Tarnishing the Earth: Gold Mining's Dirty Secret. (Focus)
Fields, Scott, Environmental Health Perspectives
Gold mining may bring to mind images of grizzled prospectors prodding stubborn, overloaded burros or standing knee-deep in cold California steams, panning for nuggets. Modern gold milling, however, is a machine- and chemical-intensive endeavor in which hundreds of tons of rock are moved and processed for every ounce of gold extracted. "It's common now to talk about a one billion ton open-pit mine," says Glenn Miller, a professor of environmental and resource sciences at the University of Nevada at Reno.
According to the Worldwatch Institute, all mineral mining in Canada generates 650 million tons of waste per year. Miller estimates that each year gold milling alone in the United States generates about 1 billion tons each of waste rock and tailings (the finely ground remains of milled ore), numbers that have actually gone down in recent years, due to the drop in gold prices and the scarcity of high-grade ore.
The gold nuggets and rich veins of gold of a hundred years ago are tapped out, and today's miners work deposits containing as little as 0.015 ounce of gold per ton of rock, in the process excavating as much as 4 billion tons of rock during the course of a mine's often short working life, Miller says. These massive operations bring with them new potentials for environmental damage including accelerated acidic runoff, accidental waste releases, and leachate that can infiltrate waterways and aquifers.
By no means, however, are modern megamines the only, or perhaps even primary, source of environmental damage. Long-abandoned North American gold mines and contemporary small-scale artisanal mines in the Amazon are an ongoing source of mercury, which is bioaccumulating in food fish.
As the extent of damages from mining becomes more apparent, scientists, engineers, and regulators are investigating ways to mitigate the impacts of old mines and prevent current and future mines from developing similar problems. The most environmentally responsible gold mining companies are spending millions of dollars restoring the sites of closed mines and developing technologies to minimize the impacts of current mines. But many of these techniques are unproven in the long term or have already been proven ineffective, environmentalists warn.
A better solution, they say, is to site gold mines in only the driest and most seismically stable locations possible and to reduce gold consumption, because most--as much as 90% by some estimates--goes to nonessential applications such as jewelry. "There's no point in destroying communities, the environment, the water that we drink to mine a mineral that has no particular use other than to fulfill certain cultural fantasies," says Catherine Baldi, information coordinator for Project Underground, an extractive industry-focused environmental group based in Berkeley, California.
Acid Mine Drainage: Eating Away at the Environment
In the United States and Canada, gold mines--some more than 100 years old, some recently closed, and some active--are leaking acidic water, resulting in hundreds of millions of dollars in remediation costs. U.S. Environmental Protection Agency (EPA) officials estimate that 40% of western U.S. watersheds are affected by mining pollution. There are more than 25 mines, some of them active, on the U.S. Superfund list.
Of all the environmental hazards that gold mining presents, the mining industry and environmentalists agree that acid mine drainage (AMD) is by far the most serious. AMD is a process in which acidic water is produced from the combination of sulfide minerals (such as pyrite, marcasite, and chalcopyrite), water, air, and highly specialized bacteria.
Naturally occurring acid rock drainage has been around as long as sulfide minerals, air, and water have, and anthropogenic AMD dates back to at least the Middle Ages. But new techniques in mining in the last three decades have produced a virtual flood of acid water throughout the American West, Canada, and overseas, resulting in billions of dollars of expenses to mining companies and, more often, taxpayers. …