Abstract. Keywords: U-Pb, Sm-Nd, pink leucogranite, Beaverlodge uranium district, Nolan Domain, Zemlak Domain

Transcription

1 A New U-Pb Age for Pink Leucogranite Hosting Mineralization in the Beaverlodge Uranium District, and New Sm-Nd Results from the Nolan, Zemlak and Beaverlodge Domains Ken Ashton 1, Nicole Rayner 2, Robert Creaser 3 and Kathryn Bethune 4 Information from this publication may be used if credit is given. It is recommended that reference to this publication be made in the following form: Ashton, K., Rayner, N., Creaser, R. and Bethune, K. (2017): A new U-Pb age for pink leucogranite hosting mineralization in the Beaverlodge uranium district, and new Sm-Nd results from the Nolan, Zemlak and Beaverlodge domains; in Summary of Investigations 2017, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report , Paper A-5, 18p. Abstract U-Pb SHRIMP dating of the pink leucogranite hosting the Intermediate uranium occurrence yielded a 2331 ±4 Ma crystallization age. Based on this result and geochemical similarities, most of the pink leucogranite within the mineralized belt that includes the Eagle shaft deposit, Gully zone, and Camdeck uranium occurrences, and the pink leucogranite south of the St. Louis fault can be assigned this 2.3 Ga age, in spite of the recrystallization that has modified them from coarse-grained rocks to fine- to mediumgrained equivalents. Pink leucogranite in the belt immediately north and south of the St. Louis fault, including that hosting the Ace-Fay-Verna mine, is probably also dominated by 2.3 Ga granite, although testing of this assumption is precluded by metasomatism associated with intense deformation that has modified the geochemical signature of the granite. New Sm-Nd results have helped to better constrain the isotopic characters of some ca Ga, ca. 2.6 Ga, and ca. 2.3 Ga rocks in the Nolan, Zemlak, and western Beaverlodge lithotectonic domains. A tonalitic migmatite in the central Nolan Domain has been reinterpreted as a metamorphosed psammopelite or derived S-type granite, whereas the gabbroic component of a mafic to ultramafic body along the Nolan/Zemlak domainal boundary is slightly evolved, suggesting that it was probably not originally emplaced in a juvenile oceanic environment. Pink leucogranite that intrudes the 2.6 Ga granites of the Nolan Domain is slightly evolved, suggesting derivation by anatexis associated with high-grade metamorphism. An inferred 2.6 Ga granite in the western Beaverlodge Domain yielded a Sm-Nd result consistent with other granitic rocks of that suite, whereas a dated gneissic granite of the same age in the southeastern Zemlak Domain is slightly evolved. Two previously dated ca. 2.3 Ga granites in the western Zemlak and western Beaverlodge (the sample dated above) domains are isotopically evolved, consistent with emplacement during crustal extension in a postcollisional setting following the Arrowsmith orogeny. A 2.94 Ga gneissic granite from the southwestern Beaverlodge Domain is highly evolved, consistent with geochemical evidence that it is distinct from a 3.0 Ga suite in the same area, and supporting detrital zircon evidence of much older crust in the region that has not yet been identified. Keywords: U-Pb, Sm-Nd, pink leucogranite, Beaverlodge uranium district, Nolan Domain, Zemlak Domain 1. Introduction Fine- to medium-grained 'pink leucogranite' is abundant in the Zemlak and Beaverlodge lithotectonic domains (Figure 1), but its age and origin remain unclear. In the Beaverlodge uranium district, the unit was formerly mapped as metasomatic granite and interpreted to be younger than the other crystalline rocks, and broadly synchronous with metamorphism (Tremblay, 1972). It was termed leucogranite on a subsequent compilation and interpreted as a product of Hudsonian metamorphism (Macdonald and Slimmon, 1985). This interpretation was supported by an intrusive relationship with presumed Paleoproterozoic supracrustal rocks of the Murmac Bay group (e.g., Ashton et al., 2013a). 1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, th Avenue, Regina, SK S4P 3Z8 2 Natural Resources Canada, Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8 3 University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3 4 University of Regina, Department of Geology, 3737 Wascana Parkway, Regina, SK S4S 0A2 Although the Saskatchewan Ministry of the Economy has exercised all reasonable care in the compilation, interpretation and production of this product, it is not possible to ensure total accuracy, and all persons who rely on the information contained herein do so at their own risk. The Saskatchewan Ministry of the Economy and the Government of Saskatchewan do not accept liability for any errors, omissions or inaccuracies that may be included in, or derived from, this product. Saskatchewan Geological Survey 1 Summary of Investigations 2017, Volume 2

2 Figure 1 Simplified geological map of the Tazin Lake area (NTS 74N 5) showing the extent of rocks mapped as pink leucogranite, the locations of previously dated pink leucogranite samples (large black dots), and the location of the pink leucogranite dated in the present study (11KA-250); black rectangle outlines extent of Figure 2; dashed lines are important faults and/or domain boundaries; dash-dot lines are approximate boundaries between inferred proto Rae craton and Taltson basement complex. 5 All UTM coordinates in this report are in NAD 83, Zone 12. Saskatchewan Geological Survey 2 Summary of Investigations 2017, Volume 2

