Meteorite Impact Related Uranium Occurrences in the Otish Basin, Quebec, Canada.

English Abstract:

The Proterozoic Otish Basin is well known for its uranium potential. Although the unconformity model has been used for prospection since its beginning, the main bodies discovered within the basin are obviously derived from strong hydrothermally driven enriched fluids. The Lavoie uranium ore body defined in 1985 and its neighbouring Epsilon showings clearly show a structural pattern relevant to a tangential tectonic transport towards the northwest. The surrounding rock units have suffered strong and pervasive alterations. The alteration pathways were mainly controlled by the capping of the sedimentary rock pile by a thick gabbroic unit. The presence of a carbonate unit reaching locally 50 meters in thickness favoured the stacking northwesterly. For many decades the tectonic modelling was founded around the hudsonian event as well as the Grenville Front because of its proximity to the basin. The exploration in this area now faces new facts. The recent discovery of planar deformation features (PDFs) must be taken into account for enlightening the mechanics involved in ore genesis in the Otish basin. PDFs have been found within the sandstone units in the eastern half of the basin up to 1000 meters in depth. The distribution of those PDFs in sandstone seems to be limited to the west by a major N010°-N020° faulting zone, i.e. the Indicator discontinuity. PDFs have also been observed in a large plurimetric enclave observed at the base of the overlying gabbroic unit. This later unit is interpreted here as a melt sheet related to a major meteorite impact event which is tentatively dated at 2,1 Ga, an interpretation also supported by the absence of feeding dykes noted throughout the basin as well as by its spatial relationship with the PDFs distribution in the underlying sandstone units.