ANCHORAGE - Cyanide seepage was discovered this winter next to a dam that holds back waste from the Fort Knox Mine near Fairbanks.
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The mine operator, Fairbanks Gold Mining Inc., has spent about $2.5 million to deal with the seep, said Dan Snodgress, the mine's operations manager. The chemical didn't spread beyond the mine site, but it prompted a flurry of construction and water testing at Fort Knox, the state's largest gold mine.
State environmental regulators and the mine "treated it as a full-blown problem," said Tim Pilon with the Alaska Department of Environmental Conservation. He said the mine reacted appropriately and the state didn't impose a fine.
Cyanide, potentially lethal in high doses, is used to separate gold from ore. Fort Knox, which produced more than 333,000 ounces of gold last year, is a zero-discharge mine, meaning no pollutants are allowed to escape.
Since the discovery of the seep in late December, none of the more than 1,000 water test results indicate cyanide entered water downstream of the dam - in Fort Knox's freshwater reservoir or in nearby fish-bearing wetlands and ponds, state regulators said this week.
Cyanide has not been detected in the mine's outlying monitoring wells, either, according to company officials.
Testing continues in various locations downstream of the tailings dam, regulators said.