Geological History of Granitic Rocks Hosting Uranium Mineralization in the Ace-Fay-Verna-Dubyna Mines Area, Beaverlodge Uranium District

Kenneth E. Ashton 1, Guoxiang Chi 2, Nicole M. Rayner 3, and Chris McFarlane 4

Ashton, K.E., Chi, G., Rayner, N.M., and McFarlane, C. (2013): 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, Sask. Ministry of the Economy, Misc. Rep. 2013-4.2, Paper A-1, 23p.

This report is accompanied by the map separate entitled: Ashton, K.E. (2013): Geology of the Ace-Fay-Verna-Dubyna mines area: 2013 update (parts of NTS 74N09 and 10); 1:10 000 scale prelim. map with Summary of Investigations 2013, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2013-4.2-(3).

Abstract The Ace-Fay-Verna-Dubyna mines area, spanning the St. Louis fault, is underlain by minor Archean granitoid rocks, the Paleoproterozoic Murmac Bay group, and ca. 1.9 Ga intrusive anatectic leucogranites, all of which were multiply deformed during two upper amphibolite facies metamorphic events. Following a period of uplift and erosion, a subsequent deformational event was responsible for brittle faulting, deposition of the unmetamorphosed Martin group, late open folding, and extensive metamorphic retrogression. Widespread hematite and ca. 1.82 Ga albitite alteration, focussed along major structural discontinuities, developed during this late, ca. 1.8 Ga deformational event. Fluids responsible for uranium mineralization also used major and secondary faults as conduits, possibly facilitated by the oxidized channels and increased permeability provided by the hematite and albitite alteration.

Keywords: Beaverlodge uranium district, vein-type uranium, albitite, rutile, Ace-Fay-Verna mine, Dubyna mine, Martin group, geochronology, Donaldson Lake granite, leucogranite.

1. Introduction Sixteen vein-type uranium deposits exploited between 1953 and 1982 constitute the historic Beaverlodge uranium district of northwestern Saskatchewan (Figure 1). An ongoing project has been aimed at updating the geological settings and descriptions of several deposits, including the Hab (Tracey et al., 2009), Gunnar (Ashton, 2010), Eagle, Camdeck, Ace-Fay-Verna, and Dubyna (Ashton, 2011; Ashton and Normand, 2012) deposits (Figure 1). The summer of 2013 was spent expanding the previous mapping around the largest of the past-producing mines, the Ace- Fay-Verna, and the Dubyna mine, both of which are located proximal to the St. Louis fault (Figure 1). Previous descriptions of the regional geology (e.g., Tremblay, 1972) and deposits (e.g., Beck, 1969) are detailed and of high quality. The purpose of this study is to update these descriptions using modern concepts and analytical techniques. Preliminary petrographic, petrogenetic, fluid inclusion, and stable isotopic results from a complementary study focussing on mineralized and barren veins associated with uranium mineralization are reported elsewhere (Liang et al., 2013). Previous work has shown that the uranium mineralization is hosted by a wide variety of rock types (Beck, 1969), although, in the Ace-Fay-Verna-Dubyna mines area (Figure 1), variably deformed anatectic leucogranites of inferred 1.93 Ga age (Hartlaub et al., 2005) and ca. 2.3 Ga Murmac Bay group amphibolites are the most common (Ashton, 2011; Ashton and Normand, 2012; Ashton et al., 2013). Much of the area mapped has been affected by a high degree of strain; initially this was ductile, forming mylonites, but this was subsequently overprinted by brittle-ductile and brittle strain, ultimately forming cataclasites and an extensive network of faults. This high degree of strain is typical of this variety of uranium deposit (Wilde, 2013), but locally led to previous misinterpretation of at least some of the host leucogranite and amphibolite as having sedimentary protoliths (e.g., Beck, 1969; Tremblay, 1972). Shear zones and faults resulting from the high strain have provided conduits for several generations and types of fluid alteration, including metamorphic retrogression, chloritization, hematization, graphitization, and albitization, as well

1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 200 - 2101 Scarth Street, Regina, SK S4P 2H9. 2 University of Regina, Department of Geology, 3737 Wascana Parkway, Regina, SK S4S 0A2. 3 Natural Resources Canada, Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8. 4 University of New Brunswick, Department of Earth Sciences, 2 Bailey Drive, Fredericton, NB E3B 5A3.

Saskatchewan Geological Survey 1 Summary of Investigations 2013, Volume 2 as silicification and carbonatization in the form of quartz, carbonate and mixed quartz-carbonate veins. Much of the uranium mineralization visible in outcrops and pit walls lines fractures and/or occurs within the quartz, carbonate, and mixed veins. A spatial association of albitization with the two largest past-producing uranium mines in the district (Ace-Fay-Verna and Gunnar) suggests a genetic relationship, although the nature of this link has yet to be determined. The Martin group, a deformed but unmetamorphosed redbed succession containing mafic volcanic rocks, is also spatially associated with the Ace-Fay-Verna and other deposits in the district, although any potential role it may have played in mineralization is also unclear (e.g., Smith, 1986).

Figure 1 – Regional setting of the Ace-Fay-Verna-Dubyna mines area, showing locations of select past-producing mines and occurrences; black box outlines area of Figure 2.

Saskatchewan Geological Survey 2 Summary of Investigations 2013, Volume 2 2. Regional Geology The Beaverlodge uranium district lies within the southwestern Beaverlodge and easternmost Zemlak domains (Figure 1). The regional (Ashton et al., 2000, 2009a, 2013; Ashton and Hartlaub, 2008) and local (Ashton, 2011; Ashton and Normand, 2012) geology has been previously described, and can be briefly summarized as follows. The oldest known rocks include ca. 3.0 and 2.6 Ga granitoids, which were metamorphosed first at ca. 2.57 Ga (Bethune et al., 2013) and later at 2.37 to 2.34 Ga (Koster and Baadsgaard, 1970; Ashton et al., 2009a; Bethune et al., 2013) during the ca. 2.5 to 2.35 Ga Arrowsmith orogeny (Berman et al., 2005, 2013). Arrowsmith metamorphism was followed by emplacement of 2.33 to 2.29 Ga syn- to post-collisional granites (Hartlaub et al., 2007) and deposition of the Murmac Bay group, which began at about 2.33 and lasted until at least 2.17 Ga, although sedimentation was likely episodic (Ashton et al., 2013). All of these rocks were then affected by regional deformation attributed to the 2.0 to 1.92 Ga Taltson orogeny, which produced a west-northwest–striking S1-S2 transposition fabric and associated amphibolite-facies metamorphism at about 1.94 to 1.92 Ga (McDonough et al., 2000; Bethune et al., 2010). The widespread leucogranite suites that host many of the Beaverlodge vein-type uranium deposits were probably generated during this Taltson orogenic event due to crustal melting. A second amphibolite-facies metamorphic event and associated northeast-striking D3 deformational overprint is apparently tied to ca. 1.91 to 1.90 Ga (Ashton et al., 2009b) tectonic events taking place in the vicinity of the Snowbird tectonic zone, about 200 km to the east. D1-D3 ductile deformational events were followed by a period of uplift that preceded widespread brittle-ductile faulting that characterized D4. The topographic relief produced by this faulting led to deposition of the unmetamorphosed Martin group, which was ongoing at 1.82 Ga (Ashton et al., 2009b), and was followed by renewed D4 faulting and north- trending open folding related to the Trans-Hudson Orogen. Following further uplift, the flat-lying and unmetamorphosed Athabasca Group was deposited between about 1.75 (Rainbird et al., 2007) and 1.50 Ga (Creaser and Stasiuk, 2007).

3. Ace-Fay-Verna-Dubyna Mines Area The Ace-Fay-Verna-Dubyna mines area, which also includes the ‘46’, ‘11’, ‘21’, and ‘83’ mineralized zones (Ashton, 2011; Ashton and Normand, 2012), spans the moderately southeast-dipping St. Louis fault northeast of Beaverlodge Lake (Figures 1, 2). The area can be broadly divided into three parts based on the degree of strain in pre-Martin group rocks. The area between Foot Bay and Schmoo Lake is dominated by variably mylonitized Archean granitoid and minor gabbroic rocks (Figure 2). To the south, a second area between central Mickey and Flack lakes is dominated by the Paleoproterozoic Donaldson Lake granite and is much less intensely deformed. Primary grain sizes are preserved in the granite, and abundant metre- to decimetre-scale xenoliths of Murmac Bay group quartzite and amphibolite range from angular and randomly oriented to variably transposed into the regional S1-S2 foliation. The third structural area is in the southwest (i.e., Beaverlodge–Collier Lake area; Figure 2), where all pre-Martin group rocks have been variably sheared to mylonitized and are characterized by a cataclastic overprint.

a) Unit Descriptions Archean Granitoid

Granitoid rocks in the Beaverlodge district were historically divided into three principal units: the ‘Foot Bay gneiss’, the ‘Donaldson Lake gneiss’, and ‘metasomatic granite’ of the ‘Tazin Lake group’ (Tremblay, 1972; Macdonald and Slimmon, 1985). Tremblay (1972) coined the term ‘Foot Bay gneiss’ for granitoid rocks exposed northeast of Foot Bay (Donaldson Lake; Figure 2), which he interpreted to be the oldest, in part because they form the core of a regional anticline. Ashton and Hartlaub (2008) used the term ‘granite-granodiorite and derived gneiss’ of inferred ca. 2.6 Ga age for Tremblay’s ‘Foot Bay gneiss’, but slightly modified its contacts and extended it another 10 km northeast of Foot Bay to the Prince-Zenith-Barker lakes area. The latter authors also pointed out that the best- preserved occurrences of these rocks closely resemble the ‘Stephens Lake granite’, which is exposed southeast of Prince Lake, on the southeastern side of the St. Louis fault (Macdonald and Slimmon, 1985; Ashton and Hartlaub, 2008). In the present study, rocks of Tremblay’s (1972) ‘Foot Bay gneiss’ are exposed east of Foot Bay and comprise a body of highly strained composite granite-gabbro and derived gneiss (unit G26). The dominant component of the composite pluton is granitic and includes pink, grey, and pink and grey varieties. The most common of these is coarse grained, retaining relict centimetre-scale feldspar augen along with 15 to 20% combined hornblende and biotite in a medium-grained recrystallized matrix (Figures 3A, 3B). Variably dismembered, pink, centimetre-scale layers are thought to represent leucosome (Figure 3B). The gabbroic component of these rocks is subordinate but present in most outcrops as decimetre-scale masses and metre-scale crosscutting dykes. It is tentatively considered broadly coeval with the granitic component because of its abundance and because it locally appears to be intruded by a less common, medium-grained granitic phase (Figure 3C). The gabbroic rocks are generally dark grey to black, fine to medium grained (Figure 3C), and contain about 50% hornblende along with minor hornblende-bearing ‘sweats’.

