The mode of occurrence and distribution of uranium deposits

Abstract
Uranium deposits occur in association with igneous, sedimentary and metamorphic rocks. The bulk of low-cost reserves, however, occurs in Precambrian rocks or in Phanerozoic sediments immediately overlying the basement. In basement rocks, as well as in more recent rocks, major uranium deposits are spatially associated with leucogranites. In Phanerozoic sediments, close to the basement uranium is enriched in continental clastic formations under reducing conditions. Favourable lithologies are alternating horizons of clay and sandstone containing carbonaceous matter. Metamorphic developments are associated with zones of crustal thickening with a world-wide era of concentration at around 1900-1700 Ma ago. Uranium is also enriched in more recent metamorphosed clastic sediments. Deposits directly associated with igneous rocks tend to occur in unsaturated facies rich in volatiles. Granitic and alaskitic pegmatites also carry economic amounts of uranium. The most important secondary deposits of recent origin are those occurring in carbonateor sulphate-cemented sediments.

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