The Geelwal Karoo heavy mineral deposit: a modern day beach placer
The Geelwal Karoo heavy-mineral placer is situated in an active beach environment along the rugged southern Namaqualand coast of South Africa. The geomorphology of the coast is controlled by resistant Precambrian and Palaeozoic basement rocks, which also dictate the narrow, elongate geometry and limited 10 km strike length of this strandline deposit. Ore reserves are small compared to the multi-million tonne analogous Quaternary sands elsewhere in the world. However, the locally high, total heavy mineral content and the favourable ore to gangue mineral ratio, coupled with the possibility of replenishment style mining, makes this an attractive resource. Garnet and ilmenite are the dominant heavy minerals followed by pyroxene, zircon, rutile and titaniferous alteration products after ilmenite. The high Ti content of ilmenite (51%) and predominantly almandine garnet suggest metamorphic source rocks, most likely part of the Namaqualand Metamorphic Complex. These rocks are considered to be the primary source. However, after numerous stages of reworking, large quantities of heavy minerals are concentrated in the Neogene marine terraces along the west coast. The 35 m terrace, a local, heavy, mineral-rich palaeostrandline, acted as a point source and supplied vast quantities to the coastal environment. A J-bay shaped headland to the south prevented excessive dispersion of the minerals by the strong northward-directed littoral drift. This allowed wave action to transport, concentrate and re-deposit the heavy minerals in their present beach environment at Geelwal Karoo. © 1995.