Geotimes Videocast Wednesday, June 18, 2008
Platinum from the deep
Gold, diamonds, platinum.
For more than a century, South Africa's vast underground riches have lured eager prospectors to the country. And in the last decade, platinum — widely used not just in jewelry but in catalytic converters and microelectronics — has become particularly valuable.
One of the most famous sources for both diamonds and platinum is South Africa's Bushveld Complex, a giant geological mishmash of ancient magmas that welled up into the crust more than 2 billion years ago. And it's unusually rich in platinum and similar elements.
Finding such wealthy deposits is difficult, so exploration geologists have been studying the Bushveld Complex to find out what's special about it.
Now, scientists reporting this week in Nature think they have an answer.
To make the Bushveld's ores, the magma reacted chemically with the original host rocks. Scientists used to think that that magma originated in the crust. But some scientists were skeptical, because the crust contains so little platinum — it's 30 times rarer than gold. The deeper mantle, on the other hand, contains much more.
So Steven Shirey of the Carnegie Institute of Washington and Stephen Richardson of the University of Cape Town in South Africa decided to use another form of riches to determine the Bushveld's origin — diamonds.
The diamonds formed at the same time as the Bushveld. And as they crystallized, they included tiny pieces of their surrounding rocks. Two billion years later, the tough diamonds still contained those original bits of rock — perfectly preserved.
By determining the chemical makeup of those rocks, they determined that the magma that formed the Bushveld didn't come from the crust after all, but instead came from the mantle.
Knowing the magma's source and how these ores formed is important, the scientists say, because that could give modern-day prospectors new strategies to locate these rare metals.
For more on this topic, see the August issue of Geotimes.