiss) were the major source of -5,/9 IJ wt%). U-Th-Ph chemical dating of the uranium. uraninite grains vielded a crysta//i::.ation age of?. 1772 ±88 Ma and other age clusters of 1429 (O I 649 Ma and This paper documents the first results ofa detailed //69 to 1233 Ma, which imply that the uraninite grains study ofuraninite-bearing granitic pegmatite, which started experiencing disturbances of their U-Th-Pb occurs near unconformity-type uranium mineralization isotopic system. We correlate these ages of isotopic in the Moore Lakes area (The Northern Miner, 2000). disturbance to the Stage 1 and Stage 2 U The aim of this work is: I) to characterize mineralization events documentedfor other petrographically and geochemically the uraninite­ unconjl1rmity-(vpe uranium deposits in the Athabasca bearing granitic pegmatite; 2) to characterize the nature Basin. Post-Athabasca alteration

I Saskatchewan Research Cnuncil. 15 Innovation Blvd. Saskatoon. SK S7'-J 2X8 'JNR lksourcc, Inc. Suite 921. 4 70 (iranvilk Street. Vancouver. BC V6C I VS ' lkpartrncnt of<.icolngical Sciences. University of Saskatchewan. 114 Science Place Saskatoon. SK S7N 51-:2

Saskatchewan Geoloiical Survey ]()/ 1989a, 1989b, 1990a 1990b, 1991 a, 1991b, 1999: 1977. 1980; Sibbald, 1983: Gilboy, 1983; Anncsley Annesley er al., 1996, I 997a, 2000; Madore et al., and Madore, 1991 a: Annesley et al. . 1996. J 997b; Tran 2000). and Yeo, 1997; Tran et al. , 1998. 1999, 2000: Madore et al.. I 999a; Orrell el al., 1999). Five main defomiarion events (Table 1) are recognized. 2. Geological Setting Metamorph ic g rade varies from amphibo li te to granulitc facies under hig h T/medium to low P The Moore Lakes area is located in the southeastern conditions. Metamorphic assemblages record part of the Athabasca Basin (Figure IA), two main phases of mineral growth, coeval w ith 0 1 and approximately 40 km northeast of the D2 defo rmation and followed by various retrograde and 35 km southeast of the McArthur River urani um events during 0 1, D~, and D,. Peak metamorphism (M!) deposit.

Basement comprises rocks of the Woll aston Domain Tahle I - Summary of Paleoproterozoic deformatio 11 mu/ (Lewry and Sibbald, 1977; Gi lboy, 1983; Lewry et al. , metamorphic events f or the basement to the eastem 1985; Hoffman, 1990; Lewry and Collerson, 1990). Athabasca B11si,r (after Pon ella and Am1es/ey. this volume). which is subdivided into two subdomains. separated by ··--- a linear break. o n the basis of aeromagnetic data. These Age Thcrmotcctonic subdomain s are characterized by rocks of high (Ma) lk formation Metamorphism Stage magnetic total fi eld and those of low total fi eld. 1860-1 835 D, M , Early co ll isio nal respectively. 1835- 1820 D: M2 Collisional 1820- 1805 late D: Mz Oblique Four main groups of basement rocks are distinguished: w llisional I) Archean o rthogneisses and subordinate rocks, 2) 1805- 1795 early D1 M., Oblique high-grade Paleoproterozoic Wollaston Group collisional metascdiments, 3) deformed calc-alkalinc granitoids and subordinate gabbroids, and 4) pcraluminous 1795-1 775 late D3 MJ I.ate ohli4uc granitoids of different petrochemical types. co llis10 11 al 1775-1 760 0 4 M4 Pust-co llisional These rocks have been subjected to polyphase 1760-1 720 D, I .ate post- defo rmation and metamorphism (Lewry and Sibbald. co llisional

110° 102" I

'. Athabasca Basin

c::..., "<' . ,2 o~(Q. Superior

Stud)· l\ra . , Craton HR H-."'-"' Lah' K~ -\. ~ . HlO TrAA, HIJJ1,tm f ~>~r:n SJIZ S 1i p,.:n or llow,J:uv Z()nc ~ ,·, 1 .oi,b,.•r'fl(II' ~hc:lr l~m~ _..,., 'i"/ ~-allc: F.oll~ ~lieu Zorw1 ~ :1 ! Sluff:~"N'l·W

Figure I - A) Location of the .<;tut~~· area i11 the southeastem pan of the Athafuu ca Basil! mul B) locatitm ofth e drill holes in the study 11re11.

