Proterozoic unconformity-related uranium deposits in Canada and Australia - geology, genesis, and impact on world uranium production

Fifteen major unconformity-related uranium deposits, cumulatively containing more than 1350 million lb U3O8, have been discovered since 1966 in almost identical geologic settings in the Pine Creek geosyncline, Northern Territory, Australia, and the Athabasca basin, Saskatchewan, Canada. A polygenetic mineralization model is preferred, involving primary syngenetic uranium accumulation in lower Proterozoic euxinic shallow marine environments near an Archean provenance; concentration as structure-stratabound mineralization during metamorphism 1800 Ma; and, subsequent to deposition of the middle Proterozoic sandstone, remobilization and reconcentration of uranium by sandstone-derived diagenetic-hydrothermal fluids. The latter upgrading process operated more strongly in the Athabasca basin, resulting in higher grades and the extensive sandstone-hosted mineralization. Grades average about 2% U3O8 in Canadian unconformity deposits and 0.3% U3O8 in Australian examples. Sizes range from restricted occurrences of a few hundred thousand lb U3O8 to concentrations of up to 450 million lb U38. The five unconformity-related deposits presently in production in Australia and Canada are low-cost producers that have made substantial inroads into western world uranium markets. From 1975 to 1984, when total western world uranium production doubled from 49.6 to 100.3 million lb U3O8, the contribution of unconformity uranium deposits in Canada and Australia increased from 0.72 to 26.2 million lb (1.4 to 26%)