The generation of sulphate and acidity as a result of the oxidation of pyrite when exposed to water and oxygen, producing sulphuric acid (H2SO4).
Drainage of water from areas that have been mined for coal of other mineral ores; the water has low pH, sometimes less than 2.0 (is acid), because of its contact with sulphur-bearing material; acid drainage is harmful to the environment.
AMD is a major cause of the contamination of groundwater in areas where coal and gold mining takes place.