Saskatchewan Geological Survey 3 Summary of Investigations 2013, Volume 2

Figure 2 – Simplified geological map of the Ace-Fay-Verna-Dubyna mines area showing locations of past-producing uranium mines and anomalous eU occurrences based on spectrometer survey (‘e’ is an abbreviation of ‘equivalent’, inferring that U is not measured directly by the spectrometer).

Saskatchewan Geological Survey 4 Summary of Investigations 2013, Volume 2

Figure 3 – Rocks of the composite granite-gabbro and derived gneiss: A) pink granitic phase with texture indicative of originally coarse grain size (UTM 646772 m E, 6608725 m N5); B) same granitic phase containing intact (black arrow) and variably dismembered (yellow arrows) centimetre-scale, pink leucosome (UTM 646982 m E, 6608837 m N); C) light grey, medium-grained, granitic phase in sharp contact with dark gabbro (UTM 646977 m E, 6608672 m N); D) sheared granite exhibiting dextrally rotated porphyroclasts derived from original feldspar and from variably segmented leucosome (yellow arrow) in beaded feldspar matrix (UTM 646638 m E, 6608813 m N); E) granitic mylonite exhibiting dismembered leucosome (pale pink) and mafic component (black semi-continuous layers), along with post-mylonitic hornblende porphyroblasts (black millimetre-scale grains) (UTM 647237 m E, 6608850 m N); F) ultramylonitic granite with attenuated, centimetre- scale, pink leucosome and black mafic component (UTM 647237 m E, 6608850 m N).

With increasing strain, σ and δ porphyroclasts (Passchier and Trouw, 2005) have been developed from feldspar augen and dismembered segments of leucosome in the granitic component (Figure 3D). The mafic component has been variably dismembered and occurs as inclusions in a matrix dominated by beaded feldspar, and locally containing hornblende porphyroblasts that developed subsequent to the mylonitization (Figure 3E). Still higher levels of strain resulted in grey-green and pink, fine-grained mylonite in which centimetre-scale layers of leucosome and gabbro are locally recognized (Figure 3F).

5 All UTM coordinates are in NAD 83, Zone 12.

Saskatchewan Geological Survey 5 Summary of Investigations 2013, Volume 2 Murmac Bay Group Rocks of the Murmac Bay group are represented both in situ and as xenoliths in widespread leucogranites. An occurrence 1 km wide north of Greer Lake in the far southwest comprises quartzite, centimetre-scale iron formation, and mafic volcanic rocks (Figure 2), which represent a progressively younging stratigraphic sequence, based on work elsewhere (Hartlaub et al., 2004). The dominant quartzite in the section hosts extensive gabbro that is geochemically indistinguishable from the stratigraphically overlying mafic volcanic rocks (Hartlaub et al., 2004). A second occurrence of relatively well preserved Murmac Bay group rocks northwest of Strike Lake contains abundant mafic volcanic rocks and minor quartzite (Figure 2). Other occurrences of the Murmac Bay group are generally dominated by more deformed mafic rocks that have been termed amphibolite due to an inability to distinguish between volcanic and intrusive protoliths. The largest of these, in the Verna Lake area, is partly mantled by quartzite and contains minor quartzite and pelitic chlorite-sericite schist within the amphibolite (Figure 2). Quartzite (unit Mq) of the Murmac Bay group is generally white, but red ferruginous and black varieties are also common in the better-preserved southwestern occurrence. The small occurrences in the central part of the area are highly strained and attenuated. They all generally lack primary features and are fine grained, recrystallized, and extensively fractured. A few centimetres of oxide facies iron formation mark the inferred upper contact of the quartzite with mafic volcanic rocks (unit Mvb) in the southwestern occurrence (Figure 2). The latter are dark grey- green to black, very fine to fine grained, and homogeneous to weakly layered in both the southwest and Strike Lake occurrences (Figure 2). Dark green to black, medium-grained rocks lacking compositional variation are interpreted as gabbro (unit Gb). Their most extensive occurrence is within the quartzite in the southwest but, as elsewhere, the rocks are variably sheared to mylonitic, with only rare ‘islands’ of weakly strained rocks preserved to establish their origins. The generally recrystallized and highly strained amphibolites (unit Ma) are grey-green to brown-green, fine- grained, schistose rocks containing various proportions of amphibole, chlorite and epidote, along with plagioclase. Carbonate and subordinate quartz veins are common in the amphibolites. Minor psammopelitic to pelitic schist (unit Mp) occurs within the large amphibolite occurrence in the central part of the area (Figure 2). These rocks are chlorite-sericite schists, similar to some of the mylonitized granitic rocks, but differ in that their quartzofeldspathic matrix is uniformly fine grained, completely lacking the millimetre-scale feldspar ± quartz porphyroclasts that characterize the deformed granites.

Syntectonic Granitoid Rocks Tremblay (1972) interpreted his second granitoid unit, the ‘Donaldson Lake gneiss’ as a variably ‘granitized’ rock comprising a white, coarse-grained granitic component and a rusty-brown, finer-grained, quartz-feldspar-biotite component thought to be derived from quartzite, amphibolite, and other supracrustal rocks. In their regional compilation, Macdonald and Slimmon (1985) included the ‘Donaldson Lake gneiss’ in a much more extensive unit of ‘migmatitic’ ‘banded quartzofeldspathic gneisses’ containing leucosome, up to 15% amphibolite layers, calc- silicate rock and rare quartzite. Ashton and Hartlaub (2008) adopted Tremblay’s more restricted occurrence, using the term ‘inclusion-rich to migmatitic leucocratic granite to tonalite’ to convey the idea that the unit was derived from the emplacement of a leucocratic granite into supracrustal rocks of the Murmac Bay group rather than by ‘granitization’ of the latter. The characteristic supracrustal component was interpreted as variably deformed xenoliths and in situ material that had been infiltrated by the leucogranite (Ashton and Hartlaub, 2008; Ashton, 2011). Ashton (2011) further qualified this interpretation by suggesting that the Donaldson Lake granite was a crustal melt derived by widespread anatexis during one of the two ca. 1.9 Ga tectonometamorphic events. This interpretation is supported by the higher values of eU6 relative to those of the composite granite-gabbro unit (Table 1) and average continental crust (Kyser and Cuney, 2008).

The medium-grained (1 to 5 mm), seriate to equigranular leucogranites that intrude the Murmac Bay group in the Ace-Fay-Verna-Dubyna mines area were previously subdivided on the bases of colour, the presence of abundant xenoliths, and the degree of deformation (Ashton and Normand, 2012). Cream-coloured, medium-grained to seriate, homogeneous rocks were assigned to the Donaldson Lake granite (unit Ald) (Figure 4A). It is characterized by up to 40% angular and previously deformed xenoliths of Murmac Bay group quartzites and amphibolites that become variably transposed with higher strain into schlieren (Figures 3A and 3B from Ashton and Normand, 2012). Pink varieties ranged from fine to medium grained but included some that were coarser and seriate. Most, but not all, were more highly strained and characterized by millimetre-scale feldspar porphyroclasts and ribbony quartz. These pink varieties were collectively termed pink leucogranite and considered part of a much more widespread suite extending discontinuously to the Alberta border (Ashton and Normand, 2012).

6 The ‘e’ is an abbreviation of ‘equivalent’ inferring that U is not measured directly by the spectrometer.

Saskatchewan Geological Survey 6 Summary of Investigations 2013, Volume 2 Table 1 – Average spectrometer1 values for major rock types in the Ace-Fay-Verna-Dubyna mines area. No. of eU2 eTh K3 Rock Type Unit Code Readings (ppm) (ppm) eTh/eU % Martin Group Martin group volcanic rocks (Pitch-Ore)4 2 7.4 5.4 0.7 0.1 Martin group clastic sedimentary rocks Rbc, Rbs, 13 9.4 12.8 1.4 3.5 Rba

Albitite Ace-Fay-Verna-Dubyna 30 13.1 25.0 1.9 1.2 Episyenite (Gunnar area)4 12 9.2 40.8 4.4 0.7

Second-generation leucogranite 6 6.7 15.1 2.3 0.4

Sheared-Mylonitic Leucogranites Cataclasite (Camdeck area)4 10 5.2 10.9 2.1 1.2 Mylonitic leucogranite (Eagle area)4 18 6.2 17.9 2.9 2.3 Mylonitic pink leucogranite (83 Zone) Alp-m 34 5.7 16.4 2.9 1.9

Anatectic Leucogranites Pink leucogranite (Eagle-Camdeck area)4 55 12.2 24.8 2.0 2.4 Pink leucogranite (Ace-Fay-Verna-Dubyna) Alp-s 94 7.6 21.0 2.8 1.7 Biotite leucogranite Alt 4 5.9 8.8 1.5 1.6 Donaldson Lake granite Ald 141 7.4 17.1 2.3 2.1 Gunnar granite (Gunnar area)4 95 7.0 34.5 4.9 3.8

Murmac Bay Group Argillite (Lorado area)4 12 6.6 17.3 2.6 2.1 Pelitic gneiss Mp 3 4.7 10.9 2.3 1.7 Mafic volcanic rocks and amphibolite Ma, Mvb 60 4.6 5.0 1.1 0.9 Quartzite Mq 37 7.6 9.4 1.2 1.3

Archean Granitoids G26 granite G26 15 1.6 14.9 9.4 2.9 G30 granite (Lorado area)4 5 3.3 13.0 3.9 2.9 Archean orthogneiss (Gunnar area)4 101 5.0 17.7 3.5 2.3

Average upper continental crust (in ppm U) 2.7 Notes: 1 Values were measured over several summers using hand-held, high-sensitivity, gamma and neutron radiation spectrometers (Radiation Solutions GR-135 and RS-230). 2 The ‘e’ is an abbreviation of ‘equivalent’ inferring that these elements are not measured directly. 3 Note that K contents are reported as %K and not %K2O. To convert, multiply %K values by 1.2047. 4 Values from other areas/deposits (Ashton, 2011; Ashton and Normand, 2012) added for comparison.

During the 2013 field work, it was recognized that many of the rocks previously assigned to ‘pink leucogranite’ (e.g., Figures 3C to 3F in Ashton and Normand, 2012) simply represent a hematized and variably deformed variety of the cream-coloured leucogranite (i.e., the Donaldson Lake granite). Polygonization resulting from overprinting deformation is extensive in the primary quartz of these pink rocks but has affected the feldspars to a much lesser degree, lending the rocks a somewhat rounded or beaded appearance at hand sample and outcrop scale (Figure 4A). The pink rocks exhibiting this modified primary igneous texture have been reclassified as a hematized variety of the Donaldson Lake granite and grouped accordingly (Figure 2, accompanying map separate). Previous maps showed the Donaldson Lake granite extending southeastward to about the southern end of Foot Bay, Donaldson Lake (Tremblay, 1972; Ashton and Hartlaub, 2008); however, inclusion of the hematized varieties and the discovery of more cream-coloured Donaldson Lake granite now increases its southeastern extent to the Fish Lake – Flack Lake area (Figure 2).

