- Bushveld Igneous Complex
The Bushveld Igneous Complex (or BIC) is a large
igneous intrusionwithin the Earth's crust which has been tilted and eroded and now outcrops around what appears to be the edge of a great geological basin. Located in South Africa, the BIC contains some of the richest ore deposits on Earth. The reserves of platinum group metals(PGMs), platinum, palladium, osmium, iridium, rhodium, and rutheniumare the world's largest, and there are vast quantities of iron, tin, chromium, titaniumand vanadium. Gabbroor noriteis also quarried from parts of the Complex and rendered into dimension stone.
The Bushveld Igneous Complex is divided into an eastern and western lobe, with a further northern extension. All three sections of the system were formed around the same time — about 2 billion years ago — and are remarkably similar. Vast quantities of molten rock from the earth's mantle were brought to surface through long vertical cracks in the earth's crust — huge arcuate differentiated
lopolithic intrusions — creating the geological intrusion known as the Bushveld Igneous Complex. The effects of these injections of molten rock over time, combined with the crystallisationof different minerals at different temperatures, resulted in the formation of a structure rather like a layered cake consisting of distinct rock strata, including three PGM-bearing layers, referred to as reefs.
The Complex includes layered
mafic intrusions (the Rustenburg Layered Suite) and a felsicphase. It has its geographic centre located north of Pretoriain South Africaat about 25° S and 29° E. It covers over convert|66000|km²|sqmi|abbr=on|lk=on, an area the size of Ireland. The complex varies in thickness, sometimes reaching convert|9|km|mi|abbr=off thick. Lithologies vary from largely ultramafic peridotite, chromitite, harzburgite, and bronzititein the lower sections to mafic norite, anorthosite, and gabbrotoward the top, and the mafic Rustenburg Layered Suite is followed by a felsic phase (the Lebowa GraniteSuite).
The orebodies within the complex include the UG2 reef containing up to 43.5%
chromite, and the platinum-bearing horizons Merensky Reefand Plat Reef. The Merensky Reef varies from 30 to 90 cm in thickness. It is a norite with extensive chromitite and sulfide layers or zones containing the ore. The "Reef" contains an average of 10 ppm platinum group metals in pyrrhotite, pentlandite, and pyriteas well as in rare platinum group minerals and alloys. The Merensky and UG-2 reefs contain approximately 90% of the world's known PGE reserves. About 80% of the platinum and 20% of the palladium mined each year are produced from these horizons.
Platinum group metals
Ultramafic to mafic layered intrusions
Stillwater igneous complex
*cite book |title=The Geology of Ore Deposits |last=Guilbert |first=John M. |authorlink= |coauthors=Park, Charles F., Jr. |year=1986 |publisher=Freeman |location=New York |isbn=0716714566 |pages=
*cite journal |last=Richardson |first=Stephen H. |authorlink= |coauthors=Shirey, Steven B. |year=2008 |month= |title=Continental mantle signature of Bushveld magmas and coeval diamonds |journal=Nature |volume=453 |issue=7197 |pages=910–913 |doi=10.1038/nature07073 |url= |accessdate= |quote=
*cite book |title=Council for Geoscience Handbook 16, Mineral Resources of South Africa |chapter=Platinum-group metals |last=Viljoen |first=M. J. |authorlink= |coauthors=Schürmann, L. W. |editor=Wilson, M. G. C.; Anhaeusser, C. R. (eds.) |year=1998 |publisher=Council for Geoscience |location=Pretoria |isbn=1875061525 |pages=
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