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.

Back to the start

What makes Chingwaru’s discoveries even more remarkable is his challenging upbringing.

Chingwaru’s father died before he was born, so young Steve and his siblings were brought up by their entrepreneur mum, Peggy, in Harare, Zimbabwe.

Things started well enough, with Chingwaru attending a prestigious boarding school in Bulawayo. But the 2008 economic downturn hit Zimbabwe – whose economy was already in an imperilled state – particularly hard, leading to a hyperinflation crisis that left people queueing for everyday items like bread and cooking oil. School fees became unaffordable, and Peggy was forced to sell the family home to stay afloat.

“I didn’t see a future for myself in Zim,” remembers Chingwaru, who was 10 or 11 at the time. “It was my decision to move to South Africa.”

Moving to South Africa to live with his aunt and her children was, he admits, “scary at first, but when I got there, it was OK”, understating the challenges he faced. The first school he went to in South Africa was so far from his aunt’s place that he had to wake up at 4am to get there on time. Commuting on overcrowded trains meant he’d often get home after dark and still have to do his homework. Tough as it was, there was never a question of giving up. “As a kid you just do it,” he says. “I liked school. And my mom always told me ‘If you go to school everything will be all right.’”

Once Chingwaru had transferred to a school that was within walking distance of his aunt’s home, he began to thrive – making many friends, dabbling in swimming and athletics, and excelling in the classroom. He did so well, in fact, that he got an award for coming first in the region for geography in his final exams.

As if this wasn’t enough of a career nudge, Chingwaru also had unfinished family business with the earth’s crust. In his final year of high school, he returned to Zimbabwe to see family and ended up visiting the ruins of Lithium Lodge, the grandiose mansion built by his grandfather, the larger-than-life prospector George Henry Nolan, in the 1950s. Despite being the first person to discover lithium in Zimbabwe, Nolan ended up losing most of his fortune – and his home was bombed during the Second Chimurenga (the Zimbabwean War of Liberation).

“I didn’t know I had this rich history,” says Chingwaru. “And I had no idea I had so many cousins … My grandfather had five wives.”

Moving on up

After high school, Chingwaru decided to move once again – “I’d had enough of Jo’burg,” he says – this time to the leafy and predominantly Afrikaans university town of Stellenbosch. “It was very different to anywhere I’d lived before,” he remembers. “But I liked it a lot. There are loads of trees. You can walk everywhere.”

Chingwaru’s success in high school geography led him to the university’s highly rated Earth Sciences department. The possibility of his degree landing him a lucrative career as a mining geologist was another driver.

He excelled academically, but he also found time to wait tables and pull pints, to indulge his passions for gaming and anime, and to go for thrice-weekly runs. On top of it all, he also maintained a very active social life.

“He’s super personable,” says his PhD supervisor Bjorn von der Heyden. “His number one attribute is that he is so nice and caring.” Von der Heyden, who first encountered Chingwaru as an undergraduate, was instantly impressed by the intelligent questions he asked in class – and the unsolicited mentoring he provided to other students. While he is softly spoken, Chingwaru “doesn’t fade into the background, because he gets involved and is genuinely interested in other people”, says von der Heyden.

After completing his honours with another professor, Chingwaru signed up for his master’s with von der Heyden. “He put together some great results, using really advanced techniques, that enabled him to upgrade to a PhD,” says von der Heyden. “Upgrading is a risk because you can end up with nothing if it goes wrong. I only offer it to my most exceptional students.”

Chingwaru didn’t just obtain his PhD – he did so in record time, finishing a full year ahead of schedule. “There were lots of late nights and cancelled weekends,” he remembers. “At one point, I thought I wouldn’t make the [self-imposed] deadline, but I pushed through.”

What made it even more demanding – but also more interesting – was the multidisciplinary nature of geometallurgy. “I was going to the tailings to collect sand. Doing lab work with cyanide and lasers. Data processing. Going to conferences. I taught myself statistics.”

When the time came to defend his PhD in front of a panel of experts, Chingwaru didn’t contemplate being nervous. Not only had he been presenting “for years”, he says, but he realised that “I know my PhD better than anyone else … I can answer anything they throw at me.”

Where to now?

With a PhD in his pocket, a flurry of media coverage – many Zimbabwean and South African news outlets seized on the $24bn figure – and job offers in five countries, the world really does appear to be Chingwaru’s oyster. While Von der Heyden insists that “there is no wrong answer for someone of his calibre”, Chingwaru is weighing his career options carefully.

On one side of the scale is his desire to experience new countries and cultures. On the other: his ambition to take his PhD research beyond the page and get involved in the extraction work itself. “On paper, it all seemed so simple,” he says. “When I was on the plants I realised it was way more complicated than I thought … I’m always up for a challenge.”

Whatever shape his career takes, Chingwaru says he is passionate about using his skillset to help the mining industry embrace a more sustainable future. Reprocessing the Witwatersrand tailings, for example, could have significant health benefits for the people of Johannesburg – especially, Becker says, “if there is a viable business case to remove the gold, the sulphur associated with pyrite, and any remnant uranium”.

While he is focussed on getting some real-world work experience, Chingwaru is equally adamant that he will sign up for a postdoc at some point in the future. “I am an academic at heart,” he says.

This will be music to Becker’s ears – “We need more fundamental research like this that not only characterises the material, but also investigates techno-economical options for processing. We need lots of ideas to ultimately develop, in partnership with industry, viable solutions … The importance of university research cannot be underestimated.”

Shortly before going to print, Chingwaru informed Al Jazeera that he had accepted an offer from the Institute of Sustainable Minerals at the University of Queensland in Brisbane, Australia. He took the job because it will allow him to combine working with industry – mainly extracting “battery metals” from tailings – with a postdoctoral research project.

He’s also “looking for adventure”.