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Hydrology of Uranium Deposits in Calcretes of Western Australia1

By
A. J. Gaskin
A. J. Gaskin
2
CSIRO Division of Mineralogy, Wembley, Western Australia 6014.
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C. R. M. Butt
C. R. M. Butt
2
CSIRO Division of Mineralogy, Wembley, Western Australia 6014.
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R. L. Deutscher
R. L. Deutscher
2
CSIRO Division of Mineralogy, Wembley, Western Australia 6014.
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R. C. Horwitz
R. C. Horwitz
2
CSIRO Division of Mineralogy, Wembley, Western Australia 6014.
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A. W. Mann
A. W. Mann
2
CSIRO Division of Mineralogy, Wembley, Western Australia 6014.
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Published:
January 01, 1981

Abstract

Carnotite is the principal uranium mineral occurring in the calcreted trunk valleys of the ancient drainage system which extends over 400,000 sq km of southwestern Australia. The calcretes, accumulations of calcium and magnesium carbonates up to 100 km long, 5 km wide, and 20 m thick, are discontinuous in character but act as aquifers for groundwaters of relatively low salinity that flow sluggishly to playa lakes. Catchment basins draining large areas of Precambrian granitic rocks can yield up to 200 parts per billion of uranium in the oxidizing environment of the water at shallow depth near the base of the calcretes. Where the product of the concentrations of active ion species of uranium, vanadium, and potassium exceeds the solubility product of carnotite, this mineral precipitates in fissures or between the carbonate and clay particles. Vanadium appears to be generally deficient in the upper levels of the aquifers; however, where it has been supplied at the required concentration from deeper reduced waters, forced up, for example, by a bar of resistant bedrock, carnotite mineralization has occurred. The incongruent dissolution of carnotite liberates vanadium preferentially. Some carnotite deposits currently are being leached and redeposited downstream. Where calerete channels reach salt lakes, great increases in the activity of calcium and potassium promote further carnotite deposition by the decomplexing of uranyl carbonate complexes carried down the aquifers. Many areas of carnotite mineralization are now known. The largest, at Yeelirrie, contains 46,000 MT of U3O8 at an average grade of 0.15%. Extraction from the ore is hampered by the carbonate content and the presence of illitemontmorillonite clay phases, but alkaline leach techniques are practicable. An appreciable proportion of the carnotite, in an extremely fine-grained form, can be associated with the clay fraction.

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Contents

AAPG Studies in Geology

Energy Resources of the Pacific Region

Michel T. Halbouty
Michel T. Halbouty
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American Association of Petroleum Geologists
Volume
12
ISBN electronic:
9781629811802
Publication date:
January 01, 1981

GeoRef

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