Abstract

Deposits of Cu, V, and U in nonmarine sandstones are numerous and widespread. Cu deposits, with or without U, are mainly resident in first-generation arkosic sandstones derived from granitic rock terrains; deposits rich in V, with or without much U, are dominantly in second-generation sandstones derived from sedimentary rocks; and the U deposits with little or no V or Cu are in either first- or second-generation sandstones, many of which are associated with beds containing volcanic debris. All metals are dispersed in igneous rocks but not in close association. Cu and U enter the hydrothermal environment, but the record of V in hydrothermal solutions and veins is scant. Some of the U and most of the Cu minerals in igneous rocks and veins oxidize readily and the metals go into surface- and ground-water solutions, but the V in igneous rocks is not so easily mobilized - under normal geologic conditions, conceivably it may require diagenetic reactions and a second period of weathering to solubilize much V. All 3 metals precipitate from solutions in the presence of a reducing agent, such as carbonaceous material or associated sulfide ions, either in sediments as they accumulate or in existing rocks. These geochemical habits permit the concept that Cu and U are made available by weathering of igneous rock terrains and hence might accumulate in first-generation sediments, whereas V would be commonly available only after a second period of weathering. Perhaps the oxidation or devitrification of volcanic debris may contribute U to ground waters as does the weathering of igneous rocks.

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