Evolution of Diamond Mining: From Cullinan to Karowe

Mining technology and equipment has changed but the end goal remains the same.

Legend has it Frederick Wells, the superintendent of the Premier Mine in South Africa, was making a routine inspection one afternoon in 1905 when he spotted a light reflecting the sun’s rays.

Curious for a closer look, he extracted what he thought was a large piece of glass embedded in the rock a few feet above him. That glass later became known as the iconic 3,106-carat Cullinan diamond, the largest rough diamond ever found.

With mining techniques continuing to develop rapidly, the opportunity to simply scoop such a stone from bedrock is, more or less, a thing of the past. So the biggest challenge facing miners is to minimize the breakage of such large stones given the numerous and complicated stages required to recover a diamond.

Mining first involves liberating the kimberlite rock through controlled explosives. In the crushing operation which occurs in underground mining facilities, large chunks of kimberlite are broken up into more easily transportable segments.

SEPARATION TECHNIQUES

At the processing plant, the ore then goes through separation with Media Dense Separation (DMS) being the most common method used. Other techniques include Rotary Pan Plant (RPP), typically applied in alluvial mining operations.

DMS uses the principle that diamonds are heavier than other material and will sink to the bottom when combined with water and a fine-grained powder called ferrosilicon.

The DMS plant uses a hydro-cyclone that spins the water at a high rate so that the lighter material will float to the top while the heavier diamondiferous material will sink to the bottom. Diamonds are eventually extracted from that material using x-ray machines and grease tables.

IT’S A BIG DIAMOND

Lucara Diamond Corp. famously replaced DMS technology with six Tomra Large Diamond Discovery XRT machines at its Karowe mine in Botswana in May 2015. Six months later, Lucara announced the recovery of the 1,109-carat Lesedi La Rona, weighing in as the second largest diamond in history.

William Lamb, Lucara’s CEO, stressed it would not have been possible to recover the Lesedi La Rona without the XRT machines. “The diamond would have gone to the crusher and fragmented,” he said.

Instead, on a November morning in 2015, Tiroyaone Mathaba, a rookie sorter at Karowe, says an object “that initially just looked like a stone” caught his eye while he was routinely examining rock and sand produced by the XRT machines. But he soon realized it was much more as the Lesedi La Rona surfaced. “At first I wanted to scream,” Mathaba was reported as saying. “Then I said in a low hoarse voice, God, it’s a diamond! It’s a big diamond!”

The mining sector may have come a long way since Frederick Well’s walking inspections in South Africa. But the excitement of finding the biggest, most beautiful gems on the planet remains the same. It just relies more on technology than luck to do so.