A combined ingress-egress model for the Kianna unconformity-related uranium deposit, Shea Creek Project, Athabasca Basin, Canada

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Sheahan, Caitlin
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The Kianna deposit is an unconformity-related uranium deposit in the western Athabasca Basin of northern Saskatchewan, hosting uraninite in three distinct zones: 1) perched above the unconformity, hosted in sandstone; 2) at the unconformity, hosted in sandstone and basement rocks; and 3) below the unconformity in two separate pods, hosted by basement paragneiss. In situ secondary ion mass spectrometry (SIMS) was used to obtain radiogenic and stable isotope data to update the genetic model for the Kianna deposit. Primary basement-hosted ingress-style uraninite, associated with hematite and muscovite, has a minimum U-Pb age of ~1500 Ma. Recrystallization of basement uraninite occurred ~1100 Ma with the precipitation of coarse-grained illite. Late basement uraninite precipitated with fine-grained illite ~850 Ma. A separate, deeper basement pod formed ~1280 Ma. Egress-style uraninite at the unconformity, and perched uraninite in the sandstone, inter-grown with alumino-phosphate sulfate (APS) minerals and chalcopyrite, formed ~750 Ma. Later unconformity and perched uraninite precipitated with hematite, pyrite, and chalcopyrite ~500 Ma. Sulfides coeval with unconformity and perched uraninite have d34S values from -1.9 to 8.1‰ and 15.1 to 25.4‰, indicating two sources of sulfur: 1) sulfides in the metamorphosed basement and 2) APS minerals in the sandstone. Average d18O and dD mineral values for muscovite are 0.7 ± 4.3‰ and -33 ± 12‰, respectively, suggesting that muscovite formed from a marine brine. Average d18O and dD mineral values for coarse-grained illite are 0.4 ± 4.1‰ and -79 ± 16‰, respectively, indicating formation from hydrothermal fluids, whereas fine-grained illite d18O and dD mineral values are 6.5 ± 1.6‰ and -144 ± 21‰, respectively, suggesting formation from meteoric fluids.
geochemistry, geochronology, uranium