202 Summar,· offm·e.1·1i,.:111 wm ]l)!HI. 1" o/ume :! was synchronous with calc-a lkaline plutonism at 1820 and essentially unaltered. It is composed mainly of to 1800 Ma. Pcgmatites o f S-type affinity yield ages of quartz, g rey feldspar, and biotite, with subordinate l 820 to 1800 Ma (Annesley et al. , 1997b). amounts of apatite (5 to 7 modal %), zircon (2 to 5 Decompression, upli ft, and cooling took place during modal %), uraninite (trace to 2 modal %), and ilmenite D, transpression under amphibo lite-facies co nditio ns. (Figures 2, 3, 4, 5, and 6). Other accessory m inerals and the timing of th is defonnatio n is constrained by include pyrite. Radioactivity reaches up to 1000 cps. monazite ages of 1806 to 1790 M a and titanite age of 1800 to l 775 Ma. These deformation and metamorphic Quartz grains, which are partly recrystallized, fonn events are related to the thcrmotectonic evolution of polycrystall ine aggregates elongated parallel to the the Trans-Hudson Orogen (Lewry and Sibbald, 1980; fol iation . Quartz grains range from 0.20 to Lewry, 1987; Bickford et al., 1990; Lewry and 4.00 mm in width and up to 6.00 mm in length. K­ Collcrson, 1990; C lowes et al., 1999; and references feldspar grains are variably recrystallized and are therein). intergrown with the quartz grains. Their grain size varies from 0.45 to 4.30 mm in width and up to Inliers of Archean/Paleoproterozoic rocks occur in the 5.30 mm in length. Biotite fl akes form massive clusters study area as part of the Moore Lakes Complex. The along the foliation planes. The fl akes range from 0.20 Moore Lakes Complex comprises A rchean to 1.00 mm in width and up to 4.60 mm in length. orthogncisses. Wo llaston Group metasediments, and They exhibit a pale brown to dark brown pleochroism. extensive diabase intrusions. Geological fe atures o f the Apatite grains, which arc distributed within biotitc-rich complex were mapped and documented by Forsythe clusters, are cuhedral and blocky to stumpy prismatic ( 1980). Ray ( 1983), and Ramaekers ( 1975, 1990). in shape. The grains vary from 0. 15 to 0.55 mm in Recently, MacDougall and Williams (1993), and width and up to 1.30 mm in length. The grains are Mac Dougall and Maxcmiuk ( 1995) mapped and colourless and strongly fractured. Two generations of sampled the Moore Lakes Complex for detai led zircon are identified (Figure 7). The first generation petrochemical work of diabases. (Zm I) is irregular in shape, strongly corroded. and overgrown by the second generation of zirco n (Zrn2). The Moore Lakes area is the site of ongoing uranium Zircon (2) grains are euhedral, very well zoned, and exploration by JN R Resources Inc. and Kennecott contain inclusions of biotite. Their grain size varies Exploration Inc. Results from a I 0-hole from 0.06 to 0.40 mm in length. It is interpreted that drilling program have identified significant the first generation of zircon was inherited fro m the unconformity-type mineralization (drill hole ML00-03) source rock and the second generation was fonned near the footwall ofa 125 m w ide (i.e. downhole) during the crystallization of the pegmatite. Uraninite structural zone (The Northern Miner. 2000). This grains are cubic in shape and 0.05 to 0.50 mm in size. drilling revealed that granitic pegmatitcs comprise <5 The grains are found within biotite flakes. They show a to I 0% of the basement complex with half estimated dark grey metallic tint under reflected light and a dark being radioactive. Relatively fresh. radioactive granitic pleochroic halo is developed around their grain marg in. pegmatite was intersected in drill hole ML00-08, Some of the grains are highly fractured and variably 400 m west of drill hole ML00-0 3. The pegmatite is altered. Trace amounts of rammelsberg ite are 10 m thick and occurs 55 m below th e unconformity developed around uraninite. Rammelsbergite displays a with sandstones of the overlying Athabasca Group. white metallic tint under reflected light. Its Intensely clay-altered pegmatite with sim ilar textural anisotropism is very strong, varying from blue to red­ characteristics to the M L0 0-0& pegmatite was brown. Pyrite grains are subhedral to cubic in shape. intersected by more recent drilling (Ml.00-11. unpubl. Thcv arc concentrated within biotite-rich clusters. JN R Resources In c. data). immediately west o f drill Their grain size varies from 0.06 to 0.40 mm in hole ML00-03. diameter. Ilmenite g rains are elongated to acicular in shape. They range from 0.25 to 0.40 mm in length. The grains arc altered and pseudomorphed by titanite 3. Analytical Methods grains. The focus of this paper is relat ively fresh uraninite­ bearing granitic pegmatite from drill ho le ML00-08. 5. Occurrence and Mineral Chemistry of Three samples of pegmatite were collected from the following in tervals: 32 1.5 to 322.0 m, 322.0 to Uraninite 322.5 m:and 322.5 to 323.0 m. Petrographic studies Petrographic and SEM observations revealed that and whole-rock geochemistry were carried out at the uraninite and lJ-rich zircon are the dominant uranium­ Saskatchewan Research Council. The microprobe and bearing accessory minerals in the granitic pegmatit c. SEM studies were performed at the Department o f SEM observations showed that some uraninite grains Geological Sciences, University of Saskatchewan. arc zoned. SEM results and EDS spectra also revealed that the uraninite grains arc highly altered in the vie in ity o f m icrofractures. 4. Preliminary Petrographic Observati ons The pristine parts of the uraninite grains (Table 2) arc The pcgmatite is greyish to bluish grey mottled black. composed mostly of U (66.42 ~UO/U,08 is ho locrystallinc, partly recrystall ized, incquigranular­ ~72.40 wt%), Th (3.:24 :5Th0 " ~8.84 wt %), and Pb pegmatitic, fine to coarse grained, sheared and foliated,

Saska1che wa11 Geolox 1col Survey 203 • J Figure 2 - The photomicrograph show.5 cubic uraninite (U) Figure 5 - Same photomicrograph as Figure 4, hut under grains intergrown with apatite (Ap) and zircon (Zrn J and reflected light. 2) grains. Uraninite occurs in biotite-rich cluMers, under plane-polarized light.

