<P> In cases where drainage from a mine is not acidic and has dissolved metals or metalloids, or was originally acidic, but has been neutralized along its flow path, then it is described as "Neutral Mine Drainage", "Mining - Influenced Water" or otherwise . None of these other names have gained general acceptance . </P> <P> Sub-surface mining often progresses below the water table, so water must be constantly pumped out of the mine in order to prevent flooding . When a mine is abandoned, the pumping ceases, and water floods the mine . This introduction of water is the initial step in most acid rock drainage situations . Tailings piles or ponds, mine waste rock dumps, and coal spoils are also an important source of acid mine drainage . </P> <P> After being exposed to air and water, oxidation of metal sulfides (often pyrite, which is iron - sulfide) within the surrounding rock and overburden generates acidity . Colonies of bacteria and archaea greatly accelerate the decomposition of metal ions, although the reactions also occur in an abiotic environment . These microbes, called extremophiles for their ability to survive in harsh conditions, occur naturally in the rock, but limited water and oxygen supplies usually keep their numbers low . Special extremophiles known as Acidophiles especially favor the low pH levels of abandoned mines . In particular, Acidithiobacillus ferrooxidans is a key contributor to pyrite oxidation . </P> <P> Metal mines may generate highly acidic discharges where the ore is a sulfide mineral or is associated with pyrite . In these cases the predominant metal ion may not be iron but rather zinc, copper, or nickel . The most commonly mined ore of copper, chalcopyrite, is itself a copper - iron - sulfide and occurs with a range of other sulfides . Thus, copper mines are often major culprits of acid mine drainage . </P>

What element in pyrite contributes to acid mine drainage
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