Mercury has a chemical affinity for precious metals, which is why gold mines are the world's number two source of mercury pollution

Historically, mercury was used in large quantities in all types of gold mining. Since the 1960s, large gold mines have mostly shifted away from the use of mercury, but it is still very popular with small-scale miners. In addition, much of the mercury expelled into the environment from large mines in earlier decades remains there to this day; an estimated 45,000 metric tons used in California gold mines, for example, have yet to be recovered.

Because gold also dissolves well in a solution of potassium cyanide, many modern mines treat their ores with cyanide instead of mercury; therefore, gold mining is also a major source of cyanide pollution worldwide.

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