What is acid rock What is acid rock drainage?drainage?

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Image: G. Plumlee, USGS

Rocks that contain useful Rocks that contain useful metals commonly contain metals commonly contain sulfide minerals - minerals sulfide minerals - minerals that combine metal with that combine metal with

sulfur.sulfur.

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Sulfide minerals in a rock sampleImage: Travis Hudson

The most common sulfide The most common sulfide mineral is pyrite - or “Fool’s mineral is pyrite - or “Fool’s

Gold” - a combination of Gold” - a combination of iron and sulfur.iron and sulfur.

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Pyrite occurs widely in Pyrite occurs widely in rocks including rocks including

disseminations through disseminations through this entire mountain.this entire mountain.

Metals-7-4Image: G. Plumlee, USGS

When pyrite comes in contact with When pyrite comes in contact with oxygen in air or water it “oxidizes” oxygen in air or water it “oxidizes” or turns into rusty iron oxides and or turns into rusty iron oxides and

sulfuric acid. Certain bacteria sulfuric acid. Certain bacteria make this process go faster.make this process go faster.

Sulfuric AcidBacteriaPyrite

Oxygen

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The sulfuric acid produced by The sulfuric acid produced by oxidation of pyrite makes nearby oxidation of pyrite makes nearby soil and water acidic - this is acid soil and water acidic - this is acid

rock drainage. Acid rock drainage rock drainage. Acid rock drainage can harm habitat.can harm habitat.

Metals-7-6Image: Travis Hudson

Acid rock drainage occurs Acid rock drainage occurs naturally and is an environmental naturally and is an environmental

concern where sulfide minerals are concern where sulfide minerals are mined. There are several ways to mined. There are several ways to

control or prevent acid rock control or prevent acid rock drainage at mines.drainage at mines.

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Image: Travis Hudson