While some acid mine drainage is the result of weathering the major influence is the action of acid forming bacteria such as
- Acidithiobacillus ferrooxidans (also known as. Thiobacillus ferrooxidans) found in pyrite deposits where it metabolizes iron and sulfur to produce sulfuric acid.
- Acidithiobacillus thiooxidans (also known as Thiobacillus thiooxidans, Thiobacillus concretivorus) which consumes sulfur and sulfides to produce produces sulfuric acid.
The sulfur and iron compounds are common in many ores and coal deposits and the waste deposits resulting from their extraction.