Saskatchewan Geological Survey 7 Summary of Investigations 2013, Volume 2 Figure 4 – A) The Donaldson Lake granite (UTM 648733 m E, 6607324 m N). B) Second generation of melt leucosome (l) mantling amphibolite xenoliths (a) in Donaldson Lake granite (g) (UTM 645192 m E, 6608497 m N). C) Second generation of melt leucosome (l) mantling and interacting with quartzite xenolith (q) within Donaldson Lake granite (g); note coarser grain size of second-generation melt (UTM 645192 m E, 6608497 m N). D) Second generation of melt leucosome (l) mantling and infiltrating amphibolite xenolith (a) within Donaldson Lake granite (g) (UTM 644867 m E, 6608623 m N). E) Gneissic rock comprising cream-coloured Donaldson Lake granite exhibiting beaded texture (g) and interlayered white, medium-grained, second-generation melt leucosome with granitic texture (l) (UTM 649009 m E, 6607839 m N). F) Gneissic Donaldson Lake granite (g) containing schlieren of Murmac Bay group amphibolite (a) infiltrated by sheets of pale pink, second-generation melt leucosome (l) (UTM 645211 m E, 6607418 m N).

Saskatchewan Geological Survey 8 Summary of Investigations 2013, Volume 2 Both cream and pink varieties of the Donaldson Lake granite are characterized by 0 to 5% variably chloritized biotite. Local remelting of the Donaldson Lake granite has produced a second generation of melt leucosome. It is generally white, medium to coarse grained, and both mantles and intrudes the Murmac Bay group quartzite and amphibolite xenoliths (Figures 4B to 4D). With increasing metamorphic grade, the abundance of second-generation melt leucosome increases to form gneissic (Figure 4E) and migmatitic rocks, many of which contain schlieren derived from Murmac Bay group xenoliths (Figure 4F). In these more complex rocks, there may be several varieties of melt leucosome that vary in colour from white to pink or red, and in grain size from medium to coarse (Figure 5A). In addition to quartzite and amphibolite, the migmatites south and southwest of Foot Bay locally contain medium-grained granitoid inclusions with a colour index of about 20. These are thought to be derived from the G26 granite, which is exposed directly along strike to the east, and may extend under the migmatitic leucogranite at depth (Figure 2). Biotite and hornblende, derived by interaction between amphibolite, the Archean granitoid, and the melt leucosome, are locally preserved in all three phases.

Figure 5 – A) Migmatite comprising gneissic Donaldson Lake granite (g) containing variably assimilated schlieren of Murmac Bay group amphibolite (a) intruded by pale pink medium-grained (ml) and pink-red coarse-grained (cl) dykes of second-generation melt leucosome; emplacement of dykes during deformation has facilitated rotation of gneissic granite blocks (UTM 647473 m E, 6607796 m N). B) Quartzite xenolith (q) within gneissic Donaldson Lake granite (g) mantled by second-generation melt leucosome (l); note that second-generation melt leucosome crosscuts main regional S1-S2 foliation (UTM 644716 m E, 6608940 m N).

The third granitoid rock type in the study area was termed ‘metasomatic granite’ by Tremblay (1972), who interpreted the unit as being derived by the ‘granitization’ of pre-existing, but largely unknown, rocks. Relatively homogeneous granite was viewed as the end result of this process, whereas layered varieties were thought to reflect relict bedding in supracrustal precursors, and represent an intermediate step in the granitization process. Several other varieties were interpreted as reflecting various deformational states and one variety, a ‘carbonatized granite’, appears to represent an alternative name for ‘albitite’ (Ashton, 2011; Ashton and Normand, 2012; also see “Alteration”). Macdonald and Slimmon (1985) roughly equated Tremblay’s ‘metasomatic granite’ unit with their ‘leucogranite’ unit but modified its contacts, particularly those shared with the ‘banded quartzofeldspathic gneiss’ unit. Ashton and Hartlaub (2008) used the term ‘pink leucogranite-leucogranodiorite’ for Tremblay’s (1972) ‘metasomatic granite’ north of the St. Louis fault, but delineated some older granitoids farther south. Based on the present study, Tremblay’s (1972) ‘metasomatic granites’ are termed pink leucogranites. Most pink leucogranites vary from pale pink (Figure 6A) to more typically pink to salmon pink (Figure 6B), and are generally more deformed than the Donaldson Lake granites, under both brittle-ductile and brittle conditions (Figure 6B). The pink leucogranites are the most common rock type in the southwestern part of the map area (Figure 2), and rocks of similar relative age and appearance underlie much of the western Beaverlodge Domain and extend westward discontinuously throughout the eastern and central Zemlak Domain (Ashton, 2009). Typical rocks of the most common form, the sheared to cataclastic pink leucogranite (unit Alp-s), are sugary textured to porcelainous with a variably preserved ductile shear fabric and local millimetre-scale feldspar porphyroclasts (Figure 6B). A strong

Saskatchewan Geological Survey 9 Summary of Investigations 2013, Volume 2 cataclastic overprint affecting most rocks is characterized by abundant, variably oriented fractures forming a millimetre- to centimetre-scale network (Figure 6C). The fractures are commonly lined with chlorite and, less commonly, hematite and/or epidote. Where best developed, this late fracturing and cataclasis, together with recrystallization, obscures the earlier ductile fabric, giving the rocks a misleading, near-massive appearance (Figures 6A, 6B). The pink leucogranite has clearly intruded Murmac Bay group quartzites and amphibolites, although xenoliths are less obvious than in the Donaldson Lake granite. This is partly because the inclusions have been strongly attenuated, most commonly appearing as centimetre-scale layers, but also because metamorphic interaction between the leucogranite and quartzite renders the latter more difficult to recognize. The second generation of partial melt leucosome recognized in the Donaldson Lake granite is thought to be present locally in the pink leucogranite, but its recognition is also hampered by the deformational overprint. Where an early platy mylonitic fabric is well preserved, the rocks have been distinguished as mylonitic pink leucogranites (unit Alp-m). They are best developed in the areas flanking the Verna Lake amphibolite body, but occur discontinuously within the sheared to cataclastic leucogranite throughout the area (Figure 2).

Gradational contacts suggest that the pink leucogranite is a more deformed and recrystallized version of the Donaldson Lake granite. The latter is characterized by a distinctive weathered surface with subhedral seriate feldspars up to 3 to 4 mm in size, set within a positively weathering quartz matrix (Figure 4A), whereas the pink leucogranite has a smoother weathered surface and individual feldspar grains are finer grained and either beaded or difficult to discern (Figures 6A, 6B). This correlation is supported by the similar proportion of mafic minerals in the two rock types (3 to 5% variably chloritized biotite) and by their similar spectrometer values, although a minor loss in uranium appears to accompany the more highly strained mylonitic version of the pink leucogranite (Table 1).

A small unit of biotite leucogranite in the eastern part of the area is situated at the contact between the Donaldson Lake granite and the sheared to cataclastic pink leucogranite (Figure 2). It also contains inclusions of Murmac Bay group rocks and its texture is transitional between that of the two adjacent granitic units. It is white to pale pink and generally fine to medium grained (1 to 2 mm), but contains centimetre-scale patches with 1 to 4 mm grain size, thought to represent second-generation melt leucosome. The leucogranite contains 3 to 5% biotite (hornblende in one outcrop), which appears somewhat less chloritized than biotite in the two bounding granitic units. Significantly lower eTh values (Table 1) may indicate an abnormality in the source area from which the biotite leucogranite was generated or that it has experienced a slightly different history than the Donaldson Lake granite or pink leucogranite, but it is interpreted as a cogenetic transitional phase. Figure 6 – Outcrop photos showing A) pale pink Alteration porcelainous variant of the sheared to cataclastic pink leucogranite (UTM 647353 m E, 6606019 m N); B) Wallrock alteration is widespread in the Beaverlodge area and salmon pink variant of the sheared to cataclastic pink leucogranite (UTM 645330 m E, 6605653 m N); and C) includes the greenschist facies retrogression of upper amphibolite pale pink leucogranite exhibiting ‘hackly’ weathered facies metamorphic assemblages. Late chlorite is the main mafic surface resulting from intense fracturing (UTM 645104 m constituent in shear and fault zones (Figure 7B in Ashton, 2011) E, 6605874 m N). and also commonly lines fractures. Poorly ordered graphite occurs as black, fine-grained, sooty veins several centimetres in thickness

Saskatchewan Geological Survey 10 Summary of Investigations 2013, Volume 2 within fault zones at the Eagle mine workings and in the 46 zone (Figures 1, 2). Hematization is more pervasive, with hematite occurring as microscopic inclusions that give feldspars, and thus many granitic rocks, their deep pink colour. It is also a common wallrock alteration associated with faults, and as specular hematite lining fractures and forming rare veinlets. Since hematite is a highly oxidized form of iron, zones affected by hematization may have acted as channels facilitating the flow of oxidized acidic fluids carrying uranium into the basement, where contact with a reduced fluid or wallrock component could have resulted in precipitation. For this reason, an attempt was made to map the extent of hematization in the Ace-Fay-Verna-Dubyna area (Figure 2). Albitite, resulting from wallrock alteration, forms a semi-continuous network in the northeastern part of the area, generally overlapping the area affected by hematization (Figure 2). It is most common in an area roughly 1 km wide between the St. Louis and Strike faults, but is also present west of Foot Bay and in the vicinity of the Fay mine shaft (Figure 2). Individual zones of albitite alteration range up to several metres in thickness. Weathered surfaces range from pale pink to red-brown with increasing hematite content, and are typically rough, being formed by millimetre- scale albite grains (Figures 3D, 3F in Ashton and Normand, 2012). Albitization involved the variable removal of primary quartz, and replacement of K-feldspar and plagioclase in the wallrock by albite, carbonate, and minor specular hematite and rutile (Ashton and Normand, 2012). Where the alteration was intense, thin sections show that the albitite contains 80 to 90% anhedral hydrothermal albite displaying characteristic ‘checkerboard’ twinning and abundant microscopic hematite inclusions (Figures 4B, 4D in Ashton and Normand, 2012), along with 3 to 15% carbonate (rarely up to 35%), 0 to 3% chlorite, and 2% specular hematite. Millimetre-scale pods occupying interstices amongst the medium-grained hydrothermal albite grains contain finer- grained subhedral albite that generally lacks the microscopic hematite inclusions, along with subhedral rutile and specular hematite, all of which are enclosed by carbonate. These small interstitial pods of alteration are thought to be filling the voids left behind by quartz dissolution. The subhedral nature of the enclosed albite, specular hematite and rutile is consistent with precipitation from a fluid phase. Spectrometer readings show that the albitite alteration has elevated eU and eTh values relative to ‘unaltered’ Donaldson Lake granite and pink leucogranite (Table 1). Potassium has been depleted, consistent with the replacement of K-feldspar by albite.