Figure 3 - Close-up view ofa cubic 11rani11ite (U) gmin Figure 6 - The photomicrograph shows an intergrowth surrounded by a thin film oframmelsbergite (Rbg), 11mler texture compo.5ed ofapfltite (Ap), biotite (Bt), anti well reflected light zoned zircon (Zrn 1 and 2), under plane-polarized light.

Figure 4 - The photomicrogrllph displays a complex Figure 7 - Clo.re-up view of well zoned zircom (Zrn I anti intergrowth ofbiotite (Bl), apatite (Ap), 11raninite (U), and 2) under reflected light. zircon (Zrn 1 and 2), under plane-polarized light.

2()./ Summary of /nvesti~ations 2000. J'olume 2 Table 2 - Microprobe a11 uly.~es of umni11ite f rom M L00-08 granitic pegmatite.

Analysis Si0 2 Number (wt %) Th02 U02 V20, Nb20s PiOs cep3 Dy20 3 CaO PbO Total l!-1 0.00 6. 18 70.6 1 0.01 0.00 0.06 0 .38 0.30 0.10 18.30 95.94 U-2 0.00 7. 15 68.19 0.00 0.06 0.08 0.43 0.30 0.50 15.11 9 1.82 U-3 0.55 6. 14 72.40 0.00 0. 10 0.3 1 0 .49 0.22 0.76 12.92 93.89 U-5 0.20 5.63 70.20 0.00 0.08 0.04 0 .37 0.26 0.28 15.87 92.92 U-6 0.02 6.50 69.10 0.05 0.17 0.00 0.35 0.39 0.00 17.89 94.46 U-7 0.00 3.93 70.82 0.00 0.03 0.23 0 .36 0.51 0.34 15.81 92.04 U-8 0.22 4.27 70.89 0.00 0.04 0.12 0 .30 0.32 0.01 18.44 94.59 U-9 0.00 5.89 69.74 0.00 0.00 0.00 0.25 0.37 0.21 16.29 92.75 U- 10 0.00 5.10 71.1 5 0.00 0.01 0.07 0 .46 0.36 0.00 18.75 95.9 1 U- 11 0.00 3.73 71.74 0.00 0.03 0.0 1 0.40 0.32 0.00 18.43 94.68 U- 13 0.00 7.99 67.64 0.06 0.00 0.00 0 .28 0.16 0.00 19.15 95.28 U-1 5 0.00 5.16 7 1.30 0.03 0.05 0.00 0.21 0.30 0.08 17.69 94.82 U- 17 0.00 8.84 66.42 004 0.08 0.00 0.39 0.28 0.00 19.05 95.10 U- 18 0.01 3.95 73.14 0.00 0.00 0.00 0.25 0.59 1. 10 13.36 92.40 U- 19 0.03 3.24 70.37 0.00 0.06 0.04 0.29 0.29 0.00 19.30 93.63 lJ-21 0. 14 7. 16 68.73 0.00 0.00 0.1 3 0.27 0.27 0.00 16.43 93.12 U-22 0. 19 7.44 70.60 0.00 0.00 0.00 0.26 0.36 1.41 12.33 92.58 U-23 0.26 7.83 69.09 0.00 0.00 0.24 0.39 0.30 0.59 15.24 93.93 U-24 0.67 6.61 68.66 0.00 0.00 0.26 0.4 1 0.35 0.24 16.41 93.6 1 U-25 ().04 7.52 67.80 0.00 0.02 0.00 0.39 0.35 0.04 18. 11 94.28 lJ-4 2.39 5.53 46.15 0.04 0.00 0.00 0.23 0.23 0.50 24.02 76.09 U-1 2 4.24 4. 18 55.20 0.09 0.06 0.00 0.29 0.31 0.46 24.65 89.47 U-16 11.32 5.43 47.89 0.04 0.00 0.6 1 0.47 0.10 065 11.84 78.34 U-20 2.96 3.69 49.83 0.1 2 0.00 0.03 0.25 0.36 0.91 10.68 68.83

