Gold mining is usually done using an open pit method, using cyanide to leach the gold out of the rock. This means that companies excavate rock out of big holes in the ground, pile the rock, and apply cyanide to remove the gold. Read more here.
Acid rock drainage or acid mine drainage is a problem that often happens with gold mining. When rock high in sulfide content is exposed (which happens frequently in areas with gold deposits, as iron sulfides are commonly known as ‘fool’s gold’) to water or air, sulfuric acid is produced. This acid is toxic in itself and also leaches other toxic heavy metals from nearby rock, including arsenic and lead. This process is extremely difficult, nearly impossible, to stop once it has begun. This is what has happened at Gilt Edge Superfund. Learn more in the section on Acid Mine Drainage here, and read specifically about the contamination at Gilt Edge and Richmond Hill here.
Many of the below companies are re-raping the land. Agnico, Coeur/Wharf, and Golden Meadow are all examples of exploratories looking to mine AGAIN, in areas that have already been mined, near waters that have already been contaminated. Agnico and Coeur/Wharf are trying to re-mine old mines that are contaminated with acid rock drainage.
Waters to be concerned about: Strawberry Creek, Bear Butte Creek, Whitetail Creek, Whitewood Creek, Fantail Creek, Deadwood Creek, Annie Creek, Spearfish Creek, Cleopatra Creek, False Bottom Creek, Rapid Creek, Redwater River, Belle Fourche River, Cheyenne River, and ALL AQUIFERS and HEADWATERS.