 Piles of ore rock are spread out, and pipes spray cyanide solution over the rock to leach out the gold. | Photo Credit: GBRW Mine pits can be several miles long and 1200-1800 feet deep. The larger pits generate piles of "waste," or unminable, rock hundreds of feet high weighing tens of millions of tons.
Approximately 25 open pit mines were active in Nevada in 2003. With recent record gold prices, the filing of claims and exploration for deposits has skyrocketed, particularly in Crescent Valley.
Acid Mine Drainage and Heavy Metal Contamination
The cyanide heap leaching process is a mainstay of Nevada mining: piles of ore are laid out in the middle of the desert and then sprayed with cyanide solution to remove gold. The bedrock of the Great Basin and other lands in the West contain sulfides and heavy metals. These elements are naturally occurring, and quite safe as long as they are undisturbed.
However, once open-pit mining exposes them to air and water, sulfuric acid is created, and the acid carries the heavy metals, such as arsenic, lead , mercury, cadmium, and other contaminants, into watersheds. This severe problem is known as acid mine drainage (AMD).
Where copper is mined, uranium is often present. At these sites, uranium and its daughter components radium, thorium and radon can be released. Link to Yerington.
AMD leaches from tailings and waste rock for decades or centuries, and existing sites will require monitoring and maintenance in perpetuity. This leaching contaminates scarce and precious surface and groundwater resources, threatens drinking water supplies, can cause airborne dust laden with heavy metals, and puts wildlife at risk.
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