From the Porgera goldmine in the highlands of Papua New Guinea around 14,500 tonnes of waste is discharged into the Porgera River every day.
The tailings are the byproduct of production that last year totalled 436,000 ounces of gold worth about US$650 million at today's prices and equivalent to about 1kg for every 4 tonnes of tailings.
These days tailings from goldmines are normally stored behind dams, but in the wet, mountainous terrain at Porgera there was no way a dam would last. According to the mine's 95 per cent owner Barrick Gold, "any structure to store fine-grained and saturated materials that was close enough to the mine to be feasible would fail, the only question being when".
So the river was the only solution. It means Porgera is today one of just four mines in the world to unload its tailings straight into a river - all of them on the island of New Guinea, three on the Papua side, one on the Indonesian side.
The reason so few mines use riverine tailings disposal is simple - the method is associated with huge damage to the environment as minerals, chemicals and silt contaminate river systems.
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