Till composition across the Keewatin Ice Divide in the Tehery-Wager GEM-2 Rae project area, Nunavut

Abstract

This report releases the field database and analytical results from a targeted surficial geology and till sampling survey completed in 2015 and 2016 south of Wager Bay in mainland Nunavut as part of Natural Resources Canada's Tehery-Wager GEM-2 Rae project. The report also provides a summary of the regional bedrock and surficial geology, an improved glacial history framework, and a detailed description of the field and analytical methods. A preliminary interpretation regarding till provenance and mineral potential integrates all previous government till surveys in the region. The uplands south of Wager Bay coincide with a relatively stable position of the Keewatin Ice Divide (KID) and are dominated by a mixture of bouldery till blankets and veneers, weathered bedrock and diamictons, and boulder fields. The deeply weathered terrain under parts of the KID indicates the preservation of a pre-LGM landscape under cold-based ice conditions. South of the divide, the predominant regional trend of streamlined bedrock and till landforms varies from SSE to SE, parallel to main striation directions. A complex system of subglacial meltwater corridors and proglacial meltwater channels overprints the streamlined till that extends away from the KID. A later S to SSE deglacial event locally cross-cuts the streamlined terrain and corridors suggesting a northward ice margin retreat. The post-glacial marine limit increases from ~118 m asl southwest of Wager Bay near Paliak Islands to 140 m along Roes Welcome Sound and stays relatively constant at 140-150 m westward towards Tehery Lake. A total of 73 regional till samples collected in 2015 and 2016 to evaluate mineral potential and characterize regional transport across the KID were analyzed for matrix texture, colour, carbon content, indicator minerals, pebble count, as well as geochemistry of the <0.063 mm fraction. All field observations (202 stations) and till composition datasets were compiled in separate spreadsheet files. Surface till consists of a silty sandy, granitic-rich diamicton and is commonly bouldery on the surface. Till has a significant local component and its composition reflects the underlying bedrock glacially transported away from the KID. The eastern sector is dominated by more immature tills, higher in sand content but with relatively high clay contents derived from highly erodible, poorly resistant weathered lithologies preserved under the KID. The distribution of heavy minerals picked as potential kimberlite indicator minerals (KIMs) in surface tills suggests glacial dispersal from diverse ultramafic and mafic bedrock sources: the Nanuq kimberlite field, mafic to ultramafic bodies within the Lorillard domain, undeformed ultrapotassic mafic intrusions, and possibly unknown kimberlite. In particular, the distribution of Ca-forsterite, eclogitic garnet and Cr-pyrope forms a 60-km long SSE-trending regional dispersal train from the Nanuq kimberlite bodies, parallel to the dominant ice flow direction. On the other hand, the presence of a significant number of Cr-pyrope, eclogitic garnet, Ca-forsterite, low Cr-diopside and bronzite grains in till south of Meen Lake suggests a clear potential for a local kimberlitic source up-ice (northwest) of the sample. The potential for Ni-Cu, platinum group elements (PGEs) and chromite mineralization in the region mainly lies in Archean komatiite/pyroxenite/peridotite ultramafic bodies of the Lorillard domain as shown by a large SE trending fan-shaped dispersal train of forsterite and a shorter SE dispersal train of chromite grains. Elevated to moderate concentrations of base and precious metals, metamorphosed or magmatic massive sulphide indicator minerals (MMSIMs) and gold grains in gossan-rich till and down-ice of supracrustal rocks within the northern part of the Lorillard domain indicates potential for base- and precious metal mineralization in this area. Smaller gossanous horizons were mapped in several other supracrustal panels (e.g. Pennington belt) north of the Chesterfield shear zone and till composition in this area indicates potential for metamorphosed volcanogenic massive sulphide (VMS) deposits.