Abstract

A textural and mineralogical study has been made of Kalahari cover sand, collected on a regular (approximately 13 kmX13 km) grid, over an area of approximately 78 500 km 2 , covering much of the central Kalahari region of Botswana. Sand textural characteristics vary systematically over the area sampled, but are not readily explained in terms of the wind patterns which have prevailed from at least the Quaternary to the present day. Rather, they indicate that deposition was dominated by fluvial processes. Zones of coarse sand associated with relatively high concentrations of heavy minerals are interpreted as lags associated with the basin margins, Ephemeral streams and sheetwash transported finer material into the distal portions of the basin, which is characterized by relatively low numbers of heavy minerals. The variation in sand texture and the distribution of heavy minerals indicate that the ground sampled covers the major portion of a subsidiary central Kalahari Basin. This is bounded by the Bakalahari Schwelle in the south, and the Ghanzi ridge in the northwest. The divide between the Limpopo and endoreic fossil drainage lines, which formerly emptied into the Makgadigadi, is inferred to form the eastern margin of this central Kalahari Basin. The mineralogical and textural data presented here have important implications for kimberlite prospecting in the sandveld of the western two thirds of Botswana.

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