Structural control of uranium mineralization at the Dominique-Peter deposit, Saskatchewan, Canada

The Dominique-Peter deposit is part of a cluster of unconformity-related uranium deposits that have been exploited since 1980 at the Cluff Lake mine in northern Saskatchewan. It is located on the south side of the 18-km basement core of the 39-km diameter circular Carswell structure. The metamorphic basement cylinder has risen at least 1,200 m through the Mesoproterozoic sandstones. Underground structural study at Dominique-Peter resulted in a revision of the understanding of the succession of tectonic events controlling mineralization emplacement and deformation. The main premineralization ductile deformation, D-1 and D-2 produced a flat-lying gneissosity and subsequent development of foliation-conformable mylonites, and exhibits ! some contrasts with the eastern Athabasca Trans-Hudsonian tectonics. East-west to northwest-southeast general extension (ca. 1.3 Ga) resulted in the formation of a set of 015 degrees to 050 degrees listric normal faults. The latter controlled the opening of quartz then uraninite veins and induced a general tilting of fault blocks to the east. Mechanisms of mineralization emplacement are described in detail. Foliation reactivation in mylonite and aluminous gneiss is favorable to vein opening. The postmineralization formation of the Carswell circular structure (ca. 480 Ma) displays a centrifugal deformation with asymmetry axis located in the center of the basement dome. A suite of pseudotachylyte veins, breccias, and shatter cones accompanies this deformation. Overall, geometry of the Carswell dome and surrounding rings as well as the nature of associated breccias presents strong similarities with those of other impact-related structures.