Digging up ore displaces huge piles of earth and rock. Processing the ore to produce metals generates immense quantities of additional waste, as the amount of recoverable metal is a small fraction of the total ore mass. In fact, the manufacture of an average gold ring generates more than 20 tons of waste.
Many gold mines employ a process known as heap leaching, which includes dripping a cyanide solution through huge piles of ore. The solution strips away the gold and is collected in a pond, then run through an electro-chemical process to extract the gold.
This method of producing gold is cost effective but enormously wasteful: 99.99 percent of the heap becomes waste.
Gold mining areas are frequently studded with these immense, toxic piles. Some reach heights of 100 meters (over 300 feet), nearly the height of a 30-story building, and can take over entire mountainsides.
To cut costs, the heaps are often abandoned. Contaminated water, containing cyanide and other dangerous chemicals, can often contaminate groundwater and poison neighboring communities such as Miramar, Costa Rica.
Metal Mining was the number one toxic polluter in the United States in 2010. It is responsible for 1.5 billion pounds of chemical waste annualy- more than forty percent of all reported toxic releases. In 2010, metal mining released the following in the United States: