Abstract

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 87 Sr/ 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 87 Sr/ 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.

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