3 An early attempt to date the Box Granite, a small pink leucogranite body hosting the past-producing Box gold mine, 14 km south-southeast of Uranium City (Figure 1), produced a poorly constrained 1994 ±37 Ma (Persons, 1983) upper intercept zircon age using thermal ionization mass spectrometry (ID-TIMS). A combined ID-TIMS and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) study of a pink leucogranite body located within the Uranium City town site (Figure 1), showed that the sample s zircon population was virtually all inherited (Hartlaub et al., 2005). A crystallization age of 1933 Ma was assigned to the unit based on the 207 Pb/ 206 Pb age of the youngest near-concordant fraction (ibid). In the same study, a second pink leucogranite from Feil Lake, 16 km southwest of Uranium City in the Zemlak Domain (Figure 1), yielded a similar scatter of inherited zircon ages and no obvious crystallization age. A 1974 ±5 Ma estimate of the crystallization age was assigned to that sample based on the 207 Pb/ 206 Pb age of the youngest near-concordant fraction in the ID-TIMS study, although the follow-up LA-ICP-MS study revealed a similar scatter of inferred inherited zircon, with only 1 of the 20 analyses having a ca Ma age (ibid). The combination of an intrusive age relationship with the Paleoproterozoic Murmac Bay group and the apparent absence of crystallization-aged zircon was taken to indicate that the pink leucogranite was a near-minimum melt rock derived by anatexis during the 1.94 to 1.90 Ga regional metamorphic events (Hartlaub et al., 2005; Ashton et al., 2013a). In the Tazin Lake area, pink leucogranite sheets and dykes have intruded ca. 2.6 Ga I-type granites and granodiorites of the Nolan Domain (Ashton et al., 2005, 2007; Cloutier et al., 2017). The extent of this Nolan pink leucogranite appears to broadly coincide with a southward-increasing metamorphic and deformational gradient. A mylonite from eastern Laird Island (Tazin Lake; Figure 1), which was interpreted as an intensely deformed variant of one of these intrusive pink leucogranite sheets, was sampled with the aim of establishing the age of thermotectonism. However, based on results from the sensitive high-resolution ion microprobe (SHRIMP) study, the sample comprised a single population of zircon grains with a weighted mean 207 Pb/ 206 Pb age of 2584 ±4 Ma (Ashton et al., 2007). A few analyses with younger 207 Pb/ 206 Pb ages were interpreted as resulting from Pb loss due to an undefined event. Based on this result, the rock was reinterpreted as one of the Nolan Domain Neoarchean granites that had not been distinguished from the intrusive, inferred Paleoproterozoic, pink leucogranite (Ashton et al., 2005) due to the mylonitic overprint (Ashton et al., 2007). Thus, it appears that the term pink leucogranite, as a rock unit, has been used in the Rae Province of Saskatchewan for rocks of more than one age. It also follows that not all such rocks have been derived by synmetamorphic anatexis during the ca to 1.90 Ga high-grade metamorphic events that have affected the area. In the western Beaverlodge Domain, pink leucocratic granites are common, and have been grouped with the pink leucogranites mapped and studied elsewhere (Figures 1, 2). However, in the main Beaverlodge uranium district, northeast of Beaverlodge Lake, mylonitization and/or recrystallization have made the different granitoid suites difficult to distinguish and age relationships tenuous. The term pink leucogranite has been used (e.g., Ashton, 2011) to describe one of the most common host rocks at many of the district s uranium deposits (e.g., Ace-Fay-Verna, Eagle shaft, Intermediate zone; Figure 2). Murmac Bay group supracrustal rocks, in zones up to the scale of kilometres, are interspersed with the pink leucogranite, and commonly exhibit vestiges of basal orthoquartzite at the margins of these zones (Ashton, 2011), suggesting a basement-cover relationship. In other places, however, pink leucogranite appears intrusive into the supracrustal rocks (Ashton, 2011), suggesting the opposite age relationship. Pink leucogranites of the western Beaverlodge area are typically pale pink to salmon pink and fine to medium grained, with colour indices of less than 10 and commonly less than 5 (Figure 3A). Most outcrops display evidence of high ductile strain and many have a strong cataclastic overprint. Unpublished whole-rock geochemical analyses show that many of these western Beaverlodge Domain pink leucogranites share a consistent geochemical signature, which was not expected in rocks thought to be derived by the partial melting of various rock types at depth. Further, the geochemical signature derived from the pink leucogranites is very similar to that of the 2.33 to 2.29 Ga granite suite (referred to as the North Shore Plutons by Hartlaub et al., 2007; see Figure 1), which is distinctive from other granitoid suites in the area. Hartlaub et al. (2007) showed that analyses from this suite span the volcanic arc granite + syncollisional granite and within-plate granite fields on the Nb versus Y plot (Pearce et al., 1984), and fall within the postcollisional granite field on the Rb versus Y + Nb plot (Pearce, 1996). Relative to ocean ridge granites (Pearce et al., 1984), the pink leucogranites of the western Beaverlodge area and the 2.33 to 2.29 Ga granite suite are characterized by depleted Ba relative to elevated Rb and Th, slightly elevated Ta and Nb, and prominent Ce and less Saskatchewan Geological Survey 3 Summary of Investigations 2017, Volume 2

4 prominent Sm peaks with flat depleted Hf, Zr, Y and Yb values. In addition to this geochemical similarity between the western Beaverlodge pink leucogranites and the 2.33 to 2.29 Ga granite suite, they share a salmon pink colour, leaving grain size and habit as their main difference. Whereas the pink leucogranites are fine to medium grained and generally highly strained, the 2.33 to 2.29 Ga granite suite is coarse grained, even where strongly sheared (Figure 3B). Nevertheless, their geochemical similarity leaves open the possibility that many of the pink leucogranites in the western Beaverlodge Domain are deformed and/or recrystallized equivalents of 2.33 to 2.29 Ga granites, rather than rocks formed by anatexis during the ca to 1.90 Ga metamorphic events. Figure 2 Simplified geological map of the Beaverlodge uranium district, showing location of dated pink leucogranite sample (11KA-250; red dot at Intermediate pit) relative to past-producing uranium mines and selected occurrences; MB Murmac Bay; PB Parker Bay. Saskatchewan Geological Survey 4 Summary of Investigations 2017, Volume 2

5 Figure 3 Outcrop photos of pink leucogranite: A) typical pink leucogranite from 425 m south-southwest of Verna shaft (UTM E, N); B) sheared outcrop of 2.32 Ga Gunnar granite hosting Gunnar mine (UTM E, N); note coarser grain size relative to pink leucogranite in A); C) northeast wall of the Intermediate pit; approximate sample locality marked by arrow; D) sampled outcrop showing pale pink weathered surface and fresh surface comprising recrystallized pink feldspar augen up to 5 mm in grey matrix (UTM E, N); E) well-foliated pink leucogranite from 125 m northeast of Intermediate pit (UTM E, N); F) less strained exposure of pink leucogranite from 100 m along strike to northeast of dated rock, showing coarse nature of quartz lenses (UTM E, N). Saskatchewan Geological Survey 5 Summary of Investigations 2017, Volume 2

