Numerical modeling of hydrothermal fluid flow in the Paleoproterozoic Thelon Basin, Nunavut, Canada

Abstract

This paper presents the first computational modeling of fluid flow and heat transport associated with the formation of unconformity-type uranium deposits in the Thelon Basin, Nunavut, Canada. A paleo-hydrostratigraphic model is developed for the time of uranium mineralization through integration of existing geological, geophysical and geochemical data, based on which a series of scenarios are designed to examine the roles of various factors in controlling ore-forming fluid flow. Our numerical experiments suggest that free convection may develop throughout the Thelon Formation at geothermal gradients of 25 to 35 °C/km, and that this may be an attractive mechanism for uranium transport. Changes to the assumed geothermal gradient, the presence of basal unconformities, or of diagenetic aquitards do not modify the fluid flow patterns at the basin scale. The highest fluid fluxes are generated at the unconformity, which supports the fact that uranium is concentrated within or around the unconformity. A change of water table slope leads to complicated streamline configurations, depending on the scale change. However, it is not the dominant driving force accounting for the formation of unconformity-type uranium deposits. The importance of faults depends on their scale, spatial distribution density, and relationship to the aquifer. Basement-derived fluids are not observed to flow through the basement faults as was expected, probably because active faulting (deformation) during flow was not included in the models.