What is mine drainage and how does it occur?

[music fades in]

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. 

And now you know. Join us again every weekday for a new CoreFact. For other CoreFacts, or for CoreCast, our in-depth science podcast, go to usgs.gov/podcasts. If you'd like to have a question featured on our show, give us an email at corefacts@usgs.gov or a phone call at 703-648-5600. Remember, long distance fees do apply.

CoreFacts is a product of the U.S. Geological Survey, Department of the Interior.

[music fade out]