6 2. U-Pb Analysis a) Sample Selection Partly to test whether at least some of the pink leucogranite of the western Beaverlodge Domain is part of the 2.33 to 2.29 Ga granitic suite and partly to establish the age of the pink leucogranite that hosts much of the uranium mineralization, a sample was collected from the rock hosting the mineralization at the Intermediate pit (Figure 2; UTM E, N). This unit is inferred to extend northwestward to include the host rock of the Eagle shaft mine (Figure 2), which has the same geochemical signature, and the rocks hosting the Camdeck zone about 2 km along strike to the northeast from the Eagle shaft (Ashton, 2011). These rocks are also thought to be correlative with pink leucogranites hosting the Ace-Fay-Verna mine, although this correlation is somewhat more tenuous. The Ace-Fay- Verna mine host rocks share the colour and colour index of the other western Beaverlodge Domain pink leucogranites, but metasomatism associated with mylonitization and cataclasis in the Ace-Fay-Verna area has significantly altered their geochemical signatures, leaving them dissimilar to any of the known granitic suites in the area, and with granitic rocks in general. For this reason, the pink leucogranite was sampled for geochronological analysis from the Intermediate pit rather than from the Ace-Fay-Verna area. The U-Pb analysis was conducted using the sensitive high-resolution ion microprobe (SHRIMP) at the Geological Survey of Canada. Analytical procedures are outlined in Stern (1997), and Stern and Amelin (2003). b) Sample Description The sample of pink leucogranite that was collected from the hanging wall of the mineralized fault extending through the Intermediate pit (Figure 3C) appears to have originally been coarse grained (Figures 3D, 3E), but now ranges from medium to fine grained as a result of recrystallization (Figure 3F). It is strongly sheared, resulting in a >10:1 quartz aspect ratio, locally exhibits an L-S fabric, and is commonly overprinted by subsequent cataclastic deformation. One of several generations of hematitization has stained the pink leucogranite salmon pink to red in many places (Figure 3F), and quartz has been locally removed in areas affected by albitization. The sample contains about 30% quartz, 50% K-feldspar, 20% plagioclase, and 1% chlorite (as veins), along with accessory zircon, apatite and opaque minerals, and late calcite, epidote and leucoxene. c) U-Pb Result The recovered zircon comprised a single population of clear, colourless stubby prisms with sharp terminations and facets (Figure 4A). Faint concentric zoning was observed in back-scattered electron (BSE) images (Figure 4B), consistent with an igneous derivation. Nineteen analyses were carried out on 19 individual zircon crystals (Table 1), yielding a simple population with a weighted mean 207 Pb/ 206 Pb age of 2331 ±4 Ma (n = 19, MSWD = 2.2; Figure 4C), which is interpreted as the crystallization age of the leucogranite. d) Discussion and Summary of U-Pb Result The similar age of the pink leucogranite from the Intermediate pit relative to those of the ca to 2.29 Ga granite suite, together with the similarity of their geochemical signatures, leaves little doubt that they are broadly correlative. This indicates that the higher degree of regional strain in the northwestern Beaverlodge Domain has resulted in recrystallization of originally coarse-grained ca to 2.29 Ga granites to the finer grain size that characterizes the dated variety of pink leucogranite. The new crystallization age for the pink leucogranite at the Intermediate zone also means that the 2.33 to 2.29 Ga granite suite hosts the Eagle shaft mine, 83, 11, Intermediate, and Gully zones, the Camdeck occurrences, as well as the Gunnar mine. As stated above, alteration associated with mylonitization makes correlation of the pink leucocratic granitic rocks hosting the Ace-Fay-Verna mine with the 2.33 to 2.29 Ga suite based on geochemical similarities somewhat tenuous. There may be components of the 3.0, 2.94, and/or 1.94 to 1.90 Ga granitic suites in the mylonites of that area, but in all likelihood, the dominant rock hosting the Ace-Fay-Verna mine is also 2.33 to 2.29 Ga granite. This would mean that the two largest mines in the camp (Ace-Fay-Verna and Gunnar), along with many of the smaller deposits (Figure 2), were hosted by the same suite, perhaps indicating a genetic link (significant source of uranium?). Saskatchewan Geological Survey 6 Summary of Investigations 2017, Volume 2

7 Table 1 U-Pb data for pink leucogranite from the Intermediate pit (sample 11KA-250) analyzed using the SHRIMP. Apparent Ages (Ma) Spot name U Th Th Yb Hf Hf 204 Pb f(206) Pb* 208* Pb % 207* Pb 206* Pb Corr 207* Pb % 206 Pb ± 206 Pb 207 Pb ± 207 Pb Disc. (ppm) (ppm) U (ppm) (ppm) Yb 206 Pb % ± % (ppm) 206* Pb ± 235 U % ± 238 U % ± Coeff 206* Pb ± 238 U 238 U 206 Pb 206 Pb (%) E E E E E E E E E E E E E E E E E Footnotes: Spot name follows the convention x-y.z; where x = sample number, y = grain number and z = spot number. Multiple analyses in an individual spot are labelled as x-y.z.z. Uncertainties reported at 1s and are calculated by using SQUID , rev. 15 Oct f(206) 204 refers to mole percent of total 206 Pb that is due to common Pb, calculated using the 204 Pb-method; common Pb composition used is the surface blank (4/6: ; 7/6: ; 8/6: ). * refers to radiogenic Pb (corrected for common Pb). Disc.: Discordance given as difference between measured 206 *Pb/ 238 U ratio and the expected 206 *Pb/ 238 U ratio at t=207*/206* age, in percent. Calibration standard 6266; U = 910 ppm; Age = 559 Ma; 206 Pb/ 238 U = Analytical details: IP µm spot, 6-7 na intensity, 6 scans. Error in 206 Pb/ 238 U calibration 0.8% (included). Standard Error in Standard calibration was 0.17% (not included in above errors but required when comparing data from different mounts). No mass fractionation correction was required (measured 207 Pb/ 206 Pb age of secondary standard z1242 = 2680±3 Ma, n=24, 1 reject). Saskatchewan Geological Survey 7 Summary of Investigations 2017, Volume 2

