Overberg Geoscientists Group
2060 Mya
Bushveld Igneous Complex
The Bushveld Igneous Complex is the world’s largest reserves of Platinum Group metals, and has also huge resources of Chrome, Iron and Gold.
It covers some 66,000 hectares and stretches from just north of Pretoria and Rustenburg north to Potgietersrus.
These are all deposited in the largest Layered Igneous Intrusion in the World. It was formed when huge amounts of magma were forced up from the Earth’s Mantle along vertical cracks in the crust. The magmas formed an enormous chamber and began to cool. The process was repeated a number of times as the cooling and crystallization continued.
The metals and heavy, dense minerals were concentrated into a number of homogeneous horizons, which are some of the layers which form the entire complex. They contain the enormous mineral reserves of the BIC.
The entire Igneous body is layered and even the non-mineralized zones show this phenomenon.
The mineralized horizons are known in mining terms as ‘Reefs’ and there are 3 main ones.
The Merensky Reef, named after Hans Merensky whose prospecting work discovered the primary source in the Bushveld Igneous Complex and traced it for several hundred kilometres by 1930.
The UG2 Chromite Reef. Which, apart from the Chromite, contains Platinum Group Metals (PGMs).
The Platreef. Largely PGMs.
These reefs contain 75% of the world’s Platinum.
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This table shows the amount of ore in the various reefs in millions of tons, and the amount of each metal that the ore body contains – in tons.
The actual mechanism of concentration of the minerals into these sharply defined and very continuous horizons is still being debated. It may involve repeated intrusions, or the gravity and size-controlled settling. The thin seams – the Merensky reef is normally less than 1m in thickness – continue along many kilometres and are also being mined at depth.
Further reading:
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R. P. Schouwstra and E. D. Kinloch (2000). "A Short Geological Review of the Bushveld Complex" (PDF). Platinum Metals Review. 44 (1)
Mondal, Sisir K.; Mathez, Edmond A. (2007-03-01). "Origin of the UG2 chromitite layer, Bushveld Complex". Journal of Petrology. 48 (3):
Hutchinson, D.; Foster, J.; Prichard, H.; Gilbert, S. (2015-01-01). "Concentration of Particulate Platinum-Group Minerals during Magma Emplacement; a Case Study from the Merensky Reef, Bushveld Complex". Journal of Petrology. 56 (1)
Michael L. Zientek; J. Douglas Causey; Heather L. Parks; Robert J. Miller (May 1, 2014). "USGS Scientific Investigations Report 2013–5090–Q: Platinum-Group Elements in Southern Africa—Mineral Inventory and an Assessment of Undiscovered Mineral Resources". pubs.usgs.gov.
Mungall, James E.; Naldrett, Anthony J. (2008-08-01). "Ore Deposits of the Platinum-Group Elements". Elements. 4 (4): 253. doi:10.2113/GSELEMENTS.4.4.253. ISSN 1811-5209.
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D J Mourant July 2023