Unconformity-type uranium deposits host high grades relative to other uranium deposits and include some of the lagest and richest deposits known. They occur in close proximity to major unconformities between relatively quartzrich sandstones comprising the basal portion of relatively undeformed sedimentary basins and deformed metamorphic basement rocks.
These sedimentary basins are typically of Proterozoic age, however some Phanerozoic examples exist.