8 Figure 4 Zircon images and analytical results from the dated pink leucogranite from the Intermediate pit (sample 11KA-250): A) typical zircon recovered; B) back-scattered electron image showing faint concentric zoning in analyzed zircon (black circles show analyzed spots; numbers refer to individual zircon grains see Table 1); C) concordia diagram for SHRIMP analysis. The presence of the 2.33 to 2.29 Ga granite suite in the main part of the uranium district may also help to explain ca Ga 207 Pb/ 206 Pb and upper intercept ages (amongst others) for uraninite obtained from the Fay mine during an LA-ICP-MS study of Beaverlodge epigenetic uranium mineralization (Dieng et al., 2013). Other geochronological studies of the epigenetic pitchblende mineralization in the Beaverlodge uranium district have all yielded results of <1.85 Ga (e.g., Collins et al., 1954; Eckelmann and Kulp, 1956; Koeppel, 1968), making the ca Ga results seem too old. The intensity of the 1.94 to 1.90 Ga metamorphic and associated deformational events, which would make preservation of pre-existing epigenetic uranium mineralization unlikely, also favours a different interpretation for the 2.29 Ga uraninite ages. One possibility is that the analyzed uraninite grains represent an accessory mineral that crystallized due to syngenetic concentration of uranium resulting from the crustal melting that led to the 2.33 to 2.29 Ga granite suite (Hartlaub et al., 2007). Saskatchewan Geological Survey 8 Summary of Investigations 2017, Volume 2

9 3. Sm-Nd Analyses The second part of this paper contains new Sm-Nd data from nine samples that were obtained as part of a separate study aimed at characterizing the crust in the Zemlak, Nolan and Beaverlodge domains. These data add to other Sm- Nd analyses (Ashton et al., 2014, 2016) collected as a way of testing a model involving the possible amalgamation of two Archean crustal blocks to form part of the southern Rae province: a Taltson basement suite to the west and south, and a proto Rae craton to the east and north (Figure 5; Ashton et al., 2014; Bethune, 2017). a) Analytical Techniques Sm-Nd analytical work was carried out at the University of Alberta. The powders were accurately weighed and totally spiked with a known amount of mixed 150 Nd- 149 Sm tracer solution this tracer is calibrated directly against the Caltech mixed Sm/Nd normal described by Wasserburg et al. (1981). Dissolution occurs in mixed 24N HF + 16N HNO 3 media in sealed PFA Teflon vessels at 160 C for 6 days. The fluoride residue is converted to chloride with HCl, and Nd and Sm are separated by conventional cation and HDEHP-based chromatography. Chemical processing blanks are <200 picograms of either Sm or Nd, and are insignificant relative to the amount of Sm or Nd analyzed for any rock sample. Further details can be found in Creaser et al. (1997), Unterschutz et al. (2002), and Schmidberger et al. (2007). b) Sample Selection Four of the new samples were collected from the Tazin Lake area (Figure 5), where the results are intended to complement ongoing U-Pb and Lu-Hf isotopic studies that form part of a GEM-2 (Geo-mapping for Energy and Minerals) study addressing the cratonic amalgamation model (Bethune, 2017). Two other samples are from previously dated (U-Pb) rocks of the Zemlak Domain that were analyzed to better establish the crustal history of different suites of rocks within the domain. Three rocks from the western Beaverlodge Domain were also analyzed to help establish the crustal history of the various suites of rocks. Two of these have also previously been dated using U-Pb SHRIMP techniques, including the pink leucogranite from the Intermediate pit described above (11KA-250). The third Beaverlodge sample has not been dated but is believed to be part of the ca. 2.6 Ga suite of granitoids based on previous mapping and follow-up geochronology (Hartlaub, 1999; Hartlaub et al., 2005). c) Sm-Nd Results 16TL-029D Mylonitic Granite from Southern Shore of Tazin Lake (Nolan Domain Adjacent to Zemlak Domain Boundary) The boundary between the Nolan Domain and Zemlak Domain in the southwestern Tazin Lake area (Ashton et al., 2005) is one of the key areas for testing the idea that the southern Rae Province is an amalgam of proto-rae and Taltson basement complex cratonic blocks (Ashton et al., 2014; Bethune, 2014). The immediate footwall of the steeply south-dipping sheared domainal boundary is made up of pink, fine- to medium-grained granite that has been variably mylonitized (Figure 6A). Recrystallization resulting from the intense ductile deformation and associated metamorphism has rendered the original coarse grain size difficult to discern, and the most intensely deformed variants are more grey than pink. The rock contains about 15 to 20% chloritized hornblende and biotite, along with minor layers of amphibolite up to a few centimetres thick. A sample of this mylonitic granite from the southern shore of Tazin Lake (UTM E, N) was collected for Sm-Nd analysis to help characterize the nature of the Nolan crust in the immediate footwall of the Nolan/Zemlak domainal boundary. The sample is broadly along strike from another Nolan Domain mylonitic granite on eastern Laird Island (Figure 1) previously dated at 2584 ±4 Ma using U-Pb SHRIMP techniques (Ashton et al., 2007). The newly sampled mylonitic granite has a depleted mantle model age (T DM; Goldstein et al., 1984) of 2.83 Ga, with an εnd value of +0.4 calculated at 2600 Ma (Table 2, Figure 7). A Sm-Nd analysis has not been obtained from the previously dated mylonitic granite on Laird Island, but the T DMs from other Nolan Domain granitoids range from 2.84 to 2.89 Ga and also have slightly positive εnd values at 2600 Ma (Ashton et al., 2016; Figure 7). Saskatchewan Geological Survey 9 Summary of Investigations 2017, Volume 2

10 Figure 5 Simplified geological map of the Tazin Lake area (NTS 74N) showing previous Sm-Nd results and the locations and Sm-Nd results of the new samples; depleted mantle model ages (TDMs) are reported in Ga; dashed lines are important faults and/or domain boundaries; dash-dot lines are approximate boundaries between inferred proto Rae craton and Taltson basement complex. Saskatchewan Geological Survey 10 Summary of Investigations 2017, Volume 2

