Multiple mineralizing events at the Cigar Lake deposit: an integrated-study of uranium oxide dating and geochemistry

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). Such a spread of ages together with a global lack of detailed characterization (paragenesis, chemistry) of the dated material make the understanding of the nature of the potential distinct U-mineralizing events difficult. To unravel this complex sequence of fluid-flow events, an integrated and systematic study coupling mineralogy, in situ U-Pb dating, and trace element geochemistry of UO2 has been carried out at the Cigar Lake deposit, a sandstone-hosted endmember of unconformity-related U deposit. This study shows that five main fluid events contributed to the formation and evolution of the deposit, at similar to 1430, similar to 340, similar to 225, and similar to 205 Ma and one poorly constrained major brecciation event occurring between 1000 and 700 Ma. Each mineralization stage is characterized by a specific fingerprint including distinct mineralogical associations and geochemical signatures in trace elements. The spatial repartition of the distinct U oxide types reveals that the U stock of the deposit was deposited during the first mineralizing stage but has been latter greatly remobilized so that the present mineable stock is in fact young mineralization (<350 Ma).