Ages of major uranium mineralization and lead loss in the Key Lake uranium deposit, northern Saskatchewan, Canada

Uranium and lead isotope ratios were measured on nine ore samples and four mineral separates from the Deilmann orebody of the Key Lake uranium-nickel deposit. The time of primary mineralization is the oldest reported for Proterozoic unconformityrelated uranium deposits in the Athabasca basin. Data obtained in this study show that lead loss (or uranium gain) has occurred in highgrade rocks and that lead gain (or uranium loss) has occurred in low-grade rocks. Lead loss rather than uranium gain in high-grade ore is suggested by the petrologic work of Cumming and Rimsaite and the presence of excess radiogenic lead in the overlying sandstone documented by Curtis and Gancarz. Some of the results obtained in this study provide evidence of preferential movement of 238U intermediate daughters out of uranium minerals and into the matrix