Geochemical and Microbial Assessment of the Unconformity-Related Uranium Prospectivity of the Hawk Rapids Area, Southeastern Athabasca Basin, Canada

Abstract

Hawk Rapids is a uranium exploration project located in the southeastern part of the Athabasca Basin, in Saskatchewan, Canada. Geochemical and mineralogical assessments of drill core from Hawk Rapids were used to evaluate the possibility of an unconformity-related uranium deposit occurring within the area. The mineral evolution of this area spans the pre-Athabasca Basin period through diagenesis to post hydrothermal alteration events. Pre-Athabasca alteration is characterized by muscovite and clinochlore while early to late diagenesis is represented by early hematite, quartz overgrowths, dickite and illite. These events were followed by dravite, both in the basement and sandstone units, kaolinite, pyrite, minor coffinite, uraninite, and siderite, which mark the hydrothermal evolution of the area. Post-hydrothermal activity is marked by the late influx of meteoric water, which resulted in formation of late kaolinite. The alteration fluids at Hawk Rapids have three distinct isotopic compositions associated with these stages of evolution. The fluid in equilibrium with pre-Athabasca alteration minerals has an isotopic composition similar to that of modified seawater or low latitude meteoric waters. Basinal brines with a meteoric component characterize the fluid in equilibrium with illite, which represents the diagenetic mineral assemblage. The precipitation of dravite in the hydrothermal stage records a mixture of both basement modified and basinal brines. Radiogenic Pb leached from the drill core samples at Hawk Rapids was derived from both internal and external sources. The breakdown of uranium-rich heavy minerals such as apatite, zircon and monazite make up the internal sources while other uranium-rich sources such as possible proximal uranium deposits constitute external sources. Microbial methane production coupled with methane consumption (microbial methane oxidation) are the major microbial activities associated with unconformity-related uranium at Hawk Rapids. The activities of these microbes are most pronounced near the unconformity where there is secondary dispersion of uranium and associated pathfinder elements that serve as nutrients. This work shows that the integration of both geochemical and mineralogical data is an effective tool in evaluating the prospectivity of an area for possible unconformity-related uranium deposits.