Gold Mining · Today
Modern Industrial Gold Mining
Open pits, cyanide leaching and mining gold at a few grams per tonne
Most gold today comes from ore so poor you cannot see the metal in it. Here is how giant open pits and chemistry pull gold from rock at a molecular scale.
The gold rushes chased visible gold, nuggets and dust you could hold. Modern gold mining is almost the opposite: it profitably extracts gold from ore containing just a few grams per tonne, invisible to the eye, using enormous scale and industrial chemistry. Global mine production now runs around 3,300 tonnes a year.
The open pit
Where gold is spread thinly through near-surface rock, the cheapest approach is the open-pit mine: a vast terraced hole, sometimes kilometers across, worked by some of the largest machines on earth. Haul trucks the size of houses move ore to crushers around the clock. The trade-off is footprint; open pits consume and reshape huge areas of land.
Where the ore is richer but deeper, mining goes underground again, and the Witwatersrand in South Africa hosts some of the deepest mines on the planet, several kilometers down, where the rock itself is hot.
Cyanide: the chemistry of low-grade gold
The breakthrough that made low-grade mining possible is cyanidation. Crushed ore is treated with a dilute cyanide solution, which dissolves the gold. Two main variants dominate:
- Heap leaching: ore is piled on huge lined pads and sprayed with cyanide solution that trickles down, dissolving gold as it goes. The "pregnant" solution is collected at the base.
- Tank leaching with carbon-in-pulp (CIP): finely ground ore is stirred with cyanide in tanks, and the dissolved gold is captured onto activated carbon, then stripped off and refined.
More than 85 percent of the world's newly mined gold now relies on cyanidation in some form.
The environmental ledger
Cyanide is highly toxic, and mine tailings can carry heavy metals. Well-run operations neutralize and contain their cyanide and line their tailings dams, but failures, dam collapses and leaks, have caused serious pollution incidents. Mercury, largely retired from industrial mining, is still widely and dangerously used in artisanal and small-scale mining across the developing world, a major source of global mercury pollution.
Who mines the most
The leading producers today are China, Russia, Australia, Canada and the United States, with China consistently the largest. Unlike the rush era, this gold is produced by multinational companies operating under (varying) environmental regulation, and it feeds directly into the modern gold market.
Modern mining is the industrial endpoint of a journey that began with a pan in a creek: the same dense yellow metal, now extracted from rock that a forty-niner would have thrown away.
