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Professor R. Grant Cawthorn has written on the subject of the occurrence of platinum group metals (pgms)*.

Much of the world’s pgm, and chromium, deposits are found in layered igneous intrusions, such as the Bushveld Complex, South Africa. This is due to the unique geological processes that lead to the formation of these intrusions. Repeated injection of magma bearing low concentrations of certain elements into a large, sub-volcanic, shallow-level chamber leads to extremely slow cooling and crystallisation processes. Different minerals precipitate as the magma cools.

In this way, layers accumulate, often composed of single minerals. This process can result in the concentration of certain minor minerals of economic importance, which can include pgms and chromium, among others.

Further information can be found in:

*‘The platinum and palladium resources of the Bushveld Complex’, R. G. Cawthorn, S. Afr. J. Sci., 1999, 95, 481–489

‘Centenary of the Discovery of Platinum in the Bushveld Complex’, R. Grant Cawthorn, Platinum Metals Rev., 2006, 50, (3), 130–133

More information on platinum production is available through the Platinum Today website.

Answer posted 29 March 2007