Sulfide mining

Sulfide mining a colloquial term used in Wisconsin, Michigan, and Minnesota to describe the act of mining of ore which contains significant quantities of sulfide minerals.

Copper, lead, zinc, and nickel ores are typically present in the sulfide minerals chalcopyrite, galena, sphalerite and pentlandite respectively, these minerals are often found with often appreciable amounts of pyrite.

From http://en.wikipedia.org/