Numerical simulation of strain localization and its relationship to formation of the Sue unconformity-related uranium deposits, eastern Athabasca Basin, Canada

摘要

Unconformity-related uranium deposits in the Athabasca Basin (Canada) are spatially associated with reactivated basement faults that cut the unconformity surface between Archean to Paleoproterozoic basement and Paleoproterozoic to Mesoproterozoic sedimentary rocks of the Athabasca Group. The Sue deposits (Sue A, B, C, D, and E) are located in the eastern Athabasca Basin along a 2-km-long north-northeast-trending structural corridor and have both sandstone-hosted (Sue A and Sue B; to the north) and basement-hosted (Sue C, Sue D, and Sue E; to the south) orebodies. All the deposits are structurally controlled by north-northeast-trending basement faults that demonstrate different degrees of reverse displacements of the unconformity surface. However, it is not clear why the mineralization is distributed in such a pattern along the corridor. In this study, both 2-dimensional (2D) and 3-dimensional (3D) numerical modeling of deformation were conducted to examine the relationship between the distribution of strain and uranium mineralization. The modeling shows that dilation (positive volumetric strain), thought to correlate with the development of extensional fracture systems and dilational jogs that represent potential mineralization sites, is primarily controlled by the rheological contrasts in basement rocks and the degree of deformation. The presence of faulted graphitic pelitic gneiss associated with the sandstone-hosted Sue A and Sue B deposits favours dilation localized within the sandstone at low degrees of deformation mainly due to the overlying competent hangingwall granitic gneiss. In contrast, the basement-hosted Sue C, Sue D and Sue E deposits are associated with dilation zones localized along the contact between the faulted graphitic pelitic gneiss and competent footwall silicified gneiss at higher degrees of deformation. The modeling results highlight the importance of both graphitic basement structures and strong rheological contrasts between basement rocks in uranium exploration in the Athabasca Basin.