Veins of albitite and albite-carbonate tend to be much thinner, generally on a millimetre scale, and can be seen lining fractures on outcrops. In thin section, these veins cut igneous K-feldspar and plagioclase in the precursor granite or leucogranite, possibly representing incipient alteration (Figure 4A in Ashton and Normand, 2012). Coexistence of hydrothermal albite and carbonate in these veins suggests that the carbonate filling the voids may have been deposited by the same fluid responsible for albitization. The absence of other precipitates on the walls of the pods is consistent with this interpretation.

Albitization is most obvious in the Donaldson Lake granite due to the colour change and ease of recognizing quartz depletion. It is unclear whether the fewer occurrences of albitite within the pink leucogranite reflect its absence or a recognition problem. The fluids responsible for albitization probably also passed through other rock types (e.g., the amphibolite), but recognition would be difficult without the characteristic quartz loss and red colour as guides.

The Donaldson Lake granite also commonly contains generally concordant, centimetre- to decimetre-scale, semi- continuous sheets of pink-red, coarse-grained to pegmatitic granite, informally termed ‘alaskite’ (Figure 3C in Ashton and Normand, 2012). Typical alaskite contains quartz in concentrations compatible with derivation from magmatic rocks and little to no ferromagnesian minerals (Figures 7A, 7B). However, single grains of coarse-grained pink-red feldspar have also developed locally within the host rocks in the vicinity of more typical alaskitic sheets. The alaskite is generally less deformed than its host rocks, locally crosscutting mylonite in the composite granite- gabbro unit, but elsewhere has been attenuated and dismembered by shearing (Figure 7B). Quartz veinlets perpendicular to the contacts of the sheets cut across coarse feldspar grains in the best preserved occurrences, possibly indicating a period of post-emplacement extension (Figure 7A). Fluid interactions between alaskite and quartzite inclusions in the Donaldson Lake granite have locally produced medium-grained, quartz-feldspar hybrid rocks with a complete variation in quartz:feldspar ratios (Figure 7C). At one locality, a pegmatitic alaskite dyke crosscuts sheared rocks marking the St. Louis fault, but has been offset in an apparent dextral sense by late brittle reactivation (Figure 7D). Quartz in the dyke exhibits a weak S4 foliation. Due to the dark pink-red, hematitic colour of most of the alaskite and its abundance in the zone of albitite alteration, a genetic link to the latter was considered. However, petrography shows that, along with an abundance of quartz, the alaskite contains K-feldspar and plagioclase that typically exhibit a degree of sericitic alteration and deformation similar to that of the host granites, rather than the much better preserved and younger hydrothermal albite characterizing the albitite (Ashton and Normand, 2012). In addition, a coarse-grained to pegmatitic granite component of the second-generation melt leucosome is quite similar in appearance, differing mainly in a much paler pink colour (Figures 4B, 4C). Together these observations indicate that at least most of the alaskite (e.g., Figures 7A, 7C) results from metamorphic processes; however, due to their dark pink-red hematized colour, local quartz-feldspar zoning, subhedral feldspar habit, and apparent late relative age locally, a younger hydrothermal origin for some alaskite occurrences cannot be discounted.

Saskatchewan Geological Survey 11 Summary of Investigations 2013, Volume 2

Figure 7 – A) Sheet of typical alaskite (a) intruding hematized Donaldson Lake granite (g); note individual coarse-grained feldspars (yellow arrow) in Donaldson Lake granite below lower contact, and quartz veinlets cutting many feldspar grains in the alaskite (black arrows) (UTM 646654 m E, 6607437 m N). B) Pegmatitic alaskite crosscutting mylonitic granite of the composite granite-gabbro unit; note zoned nature of main body in central part of photo, and attenuation and dismemberment of alaskite at bottom (yellow arrow) (UTM 647447 m E, 6608521 m N). C) Quartzite xenolith (q) containing feldspar due to interaction with discontinuously mantling alaskite (a); xenolith hosted by hematized Donaldson Lake granite (g) (UTM 646654 m E, 6607437 m N). D) Pegmatitic alaskite dyke cutting across sheared rocks marking the St. Louis fault but subsequently displaced during late brittle reactivation in an apparently dextral sense; dismembered white layers are probably quartz veins (UTM 649467 m E, 6608886 m N).

Martin Group The Martin group comprises continental clastic redbeds and minor mafic volcanic rocks that are considered broadly coeval with the 1.82 Ga Uranium City mafic dykes (Ashton et al., 2009a; Morelli et al., 2009). The group’s original stratigraphic thickness is thought to have been 4 to 6 km (Tremblay, 1972), although the succession was gently folded and faulted shortly after deposition, with preservation in the Beaverlodge area restricted to one main structural basin and several small outliers (Figures 1, 2). Basal polymictic conglomerate and siltstone of the Martin group unconformably overlie mineralized leucogranites and Murmac Bay group amphibolites in the vicinity of the Fay and Ace shafts on surface and were also found underground in the vicinities of the Fay and Verna shafts (Morton and Sassano, 1972; Figure 1). An outlier of basal Martin group conglomerate about 2.5 km northeast of the Verna mine (Figure 2), suggests that the redbed succession was originally present throughout the map area (Ashton and Normand, 2012). Clast types show that the basal conglomerate was locally derived (e.g., Ashton, 2011). In the Ace- Fay-Verna-Dubyna area, the clasts are dominated by granitoids, vein quartz and minor Murmac Bay group rocks, but also include coarse-grained alaskite of the kind described above (Figure 5B in Ashton and Normand, 2012). Red- brown clasts resembling albitite alteration were also noted in the Martin group conglomerate in the vicinity of the Fay shaft (Figure 5C in Ashton and Normand, 2012), although more work needs to be done to confirm this relationship, as it would indicate that albitite alteration predated deposition of the Martin group.

Saskatchewan Geological Survey 12 Summary of Investigations 2013, Volume 2 b) Structure and Metamorphism The structural history has been previously summarized for both the region (Ashton et al., 2009b; Ashton, 2010) and the Ace-Fay-Verna-Dubyna mine area (Ashton, 2011; Ashton and Normand, 2012). Structural data collected in 2013 are generally consistent with those previous descriptions. The earliest recognized ductile deformation (D1-D2) was responsible for development of an east-southeast–trending regional fabric, tight to isoclinal folding, and widespread shearing. Early moderately plunging tectonic stretching lineations on sheared to mylonitic rocks in the vicinity of the St. Louis fault are consistent with reverse displacement with a minor sinistral component, and are thought to have developed during D2. Metamorphism accompanying this deformation resulted in widespread anatexis and emplacement of the Donaldson Lake granite and pink leucogranite. Renewed deformation (D3), involving tight folding and renewed shearing, partially transposed the early S1-S2 fabric into a northeasterly trend and was accompanied by a second generation of upper amphibolite facies metamorphism that locally remelted the Donaldson Lake granite (Figure 4). The Black Bay fault (Figure 1) is thought to have also formed at this time, possibly as a thrust fault. Following a period of uplift and erosion, a subsequent phase of deformation (D4) took place at a higher crustal level. Associated brittle faulting resulted in accommodation space that led to deposition of the Martin group, which was subsequently affected by open north-trending late-D4 folds. Fault analysis suggests a broadly east-west shortening stress regime during D4 (Ashton et al., 2009a; Ashton and Normand, 2012), although the senses of displacement along major structures such as the St. Louis fault are difficult to discern (see discussion by Ashton, 2011), probably because of multiple reactivations. The fault itself largely overprints pre-existing sheared to mylonitic rocks. The orientation of the later brittle-ductile fault is consistent with dextral slip based on the inferred east-west shortening regional stress model (Ashton et al., 2009a; Ashton and Normand, 2012), and on apparent displacements at surface (Figure 7D), but the presence of Martin group rocks at depths of 800 to 1000 m at the sites of the Fay and Verna shafts (Morton and Sassano, 1972) suggests a period of substantial normal displacement.

c) Ages of Granitoid Rocks and Albitite Alteration

Age of the Granitic Component of the Composite Granite-Gabbro and Derived Gneiss (‘Foot Bay Gneiss’)

There have been two attempts to date the ‘Foot Bay gneiss’. A sample from about 1.5 km west-northwest of the Dubyna pit and 100 m east of Foot Bay (approximate UTM coordinate 646215 m E, 6608753 m N) produced a two- point ID-TIMS upper intercept age of 2513 +36/-22 Ma (Tremblay et al., 1981), whereas a sample of mylonitized, granulite-facies granite collected about 1 km northwest of Prince Lake (8.5 km northeast of the Dubyna mine) yielded a 2601 ±16 Ma ID-TIMS zircon age (Hartlaub et al., 2004). The latter, better-constrained result is considered more robust and suggests that the ‘Foot Bay gneiss’ is part of a more extensive 2.6 Ga granitoid suite that stretches discontinuously about 20 km to the southeast to the shore of Lake Athabasca (Hartlaub et al., 2004; Ashton, 2009; Bethune et al., 2013), and in an extensive, less deformed, multi-phase batholith that dominates the Nolan Domain about 45 km to the northwest (Van Schmus et al., 1986; Ashton et al., 2007, 2009b).

Age of the Donaldson Lake Granite

There have been several attempts to date the anatectic leucogranites, including three studies aimed at determining the age of the granitic component of the ‘Donaldson Lake gneiss’. Based on a three-point zircon discordia line, Tremblay et al. (1981) obtained a 2179 ±12 Ma upper intercept age using ID-TIMS. Using the same technique, Hartlaub et al. (2004) obtained an age of 2634 +55/-53 Ma. Ashton et al. (2013) questioned the latter result on the bases of the large error, the granite’s leucocratic composition, and its sheet-like style of emplacement, which led to the sample being re-analyzed using laser ablation techniques. That study resulted in a much broader range of results, with only two of the twelve zircon 206Pb/207Pb ages approximating 2.6 Ga. Of the remaining ten ages, one was ca. 3.1, another was 2.25 Ga, and the rest had ages of less than 2.05 Ga. According to their model, the zircon grains that produced the original 2634 Ma ID-TIMS age, along with the >2.25 Ga results from the laser ablation study, were inherited from rocks at depth during the widespread partial melting event during which the granite was derived (Ashton et al., 2013). The results of all three geochronological studies are probably best explained by a model involving the derivation of an anatectic granite from a variety of local crustal sources (e.g., ca. 3.0 Ga granites, 2.6 Ga granite, 2.3 Ga granitoids, and Murmac Bay group) during the 1.94 to 1.92 Ga or 1.91 to 1.90 Ga metamorphic event.

