Development and fluid history of the Paleoproterozoic Thelon Basin, Nunavut, Canada

The Paleoproterozoic Thelon Basin of northern Canada along with the Athabasca, Elu and Amudsen Basins are large intracratonic basins deposited on deeply weathered Archean or Paleoproterozoic basement of the Canadian Shield. These basins host, or have the potential to host, unconformity-type uranium deposits. The genesis of high-grade U deposits depends largely on the development of diagenetic aquifers and the fluid evolution of the basin within specific lithofacies. The purpose of this thesis is to look at the early depositional and diagenetic history of the Thelon Basin to understand provenance, paleohydrology and diagenesis in the stratigraphic context of the basin and how these may affect the development of uranium deposits.; The geochemical evolution of the Thelon Basin is examined through methods conventionally applied by the petroleum industry. A previously developed sequence stratigraphic succession in the Thelon Basin has been confirmed through zircon geochronology coupled with delta18O values of detrital quartz, providing insight into early development of the basin. Geochemical analysis of detrital material indicates the lower sequence was dominantly derived from surrounding Archean metasedimentary basement, the middle sequence from a more distal Paleoarchean source and the upper sequence from surrounding basement that includes granitic plutons. This suggests a complex evolution of drainage systems from proximal to distal to proximal that may have spanned up to 33 Ma.; Isotope geochemistry and microthermometry provide information on fluid events within the basin. Fluid flow within the Thelon Formation was largely controlled by early quartz overgrowths (Q1) in well-sorted facies that developed within aquifers in the near-surface environment. These cements have oxygen isotope ratios consistent with early, low-temperature formation from surface water and effectively compartmentalized the basin. Later, during deeper burial, quartz cements formed at higher temperatures from more evolved basinal brines in diagenetic aquifers within poorly sorted facies. The fluids evolved further through water-rock interaction to result in diagenetic illite at ca. 1600 Ma. Peak diagenesis is similar to that of the Athabasca Basin, which contains high-grade uranium deposits formed by cross-formational fluids responsible for clay alteration halos and vein-filling quartz and dravite. Clay alteration associated with U-mineralization at Kiggavik, just south of the presently preserved margin of the Thelon Basin, is consistent with the unconformity-type U model wherein diagenetic aquifers intersected reduced fluids or lithologies in the basement.