11 Figure 6 Outcrop photos of rocks analyzed for Sm-Nd in the Tazin Lake area: A) mylonitic granite (16TL-029D) from the immediate footwall of the steeply south-dipping shear zone marking Nolan/Zemlak domainal boundary on the southern shore of Tazin Lake (UTM E, N); B) grey tonalitic migmatite (16TL-043C) from Abitau Bay, Tazin Lake in the central Nolan Domain (UTM E, N); C) metagabbro (16KA-044) from the Nolan/Zemlak domainal boundary on a small island immediately southwest of Laird Island (UTM E, N); D) near-massive but intensely fractured pink leucogranite (16TL-017) from southwestern Laird Island in Nolan Domain (UTM E, N); E) hornblende augen granite from Harper Lake, western Zemlak Domain (UTM E, N); F) sheared Foot Bay granite from the northwestern Beaverlodge Domain (UTM E, N). Saskatchewan Geological Survey 11 Summary of Investigations 2017, Volume 2

12 Table 2 Sm-Nd isotopic data for samples described in this study. Ages in bold are calculated dates (U-Pb); ages with question marks after them are estimated. Sample Rock Location Domain UTM-E UTM-N Age Sm (ppm) Nd (ppm) 147 Sm/ 144 Nd 143 Nd/ 144 Nd0 uncert. end0 143 Nd/ 144 NdT TDM (Ga) ~TMa TMa endt ~TMa 143 Nd/ 144 NdT TMa endt 16-TL- Tazin Lake South shore Tazin Lake Nolan Ma? D mylonitic granite 16-TL- Abitau Bay tonalitic Abitau Bay, Tazin Lake Nolan Ma? C migmatite 16KA-044 Laird Island Southwest Laird Island, Nolan-Zemlak Ma? gabbro Tazin Lake 16-TL-017 Laird Island pink Southwest Laird Island, Nolan Ma? leucogranite Tazin Lake Black Bay gneissic Black Bay, Lake Zemlak Ma granite Athabasca Hornblende augen Harper Lake Zemlak Ma granite 4704-C2 Crackingstone Southwest Beaverlodge Ma gneissic granite Crackingstone Peninsula 13KA-183 Foot Bay gneiss North of Dubyna Lake Beaverlodge Ma? granite 11KA-250 Intermediate pit pink leucogranite Intermediate pit Beaverlodge Ma Note that εnd values have been calculated at 2600 Ma and 1900 Ma. UTM coordinates are in Zone 12, NAD83. All samples relative to La Jolla 143 Nd/ 144 Nd = Uncertainty is 2 standard errors on 143 Nd/ 144 Nd. TDM calculated using the linear model of Goldstein et al. (1984). Saskatchewan Geological Survey 12 Summary of Investigations 2017, Volume 2

13 Figure 7 Nd evolution curve for known suites of granitoid rocks and for samples analyzed in this study: coloured dots and dashed lines denote age and evolution of previously dated and analyzed granitoid samples; black dots and solid lines denote new Sm-Nd results. 16TL-043C Grey Tonalitic Migmatite from Abitau Bay on Northern Tazin Lake, Nolan Domain In amongst the dominantly coarse-grained ca. 2.6 Ga granitoid rocks of the Nolan Domain along Abitau Bay on northern Tazin Lake is an isolated outcrop of grey tonalitic migmatite containing about 5% inclusions of fine-grained amphibolite up to decimetre scale (Figure 5; UTM E, N). The paleosome of the tonalitic migmatite is grey, has a grain size of approximately 1 mm, and contains 10 to 15% biotite (Figure 6B). Subsequent thin section work has shown that it also contains minor anhedral garnet and sillimanite, both as fibrolite along feldspar grain boundaries and as a result of reaction with biotite (personal communication, M. Cloutier). Diffuse, white to pale pink, medium- to coarse-grained leucosome makes up about 30% of the tonalitic migmatite. The leucosome was injected (based on the absence of a distinct melanosome), and was subsequently ptygmatically folded about a northeaststriking axial plane. The protolith of the tonalitic migmatite is unclear. Its quartzofeldspathic composition and textural homogeneity (other than the leucosome) suggests an igneous protolith, but the presence of peraluminous phases suggests that it is more likely a metamorphosed psammite, perhaps correlative with paragneisses of unknown age at the eastern boundary of the Nolan Domain (Ashton et al., 2005), or a derived S-type granite. A third option is that it is a granitoid rock that was substantially altered prior to metamorphism. In order to better characterize the migmatitic tonalite and perhaps gain some insight into its origin, a sample was collected for Sm-Nd analysis. The derived T DM was 3.01 Ga, with an εnd value of -1.9 calculated at 2600 Ma (Table 2, Figure 7). 16KA-044 Gabbro from Southwestern Laird Island, Tazin Lake (Nolan/Zemlak Domain Boundary) The highly strained boundary between the Nolan and Zemlak domains generally separates ca Ma coarsegrained granitoids of the Nolan Domain (Ashton et al., 2007) from fine- to medium-grained felsic to intermediate orthogneisses containing 2520 Ma granodioritic rocks (Ashton et al., 2014) of the Zemlak Domain. However, on one small island immediately southwest of Laird Island on Tazin Lake, these two rock suites are separated by an approximately 150 m thick metamorphosed gabbro-ultramafic body (Figure 5; UTM E, N). The metagabbro is white to pale pink and dark green to black, medium grained, and contains about 25% hornblende and 20% tremolite-actinolite, along with minor chlorite, epidote, titanite, apatite and opaque minerals (Figure 6C). Small Saskatchewan Geological Survey 13 Summary of Investigations 2017, Volume 2