Age of the Pink Leucogranite An attempt to date a sample of ‘leucogranite’ from the southwestern end of the Uranium City town site (UTM 633437 m E, 6604520 m N), 10 km west of the study area, yielded a broad scatter of seven zircon analyses with 207Pb/206Pb ages ranging from 3.20 to 1.80 Ga (Hartlaub et al., 2005). Most of these were strongly discordant and interpreted as inherited, but one grain, exhibiting distinctive morphology and a near-concordant result, was interpreted as indicating a 1933 Ma crystallization age. This ID-TIMS result was followed up by a laser ablation study that produced a similarly large scatter amongst twenty-three 207Pb/206Pb zircon ages ranging from 3.66 to

Saskatchewan Geological Survey 13 Summary of Investigations 2013, Volume 2 2.17 Ga. In spite of some groupings of analyses around 2.3 Ga (n=3) and 3.0 to 3.4 Ga (n=15), all of the grains were interpreted as inherited, inferring that no zircon grown at the time of crystallization had been analyzed (Hartlaub et al., 2005).

New Geochronological Result for the Donaldson Lake Granite Previous mapping has shown that many of the Beaverlodge vein-type uranium deposits (e.g., Ace-Fay-Verna, Hab, Dubyna, Eagle) are hosted by syntectonic leucogranites (Ashton, 2011) and that at many more deposits and occurrences, syntectonic leucogranite occurs very close by, prompting suggestions that the leucogranite may have been the ultimate source of uranium for the subsequent deposits (Ashton, 2011). The Donaldson Lake syntectonic granite also hosts albitite alteration that is spatially related to uranium mineralization at some deposits (e.g., Ace-Fay- Verna, Dubyna, Gunnar). Although genetic connections have yet to be demonstrated, the close spatial relationship of the Donaldson Lake granite to the uranium mineralization was considered justification for attempting to better establish its age. As a consequence, a new sample of Donaldson Lake granite was recently analyzed using the Sensitive High-Resolution Ion Microprobe (SHRIMP) at the Geological Survey of Canada. The sample was collected from 30 m northeast of the 21 zone (sample 11KA-163, UTM 646661 m E, 6607370 m N), which is located about 250 m northwest of the St. Louis fault and about 500 m northwest of Collier Lake (Figure 2). It came from an outcrop containing amphibolite and quartzite xenoliths within the granite, similar to those depicted in Figures 3B and 3C in Ashton (2011), which occur only a few tens of metres away. Care was taken when sampling to avoid such xenoliths to minimize the effects of inheritance. The sample was pink, medium grained, seriate, and homogeneous at the outcrop scale (Figure 8A). It contained about 45% preferentially sericitized plagioclase, 30% variably polygonized quartz, 20% K-feldspar, and 5% chlorite after biotite. The plagioclase contained microscopic red-brown inclusions assumed to be hematite and there were minor carbonate veinlets, but there was no evidence of albitization in the sample.

The resultant analyses are widely scattered with 207Pb/206Pb ages ranging from 3.6 to 1.82 Ga (Figure 8B; Table 2). There are isolated and small groups of analyses at ca. 3.6, 3.1, and 2.5 Ga, along with a large cluster, representing 20 of 35 analyses, at about 2.32 Ga. Almost all of the zircon grains within these groups have Th/U ratios in the 0.5 to 1.3 range, consistent with derivation from plutonic rocks. Two younger clusters of zircon analyses at 2.1 to 2.03 Ga and 1.89 to 1.82 Ga have Th/U ratios in the 0.2 to 0.5 and 0.1 to 0.3 ranges, respectively, suggesting that they were derived by a different process(es). However, these ages were not reproducible, so the only relevant information that can be taken from these younger data is that some Pb-loss event must have occurred at about 1870 Ma, the average age Figure 8 – A) Outcrop photo of the site sampled for of the three youngest concordant zircon analyses (Table 2; geochronological analysis of the Donaldson Lake granite. B) Concordia diagram for zircon analyses (inset is an spots 2.1, 2.2, 13.1). A single population of monazite from enlargement of the Paleoproterozoic component of data. C) the same sample yielded an age of 1869 ±3 Ma (Figure 8C), Results for monazite from the same sample. similar to the ca. 1870 Ma zircon population.

Saskatchewan Geological Survey 14 Summary of Investigations 2013, Volume 2 It is tempting to interpret these new results as indicating that the Donaldson Lake granite crystallized at ca. 2.32 Ga with minor older inheritance at ca. 3.6, 3.1, and 2.53 Ga, and younger metamorphic/hydrothermal overprints at ca. 2.09 and 1.87 Ga. In support of this interpretation is the presence of ca. 2.32 Ga granites in the Beaverlodge uranium district (the closest being the Yahyah granite located about 5 km southeast of the sample site). In spite of being non- reproducible, the ca. 2.09 Ga cluster of zircon analyses could theoretically record metamorphism. The age is similar to a poorly constrained metamorphic event of that age documented in the Taltson magmatic zone about 230 km to the northwest (Bostock and van Breemen, 1994). However, a ca. 2.32 Ga crystallization age seems unlikely for several reasons. 1) The Donaldson Lake granite and pink leucogranite are unique in the Beaverlodge uranium district in that they intrude and commonly carry abundant xenoliths of the Murmac Bay group. Xenoliths are particularly common and obvious in the Donaldson Lake granite (Figures 4B, 4C; Figure 6C in Hartlaub et al., 2004; Figures 3B, 3C in Ashton, 2011; and Figure 3A in Ashton and Normand, 2012), including the outcrop sampled for geochronology. Although it has been shown that initial deposition of the Murmac Bay group began as early as 2.32 Ga, the psammopelitic component contains detrital zircon as young as 2.17 Ga, indicating much younger sedimentation (Ashton et al., 2013). Since the Donaldson Lake granite intrudes Murmac Bay group psammopelitic gneisses as well as quartzite and amphibolite north of Donaldson Lake (Hartlaub et al., 2004), its age should be post-2.17 Ga. By contrast, the ca. 2.32 Ga granite suite is characteristically homogeneous, and coarse grained (Figure 7 in Ashton, 2010). Rather than containing Murmac Bay group xenoliths, it is typically crosscut by mafic sheets thought to be intrusive equivalents of the Murmac Bay group mafic volcanic rocks (Hartlaub et al., 2004). 2) The xenoliths of Murmac Bay group rocks were foliated and probably folded prior to incorporation in the Donaldson Lake granite (Figures 9A, 9B). Of the four estimates for the age of metamorphism associated with the Arrowsmith orogeny in the southern Rae Province, all fall in the 2.37 to 2.34 Ma range (Koster and Baadsgaard, 1970; Hartlaub, 2004; Ashton et al., 2009b; Bethune et al., 2013), at least 10 Ma prior to earliest deposition of the Murmac Bay group (Ashton et al., 2013). Further, because no fabric has been identified in the lower Murmac Bay group that is not also present in the upper part of the succession, the foliation characterizing the xenoliths probably also postdates 2.17 Ga, the age of the youngest detrital zircon in pelitic rocks of the type locality (Ashton et al., 2013). Based on an abundance of previous work in the area, the first fabric-forming event after the Arrowsmith orogeny was the 1.94 to 1.92 Ga Taltson orogeny (e.g., McDonough et al., 2000; Ashton et al., 2009b, 2013; Bethune et al., 2013), suggesting that was the age of the fabrics in the Murmac Bay group xenoliths that developed prior to incorporation by the Donaldson Lake granite.

3) Two of the previous three attempts to date the Donaldson Lake granite resulted in inferred ages of 2.18 (Tremblay et al., 1981) and 2.6 Ga (Hartlaub et al., 2004). Neither of those previous studies contained any strong evidence for a ca. 2.32 Ga crystallization age. Similarly, the new data set shows no strong evidence for either a 2.18 or 2.6 Ga crystallization age. During the previous attempts to date the pink leucogranite, which is considered here to be a more deformed and recrystallized equivalent of the Donaldson Lake granite, only one of six 207Pb/206Pb ages, determined using ID-TIMS, and three of twenty-three 207Pb/206Pb ages, determined using laser ablation techniques, had ages of ca. 2.32 Ga (Hartlaub et al., 2005).

4) Zircon ages of ca. 3.6, 3.1, 2.6, 2.53, 2.32, and 2.18 Ga are all well represented in the sedimentary, and to a less well-constrained degree, in the igneous record, so their presence as inheritance in an anatectic granite derived by partial melting of the country rocks is to be expected. Thus, the preferred interpretation is that all of the zircon 207Pb/206Pb ages greater than ca. 2.28 Ga result from inheritance. Since the three 207Pb/206Pb ages in the 2.10 to 2.03 Ga range in the present study were not reproducible, it is unlikely that this age has any geochronological significance. If any meaning were to be forced upon them, they would best be interpreted as modified inheritance of 2.17 to 2.14 Ga zircon. A single granitic rock of this age is known in the Taltson basement complex of northwestern Alberta (McNicoll et al., 2000), but more importantly, 2.17 Ga was the dominant population of detrital zircon in a previously analyzed Murmac Bay group pelite (Ashton et al., 2013).

207Pb/206Pb ages within the ca. 1870 Ma cluster were also not reproducible, although the near-concordant nature of two of the analyses, together with the 1870 Ma monazite age, suggests that zircon and monazite growth did take place at about this time. While 1870 Ma is not a common age for granite crystallization in the Beaverlodge area, monazite of this age has been reported as part of the rare earth element mineralization at the Hoidas Lake deposit about 50 km to the north-northeast (Gunning and Card, 2005). Though apparently older, this period of zircon and monazite growth is not too different than the 1848 ±5 Ma estimate for the main uranium mineralizing event in the Beaverlodge uranium district (Dieng et al., 2013).

