Geochemistry of the Athabasca Basin, Saskatchewan, Canada, and the unconformity-related uranium deposits hosted by it

Abstract

ABSTRACT A large data set comprising near-total digestion analyses of whole rock samples from the Athabasca Basin, Saskatchewan, Canada (based principally on the Geological Survey of Canada open file 7495), containing more than 20,000 analyses, was used to define the average chemical composition of Athabasca Group sandstones and of unconformity-related uranium deposits hosted by the basin. The chemical composition of unaltered and un-mineralized Athabasca Group sandstones is dominated by Al (median Al2O3 of 1.14 wt.%), Fe (median Fe2O3 of 0.24 wt.%), and K (median K2O of 0.11 wt.%; Si was not measured), corresponding mostly to the presence of kaolin, illite, and hematite, in addition to the most-abundant quartz. The median concentration of U in the barren sandstones is 1 ppm, with 5 ppm Th, 3 ppm Pb, and 56 ppm ΣREE. Other trace elements present in significant amounts are Zr (median of 100 ppm), Sr (median of 69 ppm), and B (median of 43 ppm), corresponding to the presence of zircon, illite, and dravite. The elements most enriched in a typical Athabasca Basin unconformity-related uranium deposit relative to the barren sandstone are U (median enrichment of ×710), Bi (×175), V (×77), and Mg (×45), followed by five elements with enrichment factors between 20 and 30 (Co, Mo, K, As, and Ni). These correspond to the presence in the ore bodies of alteration minerals (dravite, kaolinite, illite, chlorite, aluminum-phosphate-sulfate minerals, and a suite of sulfide minerals) and are similar to what has been observed before. These elements are similar to the typical pathfinder elements described above known deposits, but their usefulness has to be assessed based on their relative mobility in the predominantly oxidizing Athabasca Basin sandstones.