( 12.92 :5Pb0 :5 19. 15 wt %). The rare earths, Ce20 3 and reflecting biotite content of the sample analyzed. Dy 10 1, are always present at the tenths of a wt% level Samples with high biotite content have high T i0 2, (0.21 :5Ce20; :50.49 wt%, and 0. 16 :5 Dyp3 Fe20 3 101, MgO, Li, Nb, and Sc, and low Si02 values. :50.59 wt %). Other rare earths are invariably present at Elevated concentrations of P20 5, CaO, HREE, and Y these levels, as well as Y. Calcium concentrations are are related to the high apatite content. The strong to highly variable at the tenths ofa wt % level. Niobium, very strong enrichment ofU-Th-Pb and Zr-Hf reflects P, and V contents vary from <0.01 to 0.31 wt %. The the high to very high concentrations ofuraninite and totals of least altered uraninite are close to 96% (Table zircon, respectively, in the analyzed samples, when 2, U- 1 and U-10). The other REE and Y could bring compared to other pegmatites in the area (Table 3). the totals close to I 00%. The very high values of Hf, Pb, Th, U, Zr, and HREE The altered parts of the uraninite grains show loss of suggest that an igneous enrichment process has taken UO/ U308 with either Pb gain (U-4, U-12) or Pb loss place since these values exceed greatly the maximum (U-1 6, U20, Table 2). Si lica enrichment is also noted values for solubility in both water-saturated and water­ with this uraninite alteration. undersaturated granitic melts at high temperatures (Watson and Harrison, 1983; Puziewicz and Johannes, The chemistry of the pristine urani nite grains is 1990; Pichavant et al., 1992). consistent with a magmatic origin. They contain Th and REE, which are rare or largely absent in 7. U-Th-Pb Chemical Age Dating hydrothermal and low-temperature sedimentary-hosted uraninite (Frondel, 1958). These impurities in the Radioelement-rich accessory minerals have the uraninite are important in understanding uraninite potential fo r U-Th-Pb,.,, age dating by electron stability and uraninite-tluid interactions (Friedrich et microprobe analysis (e.g. Suzuki and Adachi, 1991 ; al.. 1987; Finch and Ewing, 1992; Finch and Suzuki et al. , 1994; Montel et al., 1996; Rhede et al. , Murakami, 1999). 1996; Forster, 1998, 1999). Recently, most chemical age research has focussed on monazite and other minerals of the monazite group, as these minerals are less susceptible to radiation damage with 6. Petrochemistry metamictization and resultant hydration. In the The pegmatites (Table 3) are moderately rich in alkalis Athabasca Basin, uraninite and pitchblende have been

(K20+Na20 == 4.95 to 6.27 wt%) and weakly successfully used for U-Th-Pb,0 1 dating of the various et a l., peralum inous (AS I ::o 1.00 to 1.15). The oxides Ti02, U mineralization events (Parslow 1985; Fayek et al., Fe20 3 '"" and MgO values are highly variable, and Kyser, 1997; Mccready 1999; among others). These chemical ages have been calculated

Saskatchewan <' Pb, and as Cu 12 38 8 25 1 note d by Bowles ( 1990), a simple Ga 21 27 20 6 27 approximation of the age is given Hf 45.3 95.0 41.1 25.5 0.6 by t {Ma) "' Pb (wt %) x 100 (i.e. Li 47 105 78 23 98 Method l in Table 4 ). Empirical Mo 4 21 10 I 1 formulas by Ranch in ( 1968) and Nb 15 39 7 23 I Howles ( 1990) have been titted to Ni 3 5 3 11 6 1 the radioactive decay of U and Th Pb 296 630 210 4 I to Pb. Our results using these Sc 11 35 10 3 20 formulas are presented as Sn 4 5 2 I 4 Methods 2 and 3 in Table 4 . As Sr 158 59 114 6 7 1 pointed out by Bowles ( 1990 ). the Th 88 219 66 17 3 Ranch in ( 1968) formula g ives lJ 950 2400 880 9.8 2.8 results that are too o ld for v 13 38 10 20 56 samples >200 Ma. Our research w 2 2 1 I I supports this observation. Method 3 g ives good resu lts, but does not y 108 290 6 1 11 45 take in to account the contribution Zn 165 285 92 13 3 of Pb from the decay of T h. In 1360 792 5 1 Zr 1530 2810 most cases, this is not a factor, but the analyzed in this 1 20 La (ppm) 17 37 23 study contain significant amounts 46 Cc 41 96 46 4 of Th. T herefore, we have used Pr 6 16 6 1 s the rigorous iteration method of Nd 33 100 27 2 30 Bowles ( 1990) to produce a best Sm 13 .1 33.6 8.9 I. I 6.4 tit between the measured Pb and Eu 2. 1 2.6 1.6 0.6 0 .3 the calculated Pb from the Gd 13.7 39. 1 8.1 2.4 5.5 equation for production of Tb 3.5 9.0 1.9 0.3 0.9 radiogen ic Pb by the decay of lJ Dy 17.2 49.4 9.8 1.6 6 and T h . By this method, Ho 5.3 13.7 3.9 0.4 1.3 uraninites with greater than 50 Er 10.9 3 1.9 7.0 0.9 3.7 wt % U yielded ages of 1772 to Tm 1.4 3.2 0.6 0.3 0.7 11 69 Ma (Method 4, Table 4). Yb 11.9 3 1. 2 8.5 2.4 6.3 The older group of ages 1772 to Lu 1.9 4.9 1.3 08 1648 Ma, fr om least altered uraninite, are interpreted as a

assuming that the Pb,01 in the samples is entirely of minimum age of crysta ll ization. These arc younger radiogenic origin and that Pb loss or gain has not than the precise U-Pb zircon and monazite ages of occurred since mineral crystallization (Bowles. 1990). 1820 to 1803 Ma for granitic pegmatites of the eastern sub-Athabasca basement (Anneslcy el al.. l 997a.

