3D Geological and Fluid Flow Modeling of the Midwest Trend in the Northeastern Athabasca Basin: Implications for Uranium Mineralization and Exploration

@inproceedings{MCKEE_RM2021,
 abstract = { Reactivated basement faults are the main control on most unconformity-related uranium deposits in the Athabasca Basin. However, not all reactivated faults contain uranium mineralization, and this study aims to further the understanding of why mineralization exists in certain areas but not in others along the same trend with seemingly the same system and structural/lithological framework. The research is focused on the Midwest Trend, which contains typical unconformity-related uranium deposits along a NE-trending reverse-offset structure, and has been described as a uranium deposit occurring as ‘beads on a string, separated by intervening barren areas' within a deformation zone. By examining the reverse, fault-related uranium deposits along the Midwest trend (Midwest Main and Midwest A) and the barren segments between this work will aid in identifying the factors that control the placement of mineralization, which is critical in uranium exploration, particularly for determining where mineralization may be located within a given fault system. This study specifically consists of two parts: 1) construction of a 3D geological model illustrating the spatial distribution of structures, lithologies, alteration, and element concentrations; and 2) numerical modeling of fluid flow driven by deformation and thermal convection, based on a simplified version of the 3D geological model established in the first step. The 3D geological model has identified a) Spatial association of mineralization with the NNE-trending, steeply dipping Midwest structural fault trend which is bound by the graphitic pelitic gneiss lithologies on both sides throughout the trend; b) The basement faults can be traced to over 100 meters into the overlying Athabasca strata and have reverse offset on the unconformity surface; c) The unconformity hosted mineralization consists of a near-massive, high grade core surrounded by lower-grade, dispersed mineralization in the sandstone and basement, surrounded by an alteration halo; d) Crosscutting, E-W trending faults on the Midwest A deposit limit the extents of the high grade mineralization to the east and west, whereas on the Midwest Main deposit, the high grade and basement extension of the mineralization are localized at the intersection of the crosscutting structures with the main shear zone. Two-dimensional (2-D) numerical modeling of fluid convection induced by thermal gradient and deformation driven fluid flow was carried out using simplified geometries with varying fault geometry and physical properties (dip direction, permeabilities, and different extents of extension of basement faults into the basement), basement lithological variation and degrees of deformation. The results indicate that fluid convection driven flow is dominant in the sandstone, causing significant fluid flow in the Athabasca Basin. The presence of a basement fault, although not essential for the formation of convection in the sandstone, locally enhances fluid flow and causes the widening and expansion of the convection cells immediately adjacent to the fault within the sandstone, and the further the sandstone extends into the fault the more enhanced and focused the fluid flow becomes local to the fault, causing a stronger upwelling of fluids into the sandstone, indicating that extended basement faults are therefore able to pump or discharge more fluids Into the sandstone. Variations in the basement lithological complex show very little effect on the fluid flow patterns or fluid velocities. The deformation models indicate that fluid flow patterns are sensitive to the degree of bulk shortening. Fluid flows upwards along the fault towards the sandstone at early stages, or low bulk shortening; as bulk shortening continues to be increased, the fluid flow pattern switches and flow begins to be dominantly ingress, or downward flowing along the fault into the basement. Before that complete transition into downward flow, a transition can be seen at a certain intermediate bulk shortening stage in which flow is egress (upwards flowing) in the lower part of the fault and ingress (downward flowing) in the upper part of the fault. Although the exact compressional degree of the Midwest trend is not known, this has implications for exploration along the trend in that this flow behavior indicates that at geologically reasonable strain rates, deep mineralization is possible, which have yet to be thoroughly explored for. Furthermore, for a given degree of overall deformation, the depth of the ingress-egress flow interface may be different along the trend, implying that the depth of mineralization may be different along strike of the same structure. Further 3D modeling of fluid flow is required in the next step of the study in order to better understanding the factors controlling localization of mineralization. },
 author = { McKee, Kelsey AND Chi, Guoxiang AND Chemillac, Remy AND Robbins, John AND Ledru, Patrick AND Li, Zenghua AND Eldursi, Khalifa },
 booktitle = { 2021 RING Meeting },
 publisher = { ASGA },
 title = { 3D Geological and Fluid Flow Modeling of the Midwest Trend in the Northeastern Athabasca Basin: Implications for Uranium Mineralization and Exploration },
 year = { 2021 }
}