Steve Chingwaru’s grandfather made his fortune in the 1950s when he started mining a lithium deposit he’d discovered in the hills of what was then Southern Rhodesia.
Seventy years later, Chingwaru believes he has found another mineral fortune, this one worth as much as R450bn and hiding in plain sight in the gold mine dumps that stud the Witwatersrand.
“Invisible gold” — particles of submicron size locked inside other minerals — is nothing new. But the young scientist with prospecting in his blood is the first to calculate that the 6-billion short tons (t) of tailings around Joburg contain up to 420t of it.
His work is capturing attention as mine yields fall, costs rise and technological developments make tailings reprocessing more efficient and lucrative.
When the Stellenbosch University geometallurgist presented his work at last year’s conference of the Prospectors & Developers Association of Canada, he told delegates he had uncovered what was potentially the world’s largest invisible gold resource. They responded by voting his master’s research the third best at the international conference — the world’s largest on minerals exploration and investment.
Now the paper that Chingwaru, 25, wrote with his supervisors, Bjorn von der Heyden and Margreth Tadie, has been published in the prestigious journal Scientific Reports, his master’s has been upgraded to a doctorate based on his findings, and Chingwaru appears to have the world at his feet.
“I have no doubt that he will be a future leader in the field of geometallurgy, and I hope that we can retain this type of talent in the Southern African arena,” Von der Heyden tells the FM.
I grew up next to these tailings, and I guess I have a connection with them because every August it was windy and the dust used to make our house orange. But I thought they were just a natural feature of Joburg
— Steve Chingwaru
The fortune amassed by Chingwaru’s grandfather, George Nolan, was long gone by the time the Zimbabwean teenager arrived on the East Rand with his mother 12 years ago. The mansion styled on the White House that Nolan built near Bikita Mine had been looted and bombed to ruins during the Rhodesian Bush War, the old prospector — born on diamond diggings in South Africa in 1890 — died at the age of 70, and the collapse of the Zimbabwe dollar did the rest.
Chingwaru and his mother settled in Alberton, and he attended Dinwiddie High School in Germiston.
“I grew up next to these tailings, and I guess I have a connection with them because every August it was windy and the dust used to make our house orange,” he tells the FM. “But I thought they were just a natural feature of Joburg.”
Finding out where the tailings came from and reading his grandfather’s memoir, The Road to Lithium Lodge, sent Chingwaru in search of his Zimbabwean roots when he was 17. He visited the remains of Lithium Lodge in Masvingo province and the nearby Bikita open-pit mine, which is still in operation.
On his return, he won a scholarship to study civil engineering in Russia, but when he was unable to obtain a visa he took a gap year, which he spent working at Edgars. “I’ve always had an interest in mining, so I guess I inherited my grandfather’s passion,” he says. “That’s why I then decided to study geology at Stellenbosch.”
Geometallurgy grabbed his imagination when it cropped up for the first time in his honours year. It’s a field that Chingwaru says is growing in importance as the quality of mined ore falls. He recalls attending a conference where a presenter explained that “high grade” gold ore now yields as little as 5g/ton, compared with 40g in the relatively recent past.
“Geometallurgy is understanding your material in terms of its grade and, importantly, its mineralogy, because a lot of the low-grade material is controlled by mineralogy. So if you understand the mineralogy, you can then understand how to process your material,” he says.
It means a lot of time in the lab, which suits Chingwaru — “I don’t enjoy going into the field for weeks on end and getting sunburned” — but it’s the intellectual challenge that interests him most.
“It doesn’t have a straightforward approach. You have to come up with a strategy in order to find the cheapest sustainable way to get the most relevant results. And with technology growing as it is, you’re always going to come up with new ideas to approach certain problems.”
Chingwaru’s breakthrough in his paper involves the use of new technologies to show that most of the invisible gold in tailings samples from four dumps — Carletonville, Central Rand, Evander and Klerksdorp — is found in pyrite (“fool’s gold”), the most common sulphide mineral on Earth, and arsenian pyrite.
“Targeted remining” will improve gold recovery, leave valuable byproducts in the form of heavy metals such as copper, cobalt and nickel, and reduce or even eliminate the heavy metal pollution and acid mine drainage associated with tailings dumps, he says.
“When sulphides become oxidised, they produce sulphuric acid, and when that goes into the groundwater it becomes toxic,” Chingwaru says. “It’s a big problem now in Joburg, where they’re scared that their groundwater is becoming very polluted with tailings acid mine drainage, particularly from historical unlined storage facilities.”
Technological progress has also delivered a way to free gold from sulphides that surround them. Biological oxidisation uses bacteria to perform this process naturally, and the first “biox” plant has processed ore at Fairview mine in Barberton since 1986.
The world’s biggest biox plant — at an open-pit gold mine in Uzbekistan — processes 2,100t of material daily, meaning it would take thousands of years to work its way through the Witwatersrand tailings.
But as Chingwaru tells the FM, the technology will gradually become a more attractive option as mines’ ore yields drop and costs increase. “You might have to build multiple huge [plants] to process all this material. But I think slow and steady sometimes wins the race, because this stuff has been sitting for over a century doing nothing.”
RioZim’s new biox plant at its Cam & Motor gold mine in Zimbabwe went into full production last April and is expected to make a significant difference to the mine’s viability for an investment of only $17m. The material it unlocks will add to the 3.5% of global gold produced using biotechnology.
Chingwaru’s doctoral research continues, and his next paper will describe the methodology he used to quantify invisible gold in the dumps that have multiplied in the Witwatersrand over nearly 140 years of mining.
Using new technologies to find invisible gold would allow for ‘targeted remining’, improving gold recovery and leaving valuable byproducts — potentially without acid mine drainage
— What it means:
“These tailings are not governed by any sort of mineralisation. It’s just random. It’s crushed stuff which has just been dumped,” he says. “You have to find a statistically relevant way to analyse them, because if you go ahead without a game plan your results are useless. You’ve wasted a lot of money and you’ve wasted your own time.”
He’s also working with Tadie, co-holder with Von der Heyden of the African Rainbow Minerals geometallurgy research chair at Stellenbosch, on ways of analysing the contents of slimes dams.
“There are technological limitations for analysing very fine-grained material because even automated electron microscopy has a grain-size limitation or a pixel-size limitation,” he says. “We’re trying to do chemical tests in order to quantify gold in the slimes fraction.”
Von der Heyden says interest in his student’s findings so far goes beyond mining and environmentalism. “The insight that most of this gold is locked in detrital sulphides that formed more than 2.8-billion years ago is of interest to scientists studying the early Earth and the formation of the super-giant world-class Witwatersrand gold endowment,” he says.
He’s looking forward to seeing Chingwaru’s career and reputation grow with the continued support of the Centre of Excellence for Integrated Mineral & Energy Resource Analysis, funded by the department of science & innovation and the National Research Foundation.
“Steve has always been a standout student who has the ability to ask insightful questions coupled with a devout work ethic that ensures he can find answers to these questions in an efficient and scientific manner,” he says.
Within the next few years, Chingwaru expects the answers he has found to start finding application. “I went to the Mining Indaba in Cape Town in February and realised there is a big move towards sustainable mining,” he says. “More efficient reprocessing of tailings can be part of that.”
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