JOHANNESBURG—Miners are sifting through the detritus of a century-long gold rush here, scavenging through 150-foot-high mounds of discarded ore for traces of gold they may still contain.
The mounds are the legacy of a mining industry that has yielded nearly half of the world’s gold bullion and jewelry since the precious metal was discovered here in the late 1880s. After digging out raw ore from the ground, miners extract what gold they can from the mix, leaving behind hills of discarded ore as waste.
Over the years, these mounds—many now overgrown with scrub or abutting shantytowns—have been subsumed by the sprawling city, becoming part of its geography. But the mounds still contain trace amounts of gold. Until recently, going back for those scraps wasn’t worth the trouble.
Today, though, companies like DRDGold Ltd. are using high-powered water cannons to blast many of the towering dumps open again, pushing their contents through miles-long pipes to processing plants that can extract tiny gold remnants.
While gold prices have fallen sharply from their all-time high in late 2011, they are still buoyant enough to make the effort profitable. Executives also style the work as part of a cleanup drive, ridding the city of waste that irritates eyes and throats and contains cyanide, a chemical used in conventional mining, and uranium that is latent in the dug-up earth.
“Hopefully one day, 20 years from now, all the mine dumps in Johannesburg will be gone,” said Niël Pretorius, Chief Executive of DRDGold, the biggest company here focused solely on reprocessing mine waste.
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