Saskatchewan Geological Survey 15 Summary of Investigations 2013, Volume 2

Table 2 – SHRIMP U/Pb data for Donaldson Lake granite (sample / station number 11KA-163), southwest Beaverlodge Domain. Apparent Ages (Ma) U Th Th Yb Hf 204Pb % 206*Pb f(206)204 208*Pb 207*Pb 206*Pb Corr 207*Pb 206Pb ±206Pb 207Pb ±207Pb Disc. Spot Name (ppm) (ppm) U (ppm) (ppm) 206Pb ± (ppm) % 206*Pb % ± 235U % ± 238U % ± Coeff 206*Pb % ± 238U 238U 206Pb 206Pb (%) 10739-37.1 498 137 0.283 81 10995 5.8E-5 26 125 0.101 0.087 1.6 4.49 1.10 0.2924 1.03 0.934 0.1113 0.4 1653 15 1821 7 10.4 10739-2.1 267 67 0.258 53 11952 6.2E-5 43 77 0.108 0.078 2.1 5.22 1.16 0.3353 1.03 0.883 0.1128 0.5 1864 17 1846 10 -1.1 10739-2.2 362 104 0.297 43 11366 2.7E-5 34 103 0.046 0.088 1.5 5.22 1.07 0.3297 1.02 0.945 0.1148 0.4 1837 16 1876 6 2.4 10739-13.1 708 77 0.113 166 11790 5.8E-6 49 204 0.010 0.034 1.8 5.33 1.04 0.3348 1.01 0.970 0.1155 0.3 1862 16 1888 5 1.6 10739-22.2 1180 471 0.412 324 11731 2.4E-5 29 359 0.041 0.121 1.9 6.13 1.05 0.3544 1.02 0.970 0.1255 0.3 1955 17 2035 5 4.6 10739-22.1 707 330 0.483 342 9896 2.4E-5 27 234 0.042 0.142 0.9 6.87 1.04 0.3847 1.01 0.973 0.1296 0.2 2098 18 2093 4 -0.3 10739-45.1 821 156 0.196 302 12752 6.4E-5 15 261 0.112 0.063 1.3 6.63 1.04 0.3703 1.01 0.967 0.1299 0.3 2031 18 2096 5 3.6 10739-36.1 324 216 0.688 195 10421 1.8E-5 22 113 0.031 0.203 1.1 8.11 1.08 0.4072 1.02 0.949 0.1445 0.3 2202 19 2282 6 4.1 10739-19.2 87 96 1.137 219 8720 1.6E-4 29 31 0.281 0.340 1.8 8.27 1.35 0.4130 1.09 0.806 0.1453 0.8 2229 21 2291 14 3.2 10739-60.1 30 25 0.874 128 8919 3.0E-4 31 11 0.512 0.245 3.2 8.51 1.83 0.4245 1.22 0.668 0.1455 1.4 2281 23 2293 23 0.7 10739-21.1 176 92 0.540 117 11780 1.1E-4 21 63 0.197 0.153 1.7 8.35 1.18 0.4150 1.06 0.901 0.1459 0.5 2238 20 2298 9 3.1 10739-19.1 92 94 1.050 208 8589 5.0E-5 75 34 0.086 0.313 1.4 8.58 1.23 0.4263 1.06 0.861 0.1459 0.6 2289 20 2298 11 0.5 10739-41.1 121 127 1.090 267 8762 2.1E-5 66 44 0.037 0.320 1.5 8.57 1.19 0.4225 1.06 0.887 0.1471 0.6 2272 20 2313 9 2.1 10739-45.2 918 250 0.281 322 14498 5.3E-6 43 316 0.009 0.081 1.1 8.14 1.04 0.4010 1.01 0.976 0.1471 0.2 2174 19 2313 4 7.1 10739-7.1 484 359 0.765 468 8726 8.5E-6 96 175 0.015 0.224 0.8 8.56 1.04 0.4205 1.01 0.969 0.1476 0.3 2263 19 2318 4 2.8 10739-20.1 264 326 1.276 369 9662 7.6E-5 18 95 0.132 0.372 0.8 8.57 1.08 0.4193 1.02 0.943 0.1482 0.4 2257 19 2325 6 3.5 10739-21.2 87 90 1.071 154 9177 1.3E-4 31 29 0.228 0.322 1.9 8.01 1.41 0.3920 1.17 0.829 0.1483 0.8 2132 21 2326 13 9.8 10739-51.1 150 123 0.846 166 9768 4.4E-5 21 54 0.077 0.244 1.6 8.60 1.17 0.4203 1.05 0.897 0.1484 0.5 2262 20 2327 9 3.3 10739-31.1 61 71 1.193 258 8810 4.8E-5 240 22 0.084 0.336 2.0 8.57 1.70 0.4183 1.13 0.666 0.1486 1.3 2253 22 2330 22 3.9 10739-57.1 60 52 0.884 135 8770 1.6E-4 36 22 0.271 0.255 2.3 8.68 1.44 0.4230 1.12 0.773 0.1487 0.9 2274 21 2331 16 2.9 10739-60.2 29 23 0.830 121 9263 1.5E-4 45 10 0.253 0.231 3.7 8.25 1.79 0.4011 1.24 0.691 0.1491 1.3 2174 23 2336 22 8.2 10739-29.1 40 46 1.183 205 8565 8.1E-5 64 14 0.141 0.349 2.2 8.66 1.77 0.4199 1.48 0.835 0.1496 1.0 2260 28 2342 17 4.1 10739-11.1 458 214 0.483 325 10202 7.8E-6 145 170 0.013 0.140 1.2 8.88 1.06 0.4306 1.02 0.956 0.1497 0.3 2308 20 2342 5 1.7 10739-63.1 67 1 0.022 37 10528 6.9E-5 47 24 0.119 0.006 11.3 8.86 1.37 0.4248 1.14 0.831 0.1513 0.8 2282 22 2360 13 3.9 10739-9.1 343 249 0.748 178 9999 3.3E-5 43 132 0.057 0.209 1.0 9.58 1.09 0.4489 1.04 0.953 0.1548 0.3 2390 21 2399 6 0.5 10739-63.2 87 2 0.027 37 10936 4.8E-5 66 31 0.083 0.009 9.4 8.96 1.47 0.4177 1.30 0.882 0.1556 0.7 2250 25 2408 12 7.8 10739-9.2 183 136 0.767 163 9873 7.1E-5 27 68 0.122 0.221 1.5 9.29 1.18 0.4306 1.08 0.914 0.1565 0.5 2308 21 2418 8 5.4 10739-33.1 276 234 0.874 314 11250 3.4E-5 67 111 0.059 0.255 1.0 10.81 1.09 0.4681 1.03 0.940 0.1674 0.4 2475 21 2532 6 2.7 10739-6.1 95 79 0.864 211 10977 1.7E-5 97 48 0.030 0.249 1.5 18.82 1.16 0.5885 1.07 0.920 0.2320 0.5 2983 26 3066 7 3.4 10739-49.1 157 85 0.563 108 11075 3.7E-4 10 77 0.641 0.156 1.5 18.47 1.20 0.5738 1.06 0.891 0.2335 0.5 2923 25 3076 9 6.2 10739-34.1 56 0 0.004 30 9012 4.3E-5 87 29 0.074 0.002 17.3 20.00 1.26 0.6090 1.11 0.884 0.2382 0.6 3066 27 3108 9 1.7 10739-47.1 20 18 0.932 86 10165 4.1E-4 25 13 0.704 0.234 3.1 33.83 1.60 0.7466 1.32 0.826 0.3286 0.9 3595 36 3611 14 0.6 10739-44.1 354 256 0.748 368 9998 1.9E-5 29 215 0.033 0.207 0.9 32.75 1.05 0.7069 1.02 0.976 0.3360 0.2 3447 27 3644 3 7.0 Notes (see Stern, 1997): 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 2.22.08.04.30, rev. 30 Apr 2008. f(206)204 refers to mole percent of total 206Pb that is due to common Pb, calculated using the 204Pb method; common Pb composition used is the surface blank (4/6: 0.05770; 7/6: 0.89500; 8/6: 2.13840). * Refers to radiogenic Pb (corrected for common Pb). Discordance (Disc.) relative to origin = 100 * ((207/206 age - 206/238 age)/(207Pb/206Pb age)). Calibration standard 6266; U = 910 ppm; age = 559 Ma; 206Pb/238U = 0.09059. Analytical details: IP654, 25 µm spot, 12 nA primary intensity, 5 scans; error in 206Pb/238U calibration 1.0% (included); no mass fractionation correction applied to 207/206 results.

Saskatchewan Geological Survey 16 Summary of Investigations 2013, Volume 2

Figure 9 – A) Donaldson Lake granite containing randomly oriented, previously foliated, xenoliths of Murmac Bay group quartzite (q) and amphibolite (a) (UTM 646527 m E, 6607526 m N). B) Murmac Bay group xenolith comprising quartzite and amphibolite that exhibits an S1 foliation that has been folded by F2 prior to incorporation in Donaldson Lake granite (UTM 646654 m E, 6607437 m N).

Another important constraint on the age of the Donaldson Lake granite is that it has locally been remelted to form a second-generation leucosome, suggesting that it experienced an upper amphibolite facies metamorphic event subsequent to its emplacement. Therefore, the Donaldson Lake granite, which is interpreted as resulting from widespread anatexis, must have developed during the first upper amphibolite facies metamorphic event associated with D1-D2 deformation at 1940 to 1920 Ma (Table 3). This infers that the granite was emplaced towards the end of the event responsible for fabric development in the Murmac Bay group xenoliths, an interpretation supported by the presence of this main regional fabric in foliated to sheared varieties of the granite (Figures 4B to 4F, 5B). The second generation of melt leucosome clearly crosscuts this regional fabric (Figure 5B), consistent with its later development, during the second upper amphibolite facies event (i.e., that associated with D3) ca. 1910 to 1900 Ma.

Table 3 – Inferred geological history of the Ace-Fay-Verna-Dubyna mines area.

Age Deposition Deformation/Metamorphism Tectonic Event (Ma) Local Event (Group) (Facies) (Orogeny) 1500 1590 ± Unconformity-type uranium mineralization, Eastern Athabasca Athabasca Basin 1750 1780 ±20(?)* Main Beaverlodge mineralization 1817 ±28 Albitization Martin D Trans-Hudson 1818 ±4 Uranium City mafic dykes 4 1848 ±5(?)+ Main Beaverlodge mineralization 1910 to 1900 Second generation melt D3; upper amphibolite Snowbird/Early Trans-Hudson 1940 to 1920 Donaldson Lake granite and pink D1-D2; upper amphibolite Taltson leucogranite

2171 Youngest detrital zircon Murmac Bay

2330 to 2290 Arrowsmith granites 2370 to 2340 Arrowsmith metamorphism No fabric distinguished; Arrowsmith local amphibolite 2566 ±8 No fabric distinguished; Unamed local amphibolite 2600 G26 granite-gabbro * Based on Koeppel (1968) + Based on Dieng et al. (2013)

