Abstract

Extensive surficial uranium mineralization has been identified in the Namib Desert in central Namibia. The mineralization comprises of uranium-rich zones in excess of 500 ppm for more than 3 m in tertiary sediment channels within the Kalahari succession. In places zones over 10 000 ppm over 3 m were observed in the near surface sediments. The mineralization is unusual in that it is entirely within the recent sands and is unconnected to any bedrock anomalies indicating transport of uranium by supergene processes.

A reconnaissance level exploration program has been completed to determine the geological extent and controls on such mineralization and use this to determine potential viability of such deposits. Historic data combined with geophysical data were used to identify potentially high grade uranium anomalies including historically identified anomalies. In addition additional anomalies were also discovered during the course of the work.

Bedrock geology in the area comprises of high thorium granites with highly variable but generally low concentration of uranium that has complicated identification of potential radiometric targets requiring ground based studies to distinguish uranium anomalies. These are intruded into Kuiseb shists that most likely supplied vanadium. Detailed investigation of the identified uranium anomalies found mineralization was confined to the regolith only with high grade uranium (VI) mineralization confined to ferric oxide-rich aeolian sand horizons and black weathered biotite schist horizons, indicating the mineralization was likely of secondary origin.

The assessment of the geology and recent sedimentology indicates that the uranium source is likely to be from the Damara intrusives to the east of the field area with extensive hydrogeochemical mobilization of uranium post-uplift in the Cretaceous period. A complex uranium mineralogy in the sands indicates bi-modal formation of uranium with both oxidation and reduction mechanisms having some control on uranium precipitation in various parts of the deposit.

The mineralization demonstrates the dynamic geochemistry of uranium and the ability to concentrate the metal by entirely supergene processes. Although such deposits of this type are challenged to form a sufficiently large size to be considered economic, potential still exists to identify further high grade zones.

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