14 inclusions of more highly strained gabbroic rocks occur within the felsic to intermediate orthogneisses making up the Zemlak Domain along southern Tazin Lake. The Laird Island gabbro to ultramafic body may simply be a component of this Zemlak gabbroic suite that coincidentally occurs at the Nolan/Zemlak domain boundary; however, its presence along the domainal boundary allows for the possibility that the gabbro to ultramafic body was derived from a juvenile oceanic tectonic setting (i.e., if that domainal boundary represents a suture). To test this, a sample of the metagabbro was collected for Sm-Nd analysis. It yielded a T DM of 2.83 Ga, with an εnd value of +1.3 calculated at 2600 Ma (Table 2, Figure 7). Calculated at 2520 Ma, the crystallization age of some adjacent Zemlak Domain granodioritic gneisses to the south, the εnd value is TL-017 Pink Leucogranite Cutting Neoarchean Coarse-Grained Granite on Southwestern Laird Island (Nolan Domain) As previously discussed, pink leucogranite is a common rock type in the Nolan, Zemlak and southwestern Beaverlodge domains (Figure 1). Although much of it has been previously interpreted as anatectic and derived during the 1.94 to 1.90 Ga high-grade metamorphic events (Macdonald and Slimmon, 1985; Ashton et al., 2000), recent work has shown that the unit contains components of other, older granitic suites (Ashton et al., 2007; this paper). Included in this latter group is a mylonitic pink leucogranite from southeastern Laird Island (Figure 1) that was subsequently interpreted as an intensely deformed component of a 2584 ±4 Ma Nolan granite (Ashton et al., 2007). Nevertheless, pink leucogranites of inferred anatectic origin intrude the Neoarchean Nolan granitoids and appear to extend into the Zemlak Domain, where they intrude the felsic to intermediate orthogneisses. In their most pristine state, they are salmon pink, fine to medium grained, and contain less than 5% chlorite (commonly less than 1%; Figure 6D). The dearth of phyllosilicate minerals leaves the least-deformed end members nearly massive, although cataclastic deformation in the form of fracturing is generally intense, imparting a hackly appearance (Figure 6D). A sample of such pink leucogranite was collected for Sm-Nd analysis from southwestern Laird Island (Figure 5; UTM E, N) to better understand the origin of the rock unit and to complement the ongoing GEM-2 U-Pb and Lu-Hf studies. The derived T DM of the sample was 2.89 Ga and the εnd value at 2600 Ma was -0.3 (Table 2, Figure 7). Calculated at the alternative 1930 Ma crystallization age of the pink leucogranite, the εnd value is Gneissic Granite from Black Bay, Lake Athabasca (Zemlak Domain) Two samples from the Zemlak Domain, previously dated using the SHRIMP, were analyzed for Sm-Nd to better understand the domain s crustal history and make up. A gneissic granite from a multicomponent orthogneiss along the shore of Black Bay (Lake Athabasca) in the southeastern Zemlak Domain (Figure 5; UTM E, N) previously yielded a 2606 ±12 Ma crystallization age. Metamorphic overprints at 2366 ±9 and 1931 ±10 Ma in this rock were attributed to the Arrowsmith (Berman et al., 2013) and Taltson (McDonough et al., 2000) orogenies, respectively (Ashton et al., 2009). The gneissic granite yielded a T DM of 2.96 Ga and an εnd value of -0.4 calculated at its approximate crystallization age of 2600 Ma (Table 2, Figure 7) Hornblende Augen Granite from Harper Lake (Western Zemlak Domain) A variably mylonitized augen granite (Figure 6E) from northeastern Harper Lake in the western Zemlak Domain (Figure 5; UTM E, N) was previously dated using the SHRIMP to help constrain the age of an extensive zone characterized by a strong positive aeromagnetic signature (Ashton, 2009). The dated granite yielded a U-Pb crystallization age of 2330 ±7 Ma and a Taltson-aged metamorphic overprint at 1925 ±10 Ma (Ashton et al., 2007). The Sm-Nd analysis from the present study produced a T DM of 2.90 Ga with an εnd value of -0.3 calculated at 2600 Ma (Table 2, Figure 7). Calculated at its crystallization age of 2330 Ma, its εnd value is C2 Gneissic Granite from Southwestern Crackingstone Peninsula (Southwestern Beaverlodge Domain) Three samples from the western Beaverlodge Domain, two of which have been previously dated using the SHRIMP, were analyzed for Sm-Nd to better constrain the isotopic character of their igneous suites. A gneissic granite from the southwestern Crackingstone Peninsula (Figure 5; UTM E, N) previously yielded a zircon crystallization age of 2941 ±8 Ma (Ashton et al., 2009), which is about 60 Ma younger than dated members of the ca. 3.0 Ga granite suite (Persons, 1983; Hartlaub et al., 2004) exposed on the eastern Crackingstone Peninsula and Saskatchewan Geological Survey 14 Summary of Investigations 2017, Volume 2