Saskatchewan Geological Survey 17 Summary of Investigations 2013, Volume 2 New Geochronological Result for the Albitite Alteration The spatial relationship of albitite alteration to mineralization at the two largest deposits in the Beaverlodge uranium district (i.e., Ace-Fay-Verna and Gunnar) as well as several others (e.g., Dubyna, Eagle), suggests that it may play a role in the mineralizing process. Where mineralization is hosted by the albitite, it occurs in crosscutting carbonate veins, so mineralization must postdate or be broadly coeval with albitization. Thus, the age of the albitization can be used to constrain the age of mineralization. Petrographic study shows that hydrothermal rutile, which is not present in the unaltered rocks, is a common constituent of the albitite, occurring both within the medium-grained hydrothermal albite that dominates the alteration (Figures 4B and 4C of Ashton and Normand, 2012), and within interstitial pods thought to represent filled voids resulting from quartz dissolution (Figures 4D and 4E of Ashton and Normand, 2012). These age relationships indicate that rutile grew during the albitization process and, since rutile is a datable mineral using the U-Pb system, its presence provides an opportunity to date albitization. Rutile is a difficult mineral to date due to generally low uranium contents and high common lead. In addition, the presence of minute uranium-rich inclusions precluded the use of some samples. In the end, however, data was collected from three polished sections made from two samples: one from 100 m northeast of the 21 zone (sample 11KA-169, UTM 646765 m E, 6607403 m N), the other from the main wall of the Dubyna pit (sample 11KA-196, UTM 647882 m E, 6608445 m N). The dating was conducted using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at the University of New Brunswick using standard thickness (~30 µm) polished thin sections. Ablation was conducted using a Resonetics M-50-LR 193 nm Excimer laser ablation system. Samples and standards were loaded together into a two-volume, low-volume Laurin Technic Pty S-155 sample cell that was repeatedly evacuated and backfilled with He to remove traces of air from the cell after each sample exchange. The cell was subsequently pressurized using high-purity He and Ar cell gases (300 mL/min and 930 mL/min, respectively) that were mixed downstream of ® the cell with 2.0 mL/min high-purity N2. All gas lines are fitted with VICI Metronics high-flow Hg traps that maintain the 204Hg gas background at <200 cps. A Laurin Technic Pty ‘squid’ smoothing device was placed between the ablation cell and the ICP-MS torch. Laser output energy was set and regulated at 120 mJ corresponding to a fluence of ~3.5 J/cm2 on target. Standards and unknowns were ablated using 33 or 48 μm diameter craters and a repetition rate of 4 or 4.5 Hz. A single long ablation sequence was constructed for each sample and comprised at least 15 analyses of the rutile R10 standard (concordia age = 1088 ±3 Ma; Schmitt and Zack, 2012), which was interspersed with the unknown target grains and used as an external standard to correct for down-hole fractionation, instrument drift, and mass-bias. Each ablation in the sequence comprised 30 sec of gas background collection followed by 30 to 35 sec of ablation. Time-resolved intensities were collected using an Agilent 7700x quadrupole ICP-MS configured with dual external rotary pumps. The measured isotopes and dwell times were 49Ti (10 ms), 204Pb (70 ms), 206Pb (35 ms), 207Pb (70 ms), 208Pb (10 ms), 232Th (10 ms), and 238U (15 ms), giving a total quadrupole sweep time of ~0.23 seconds. Oxide production monitored as 248ThO/232Th on NIST610 glasses was < 0.4%, and 238U/232Th was ~1.05. At the end of the ablation sequence, the laser log file and ICP-MS intensity data file were synchronized using Iolite™ (Paton et al., 2011) running as a plugin for Wavemetrics Igor Pro 6.22™. Laser-induced Pb/U fractionation corrections, corrected isotope ratios, and elemental abundances were calculated offline using Iolite™ version 2.3 and VizualAge™ (Petrus and Kamber, 2012). Time-slices from which the isotope ratios were calculated were selected by examining the time-series data for drift-, fractionation-, and mass-bias–corrected 207Pb/206Pb and selecting the interval that resulted in the smallest error for this ratio. Time-slices of <10 seconds in duration were typically discarded because of the resulting high propagated errors. The exported data were additionally inspected using Isoplot™ v3.71 (Ludwig, 2012). The accuracy of the LA-ICP-MS data was verified by periodically analyzing the 490 ±3 Ma R19 rutile standard (Schmitt and Zack, 2012) under the same analytical conditions. The results are presented on an inverse isochron, which represents a mixing line between 100% common Pb and 100% radiogenic Pb (Figure 10). The upper intercept partly depends on the composition of the common Pb and is geologically meaningless. The lower intercept age of 1817 ±28 Ma is interpreted as the best estimate for the age of the rutile and the albitite (Table 3). This age is significantly younger than an 1848 ±5 Ma estimate for the main uranium mineralizing event at Beaverlodge, but is within error of an 1812 ±15 Ma estimate for mineralization that was tied to deposition of the Martin group (Dieng et al., 2013). The timing of Martin group deposition is based on an 1818 ±4 Ma age for the Uranium City mafic dykes, which are considered broadly coeval with Martin group mafic volcanism (Morelli et al., 2009). Thus, the development of albitite alteration temporally overlapped deposition of the Martin group. The 1817 ±28 Ma estimate for the age of albitization is also consistent with an alternative 1780 ±20 Ma estimate for the main period of Beaverlodge uranium mineralization (Koeppel, 1968).

Saskatchewan Geological Survey 18 Summary of Investigations 2013, Volume 2 Figure 10 – Inverse isochron diagram showing a mixing line between 100% common Pb and 100% radiogenic Pb for the analyzed rutile in albitite. The lower intercept age of 1817 ±28 Ma is interpreted as the best estimate for the time of rutile precipitation.

d) Economic Geology of the Ace-Verna-Dubyna Mines Area Historical summaries of the Beaverlodge uranium deposits, including descriptions of many of the past-producing mines (Beck, 1969; Tremblay, 1972) are important because they were prepared when there was still underground access to the mine workings. Geological observations for the present study are restricted to surface showings and open pits, which presumably represent mineralization that was considered sub-economic at the time of mining. This imposes a bias towards fracture- and vein-hosted mineralization relative to mineralization associated with fault breccias that are commonly referred to in historical studies.

Preliminary observations have been previously presented (Ashton, 2011; Ashton and Normand, 2012). The 2013 mapping was designed to more accurately and completely determine the context of mineralization in the Ace-Fay- Verna-Dubyna mines area. Widespread hematite and albitite alteration, both of which are mainly hosted by the Donaldson Lake granite, form wide corridors spanning the St. Louis fault (Figure 2). Both types of alteration tend to follow brittle discontinuities, both at outcrop and map scale, although both also occur as veins in the absence of structural discontinuities. Hematite is spatially associated with most of the fracture-controlled mineralization, and a thorough search of such mineralized fractures will generally reveal both minor albitite and narrow quartz and/or carbonate veins; but there are exceptions. Where mineralization is found within extensive zones of albitite, however, it appears restricted to specific crosscutting veins. Therefore, albitite may represent alteration by a fluid that was leaching and transporting uranium that precipitated as mineralization only where it encountered a reductant in a second fluid (i.e., represented by veins). However, albitite could alternatively predate the mineralization; its role involving the establishment of oxidized fluid conduits with enhanced permeability that would provide access for later mineralizing fluids. In this scenario, mineralization could result from interaction of the oxidized mineralizing fluid with the generally reduced basement rocks, or when the physical conditions of the fluid changed so that uranium solubility was reduced. Most of the deposits are in, or adjacent to, zones of sheared to mylonitic rocks (Figure 2). This is a common feature of uranium deposits that are spatially associated with albitite worldwide, although a genetic link is unclear (Wilde, 2013). The mechanical deformation, recrystallization, and potential metasomatism accompanying this early shearing may have helped to destabilize or destroy primary uranium-bearing minerals in the granitoid and other host rocks.

Saskatchewan Geological Survey 19 Summary of Investigations 2013, Volume 2 Uranium liberated in this way can be adsorbed to the minerals that remain or become stable during the shearing event, leaving it much more accessible for dissolution by subsequent circulating fluids (Guthrie and Kleeman, 1986). Therefore, these early ductile shear zones may represent the source of the uranium destined for the ore deposits. Whether they were the source rocks or not, these zones of structural weakness were used repeatedly by more brittle overprinting structures, which provided more discrete fluid pathways for the leaching, transport and/or precipitation of uranium. Martin group mafic volcanic rocks host uranium mineralization at the Martin Lake and Pitch-Ore deposits (Figure 1), although it is unclear whether this results from the main mineralizing event or later remobilization. Due to its close spatial relationship to many of the large deposits (e.g., Ace-Fay-Verna, Eagle, Lorado), it has been suggested that the basal unconformity of the Martin group played a genetic role in the mineralizing process (e.g., Smith, 1986). The Bolger, Dubyna, and Hab (6 km due north of the Verna shaft, see Figure 1) open pits were mapped in some detail as part of a complementary study directed towards better understanding the mineralization process. Vein parageneses were determined for each pit area and representative veins were sampled for fluid inclusion and stable isotope study. Descriptions of this work along with preliminary results from samples collected in 2012 can be found in Liang et al. (2013). During this complementary deposit-focussed study, it was noted that the veins cutting Martin group rocks were similar in appearance and mineralogical make up to both barren and mineralized veins cutting the basement rocks at many of the deposits. Preliminary stable isotopic results from samples collected in 2012 show isotopic similarities between the veins cutting Martin group rocks and barren and mineralized veins cutting the basement rocks as well (Liang et al., 2013). Although inconclusive, these observations are consistent with a model in which much of the uranium mineralization took place during or after deposition of the Martin group.

4. Conclusions Extended mapping in the vicinity of the Ace-Fay-Verna and Dubyna mines in 2013 showed that the area is dominated by variably sheared and recrystallized granitic rocks. Geochronological study of the main phase, the Donaldson Lake granite, proved inconclusive, but it is thought to have formed at 1.94 to 1.92 Ga by anatexis associated with D1-D2 deformation. Remelting of the granite to form a second generation of melt leucosome was probably coeval with the second of two upper amphibolite facies metamorphic events during D3 at 1.91 to 1.90 Ga. Growth of zircon and monazite at 1.87 Ga may have taken place at the tail end of this metamorphic event or have developed through subsequent hydrothermal alteration. The Ace-Fay-Verna-Dubyna mines area is also characterized by extensive corridors of hematite and albitite alteration, the latter of which developed at about 1.82 Ga, the age of rutile that developed during albitization. Both mines and abundant uranium occurrences and showings are spatially associated with the albitite alteration but, where found together, the mineralization is generally restricted to discrete carbonate veins that cut the albitite. It is unclear whether albitite represents the fluid that leached and/or transported the uranium to the sites of precipitation or is an earlier process that prepared the ground for later mineralizing fluids.

5. Acknowledgements The field-based component of this project is being done in conjunction with an analytical follow-up at the University of Regina. Rong Liang is studying fluid inclusions and stable isotopes as part of an MSc thesis, and Travis LeGault, who provided cheerful and able assistance during the field work, is studying the albitite alteration as part of an honours BSc thesis. Additional sampling for these studies was carried out this summer, with the help of both students and the thesis co-supervisor, Dr. Guoxiang Chi. Thanks also to Harold Grasley for providing our accommodations, Dean Classen for renting us a vehicle, and Dixie Parkes for supplying our groceries. The original manuscript was much improved thanks to constructive reviews by Ralf Maxeiner and Colin Card. The principal author is also grateful to Colin for many fruitful and ongoing discussions concerning uranium mineralization.

