Mineral commodities in the Western Cape Province, South Africa

This report describes the mineral commodities in the Western Cape Province focussing on those which are currently economic or potentially economic. A comprehensive database was compiled involving a total of 2461 mineral points representing 37 commodities. Twenty six of these are economic or potentially economic. Some 18 commodities are currently exploited and are dominated by construction materials, namely stone aggregate, brick clay, building sand and gravel, which in 2013, accounted for 155 or 73 per cent of the 211 working mines in the Western Cape. Stone aggregate is exploited from Table Mountain Group sandstone, granite of the Cape Granite Suite and metamorphosed shale (hornfels) of the Malmesbury Group. Resources are enormous. Brick clay is derived from residual clay of the Malmesbury, Gifberg, Kaaimans and Bokkeveld Groups and the Kirkwood Formation over most of the province except the Karoo, where alluvium is exploited on a small scale. Building sand from windblown dunes, hillwash and alluvial sediments is present over most of the province except the northeastern part, which is underlain by Karoo Supergroup sedimentary rocks and dolerite. Active mining is concentrated in the Greater Cape Town area, but the resources are limited with possible alternatives being sourced from crushed sandstone of the Table Mountain Group or from windblown and alluvial sands in southern Namaqualand. Gravel is derived from a variety of rocks and sediments and from ferricrete throughout the province. Limestone and dolomite are important commodites with the former exploited for cement, metallurgical flux, chemicals, water purification, agricultural lime and building lime and the latter for metallurgical flux, agricultural lime and refractories. They occur in the western and southern parts of the province in the Gifberg, Vanrhynsdorp, Malmesbury and Kango Groups with limestone also present in the Prospect Hill, Langebaan, Velddrif, Wankoe and De Hoopvlei Formations. There were 19 working mines in 2013 and the resources are enormous. Alluvial and marine placer diamonds are present in the northwestern part of the province, but only the marine placers in the foreshore northwest of Donkin’s Bay are viable with 9 working operations in 2013. Heavy minerals containing the economic minerals zircon, ilmenite and rutile, occur in beach and aeolian placers along the west coast north of Dwarskersbos. Only two viable deposits have been discovered, the unworked Geelwal Karoo deposit and Namakwa Sands northwest of Lutzville, which has been mined since 1994. Dimension stone in the form of granite is exploited from granite of the Paarl Pluton and from granite of the Namaqualand Metamorphic Province in the northwestern part of the province. There were two working mines in 2013 and resources are large. Silica sand, which is used for glass manufacture and foundry sand, is present in the Philippi, Atlantis and Hopefield areas. It is exploited from single sites in Philippi and Atlantis and resources are large with 315 million tons of silica sand being calculated for Philippi. Bentonite, which is used for soil sealant, drilling mud and wine and fruit-juice decolourants, occurs in lacustrine mudstone of the Kirkwood Formation in five rift-related basins between Robertson and Plettenberg Bay. There were five working mines in 2013 and the resources are large. Plastic clays of Tertiary age, which comprise transported sedimentary clays rich in kaolinite, form several small deposits in the Greater Cape Town area and near Albertinia. They are exploited for use as a plasticiser and strengthener in the brickmaking industry with four mines operational in 2013. There are probably sufficient resources for about 50 years. Gypsum occurs in the northwestern part of the province and in the Whitehill Formation in the Karoo region. In the former region, the grade is high and it was exploited for plaster, cement retarder and soil conditioner with only one mine working at present near Vanrhynsdorp. Resources of about 9 million tons have been calculated.

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