A Combined Ingress-Egress Model for the Kianna Unconformity-Related Uranium Deposit, Shea Creek Project, Athabasca Basin, Canada

Abstract

The Kianna deposit is an unconformity-related uranium deposit in the western Athabasca Basin, hosting mineralization in three zones: (1) perched in sandstone above the unconformity, (2) unconformity and shallow basement hosted, and (3) deep basement hosted. In situ secondary ion mass spectrometry was used to obtain radiogenic and stable isotope data to update the genetic model for the Kianna deposit. Primary basement-hosted ingress-style mineralization, intergrown with hematite and muscovite, has a minimum U-Pb age of ~1500 Ma. Recrystallization of basement uraninite occurred at ~1100 Ma with the precipitation of coarse-grained illite. Late basement uraninite precipitated with fine-grained illite at ~850 Ma. A separate, deeper basement pod formed at ~1280 Ma. Egress-style mineralization at the unconformity and perched uraninite in the sandstone, intergrown with aluminophosphate sulfate minerals and chalcopyrite, formed at ~750 Ma. Later unconformity and perched uraninite precipitated with hematite, pyrite, and chalcopyrite at ~500 Ma. Sulfides coeval with unconformity and perched uraninite have δ 34 S values ranging from −1.9 to +8.1‰ and 15.1 to 25.4‰, indicating two sources of sulfur: sulfides in the metamorphosed basement and aluminophosphate sulfate minerals in the sandstone. Average δ 18 O and δ D mineral values for muscovite are 0.7 ± 4.3‰ and −33 ± 12‰, respectively, suggesting formation from a marine brine. Average δ 18 O and δ D mineral values for coarse-grained illite are 0.4 ± 4.1‰ and −79 ± 16‰, respectively, indicating formation from hydrothermal fluids, whereas fine-grained illite δ 18 O and δ D mineral values are 6.5 ± 1.6‰ and −144 ± 21‰, respectively, suggesting formation from meteoric fluids.