3D modeling of uranium-bearing solution-collapse breccias in Proterozoic sandstones (Athabasca Basin, Canada)-Metallogenic interpretations

Unconformity-related uranium deposits are the highest grade, large tonnage uranium resources in the world. In the Athabasca Basin (northern Saskatchewan, Canada), which is the premier host for unconformity-type deposits, the ore deposits are frequently hosted and surrounded by breccias in sandstone. The significance of these breccias and their relation to mineralization are of major importance for the genesis of these high-grade deposits. Therefore, a modeling study, integrating results from structural geology and petrology, was performed with the gOcad 3D modeling software, in order to decipher geometrical and geological relationships between breccias, faults and mineralization zones. Mineralized bodies and the sudoite-dravite breccia bodies display strong spatial correlations. They appear to be controlled by reverse shear zones cross-cutting the unconformity and containing graphite in the basement. Geochemical computations evidenced that volumetric water-rock ratios up to 10,000 could be obtained in these breccia bodies for volume losses of up to 90%. Assuming reasonable values for quartz saturation, hydraulic conductivity and connected porosity, the minimal fluid volume and the time duration necessary to generate the sudoite-dravite breccia bodies were estimated at ca. 2 km(3) and ca. 1 Myr, respectively. The comparison of these results with literature data suggests that the formation of sudoite-dravite breccia and mineralization could have been coeval. It may be proposed that within the space created by the quartz dissolution in the breccia body, a mixing between basement and basinal fluids could have induced U deposition and allowed the development of high-grade mineralization. The first-order uranium solubility that this coeval formation would imply is consistent with literature data, which suggests that this conceptual model is reasonable. (C) 2007 Elsevier Ltd. All rights reserved.