Numerical modeling of fluid pressure regime in the Athabasca basin and implications for fluid flow models related to the unconformity-type uranium mineralization

Various fluid-flow models have been suggested for the formation of unconformity-type uranium deposits in the Athabasca basin, including fluid flow driven by fluid overpressure, topographic relief, fluid density variation due to temperature or salinity change, and tectonic deformation. In order to evaluate the fluid-flow mechanisms responsible for mineralization, it is necessary to know the distribution and evolution of fluid pressure during the history of the basin. A numerical modeling study of the development of fluid overpressure due to disequilibrium sediment compaction was carried out, and the results suggest that no significant fluid overpressure was developed in the basin throughout the sedimentation history. Fluid flow related to sediment compaction was very slow and the temperature profile was undisturbed, implying that if compaction-driven flow was responsible for mineralization, the sites of mineralization would not show a thermal anomaly. The development of near-hydrostatic pressure regime in the Athabasca basin may have facilitated circulation of oxidizing fluids from the shallow part of the basin into the basal part, favoring the formation of unconformity-type uranium deposits, as opposed to other sedimentary basins where elevated fluid overpressures within the lower part of the basin may have prevented downward infiltration of oxidizing fluids, limiting uranium mineralization to the upper part of the basin.

► Athabasca basin had low fluid overpressure throughout its history.
► Downward flow is possible assuming the presence of thick eroded strata.
► Thermal profile was not disturbed by compaction-driven flow.
► Low overpressure favors U mineralization near unconformity.