206 Summary of lnvesligalions 2000 , I 'olume 2 T11ble 4 - U- Pb-T/1 chemical age d11ting resulrs for uraninite f rom M L00-08 granitic fractured basement rocks, and pegmulite. comprises chloritization, sericitization, and clay alteration. u Th Pb Ma Ma Ma Ma (± Ma) Their preliminary fluid inclusion Pt# (wt %) (wt %) (wt%) Method I Method 2 Method 3 Mt:thod 4 error work confirms the circulation of I 59.88 5.43 16.99 1699 2074 1757 1648 85 brines in these hydrothermally 2 57.82 6.28 14.03 1403 1763 1530 1439 70 altered rocks. The mobilization 3 6 1.40 5.39 12.00 1200 1430 1259 11 99 60 and redistribution are marked by 5 59.53 4.95 14.73 1473 1814 1557 1472 74 the replacement of monazite by a 6 58.59 5.7 1 16.61 1661 2068 1755 1644 83 Th-silicate phase with concurrent 7 60.06 3.46 14.67 1467 1807 1539 1464 73 liberation of approximately 75% 8 60. 11 3.75 17.12 17 12 21 03 1762 1663 86 of the U, P, and LREE. This 9 59.14 5. 18 15.12 1512 1871 1603 151 1 76 monazite (±uraninite) alteration 10 60.34 4.48 17.40 1740 2120 1782 1676 87 by brines prov ides an attractive II 60.84 3.28 17.11 17 11 2083 1743 1649 86 mechanism for releasing uranium. 13 57.36 7.02 17.78 1778 2242 1897 1759 89 60.47 4.54 16.43 1643 1997 1691 1595 82 Our study adds to the research of 15 Hecht and Cuney (2000, in press) 19 18 1772 88 17 56.32 7.77 17.68 1768 2258 by demonstrating weak to locally 18 62.03 3.47 12.40 1240 1479 1286 1233 62 moderate mobilization of uranium 19 59.68 2.85 17.92 1792 2229 1846 1742 90 from a weakly altered, variably 2 1 58.28 6.29 15.25 1525 1902 1636 1534 76 fractured granitic pegmatite. SEM 22 59.87 6.54 11 .44 1144 1388 1234 1169 57 and microprobe resu lts showed 23 58.59 6.88 14. 14 14 14 1748 1523 1429 7 1 that uraninite alteration is greatest 24 58.22 5.81 15.23 1523 1907 1636 1537 76 along grain boundaries and 25 57.50 6.6 1 16.8 1 1681 2120 1803 1680 84 fractures, with significant U loss Notes: and Pb gain/loss. Method I - Bowles lf990) - age(t) -0 Pb x 100 Method 2 - Ranch in ( 1968) - age(t) = Pb x 7550 I (lJ + 0.36Th) U-Th-Pb chemical dating of Mt:thod 3 - Bowles ( 1990) - agc(t) = ( 1/0.000155 125) x In (( I.I 04 x Pb/U) + I) uraninite grains yields a Mcthod 4 - Bowles ( 1990) - age(t) calculated by iteration program using lJ. Th, and Pb crystal! izat ion age of~ 1772 Error estimatc •· 5 percent of th e Pb analyst:s ±88 Ma. This chemical dating also yielded age clusters of 1429 to 1649 Ma and 1169 to 1233 Ma, I 997b, I 999a, I 999b. I 999c, 2000; Madore et al., which im ply that the uraninite 1999b). grains in th is paper started experiencing disturbances of their U-Th-Pb isotopic system. We correlate these ages of isotopic disturbance to the Stage I and Stage 2 U mineralization events of Fayek and Kyser ( 1997). 8. Discussion and Conclusions Prel iminary drill hole observations and geophysical The diagenetic hydrothennal model of Hoeve and logging (R. Kusmirski, pers. comm., 2000) from Sibbald ( 1978) is the favored model for the genesis of nearby, highly al tered pegrnatites indicate that unconformity-type uranium deposits, however, the significant mobilization/redistribution of uranium may source of uranium is still debated. Some researchers have occurred. If this post-regolith alteration covers a appeal to the basement as a direct source of the large area or zone with approximately 5% radioactive uranium, still others to the basement regolith (Pagel, pegmatites, do we have enough uranium for 1991 ), whereas some researchers (Fayek and Kyser. mobilization, redistribution, and precipitation? Mass­ 1997) and most exploration geologists favor balance calculations for an cast-west structural corridor sandstones of the Athabasca Group as the main source. ( 10 km long by 0.5 km wide by 2.0 km deep) gives a 1 3 Annesley and Madore ( 1999) suggested that the vol um~ of 1.0 x I 0 ~ Cf:1 • Five percent pegmatite with radioelement-enriched leucogranite suite is the most a density of2.66 g/crn ' would give a mass of 1.33 x 10 12 kg. If the granitic pegmatite for the corridor important basement source of uranium in the eastern 7 part of th e Athabasca Basin. H igh-U monazite and averaged 30 ppm U. then 3.99 x 10 kg of uranium uraninite are the major contributors of uranium. would be available fo r leaching. Five percent Likewise, I Iecht and Cuney (2000, in press) from a ca. mobilization, redistribution, and precipitation of th is 1500 km 2 area suggested that granitic rocks of the sub­ amount would give 2 000 000 kg (4,400,000 lb) U, Athabasca basement are the most important source of whereas 25% would give IO 000 000 kg uranium in the western Athabasca Basin. These (22,000,000 lb) U. researchers demonstrated that hydrothermal alteration of basement lithologies beneath the paleoweathered We conclude that relatively fresh uraninite-bearing zone do~n to at least 200 m be low the unconfo rmity granitic pegrnatites in the Moore Lakes area record the resu lted m substantial mobilization and redistribution age of ~tage I and Stage 2 U mineralization events in of uranium. This post-regolith hydrothermal alteration the basin. We also suggest that post-Athabasca is present in thick (tens of metres) zones of highly alteration of these pegmatites may have provided some