15 southeast of Beaverlodge Lake (Figure 5). The ca. 3.0 Ga granite suite has yielded T DMs of 3.1 to 3.2 Ga, with εnd values of +0.5 to +1.7 calculated at 3000 Ma (Hartlaub et al., 2005). The 2941 ±8 Ma gneissic granite yielded a T DM of 3.47 Ga with an εnd value of -8.9 at 2600 Ma (Table 2, Figure 7), and -4.4 at its crystallization age of 2940 Ma. 13KA-183 Granite of the Foot Bay Gneiss from North of Dubyna Lake (Western Beaverlodge Domain) The Foot Bay Gneiss was a term originally used for rocks considered to be the oldest in the western Beaverlodge Domain (Tremblay, 1978). Recent mapping showed that the western end of the unit mainly comprises variably mylonitized granitoid rocks containing inclusions and crosscutting dykes of gabbroic material (Ashton et al., 2013a). A granitic knocker within ultramylonitic granite from near the Train Domain boundary yielded a U-Pb ID-TIMS age of 2601 ±16 Ma (Hartlaub et al., 2005). The dated rock is tentatively thought to be correlative with both the granitoid rocks recently mapped at the western end of the unit about 9 km away and the Stephens Lake granite to the southeast (Figure 5; Hartlaub, 1999). A sample of the least mylonitized granite from the western end of the Foot Bay Gneiss (Figure 5; UTM E, N) was sampled for Sm-Nd analysis, in part to test its inferred 2600 Ma age. The sample is pink and grey, medium grained, and contains pink quartzofeldspathic lenses and layers that probably include both feldspar augen and leucosome (Figure 6F). Petrography shows that the granite contains about 8% mostly chloritized hornblende and biotite. The derived T DM was 2.86 Ga with an εnd value of +0.3 calculated at 2600 Ma (Table 2, Figure 7). 11KA-250 Pink Leucogranite from the Intermediate Pit (Western Beaverlodge Domain) The 2331 ±4 Ma pink leucogranite from the Intermediate pit (Figures 1, 2, 5; UTM E, N) that was dated and described at the beginning of this paper was also sampled for Sm-Nd analysis to help constrain the Sm-Nd signature of the ca. 2.3 Ga granite suite. The resulting T DM was 3.06 Ga and the εnd value was -2.4 calculated at 2600 Ma, and -5.9 calculated at its approximate 2330 Ma crystallization age (Table 2, Figure 7). d) Discussion and Summary of Sm-Nd Results The 2.83 Ga T DM and slightly positive εnd value (+0.4 at 2600 Ma) for the mylonitic Nolan granite (16TL-029D) are both typical of values derived from members of the ca. 2.6 Ga granitic suite (Figure 7). Together with the field relationships, it is very likely that the analyzed rock is a member of this suite. The grey tonalitic migmatite (16TL-043C) from the Nolan Domain, however, yielded an uncharacteristically old 3.01 Ga T DM and a more evolved εnd value (-1.9 at 2600 Ma). These values are well outside the normal range for the 2.6 Ga Nolan granitic suite (Figure 7) and indicate the involvement of older crustal material. Although such involvement could have taken place in a number of ways, the presence of sillimanite and garnet in these rocks suggests that a sedimentary origin is the most likely. Assuming that this is the case, the tonalitic migmatite may be a partially melted psammopelite or derived diatexite that represents an outlier of the belt of psammopelitic to pelitic rocks at the eastern end of the Nolan Domain for which Sm-Nd data are not available (Figure 5). The 2.83 Ga T DM and positive εnd value (+1.3 at 2600 Ma) obtained for the gabbro (16KA-044) from the gabbro to ultramafic intrusion along the Nolan/Zemlak domainal boundary are consistent with derivation from the 2.3, 2.5 or 2.6 Ga igneous suites (Figure 7). The observation of similar-looking gabbroic rocks within Zemlak orthogneiss that also contains 2.52 Ga granodiorites, however, suggests that it likely belongs to that suite. Geochemical analysis and U-Pb dating would be useful to better evaluate its origin and tectonic setting. Calculated at 2.52 Ga, its εnd value is +0.3, suggesting minor interaction with pre-existing crustal material and therefore, that it is probably not of oceanic origin. The pink leucogranite (16TL-017) from southwestern Laird Island has a T DM of 2.89 Ga and a slightly evolved εnd value (-0.3 at 2600 Ma), suggesting that it has interacted with older crustal material. The three previously analyzed samples of the 2.6 Ga granite suite in the Nolan Domain all have slightly positive εnd values in the +0.2 to +1.3 range (Figure 7; Ashton et al., 2016). Although the pink leucogranite could represent a late phase of the 2.6 Ga granite suite with a greater component of crustal interaction, the intrusion of similar-looking pink leucogranites into 2.52 Ga granodiorites on the Zemlak side of the domainal boundary suggests that they are younger and contain a significant amount of older crustal material. Therefore, the possibility that the Laird Island pink leucogranite was Saskatchewan Geological Survey 15 Summary of Investigations 2017, Volume 2

16 derived by anatexis of mainly the Neoarchean granitic rocks at about 1.9 Ga (Ashton et al., 2005) or even 2.3 Ga remains viable. The 2330 Ma hornblende augen granite ( ) from Harper Lake, with a T DM of 2.90 Ga and an εnd value of -4.0 calculated at its crystallization age, is typical of other members of the 2.3 Ga granitic suite and supports its highly evolved nature (Figure 7). Likewise, the 3.06 Ga T DM and -5.9 εnd value (at its crystallization age) of the newly dated 2331 ±4 Ma pink leucogranite from the Intermediate pit (11KA-250) are within the ranges of normal values for the 2.3 Ga granitic suite (Figure 7), and consistent with the suggestion that these rocks formed in a postcollisional setting that was probably undergoing crustal extension in the aftermath of the Arrowsmith orogeny (Hartlaub et al., 2007; Ashton et al., 2013b). The T DM of 2.86 Ga and εnd value of for the Foot Bay granite (13KA-183) are consistent with a ca. 2.6 Ga crystallization age (Figure 7), as inferred from the apparent physical continuity between it and the previously dated 2601 ±16 Ma Prince Lake knocker (Hartlaub et al., 2005). The 2606 Ma gneissic granite ( ) from Black Bay (Lake Athabasca) in the southeastern Zemlak Domain, however, with a T DM of 2.96 Ga and an εnd value of -0.4, is more evolved than other members of the 2.6 Ga granitic suite from either the Nolan or western Beaverlodge domain (Figure 7; Ashton et al., 2016). The inferred increased interaction with older crustal material may result from minor contamination by, or interaction with, other intercalated rock types and/or phases of melt leucosome in the multiphase outcrop that was sampled (Ashton et al., 2009) or, alternatively, the 2.6 Ga granitic suite in the southeastern Zemlak Domain may have experienced a different tectonic history. Perhaps the most surprising results are from the 2.94 Ga orthogneiss (4704-C2) on the southwestern Crackingstone Peninsula with a T DM of 3.47 Ga and an εnd value of -4.4 calculated at its crystallization age (Figure 7). The U-Pb geochronological analysis indicated a single population of zircon grains that gave rise to the interpreted crystallization age, except for one of the forty-two analyses, which had a 207 Pb/ 206 Pb age of about 3.1 Ga (Ashton et al., 2009). Thus, the nature of the substantial interaction with older crustal material is not reflected in the contained zircon content and remains unknown. However, an abundance of Meso- to Paleoarchean detrital zircon from an unknown source is contained in the lower Murmac Bay group (Hartlaub et al., 2004; Ashton et al., 2013b), indicating that suitable Meso- to Paleoarchean crustal material was available for interaction ca. 2.3 Ga. Based on the Sm-Nd isotopic results (Figure 7) and unpublished geochemical data, it is also clear that the ca Ga orthogneiss is distinct from the ca. 3.0 Ga granite suite. 4. References Ashton, K.E. (2009): Compilation Bedrock Geology, Tazin Lake, NTS Area 74N; Saskatchewan Ministry of Energy and Resources, Map 246A, scale 1: Ashton, K.E. (2011): A new look at selected deposits in the historic Beaverlodge uranium district: variations on the vein-type uranium theme; in Summary of Investigations 2011, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of Energy and Resources, Miscellaneous Report , Paper A-1, 23p. Ashton, K.E., Card, C.D., Davis, W. and Heaman, L.M. (2007): New U-Pb zircon age dates from the Tazin Lake map area (NTS 74N); in Summary of Investigations 2007, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of Energy and Resources, Miscellaneous Report , Paper A-11, 8p. Ashton, K.E., Card, C. and Modeland, S. (2005): Geological reconnaissance of the northern Tazin Lake map area (NTS 74N), including parts of the Ena, Nolan, Zemlak, and Taltson domains, Rae Province; in Summary of Investigations 2005, Volume 2, Saskatchewan Geological Survey, Saskatchewan Industry and Resources, Miscellaneous Report , Paper A-1, 24p. Ashton, K.E., Chi, G., Rayner, N. and McFarlane, C. (2013a): Geological history of granitic rocks hosting uranium mineralization in the Ace-Fay-Verna-Dubyna mines area, Beaverlodge uranium district; in Summary of Investigations 2013, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report , Paper A-1, 23p. Ashton, K., Creaser, R.A. and Bethune, K. (2016): New Sm-Nd data from the Zemlak Domain: testing the model for tectonically amalgamated Taltson basement complex and proto-rae cratonic blocks within the Rae Province of northwestern Saskatchewan; in Summary of Investigations 2016, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report , Paper A-7, 12p. Saskatchewan Geological Survey 16 Summary of Investigations 2017, Volume 2

