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Recent studies of uranium occurrences in the Precambrian crystalline terrain of the Reading Prong show a definite correlation between the presence of uranium and late stage magmatic activity during the Grenville orogeny. All uranium concentrations examined show a close spatial association with catazonally emplaced granitic, alaskitic, or pegmatitic rock of anatectic origin. Published age dates indicate that uranium concentrations developed during the period 975 to 950 m.y. The ultimate source of the uranium is a granitic magma formed by partial melting of the metasediments in the root zones of the Reading Prong. Emplacement of granitic layers into a variable metamorphic sequence has resulted in different types of uranium occurrences. (1) Anatectic granite association: gra itic stocks and sheets intruded into the metasedimentary section near the zone of anatexis may show internal enrichments of uranium. (2) Magnetite association: magnetite ore bodies provide locally reducing conditions ("oxygen-sink") to precipitate uranium released from nearby intrusions. (3) Metasedimentary contact association: granitic intrusion into a lower pressure zone in a metasedimentary sequence may result in release and concentration of uranium from a fluid phase along the intrusive contact. (4) Skarn association: similar to type 3, uranium concentrations may develop where uraniferous granites intrude a calc-silicate assemblage. (5) Massive sulfide assemblage: uranium concentrations can develop in the reducing environment where a granitic magma intrudes or abuts a massive sulfide body.
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