Saskatchewan Geoloxical Survey 207 U for unconfonnity-type uranium mineralization in th e _____ ( 1991 b): The Wo llaston Group and its Moore Lakes area. underlying Archean basement: Append ices A, B, C, D. E, and F of the Final Report (Volumes I, 2, and disk); Sask. Resear. Counc., Pu b I. R- I 230-5- 9. Acknowledgments C-9 I , 472p. The authors acknowledge the support of JNR ____ _ ( l 999): Leucogranites and peg matites o f Resources In c. and Kennecott Canada Exploration Inc. the sub-Athabasca basement, Saskatchewan: U for providing samples and background information to protore?; in Stanley, C.J. et al. (eds.), Mineral this study. Funding for the first and second authors was Deposits: Processes to Processing, Balkema, v I , provided by Saskatchewan Research Council. The p297-300. senior author thanks Dr. Alistair McCready of Belfast University for the introduction to chemical age dating. Annesley. l.R., Madore. C., Kamo, S.L., and Krogh, The review and critical comments by Saskatchewan T. E. ( I 999a): U-Pb zircon and monazite ages from Energy and Mines geolog ists are gratefully the sub-Athabasca basement o f the P-patch acknowledged. uranium deposit, Wollaston Domain, Saskatchewan; Geo!. Assoc. Can./Miner. Assoc. Can., A bstr., v24, pA-3. 10. References Annesley, I.R., Madore, C., and Krogh, T.E. ( I 997a): Annes ley, I.R. ( I 989): The Wollaston Group and its U-Pb geochronology of peralumino us pegmatites underlying Archean basement in Saskatchewan: from the area, northern An Update; Sask. Resear. Counc., Publ. R-855-5- Saskatchewan; Geo!. Assoc. Can./Miner. Assoc. E-89, 86p. Can. , Abstr., v22, pA-4.

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Finch, R.J. a nd Ewing, R.C. ( 1992): The corrosion of Hoffman, P.F. (1990): Subdivision of the Churchill uraninite; J. Nuclear Mate rials, v 190, p 133-1 56. province and extent o f the Tra ns-Hudson Orogen: in Lewry, J.F. and Stauffer, M.R. (eds.), Early Finch, R.J . and Murakami, T . ( 1999): Systematics and Proterozoic Trans-Hudson Orogen of North Paragenesis of Uranium Minerals; in Burns, P.C. America, Geo I. Assoc. Can., Spec. Pap. 37, p I 5- and Finch, R. (eds.), Uranium: , 39 . Geochemistry and the Environment, Mineral. Soc. Arner., Reviews in Mineralogy , v38, p9 I- I 79. Kotzer, T. and Kyser, T. K. ( I 991 ): Retrograde alteration of clay minerals in uranium deposits: Forster, H.-J. (1998): The c hemical composition of Radiation catalysed or simply low-temperature REE-Y-Th-U-rich accessory minerals in exchange?; Che rn . Geo!., v86, p307-32 I . peraluminous granites of the Erzgebirge­ Fichtelgebirge region, Germany. Part I. The _____ (1992): Isotopic, rnineralogic and rnonazite-(Ce)-brabantite solide so lution series: chemical evidence for multiple episodes o f fl uid Amer. Mineral. , v83. p59-272. movement during prograde and retrograde diagenesis in a Proterozoic Basin: in Kharaka, ______( 1999): The c hemical composition of Y.K. and Maest, A. S. (eds.), Proc. 7th Inter. uraninite in Variscan granites of the Erzgebirge, Symp. on Water-Rock Interaction, Utah, July I 3- Germany: Mineral. Mag .. v63, p239-252. 18, pl 177- 1181.

