According to the annual world gold survey by Thomson Reuters, the total amount of gold mined in
the history of the world is 171,300 tons – enough to fill a cube with 20.7-metre (68-foot) sides. But opinions differ, mainly because experts can’t agree on how much was mined by ancient civilisations, and how much is hidden in the world’s bank vaults. So it might be a little less, or a lot more; the Gold Standard Institute estimates there may be as much as 2.5 million tons hidden away out there! On top of that, the US Geological Survey estimates there is about 52,000 tons to still be profitably mined, with huge quantities locked deep within the Earth’s interior.
Answered by Giles Sparrow.