A seminar by Pierre Martz at ENSG, Nancy, room G201

On Friday 23d of June, 1:00 pm.

Multiple ages from uranium oxides spanning over more than 1 Ga have been proposed as markers of several U-mineralizing events in the Athabasca basin (Saskatchewan, Canada) but the understanding of the nature and significance of the potential distinct U-mineralizing events is difficult. To unravel this potential complex sequence of fluid-flow events and to assess the importance of each events in the formation and evolution of the deposit as it is currently depicted, an integrated and systematic study has been carried out in 2D by coupling mineralogy, in situ U-Pb dating, and trace element geochemistry of UO2 from samples coming from two crossections crosscutting the Cigar Lake orebody, a world-class sandstone-hosted archetype of unconformity-related U deposit. This study shows that a first and major event of U deposition occurred at ~1430 followed by one poorly constrained non mineralizing major brecciation event occurring between 1000 and 700 Ma and three much younger events of U remobilization and deposition at ~340, ~225, and ~205 Ma. Each mineralization stage is characterized by a specific fingerprint including distinct mineralogical associations and geochemical signatures in trace elements. Using geochemical data from drillholes, a 3D scale modelization has been built showing the spatial repartition of the distinct U oxide types. It reveals that the U stock of the deposit was deposited during the first mineralizing stage, currently preserved in the core of the deposit, right at the unconformity and along the E-W shear structurally controlling the deposit. However younger fluid flow events have greatly remobilized the primary U stock so that the present mineable volume is now in fact formed by young mineralization (<350 Ma).