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Gilboy, C.F. ( 1983): Sub-Athabasca Basement Lewry, J.F. and Collerson, K.D. (1990): The Trans­ Geology Project; in Summary of Investigations lludson Orogen: Extent, subdivision and

Saskatchewan Geolo,tical Survey ! 09 problems; in Lewry, J.F. and Stauffer, M.R. (eds.), Investigations 1999, Volume 2, Saskatchewan The Early Proterozoic Trans-Hudson Orogen of Geological Survey, Sask. Energy Mines, Misc. North America, Geo!. Assoc. Can., Spec. Pap. 37. Re:. 99-4.2, pl 10-1 20. pl-14. Montel, J .-M., Foret. S., Veschambre, M., N icollet, C., Lewry, J.F. and Sibbald, T.1.1 . ( 1977): Variation in and Provost, A. ( 1996): Electron microprobe lithology and tectonometamorphic relationships in dating of monazite; Chem. Geo!., v 131 , p37-53. the Precambrian basement of northern Saskatchewan; Can. J. Earth Sci., v 14, p I453- Orrell , S.E .. Bickford, M.E., and Lewry. J.F. (1999): 1467. Crustal evolutio n and age of thermotecton ic reworking in the western hinterland of the Trans­ ( 1980): Thenno tecton ic evolution of the Hudso n Orogen, northern Saskatchewan: Precamb. -~urchill Province in northern Saskatchewan; Resear. , v95, pl87-223. Tectonophys .. v68. p45-82. Pagel, M. ( 199 1) Lateritization and Lewry, J.F., Sibbald, T.1.1., and Schledewitz, D.C.P. paleogeomorphology: Their roles in the genesis of ( 1985): Variation in character of Archean rocks in unconfonnity-type uranium deposits in the western Churchill Province and its Saskatchewan, Canada; in Pagel, M. and Leroy, L. sig nificance; in Ayers, L.D., Thurston. P.C., Card, (eds.), Source, Transport, and Deposition of K.D., and Weber, W. (eds.), Evolution of Archean Metals, Balkerna, Rotterdam. p33 l-332. Supracrustal Sequences, Geo!. Assoc. Can., Spec. Pap. 28, p239-26 I . Pagel, M .. Poty, B., and Sheppard, S.M .F. ( 1980) Contribution to some Saskatchewan deposits MacDougall, D.G. and Maxemiuk, L.M.T. (1 995): mainly from fluid inclusion and isotope data: in Moore Lakes revisited-gold and palladium Ferguson. S. and Goleby, A. (eds.). Uranium in the concentrations in altered diabase from the Moore Pinc C reek geosyncline; IA EA, Vienna, p639-654. Lakes Complex (part of NTS 74H-6 and -7); in Summary of Investi gati o ns 1995. Saskatchewan Parslow, G. R., Brandstatter. F., Kurat, G .• and Thomas, Geological Survey. Sask. Energy Mines, Misc. D.J. ( 1985): Chem ical ages and mobility of lJ and Rep. 95-4, p68-78. Th in anatectites of the Cree Lake zone. Saskatchewan: Can. Mineral., v23. p543-55 J. MacDougall, D.G . and Williams D.H. ( 1993): The Moore Lake Complex, Neohelikian olivine Pichavant, M .. Mantel, J.-M .. and Richard. L.R. diabase lopoliths in the Athabasca Group (part of ( 1992): Apatite solubility in peralurnino us liquids: NTS 74H-6 and -7); in Summary of Investigations Experimental data and an extension of the 1993, Saskatchewan Geolog ical Survey, Sask. Harrison- Watson model: Geoch im. Cosmochim. Energy Mines, Misc. Rep. 93-4, p86-91. Acta, v56, p3855-386 l.

Madore. C., Annesley. I.R., and Tran. H.T. ( l 999a): Pu ziewicz. J. and Johannes. W. ( 1990) Ex perimental Petrology and geochemistry of Paleoproterozoic study of a biotite-bearing granitic system under Wollaston Group rnetasediments from the eastern water-saturated and water-undersaturated Keller Lake- Siemens Lake area. Saskatchewan: A conditions: Contrib. Mineral. Petrol., v I 04. p397- preliminary interpretation; in Summary of 406. Investigati ons 1999, Volume 2, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Quirt, D. ( 1997): Geochem istry, host- rock alteration, Rep. 99-4.2, p80-89. minera li zation, and uranium metallogenesis of the Wollaston EAGLE Project Area; in Madore, C., Annesley, I.R. , and Wheatley, K. (2000): Thermo tectonic and Uranium Metallogenic Petrogenesis, age. and uran ium fertility of Evolutio n of the Wollaston EAGLE Project Area, peraluminous leucogranites and pegmatites o f the Sask. Resear. Coun c. , Publ. No. R- 1420-2-C -97. McC lean Lake/Sue and Key Lake/P-Patch deposit 98p. areas, Saskatchewan. GeoCanada 2000, Calgary. May 2000, Conference C D. ext. abstr. # l 041. Ranch in, G. ( 1968): Contribution a l'etude de la repartition de !'uranium it l'etat de traces dans lcs Madore, C. , Anneslcy. l.R., Kwok, K.K., and Krogh. roches granitiques saines les uranitcs a teneur T.E. ( t999b): Petrography, geochemi stry. and age clevee du Massif de Sain t-Syivestrt: (Lim ousin - of granitic pegmatites from the C lose Lake and Massif Central Frarn;ais): Sc i. Terre .. v 13, p I 61 - Epp Lake areas, Mudjatik Domain. Saskatchewan; 205. Geo!. Assoc. Can./Mincr. Assoc. Can., Abstr., v24. pA-77. Ramaekers. P. ( 1975): Athabasca Formation, southeast edg e (74H): Part I: Reconnaissance geological McCready, A.J ., Annesley, I.R .. Parnell. J., and mapping; in Summary of Investigations 1975 by Richardson, L.C. ( 1999): Uranium-bearing the Saskatchewan Geological Survey. Sask. Miner. carbonaceous matter. McArthur River uranium Reso ur., p48-52. deposit, Saskatchewan; in S ummary of

