A scientist in South Africa has calculated that 420 tons of gold – with a value of $24bn – in the form of minuscule particles are locked inside other minerals in the mine dumps found all over the Johannesburg and Witwatersrand area.
Steve Chingwaru says mining companies are reprocessing the tailing dumps in the Johannesburg area, but they are only achieving a 30 percent recovery rate. He set out to locate the remaining 70 percent and determine how to extract it safely.
The Witwatersrand area, stretching across the provinces of Gauteng and Free State is home to the world’s largest known gold deposit, and has produced a staggering amount of the gold ever mined – some estimates say around 22 percent of all the gold ever found above ground.
The Witwatersrand Basin is a giant trough filled with ancient sedimentary rocks, and it’s within these rocks that the gold is found. The gold-bearing reefs extend for hundreds of kilometers and can reach depths of over 3 kilometers.
Chingwaru’s research has attracted the attention of major mining companies, and he has also received interest from China.
Gold in South Africa was hidden in a mineral called pyrite
His research, which examined samples from mine dumps across the Witwatersrand, found that the majority of the gold was hidden in a mineral called pyrite (sometimes called “fool’s gold”) – and was being entirely overlooked by the current extraction techniques.
“We already know how to get gold out of pyrite,” he told Al Jazeera, citing the example of the Carlin mine in Nevada. “But at the moment, all the tailings processors in South Africa are only extracting free gold, using cyanide.”
Chingwaru is the first person to work out how much “invisible gold” is hidden in tailings across the Witwatersrand. The problem is that it will take a lot of time and effort to extract all 420 tones.
“His research shows that there is a lot of gold. The big question, however, is whether we currently have the technology to economically extract all of the gold and make a profit,” Associate Professor Megan Becker, who works at the Centre for Minerals Research in the Department of Chemical Engineering at the University of Cape Town told Al Jazeera.
“Unless this can be done, no company will invest in it.”
The intense interest from several South African tailings reprocessors suggests it’s an investment they would be willing to make.
Since news of his research got out, Chingwaru has spoken to some pretty senior figures in the South African gold industry: “They all said that, yes, it would be expensive to extract the gold, but they could still make a decent profit. Especially if the gold price stays where it is.”
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