2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 4
Presentation Time: 9:00 AM-6:00 PM


MCKECHNIE, Christine Louise, Watts, Griffis and McOuat Limited, 136 - 410 Stensrud Road, Saskatoon, SK S7W 0B7, Canada, ANSDELL, Kevin M., Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2, Canada and ANNESLEY, Irvine R., Independent Consultant, Saskatoon, SK S7J1J1, Canada, christine.mckechnie@usask.ca

The richest uranium deposits in the world are unconformity-type deposits of the Proterozoic Athabasca Basin, Saskatchewan, Canada. However, about 55 km east of the Key Lake uranium mine, uraniferous granitic pegmatites and leucogranites intrude into a shear zone at the contact between deformed Paleoproterozoic Wollaston Group metasedimentary rocks and Archean orthogneisses. The uranium mineralization is directly related to these igneous rocks, and the aim of this project is to determine whether these represent a distinct target for uranium exploration in Saskatchewan or if the mineralization is related somehow to unconformity-type uranium deposits.

The magmatic-hosted deposits (Fraser Lakes Zones A and B) are in NE-plunging regional fold noses adjacent to a 5 km long folded EM conductor (i.e. graphitic pelitic gneisses). The more prospective Zone B sits within an antiformal fold nose, from which several drill holes have intersected multiple intervals of uranium and/or thorium mineralization (up to 0.183% U3O8 over 1.0 m in drill core). The zones are cross-cut by a number of E-W-, NNE-, and NNW-trending structures. Associated with the uranium are thorium and LREE mineralization with elevated amounts of pathfinder elements including Co, Cu, Mo, Ni, Pb, V, and Zn.

Drill core observations revealed the existence of multiple generations of granitic pegmatites, including mineralized (generally subcordant to gneissosity, and believed to be syndeformational) and non-mineralized (discordant to gneissosity, and probably post-tectonic) varieties, with some of the pegmatites showing compositional zoning due to igneous AFC processes.

While this is a magmatic-hosted U-Th deposit, the presence of clay alteration and structural features in Zone B drill core similar to that of basement-hosted unconformity uranium deposits (e.g. Millennium, P-Patch, Eagle Point, and McArthur River Zone 2) raises the possibility that altered remobilized parts of the Fraser Lakes zones formed at the same time as unconformity-type mineralization in the Athabasca Basin. This project will integrate field observations and geological, geochemical, and geophysical datasets so to develop a metallogenetic model for the Fraser Lakes deposit, and clarify its relationship with the rich uranium deposits in the Athabasca Basin (e.g. U protore).