Calcrete valley

Nash, D.J. Mclaren, S.J. 2003 Kalahari valley calcretes Their nature, origins and environmental significance. Quaternary International, 111, 3-22. 

Figure 2.10 Geometries of groundwater calcretes and dolocretes. Linear, ribbon-like valley calcretes are known from the late Cenozoic of central and Western Australia, and the late Triassic of the Paris Basin (see text). Lacustrine groundwater calcretes or dolocretes forming halo-like masses are known from the Danian of Provence (see text). Alluvial fans are associated with sheet-like bodies, and are known from the Plio-Pleistocene of Oman and the Palomas Basin (New Mexico), and the Paleocene of the Lisbon and Sado basins (see text).

The most important uraniferous calcrete deposit is Yeelirrie, Western AustraliaYeelirrie is an area of interior drainage, deep valley fills, abundant evaporite lakes and clay pans in an arid region. Valley calcretes are typically elongate masses of carbonate-cemented alluvium deposited parallel to subsurface valley drainage courses, but some form delta-like deposits that fringe salt lakes. 

Uranium from weathered granites and vanadium derived from greenstones are present in the groundwater and valley-fill sediments. Uranium, vanadium and potassium concentrate downstream by evaporation and combine in the oxidizing environment to form carnotite, which fills cavities and fractures in the calcrete. Carnotite also forms in a clay-quartz unit beneath the calcrete. Resources at Yeelirrie are estimated at 47000 ton UgOg at grades of 0.05-0.10%. 

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