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What is mine drainage and how does it occur?

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Welcome to CoreFacts, where we're always short on time and big on science. I'm Danielle Eganhouse. Today's question is an interesting one.

What is mine drainage and how does it occur?

Mine drainage is metal-rich water formed from a chemical reaction between water and rocks containing sulfur-bearing minerals. Or more specifically, mine drainage occurs when pyrite is exposed and reacts with air and water to form sulfuric acid and dissolved iron.  Some or all of this iron can precipitate to form the red, orange, or yellow sediments in the bottom of streams containing mine drainage. The runoff formed frequently comes from areas where ore- or coal mining activities have exposed rocks containing pyrite and can further dissolve heavy metals such as copper, lead, and mercury into ground or surface water. However, metal-rich drainage can also occur in mineralized areas that have not been mined. 

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