14 DAY TRIAL // Most of the platinum metal extracted around the world comes from the Bushveld Complex located in South Africa, a region believed to have been created out of ancient magma some two billion years ago. However, why that particular area is so rich in platinum and other related metals remained a topic open for debate for many years. Diamonds, another important part of the riches of South Africa, are now revealing the origin of the unique platinum group element ore deposits in the Bushveld Complex.
According to a study carried out by the Carnegie Institution and the University of Cape Town the platinum deposits in South Africa could have come from parts of the mantle under the African continent. Platinum group elements that platinum, palladium, rhodium, ruthenium, osmium and iridium are part of are amongst the rarest elements found on Earth. Gold for example, is at least 30 times more abundant than platinum.
The vast majority of PGEs have unique properties that make them extremely important in the pollution control area, since they are used as catalyzers in fuel cell powered vehicles as well as in the industry of microelectronics. The results of previous studies showed that the magma that formed the Bushveld Complex came from a shallow part of the Earth crust, but do not explain why these elements are so much rarer in other parts of the Earth's mantle.
"But the ore layers are extremely homogeneous over hundreds of kilometers. The crust is very heterogeneous. That suggests a deeper source for the platinum", says Steven Shirey of the Carnegie Institution's Department of Terrestrial Magnetism.
By studying the inclusions of 20 diamonds extracted from the Bushveld Complex, Shirey along with Sthephen H. Richardson from the University of Cape Town showed that the ratios of strontium, osmium and neodymium isotopes point towards the regions of the mantle where the diamonds were formed. A comparison between the isotopic signature in diamonds with the one in the ore extracted from the Bushveld Complex revealed a perfect match, if we assume that the rock mixtures of the mantle are varied accordingly.
Seismic studies also suggest that similar parts of the mantle produce such magmas that rise to the surface in these particular areas. "This helps explain the richness of these deposits. The old subcontinental mantle has a higher PGE content than the crust and there is more of it for the Bushveld magmas to traverse and pick up the PGEs found in the ores", Richardson said.