Varieties of granitic uranium deposits and favorable exploration areas in the eastern United States

Abstract

Primary uranium deposits formed by granitic magmas can be classified on two bases: petrologle process of ore formation and tectonic occurrence. The processes of ore oeormation can be subdivided as follows: 1. $yngenetic, orthomagmatic disseminations. 2. High-temperature, late-magmatic deposits, including pegmatite stage deposits, such as the pegmatite-alaskite deposits of R6ssing, .Bancroft, and Crocker Well; contact metasomatic deposits, including occurrences of garnetiferous skarns around pegmatite-alaskite bodies; high-temperature vein deposits, commonly associated with quartz-fluorite veins; and autometasomatic deposits, including many of the dis~ semihated and local concentrations in albite-riebeckite granites. 3. Local pegmatites formed by in situ melting of country rocks. Based on occurrence, granitic uranium deposits can be described in the context of two ideal end members: (1) anatectic, mignmtitic, pegmatite-alaskite bodies formed by remobilization of preexisting basement-a type example is the R6ssing deposit of Namibia (South West Africa)-limited geochemical information suggests that these deposits have very low Th/U ratios, are probably rich in elements that are concentrated by surface processes, and may have high initial S7$r/S6$r 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 aliapirie 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 SVSr/SOSr 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 ;vindow 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. vestigation of economic uranium concentrations in igneous rocks. Two reports have been issued as a result of this work. Xishimori et al. (1977) discuss the theoretical basis for exploration for uranium in granitic rocks, and Greenberg et al. (1977) apply these criteria to the identification of zones of potential economic interest in the eastern United States. Uranium is a mobile element. In internal processes in the earth (generally in the reduced, tetravalent, form) it is classified as a lithophilic element and tends to accumulate in the later differentiates of igneous melts. It may oxidize to the hexavalent 1539 1540 ROGERS, R./tGL./tND, NISHIiIIORI, GREENBERG. ./tND H./tUC...

Geophysical interpretation of the gneiss terrane of northern Washington and southern British Columbia, and its implications for uranium exploration

“…Uranium in such deposits is concentrated in anatectic granite and migmatite derived from reworked sialic crust. High uranium concentrations are expected "in the more deeply eroded portions of the orogen where basement rocks, high-rank metasedimentary rocks, and anatectic granites are closely intermingled" (Rogers andothers, 1978, p. 1547). We have inferred that local gravity highs indicate upwarped highmetamorphic-grade domes within the metamorphic terrane, where we would expect to find the most deeply eroded section.…”

Radioelement geochemistry of alkali granites of the Kerala region, south-west India

“…Higher Th-eontent as compared to U is noted to be a common feature of these granites, yielding high Th/U ratios. Rogers et al (1978) suggest that there is a preferential release of U relative to Th from the mantle into the derived melt during partial melting. U is released from the mantle not only into the magma but also directly into the volatile phases.…”

“…However, they are closely comparable with the generally high Th values exhibited by alkali granites of other regions as compiled in table 4. Rogers et al (1978) observe that Pan-African granites are Th-rich. In this regard, it is significant to mention that the beach placers in the western coastal tract of Kerala are rich in Thbearing minerals, the probable provenances of which are the granite and syenite bodies as well as the rare metal and rare earth bearing pegmatites of the region (Santosh 1984;Soman et al 1983).…”

Natural Radioactivity of Intrusive-Metamorphic and Sedimentary Rocks of the Balkan Mountain Range (Serbia, Stara Planina)

“…Detailed information about granite and radioactivity in general is available in Mayers [15], Rorers et al [16] and René and Dolníček [17].…”