1. What is acid rock drainage?
Image: G. Plumlee, USGS
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2. Rocks that contain useful metals commonly contain sulfide minerals - minerals that combine metal with sulfur.
Image: Travis Hudson
Sulfide minerals in a rock sample
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3. The most common sulfide mineral is pyrite - or “Fool’s Gold” - a combination of iron and sulfur.
Image: R. Busch
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4. Pyrite occurs widely in rocks including disseminations through this entire mountain.
Image: G. Plumlee, USGS
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5. When pyrite comes in contact with oxygen in air or water it “oxidizes” or turns into rusty iron oxides and sulfuric acid. Certain bacteria make this process go faster.
Oxygen
Sulfuric
Acid
Pyrite
Bacteria
Images: USGS, DeAtley Design
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6. The sulfuric acid produced by oxidation of pyrite makes nearby soil and water acidic - this is acid rock drainage. Acid rock drainage can harm habitat.
Image: Travis Hudson
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7. Acid rock drainage occurs naturally and is an environmental concern where sulfide minerals are mined. There are several ways to control or prevent acid rock drainage at mines.
Image: Travis Hudson
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