6. References Ashton, K.E. (2009): Compilation Bedrock Geology, Tazin Lake, NTS Area 74N; Sask. Ministry of Energy and Resources, Map 246A, scale 1:250 000. Ashton, K.E. (2010): The Gunnar mine: an episyenite-hosted, granite-related uranium deposit in the Beaverlodge uranium district; in Summary of Investigations 2010, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of Energy and Resources, Misc. Rep. 2010-4.2, Paper A-4, 21p.

Saskatchewan Geological Survey 20 Summary of Investigations 2013, Volume 2 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, Sask. Ministry of Energy and Resources, Misc. Rep. 2011-4.2, 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, Sask. Ministry of Energy and Resources, Misc. Rep. 2007-4.2, CD-ROM, Paper A-11, 8p. Ashton, K.E. and Hartlaub, R.P. (2008): Geological compilation of the Uranium City area; Sask. Ministry of Energy and Resources, Open File 2008-5, set of four 1:50 000-scale maps. Ashton, K.E., Hartlaub, R.P., Bethune, K.M., Heaman, L.M., Rayner, N., and Niebergall, G.R. (2013): New depositional age constraints for the Murmac Bay group of the southern Rae craton, Canada; Precamb. Resear., v232, p70-88. Ashton, K.E., Hartlaub, R.P., Heaman, L.M., Morelli, R., Bethune, K.M., and Hunter, R.C. (2009a): Post-Taltson sedimentary and intrusive history of the Rae Province along the northern margin of the Athabasca Basin: Western Canadian Shield; Precamb. Resear., v175, 16-34. 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, Sask. Energy Mines, Misc. Rep. 2000-4.2, p3-15. Ashton, K.E. and Normand, C. (2012): Bedrock geology of the Ace-Fay-Verna-Dubyna mines area, Beaverlodge uranium district; in Summary of Investigations 2012, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2012-4.2, Paper A-3, 21p.

Ashton, K.E., Rayner, N.M., and Bethune, K.M. (2009b): 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, Sask. Ministry of Energy and Resources, Misc. Rep. 2009-4.2, Paper A-5, 9p.

Beck, L.S. (1969): Uranium Deposits of the Athabasca Region, Saskatchewan; Sask. Dept. Miner. Resour., Rep. 126, 139p.

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; Precamb. Resear., v232, p44-69.

Berman, R.G., Sanborn-Barrie, M., Stern, R.A., and Carson, C.J. (2005): Tectonometamorphism at ca. 2.35 and 1.85 Ga in the Rae Domain, western Churchill Province, Nunavut, Canada: insights from structural, metamorphic and in situ geochronological analysis of the southwestern Committee Bay belt; Can. Mineral., v43, p409-442.

Bethune, K.M., Berman, R.G., Rayner, N., and Ashton, K.E. (2013): Structural, petrological and U-Pb SHRIMP geochronological study of the western Beaverlodge domain: implications for crustal architecture, multi- stage orogenesis and the extent of the Taltson orogen in the SW Rae craton, Canadian Shield; Precamb. Resear., v232, p89-118. Bethune, K.M., Hunter, R.C., and Ashton, K.E. (2010): Age and provenance of the Paleoproterozoic Thluicho Lake Group based on detrital zircon U-Pb SHRIMP geochronology: new insights into the protracted tectonic evolution of the southwestern Rae Province, Canadian Shield; Precamb. Resear., v182, p83-100. Bostock, H.H. and van Breemen, O. (1994): Ages of detrital and metamorphic zircons and monazites from a pre- Taltson magmatic zone basin at the western margin of Rae Province; Can. J. Earth Sci., v31, p1353-1364. Creaser, R.A. and Stasiuk, L.D. (2007): Depositional age of the Douglas Formation, northern Saskatchewan, determined by Re-Os geochronology; in Jefferson, C.W. and Delaney, G. (eds.), EXTECH IV: Geology and Uranium EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, Geol. Surv. Can., Bull. 588, p341-346 / Sask. Geol. Soc., Spec. Publ. No. 18 / Geol. Assoc. Can., Min. Dep. Div., Spec. Publ. 4. 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; Precamb. Resear., v224, p316-340.

Saskatchewan Geological Survey 21 Summary of Investigations 2013, Volume 2 Gunning, M.H. and Card, C.D. (2005): Transects across the Black Bay Shear Zone and Hoidas-Nisikkatch rare- element trend, northwest Saskatchewan; Sask. Industry Resources, Open File 2004-2, CD-ROM. Guthrie, V.A. and Kleeman, J.D. (1986): Changing uranium distributions during weathering of granite; Chem. Geol., v54, p113-126. Hartlaub, R.P. (2004): Archean and Proterozoic Evolution of the Beaverlodge Belt, Churchill Craton, Canada; unpubl. PhD thesis, University of Alberta, Edmonton, 189p. 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; Precamb. Resear., v141, p137-153. 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; Precamb. Resear., v131, p345-372. 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; J. Geol., v115, p181-195. Koeppel, V. (1968): Age and history of the uranium mineralization of the Beaverlodge area, Saskatchewan; Geol. Surv. Can., Pap. 67-31, 111p.

Koster, F. and Baadsgaard, H. (1970): On the geology and geochronology of northwestern Saskatchewan. I. Tazin Lake region; Can. J. Earth Sci., v7, p919-930.

Kyser, K. and Cuney, M. (2008): Geochemical characteristics of uranium and analytical methodologies; in Cuney, M. and Kyser, K. (eds.), Recent and Not-so-recent Developments in Uranium Deposits and Implications for Exploration, Min. Assoc. Can., Short Course Series, Vol.39, 257p.

Liang, R., Chi, G., and Ashton, K. (2013): Characterization of fluids associated with uranium mineralization in the Beaverlodge area, northern Saskatchewan: preliminary field, petrographic, fluid inclusion, and C-O isotope studies; in Summary of Investigations 2013, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2013-4.2, Paper A-2, 25p.

Ludwig, K.R. (2012): User’s Manual for Isoplot 3.75: A Geochronological Toolkit for Microsoft Excel; Berkeley Geochronological Centre, Spec. Publ. No. 5, 75p.

Macdonald, R. and Slimmon, W.L. (1985): Bedrock Geology of the Greater Beaverlodge Area, NTS 74N-6 to -11; Sask. Energy Mines, Map 241A, scale 1:100 000.

McDonough, M.R., McNicoll, V.J., Schetselaar, E.M., and Grover, T.W. (2000): Geochronological and kinematic constraints on crustal shortening and escape in a two-sided oblique-slip collisional and magmatic orogen, Paleoproterozoic Taltson magmatic zone, northeastern Alberta; Can. J. Earth Sci., v37, p1549-1573.

McNicoll, V.J., Theriault, J., and McDonough, M.R. (2000): Taltson basement gneissic rocks: U-Pb and Nd isotopic constraints on the basement to the Paleoproterozoic Taltson magmatic zone, northeastern Alberta; Can. J. Earth Sci., v37, p1575-1596. Morelli, R., Hartlaub, R.P., Ashton, K.E., and Ansdell, K.M. (2009): Evidence for enrichment of subcontinental lithospheric mantle from Paleoproterozoic intracratonic magmas: geochemistry and U-Pb geochronology of Martin Group igneous rocks, western Rae Craton, Canada; Precamb. Resear., v175, p1-15. Morton, R.D. and Sassano, G.P. (1972): Structural studies on the uranium deposit of the Fay Mine, Eldorado, northwest Saskatchewan; Can. J. Earth Sci., v9, p803-823. Passchier, C.W. and Trouw, R.A.J. (2005): Microteconics, 2nd Edition; Springer-Verlag, Berlin, 366p. Paton, C., Hellstrom, J.C., Paul, B., Woodhead, J.D., and Hergt, J.M. (2011): Iolite: Freeware for the visualisation and processing of mass spectrometric data; J. Analyt. Atom. Spectrom., v26, p2508-2518. Petrus, J.A. and Kamber, B.S. (2012): VizualAge: a novel approach to laser ablation ICP-MS U-Pb geochronology data reduction; Geostandards and Geoanalytical Research, v36, p247-270.

Saskatchewan Geological Survey 22 Summary of Investigations 2013, Volume 2 Rainbird, R.H., Stern, R.A., Rayner, N., and Jefferson, C.W. (2007): Age, provenance, and regional correlation of the Athabasca Group, Saskatchewan and Alberta, constrained by igneous and detrital zircon geochronology; in Jefferson, C.W. and Delaney, G. (eds.), EXTECH IV: Geology and Uranium EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, Geol. Surv. Can., Bull. 588, p193-209 / Sask. Geol. Soc., Spec. Publ. No. 18 / Geol. Assoc. Can., Min. Dep. Div., Spec. Publ. 4. Schmitt, A.K. and Zack, T. (2012): High-sensitivity U-Pb rutile dating by secondary ion mass spectrometry (SIMS) with an O-2(+) primary beam; Chem. Geol., v332, p65-73. Smith, E.E.N. (1986): Geology of the Beaverlodge operation Eldorado Nuclear Limited; in Evans, E.L. (ed.), Uranium Deposits of Canada, CIM Spec. Vol. 33, p95-98. Stern, R.A. (1997): The GSC Sensitive High Resolution Ion Microprobe (SHRIMP): analytical techniques of zircon U-Th-Pb age determinations and performance evaluation; in Radiogenic Age and Isotope Studies: Report 10, Geol. Surv. Can., Current Research 1997-f, p1-31. Tracey, G.M., Lentz, D.R., Olson, R.A., and Ashton, K.E. (2009): Geology and associated vein- or shear zone– hosted uranium mineralization of the 46 Zone and Hab Mine areas, Beaverlodge Uranium district, northern Saskatchewan; in Summary of Investigations 2009, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of Energy and Resources, Misc. Rep. 2009-4.2, Paper A-4, 18p. Tremblay, L.P. (1972): Geology of the Beaverlodge Mining Area, Saskatchewan; Geol. Surv. Can., Mem. 367, 265p.

Tremblay, L.P., Loveridge, W.D., and Sullivan, R.W. (1981): U-Pb ages of zircons from the Foot Bay Gneiss and the Donaldson Lake Gneiss, Beaverlodge area, northern Saskatchewan; in Geol. Surv. Can., Current Research, Part C, Pap. 81-1C, p123-126.

Van Schmus, W.R., Persons, S.S., Macdonald, R., and Sibbald, T.I.I. (1986): Preliminary results from U-Pb zircon geochronology of the Uranium City region, northwest Saskatchewan; in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86-4, p108-111.

Wilde, A. (2013): Towards a model for albitite-type uranium; Minerals, v3, p36-48.

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