Cyanide Gold Mining in West Raises Specter of Ground-Water Pollution
Cyanide, the infamous darling of mystery writers, murderers and madmen, is every bit as deadly as reputed. A speck the size of a grain of rice will kill an adult in seconds.
But it is a workhorse as well. Gold miners are buying it by the barrel, by the truckload, by the ton. About 25 million pounds of it were sold in Montana alone last year.
Cyanide is the crucial ingredient in the recent, worldwide gold-mining boom. In Montana, it’s being used in nine big mines and at least 10 small ones. Its presence is making a lot of people very nervous.
The anxiety stems from the practice of cyanide leaching. Dissolved in water, cyanide will melt gold and silver out of otherwise unprofitable ore--rock that holds perhaps 0.02 or 0.03 of an ounce of gold per ton.
In essence, the miners pile up a lot of ore, pour diluted cyanide through it and collect the gold-laden solution below.
Cyanide leaching was used widely, but crudely, by small mine operators in Montana from the 1890s until about the 1930s. That history is partly what is making people nervous now.
"(The early miners) left ponds full of cyanide and ore full of cyanide, in many, many locations,” said Kevin Keenan, an investigator with the Montana’s Water Quality Bureau.
The boom began about 20 years ago, after U.S. Bureau of Mines research showed how the leaching process could be refined.
“The technology made it feasible to remove small amounts of gold from ore,” said Keenan. “In fact, we saw a lot of companies in the ‘70s wanting to reprocess old tailings.”
Montana has adopted stringent environmental protections, and so today’s miners must follow rules their predecessors did not. Nevertheless, spills have occurred, and millions of gallons of cyanide solution have poured into the earth.
The Montana Department of State Lands estimated that three-fourths of all cyanide leaching operations have leaked. And recovering a spill is a major problem.
“It’s like spilling a dump truck full of marbles and then trying to pick them all up by hand,” Keenan said. “You’re looking at an extremely complicated process. The marbles may be simpler, in fact, because you can see them.”
Mining representatives say that there has been no known case of cyanide causing a mining-related death.
As deadly poisons go, cyanide is oddly benign. It doesn’t accumulate in body tissues as most poisons do, so the body quickly recovers from a less than lethal dose. Cyanide occurs naturally in many forage plants and breaks down quickly in sunlight and oxygen. Common soil organisms convert it to harmless substances in most instances, sometimes to fertilizers.
Waste cyanide solutions used in gold leaching, after they are neutralized as much as possible, are often sprayed onto surface soil.
The Du Pont Co., the largest U.S. producer of cyanide, said U.S. production last year totaled about 160 million pounds. About 80 million pounds of that went to Nevada, the source of 65% of domestic gold production.
“So there’s a lot of cyanide out there, and with that kind of exposure, there have been no significant environmental problems at all,” said Tim Fitzpatrick of Denver, Du Pont’s environmental manager for mining.
Environmentalists say the rising number of cyanide operations is escalating the risk of a major accident occurring.
“The technology to do heap leaching developed much faster than the technology for handling the materials,” said Jim Jensen of the Montana Environmental Information Center in Helena.
Although cyanide on the surface quickly breaks down, environmentalists note, cyanide below ground--away from sunlight, oxygen and microorganisms--can last indefinitely.
There also is the problem of unknown chemical reactions. The chemical process in leaching is so complicated that it is not yet fully understood.
“There are about 50 different cyanide-related reactions that can take place in a heap, depending on the particular ore chemistry, the water chemistry at the site and . . . the soil chemistry,” said Sandi Olsen, chief of the state’s hard rock mining bureau.
“No matter how much studying you do, there’s no way you can ever pin down entirely the geology and hydrology of an area,” Olsen said. “In some respects, the ground is the classic black box: You put something in it and you never quite know what’s going to come out the other end.”
And there is the danger of cyanide poisoning in the wild.
“Cyanide is so toxic that a concentration of less than one-tenth of a part per million, though it would have no effect on a human, it would on aquatic organisms,’ said Frank Munshower of Montana State University. “So if it gets into a ground water system feeding into a fishery resource, it’s potentially a major problem.”
Mine operators place their confidence in protective measures. The Mineral Hill Mine at Jardine, just north of Yellowstone National Park, is in the most environmentally cherished part of Montana. The safeguards it observes may be the most elaborate of all.
Mineral Hill is an underground mine that leaches ore in vats, not in open-air heaps, said administrative superintendent John Hoak, himself a wildlife biologist.
The mill was purposely “over-designed, with the primary consideration given to protection of the environmental qualities,” Hoak said. That included precautions against earthquakes.
Mineral Hill’s tailings are triple-washed and triple-filtered with a patented cyanide-destruction process, then buried in a closed, lined impoundment of about six acres, Hoak said. Because the mine’s permit forbids it to release cyanide solution, used solution is re-charged with cyanide and recycled.
“I think you’ll find that the mining industry as a whole has turned the corner quite some time ago with regard to recognizing that the environmental costs and the costs of protecting the environment are part of the cost of doing business,’ Hoak said.
Regulators tended to give the larger operations high marks for putting money behind the rhetoric.
“The larger facilities . . . still have problems, and they still represent major regulatory consumers, in terms of time, when they have a problem,” Keenan said, “but at least they . . . can present the kind of funds for correction of the problems that they encounter.”
The Golden Sunlight mine, south of Helena, is a showcase operation, yet several million gallons of cyanide-laced water leaked around an underground slurry wall almost as soon as it began operations in 1983.