Varieties of granitic uranium deposits and favorable exploration areas in the eastern United States
Varieties of granitic uranium deposits and favorable exploration areas in the eastern United States (in Uranium geology in resource evaluation and exploration, J. T. Nash (editor))
Economic Geology and the Bulletin of the Society of Economic Geologists (December 1978) 73 (8): 1539-1555
Primary uranium deposits formed by granitic magmas can be classified on two bases: petrologic process of ore formation and tectonic occurrence. The processes of ore formation can be subdivided as follows:1. Syngenetic, orthomagmatic disseminations.2. High-temperature, late-magmatic deposits, including pegmatite stage deposits, such as the pegmatite-alaskite deposits of Roessing, Bancroft, and Crocker Well; contact metasomatic deposits, including occurrences of garnetiferous skarns around pegmatite-alaskite bodies; high-temperature vein deposits, commonly associated with quartz-fluorite veins; and autometasomatic deposits, including many of the disseminated and local concentrations in albite-riebeckite granites.3. Local pegmatites formed by in situ melting of country rocks.Based on occurrence, granitic uranium deposits can be described in the context of two ideal end members: (1) anatectic, migmatitic, pegmatite-alaskite bodies formed by remobilization of preexisting basement--a type example is the Roessing deposit of Namibia (South West Africa)--limited geochemical information suggests that these deposits have very low Th/U ratios, are probably rich in elements that are concentrated by surface processes, and may have high initial (super 87) Sr/ (super 86) Sr ratios; and (2) post-tectonic, alkali-rich (including albite-riebeckite) granites in stocks probably derived directly from mantle or deep crustal levels in the form of diapiric magmas--limited geochemical evidence suggests that these deposits have Th/U ratios > 1 and are rich in elements that form late differentiates during magmatic and deuteric processes; some bodies have low initial (super 87) Sr/ (super 86) Sr ratios.The preceding considerations permit the selection of seven areas in the eastern United States that are most favorable for the development of uranium deposits in crystalline, dominantly granitic, rocks: (1) the Lithonia Gneiss of Georgia; (2) the northern North Carolina Blue Ridge (Grandfather Mountain window and Crossnore plutons); (3) the central and northern Virginia Blue Ridge (Irish Creek tin district and Robertson River and Lovingston Formations; (4) the Raleigh belt of North Carolina and Virginia; (5) the 300-m.y.-old pluton belt of Georgia, South Carolina, North Carolina, and Virginia; (6) portions of the White Mountain Magma Series of New England; and (7) the molybdenum-copper province of Maine.