The Effects of Basement Faults on Fluid Convection in the Athabasca Basin and Significance for Localization of Uranium Mineralization

English Abstract:

A common feature of the unconformity-type uranium deposits in the Athabasca Basin is their close spatial association with reactivated basement faults intersecting the unconformity surface. It has been proposed that the fluid flow related to uranium mineralization in this basin was driven by thermal convection; however, little is known regarding how basement faults influence fluid convection and how this may affect the localization of mineralization. These questions are addressed through simulations of thermal convection with various configurations of basement faults using the FLAC3D software. Our numerical modelling indicates that the location, spacing and networks of basement faults influence the size and location of thermally-driven fluid convection. In a model with a single, isolated fault, the fault coincides with an upwelling plume. When the fault is moved from the centre laterally, the upwelling plume shifts accordingly. In the case of two faults, the faults may coincide with upwelling flow or alternatively be centrally located below convection cells, depending on fault spacing. In the latter case, the size of the convection cells tends to get larger and fluid may flow into and out of individual fault zones. In contrast, for connected faults, either in a pop-up or imbricated pattern, fluid may flow into one fault zone and out of the other, correlating closely with real-world attributes of unconformity-type deposits (i.e., ‘ingress’ versus ‘egress’ deposits). Collectively, this exploration of the relationship between thermal convection and faults (position, spacing and network) will shed light on why some faults are more favourable for fluid flow than others, which will in turn help to evaluate whether a given structure has the potential to host mineralization.