Uranium-rich diagenetic fluids provide the key to unconformity-related uranium mineralization in the Athabasca Basin

• Published in: Scientific reports 2019-04, Vol.9 (1), p.5530-5530, Article 5530
• Main Authors: Chi, Guoxiang, Chu, Haixia, Petts, Duane, Potter, Eric, Jackson, Simon, Williams-Jones, Anthony
• Format: Article
• Language: English
• Subjects: 140/125; 704/2151/209; 704/2151/213; Brines; Deposits; Fertility; Humanities and Social Sciences; Leaching; Mineralization; multidisciplinary; Science; Science (multidisciplinary); Unconformity; Uranium
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-42032-0

The Proterozoic Athabasca Basin is well known for its unusually large-tonnage and high-grade ‘unconformity-related’ uranium (U) deposits, however, explanations for the basin-wide U endowment have not been clearly identified. Previous studies indicate that U-rich brines with up to ~600 ppm U and variable Na/Ca ratios (from Na-dominated to Ca-dominated) were present at the sites of U mineralization, but it is unknown whether such fluids were developed solely in the vicinity of the U deposits or at a basinal scale. Our microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz overgrowths from the barren part of the basin indicate that U-rich brines (0.6 to 26.8 ppm U), including Na-dominated and Ca-dominated varieties, were widely developed in the basin. These U concentrations, although not as high as the highest found in the U deposits, are more than two orders of magnitude higher than most naturally occurring geologic fluids. The basin-scale development of U-rich diagenetic fluids is interpreted to be related to several geologic factors, including availability of basinal brines and U-rich lithologies, and a hydrogeologic framework that facilitated fluid circulation and U leaching. The combination of these favorable conditions is responsible for the U fertility of the Athabasca Basin.