Uranium Geoscience in the Athabasca Basin and Western Canada Sedimentary Basin in Northwestern Saskatchewan (NTS 74F and 74K) Sean A. Bosman 1, Jared Noll 2, Derek Johnson 3 and Brody Strocen 3 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: Bosman, S.A., Noll, J., Johnson, D. and Strocen, B. (2017): Uranium geoscience in the Athabasca Basin and Western Canada Sedimentary Basin in northwestern Saskatchewan (NTS 74F and 74K); in Summary of Investigations 2017, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2017-4.2, Paper A-4, 14p. Abstract The Patterson Lake region of northwest Saskatchewan, at the southwest margin of the Athabasca Basin, contains at least three high-grade uranium deposits, the Triple R, Arrow and Spitfire. This area is unique to the Athabasca region within Saskatchewan because of the presence of rocks of the Western Canada Sedimentary Basin, which overlie rocks of both the Taltson/Clearwater domains and the Athabasca supergroup. Phanerozoic stratigraphy in the area includes carbonate-rich rocks of the Lower to Middle Devonian Elk Point Group, sandstones and mudstones of the Lower Cretaceous Mannville Group, moderately lithified diamictites (probably Quaternary?) and unconsolidated Quaternary sediments. The Elk Point Group in this area can be further divided, from oldest to youngest, into the La Loche, Contact Rapids and Winnipegosis/Methy formations (Alberta nomenclature), or the Ashern and Winnipegosis formations (Saskatchewan nomenclature). The Mannville Group is divided, from lower to upper, into the McMurray, Clearwater and Grand Rapids formations (Alberta nomenclature), or the Cantuar and Pense formations (Saskatchewan nomenclature). The Cretaceous rocks are widespread, but the distribution of the Devonian rocks along the Patterson Lake corridor seems to be somewhat restricted to areas overlying uranium deposits, such as the Triple R and Arrow deposits, suggesting that structural controls are affecting deposition and/or preservation well into the Phanerozoic. This spatial correlation may be a useful tool in exploring for other uranium deposits in the area. Elevated uranium concentrations and clay alteration within the Phanerozoic rocks also suggests that there was late mobile uranium in the Patterson Lake area, allowing the potential for lower-grade sandstone-hosted deposits. Work on the Athabasca supergroup focused on mapping outcrops of the Douglas Formation and logging lower stratigraphy in the Shea Creek area. On Carswell Lake an in-place contact between the overlying Carswell Formation and the underlying Douglas Formation was discovered. In the Shea Creek area the logging suggests that the Smart Formation of the Manitou Falls Group is absent from the stratigraphy, with a sandy member of the Read Formation of the Manitou Falls Group directly overlying the Fair Point Group. Keywords: Phanerozoic, Cretaceous, Devonian, diamictite, carbonate, sandstone, Athabasca supergroup, uranium, Western Canada Sedimentary Basin, Patterson Lake, Athabasca Basin, sandstone-hosted uranium, Douglas Formation 1. Introduction This report focuses on the stratigraphy of the sedimentary material (the term ‘material’ is used in this report to include both unconsolidated sediments and rocks) within National Topographic System (NTS) map sheets 74F and 74K at the southwestern margin of the Athabasca Basin (Figure 1). The sedimentary material in this region includes Proterozoic rocks of the Athabasca supergroup, Phanerozoic rocks of the Western Canada Sedimentary Basin and Quaternary sediments. Rocks of the Clearwater and Taltson domains form the crystalline basement material, which is overlain in part by the Athabasca supergroup, the southwest edge of which trends northwest-southeast (Figure 1). 