Johannesburg, South Africa – As a teenager living on the East Rand of Johannesburg, Steve Chingwaru thought the flat-topped mounds of rock and earth that dotted the skyline were a natural feature of the cityscape. Jo’burg isn’t very windy, but when the wind does blow – usually around August – the air is filled with orange dust. “It gets in your hair, your clothes, your throat,” says Chingwaru.
Now, barely a decade later, the 26-year-old geometallurgist is being flown up to the city of his youth on an almost weekly basis by mining companies who want him to help them extract maximum value from the mounds of orange dust. That’s because the mounds are made up of mine waste from the richest gold deposit ever discovered, and Chingwaru has just calculated that approximately 420 tonnes of “invisible gold” – with a value of $24bn – is buried in the Witwatersrand’s mine dumps.
The massive discovery came from research for his master’s thesis — that was so impressive it saw his degree upgraded to a PhD.
Soon after enrolling in a geology degree at Stellenbosch University, Chingwaru realised he didn’t want to be an exploration geologist. “Camping in the middle of nowhere wasn’t for me,” he says, flashing a winning smile. He was drawn to the nascent field of geometallurgy, which combines classic geology with metallurgy – and typically involves working at a processing plant. For his academic research, Chingwaru focused on Johannesburg’s iconic mine dumps, known as “tailings” in the industry.
“They were already extracting the gold from these tailings,” he explains. “But they were only managing to get out 30 percent of the gold they contained.” I wanted to know what was happening to the other 70 percent … Where was it sitting? Why weren’t they getting it out? Seventy percent is a lot,” he says, before breaking into an unexpected chortle.
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 says, 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.”
Which begets an obvious question – why?
The answer is twofold. One, Chingwaru is the first person to work out how much “invisible gold” is hidden in tailings across the Witwatersrand. And two, it will take a lot of time and effort to extract all 420 tonnes.
“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,” says Associate Professor Megan Becker, who works at the Centre for Minerals Research in the Department of Chemical Engineering at the University of Cape Town (she was not involved in Chingwaru’s research). “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.”
To underline this point, Chingwaru has also received job offers from companies in Australia, Canada, Germany and the United States.