2/0 S11m111an- of lnvesligotions ] ()IJ(). 1· oh 11111! 2 ( 1990): Geology of the Athabasca Group Watson, E.B. and Harrison, T.M. (1983): Zircon · - (Helikian) in Northern Saskatchewan: Sask. saturation revisited: Temperature and composition En ergy Mines, Rep. 195, 49p. effects in a variety of crustal magma types; Earth Planet. Sci. Lett., v64, p295-304. Ray. G.E. (1983): Compilation Bedrock Geology. Geikie River, NTS Area 74H; Sask. Energy Mines, Wilson, M.R. and Kyser, T.K. (1987): Stable isotope Rep. 229 ( I :250 000 scale map with marginal geochemistry of alteration with the Key Lake notes). Uranium Deposit, Canada; Econ. Geol.. v82, p 1540-1557. Rhede. D., Wendt, I.. and Forster, H.-J. (1996): A three-dimensional method for calculating Appendix 1 : Microprobe Analytical independent chemical U/Pb- and Th/Pb-ages of Technique accessory minerals; Chem. Geo!., vi JO, p247-253. Microprobe analyses were performed on polished thin Sibbald. T. 1.1 . (1983): Geology of the crystalline sections using a JEOL 8600 Superprobe electron basement, NEA/IAEA Athabasca Test area; in microprobe analyzer housed at the University of Cameron, E.M. (ed.). Uranium Exploration in Saskatchewan, Department of Geological Sciences. Athabasca Basin, Geol. Surv. Can., Pap. 82-1 I, The probe was operating at an accelerating voltage of p 1-14 . 20 kV, beam current of 10 riA and a beam diameter of <5 ~1rn . High purity metals were used as standards for Suzuki, K. and Adachi, M. ( 1991 ): Precambrian U, Th, V, and N b. Quartz was used as standard for Si, provenance and Silurian metamorphism of the diopside for Ca, apatite for P, cerium phosphate for Ce, Tsubonosawa paragneiss in the South Kitakami dysprosium phosphate for Dy, and crocoite for Pb. terrane, northeast Japan. revealed by the chemical Th-U-total Pb isochron ages of monazite, zircon All elements w ith the exception of Th and Pb were and xenotirne; Geochem. J., v25, p357-376. analyzed using a count tim e of 40 s. Th and Pb were analyzed using 100 s count times. Matrix and ZAF Suzuki, K., Adachi. M .. and Kajizuka, I. ( 1994): corrections were performed using formulas modeled Electron microprobe observations of Pb diffusion after Heinrch/Duncumb-Reed. in metamorphosed detrital monazites: Earth Pl anet. Sci. Lett .. v 128, p39 l-405.

The Northern Miner (2000): JNR sizes up Moore Lake drill core: v86, no20, pl6.

Tran, 11.T. and Yeo, G.M. ( 1997): Geology ofthe Burbidge Lake -northern upper Foster Lake area, eastern Wollaston Domain (NTS 74A-14); in Summary of Investigations 1997, Saskatchewan Geol. Surv. Misc. Rep. 97-4, p72-89.

Tran. H.T.. Yeo. G.M., and Bethune, K., (1999): Geology of the McKenzie Falls area, Haultain Ri ver, Wollaston-Mudjatik domains boundary (NTS 748-7 and -8); in Summary of Investigations 1999, Volume 2, Saskatchewan Geol. Surv., Sask. Energy Mines. Misc. Rep. 99- 4.2, p55-67.

Tran. H.T., Yeo. G.M .. Bradley, S., and Lewry, J.F. ( 1998): Geology of the Daly-Suttle-Middle Foster lakes area. eastern Wollaston Domain (NTS 74A- 5, -11. and 12); in Summary of Investi gations 1998_ Saskatchewan Geo I. Surv ., Sask. Energy Mines, Misc. Rep. 98-4. p48-65.

Tran. H.T .. Lewry, J.F .. Bethune, K., Ashton, K., Yeo, G .. and Ansdell, K. (2000): Crustal thrusting and tectonic imbricati on in the Cree Lake Zone, northern Saskatchewan: implications for the tectonic evolution of western foreland of the Trans-1 ludson Orogen; GcoCanada 2000. Calgary. May 2000. Conference CD, ext. abstr. #579.

S C1slw 1d1ewC111 Geological Survey ] /I