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. Major uranium mineralization occurred at Key Lake 1,350 + or - 4 m.y. ago. Uranium and lead were fractionated at 300 + or - 6 m.y. These ages are defined by a straight line on the concordia diagram determined by four of nine whole-rock ore analyses. The time of primary mineralization is the oldest reported for Proterozoic unconformity-related uranium deposits in the Athabasca Basin. Data obtained in this study show that lead loss (or uranium gain) has occurred in high-grade rocks and that lead gain (or uranium loss) has occurred in low-grade rocks.--Modified journal abstract.