Hunting For Gold In World's Deepest Mine

Naashon Zalk | Bloomberg | Getty Images The deepest mine in the world. The Mponeng mine owned by AngloGold Ashanti, just one hour outside of Johannesburg.

There's almost no surface gold left on earth. Yet with increasing demand for the precious metal, miners are forced to drill deeper, at higher costs, and greater danger.

Approximately 2.2 miles deep, the Mponeng mine west of Johannesburg, South Africa, is the deepest in the world and is run by AngloGold Ashanti

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[AU'A  Loading...      ()   ]. AngloGold says deeper drilling means higher costs.

"We're struggling to find new gold. We're spending twice as much money on an annual basis, and still only finding less than we did the year before. And so, the supply side is really constrained," says Mark Cutifani, CEO of AngoGold.  

For the drilling business, high costs are also met with increasing physical danger. About 2.2 miles under the surface, an underground an army of miners blast through the ore, and the closer to drilling, more dangerous it becomes. Inside the deepest mine, the dangers are three-fold:

Heat. The deeper it gets, the hotter is gets. It is almost 100 degrees farenheit inside the Mponeng mine — while cooling machines are running.

Seismic activity. Even small amounts of seismic activity can produce disturbances in the rock and in the drilling support structure.

Methane gas explosions. Dangerous and hazardous, methane levels are constantly monitored.

Yet despite these dangers, Mponeng 's miners produce an estimated 550,000 ounces of gold a year, and can produce about 1,700 ounces of gold a day. Gold is then transported to the surface, and smelted on site into a bar of about 90 percent purity, destined for the Rand refinery in Johannesburg, City of Gold, and ultimately for the global gold market.