A New Zealand environmental group, Coromandel Watchdog, is calling for action to counter a serious risk of cyanide contamination from the tailings dam of a gold mine.
Sampling by the Waikato Regional Council indicates that cyanide in the tailings at the Golden Cross mine has regularly been 50% over the legal limit set by the council, says the environmental group. The limit is 20 parts per million, but samples have revealed consistent levels of 26 ppm to 34 ppm.
The tailings dam holds 2.9 million tonnes of tailings and 150,000 cubic metres of water. It is nearly full, and there are fears of an overflow. Despite this, the council has failed to enforce compliance by mine operator Coeur Gold NZ, says Coromandel Watchdog. In a recent letter to the environmentalists, council chairperson Neil Clarke said it was "possible" there was non-compliance, but he did "not regard the matter as critical".
"The Resource Consent requires removal of cyanide 'to reduce the potential environmental risk associated with the disposal of untreated tailings', and this is exactly the risk we now confront with the tailings water in danger of spilling out", said Watchdog spokesperson Denis Tegg. "A nearby natural spring has already been contaminated with cyanide from under the dam. There is a serious risk that further pathways for cyanide to get into waterways will be opened up by the uncontrolled ground movement under the dam."
The top of the tailings dam has slumped by nearly a metre, leaving the cyanide-laden contents only 300 mm from spilling out. For this reason, the council has required Coeur Gold to halt production, although it may now be too late.
Said Coromandel Watchdog spokesperson Mark Tugendhaft: "When a landslide was discovered under the dam last December, Watchdog called on the regional council and the government to stop the placement of further mine waste behind the dam — but we were ignored. If the dam breaches, there will catastrophic damage to the environment and property when thousands of tonnes of toxic sludge pour down the Waitekauri valley. It is outrageous that the authorities have allowed Coeur to continue to dump more waste into an unstable dam."
The emergency adds urgency to Watchdog's repeated pleas to the government that it insist that Coeur d'Alene Mines Corp (US, 80% owner of the mine) and the Todd Corporation (NZ, 20% owner) give full financial security to cover the cost of shifting the tailings to a new and safer site. Watchdog estimates the cost will exceed $100 million, but the performance bonds held now total only $12 million.
"Coeur have written off the mine as an asset and declared it unprofitable. If they walk way from their responsibilities to clean up their mess, the New Zealand taxpayer will have to pay", said Tugendhaft.
Coeur d'Alene was warned not to purchase the mine because of major structural flaws existed in the tailings dam. The warning came from Coromandel Watchdog in April 1993. Now Coeur has admitted that the ground beneath the dam is unstable; that the ground was moving at the time it purchased the mine; that movement accelerates after heavy rain; and that the integrity of the dam cannot be guaranteed. The ground has moved down slope by over 300 mm in the last four years, according to Coeur's engineers.