1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 1000-2103 11th Avenue, Regina, SK S4P 3Z8 2 NexGen Energy Ltd., 212-4014 Arthur Rose Avenue, Saskatoon, SK S7P 0C9 3 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 Figure 1 – Generalized geological map showing parts of NTS 74F and 74K. Translucent light-green polygons represent previously inferred extent of Phanerozoic sedimentary material (rocks of the Western Canada Sedimentary Basin) that in part overlie the Athabasca supergroup. Yellow, orange, and brown colours (and variants) represent rocks of the Athabasca supergroup (for details see Bosman and Ramaekers, 2015). White areas represent Quaternary cover and crystalline basement rocks. Red rectangles show the generalized areas containing drillholes that were logged from each company. Yellow rectangles show generalized locations of outcrop referred to in text. Inset shows location of main area of figure and outline of the Athabasca Basin. Red stars show locations of selected uranium deposits. Saskatchewan Geological Survey 2 Summary of Investigations 2017, Volume 2 The northern limit of the Western Canada Sedimentary Basin rests, in part, unconformably on the Athabasca supergroup as well as on the basement rocks south of Patterson Lake. Quaternary sediments cover most of the area and only limited exposures of underlying rocks were seen. The work was therefore primarily achieved through the logging of core from drillholes (ddh) that were drilled by various uranium exploration companies. Sites visited for this study include several core repositories and outcrop locations (Table 1). The aim of the current work is to further develop our understanding of the sedimentary basins associated with Saskatchewan’s world-class, high-grade uranium deposits, such as the Triple R, Arrow and Spitfire deposits in the Patterson Lake area (Figure 1). This summary encompasses results of summer field investigations carried out in 2016 and 2017 and is part of the broader Athabasca Basin Ore Systems project, which is a multi-faceted initiative involving both regional compilation work and new geoscience. The goal of this broader project is to collect and interpret regional multidisciplinary data (e.g., stratigraphy, basement geology, clay mineralogy) from the Athabasca Basin region and make them available as datasets compatible for 3-D display. In addition to mapping the Phanerozoic succession, part of the field time was assigned to reconnaissance mapping of outcrops of the Douglas Formation from near the stratigraphic top of the preserved Athabasca supergroup. Outcrops of this formation are few in number so the goal was to investigate as many as could be found and to collect samples from each site. Table 1 – Locations of drillcore and outcrop examined for this report, and uranium exploration companies responsible for the drilling. Location Core/Outcrop Company Carswell Lake Core and outcrop Amok Ltd. Cluff Lake Core AREVA Resources Canada Inc. (AREVA) Patterson Lake Core Fission Uranium Corp. (Fission) Patterson Lake Core NexGen Energy Ltd. (NexGen) Patterson Lake Core Purepoint Uranium Group Inc. (Purepoint) Vermeersch Lake Core Forum Uranium Corp. (Forum) Douglas River – Hwy 955 Outcrop Big Bear camp at Grygar Lake Core Titan Uranium Inc. (Titan) Big Bear camp at Grygar Lake Core ESO Uranium Corp. (ESO) Big Bear camp at Grygar Lake Core Makena Resources Inc. (Makena) 2. Phanerozoic Units a) Previous Work Norris (1963) first described, in some detail, the Devonian stratigraphic section in northeastern Alberta (several locations) and northwestern Saskatchewan (Clearwater River). The three main rock types he described from the Elk Point Group, in younging stratigraphic order, include 1) sandstones and breccias of the La Loche Formation, 2) argillaceous dolomites of the McClean River Formation (i.e., Contact Rapids Formation of Sherwin (1962)), and 3) dolomites of the Methy Formation (i.e., Winnipegosis Formation). Following this work, Paterson et al. (1978) described the sedimentary geology of the area covered by NTS sheet 74C (Saskatchewan 1:250 000 scale map sheet directly south of 74F), mainly focusing on the Phanerozoic strata. The authors describe the same Devonian stratigraphic section outlined in Norris’ (1963) work (i.e., La Loche, Contact Rapids and Winnipegosis formations) as well as Cretaceous rocks. They use north-central Alberta nomenclature and break the Mannville Group down into the McMurray, Clearwater and Grand Rapids formations (Alberta Geological Survey, 2015). The McMurray, as described by Paterson et al. (1978), contains quartzose sand to granules; the Clearwater mainly comprises mudstone to shale; and the Grand Rapids is dominated by brownish green sandstone. Scott and Slimmon (1986) completed a compilation bedrock geology map of the area covered by NTS sheet 74F; however, the focus was not the Phanerozoic rocks, which were essentially extrapolated from the work of Paterson et al. (1978) to the south, and digital elevation data. Kohlruss (2012) and Kohlruss et al. (2013) did