Structural Controls on Fluid Flow During Compressional Reactivation of Basement Faults: Insights from Numerical Modeling for the Formation of Unconformity-Related Uranium Deposits in the Athabasca Basin, Canada

Abstract

The unconformity-related uranium deposits in the Athabasca basin, Canada, are generally associated with reactivated basement faults crosscutting the basin-basement unconformity. Two-dimensional (2-D) numerical modeling of coupled compression and fluid flow in a reverse fault system was carried out with varying dip angles, preexisting offsets, and degrees of deformation. The results indicate that the fluid flow pattern associated with structural reactivation is sensitive to the degree of bulk shortening. At a low bulk shortening stage, fluid is driven up along the fault zone into the sandstone in the basin, whereas at a relatively high bulk shortening stage, fluid tends to flow down into the fault zone and the basement. This is interpreted to indicate that the fluid pressure within the fault zone increases at the early stage of deformation due to pore volume decreases in relation to shortening, whereas the fluid pressure within the fault zone decreases at later stages of deformation due to dilation in relation to fracturing and reverse displacement. Variation of the dip angles and preexisting offsets of the faults shows little effect on the strain distribution and fluid flow patterns. The simulation results demonstrate that both unconformity contact and basement-hosted orebodies may be generated at different stages of deformation within the same fault system under a unified compressional stress regime.