Copyright: RTimages

Finding diamonds

Charles Fipke studied Geology at the University of British Columbia because “with Geology you can at least get a job”. He is now a multimillionaire diamond magnate. How did he do it? Where does one start in the hunt for diamonds?

Just outside the South African city of Kimberley lies Big Hole: 463 metres wide and 240 metres deep, it is the world’s largest excavation dug entirely by hand. It was also here, in 1871, that the De Beer brothers started the first diamond rush when a 16.7 gram gem was found nearby.

Diamonds are composed of carbon and form under very high temperatures and pressures. Such conditions exist deep within the Earth’s mantle at depths of over 150 kilometres. However, diamonds aren’t usually found at the Earth’s surface because ordinarily any carbon that is brought up from these depths reverts to graphite. The only way that diamonds can travel safely to the surface is via rare volcanic pipes, which contain exotic magmas that ascend extraordinarily quickly. The pipes are called kimberlites, after the city of Kimberley, and the magmas are much studied by geologists because they also bring up our only samples of the Earth’s mantle. But the precise mechanism by which the magmas are able to ascend hundreds of kilometres through solid rock in a matter of hours remains elusive.

Kimberlite pipes are rare: currently, they are only known to exist in Africa, Siberia, Australia and northern Canada. The common feature of these locations is that they all lie within continental cratons, unusually old and stable portions of the Earth’s outermost layer. Prospectors hunt for the pipes by looking for other indicator minerals which are diagnostic of kimberlite magmas: large, purple, pyrope garnets and bright, green, chrome diopsides. Years are spent panning streambeds, beaches, and even anthills to look for these minerals and pinpoint the kimberlites. But even then, only one in every 200 kimberlite pipes contains gem quality diamonds.

It was in 1981 that the monopolistic De Beers company, and subsequently Fipke, found indicator minerals in the Mackenzie Mountains of northwest Canada. Fipke soon realised that he was looking at glacial debris from the last glaciation 10,000 years ago. Painstakingly, he tracked the path of the glaciers east for hundreds of miles into the Barren Lands before he finally found the original kimberlite deposits. Before long, the region was crawling with competitors. Helicopter crews, with the aid of GPS, threw stakes out of the door in the hopes of marking their territory; drilling rigs, used to check that deposits existed at depth, were covered with camouflage nets; airborne geophysical surveys were employed to map the kimberlite indicator minerals magnetically; and companies even laid electric cables to produce magnetic fields that would confound rivals who were trying to calibrate their magnetic instruments.

Even once the diamonds have been found and the land claimed, the obsessions do not stop: at some diamond mines, workers are forbidden to bend down to pick something off the ground for fear they might pocket a priceless gem. Despite this, extracting the diamonds is far from straightforward; every ton of kimberlite deposits contains only 600 milligrams of diamonds. To separate the diamonds, kimberlite rubble from huge opencast mines is fed into crushing towers and rinsed to remove the other minerals. If the calibre of the crusher is too big, not enough of the smaller diamonds will be found to make the exercise profitable; if it is too small, any big diamonds will be broken. It’s a tough decision to make, and unfortunately diamonds are not forever: we’ve almost certainly destroyed the biggest diamonds we’ve ever found.

Featured image credit: RTimages via Shutterstock

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