The uranium potential of the north-eastern part of the Paleoproterozoic Thelon Basin, Canada

The Paleoproterozoic Thelon Basin is located in the Churchill Province of the Canadian Shield, Nunavut, Canada, and is host to economic unconformity-type uranium mineralization (the Kiggavik deposit) and has the potential to host other deposits. The Thelon Formation sandstones and conglomerates and the Pitz Formation sandstones from the Garry Lake area contain phosphates, illite, minor chlorite and quartz as cements. The matrix phosphates are fluorapatite with U concentrations up to 103.5 ppm in the Thelon Formation rocks and up to 991 ppm in the Pitz Formation rocks. Lead isotope ratios and associated trace element concentrations extracted from sandstones and conglomerates by partial leaching with 2% nitric acid show that rocks with phosphates in the matrix have radiogenic Pb-206/Pb-24 ratios as well as high U, Pb, Th, Ca and P concentrations. Some radiogenic Pb is interpreted to be produced in situ by breakdown of fluorapatites. However, a (206)pb/(204)pb vs. U-238/Pb-206 diagram indicates that in some samples there is an excess of Pb-206 that could not have been produced by the amount of U in the sample and that must have been derived from an extraneous U-rich source and then introduced into the rock by later fluids. The Pb- Pb model for leachates gives an age of ca. 1593 Ma, which is younger than the age of the detrital and early diagenetic phosphates and is close to the age of the phosphate cements from the Garry lake area of 1558 Ma. This suggests that there was later remobilization and migration of uranium-bearing fluids when the aquifers were open to diagenetic fluids, which could have resulted in formation of a deposit in the north-eastern part of the Thelon Basin. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.