17 Ashton, K.E., Hartlaub, R.P., Bethune, K.M., Heaman, L.M., Rayner, N. and Niebergall, G.R. (2013b): New depositional age constraints for the Murmac Bay group of the southern Rae craton, Canada; Precambrian Research, v.232, p Ashton, K.E., Kraus, J., Hartlaub, R.P. and Morelli, R. (2000): Uranium City revisited: a new look at the rocks of the Beaverlodge Mining Camp; in Summary of Investigations 2000, Volume 2, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report , p Ashton, K.E., Rayner, N.M. and Bethune, K.M. (2009): Meso- and Neoarchean granitic magmatism, Paleoproterozoic (2.37 Ga and 1.93 Ga) metamorphism and 2.17 Ga provenance ages in a Murmac Bay Group pelite: U-Pb SHRIMP ages from the Uranium City area; in Summary of Investigations 2009, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of Energy and Resources, Miscellaneous Report , Paper A-5, 9p. Ashton, K.E., Rayner, N.M., Heaman, L.M. and Creaser, R.A. (2014): New Sm-Nd and U-Pb ages from the Zemlak and southcentral Beaverlodge domains: a case for amalgamated Taltson basement complex and proto-rae cratonic blocks within the Rae Province of northwestern Saskatchewan; in Summary of Investigations 2014, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report , Paper A-6, 28p. Berman, R.G., Pehrsson, S., Davis, W.J., Ryan, J.J., Qui, H. and Ashton, K.E. (2013): The Arrowsmith orogeny: geochronological and thermobarometric constraints on its extent and tectonic setting in the Rae craton, with implications for pre-nuna supercontinent reconstruction; Precambrian Research, v.232, p Bethune, K. (2014): New perspectives on tectonic assembly of the western Rae craton: evidence from the Athabasca region of Saskatchewan, Canada (abstract); Geological Society of America, 2014 Annual Meeting, Vancouver, Paper Bethune, K.M. (2017): Crustal dynamics and tectonic assembly of the west-southwest Rae craton What are key relationships in the Athabasca region telling us?; Geological Association of Canada Mineralogical Association of Canada, Abstracts, v.40, p.25. Cloutier, M., Bethune, K.M. and Ashton, K.E. (2017): Geochemistry and isotopic character of Precambrian granitoid suites across the Nolan-Zemlak domain boundary, west-southwest Rae craton: testing the possibility of a cryptic internal suture zone; in Geological Association of Canada Mineralogical Association of Canada, Joint Annual Meeting, Volume 40, Kingston, p.66. Collins, C.B., Farquhar, R.M. and Russell, R.D. (1954): Isotopic constitution of radiogenic leads and the measurement of geologic time; Geological Society of America Bulletin, v.65, p Creaser, R.A., Erdmer, P., Stevens, R.A. and Grant, S.L. (1997): Tectonic affinity of Nisutlin and Anvil assemblage strata from the Teslin tectonic zone, northern Canadian Cordillera: constraints from neodymium isotope and geochemical evidence; Tectonics, v.16, p Dieng, S., Kyser, K. and Godin, L. (2013): Tectonic history of the North American shield recorded in uranium deposits in the Beaverlodge area, northern Saskatchewan, Canada; Precambrian Research, v.224, p Eckelmann, W.R. and Kulp, J.L. (1956): Uranium-lead method of age determination; Geological Society of America Bulletin, v.67, p Goldstein, S.L., O Nions, R.K. and Hamilton, P.J. (1984): A Sm-Nd isotopic study of atmospheric dusts and particulates from major river systems; Earth and Planetary Science Letters, v.70, p Hartlaub, R.P. (1999): New insights into the geology of the Murmac Bay Group, Rae Province, northwest Saskatchewan; in Summary of Investigations 1999, Volume 2, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report , p Hartlaub, R.P., Chacko, T., Heaman, L.M., Creaser, R.A., Ashton, K.E. and Simonetti, T. (2005): Ancient (Meso- to Paleoarchean) crust in the Rae Province, Canada: evidence from Sm-Nd and U-Pb constraints; Precambrian Research, v.141, p Hartlaub, R.P., Heaman, L.M., Ashton, K.E. and Chacko, T. (2004): The Archean Murmac Bay Group: evidence for a giant Archean rift in the Rae Province, Canada; Precambrian Research, v.131, p Hartlaub, R.P., Heaman, L.M., Chacko, T. and Ashton, K.E. (2007): Circa 2.3 Ga magmatism of the Arrowsmith Orogeny, Uranium City region, western Churchill Craton, Canada; Journal of Geology, v.115, p Koeppel, V. (1968): Age and history of the uranium mineralization of the Beaverlodge area, Saskatchewan; Geological Survey of Canada, Paper 67-31, 111p. Macdonald, R. and Slimmon, W.L. (1985): Bedrock Geology of the Greater Beaverlodge Area, NTS 74N-6 to -11; Saskatchewan Energy and Mines, Map 241A, scale 1: Saskatchewan Geological Survey 17 Summary of Investigations 2017, Volume 2