Geochemistry of uraniferous bitumen in the Athabasca Basin, Canada

Solid hydrocarbons are present in most unconformity-related uranium deposits in the Athabasca Basin, Saskatchewan. Uraniferous bitumen is present in uranium deposits elsewhere, e.g. the 'natural fission reactors' at Oklo, Gabon, and in uranium occurrences in Great Britain, Scandinavia, and South Africa. Despite the sub-ubiquitous presence of uranium-rich bitumen in the Athabasca basin, it has been systematically understudied, with a few notable exceptions that, however, conclude that bitumen had no role in uranium mineralization, contrary to the opinion that uranium is closely associated with bitumen in other deposits in the world. The present work aims to answer the questions of the nature of the association of uranium and bitumen, the form of uranium, relative and absolute age, and genetic relationship, using geochemical analyses of uraniferous bitumen samples from the Southwest Athabasca Basin in Canada. The samples studied come from the Southwest Athabasca Basin in northern Saskatchewan, Canada. The basement here is composed of Archean and Aphebian rocks of the Wollaston Domain with mainly continental crust and unfolded continental margin supracrustal rocks. Uraniferous bitumen is present as disseminated or small vein-filling globular grains (<1 mm). The typical globular morphology of the bitumen in Southwest Athabasca, as seen in reflected light microscopy, is quite similar to that of uraninite-related bitumen from Oklo, Gabon, and of uraniferous bitumen from Ty Gwin, Wales. The samples studied come from the Southwest Athabasca Basin in northern Saskatchewan, Canada. The basement here is composed of Archean and Aphebian rocks of the Wollaston Domain with mainly continental crust and unfolded continental margin supracrustal rocks. Uraniferous bitumen is present as disseminated or small vein-filling globular grains (<1 mm). The typical globular morphology of the bitumen in Southwest Athabasca, as seen in reflected light microscopy, is quite similar to that of uraninite-related bitumen from Oklo, Gabon, and of uraniferous bitumen from Ty Gwin, Wales. Polished thin sections were examined under reflected light optical microscopy and scanning electron microscopy (SEM), and quantitative analyses were performed on an electron microprobe for Si, Ca, Fe, Mg, Ti, S, P, Y Pb, Th, and U. Carbon, nitrogen, and sulphur isotopes were analysed by combustion extraction, chromatographic separation, and IRMS. U/Pb LA-HR-ICP-MS dating of uraninite samples were performed on uraniferous bitumen. Paragenesis, bitumen morphology, chemical composition of uraniferous bitumen as well as its carbon and nitrogen isotopic composition and the age of formation are discussed