Gangue

In mining, gangue (/ɡæŋ/)[1] is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit.

[2] For example, galena, an ore of lead, is usually found in large pieces within its gangue, so it does not normally need extensive processing to remove it; but cassiterite, the chief ore mineral of tin, is usually disseminated as very small crystals throughout its gangue, so when it is mined from hard rock, the ore-bearing rock first needs to be crushed very finely,[3] and then has to be subjected to sophisticated processes to separate the ore. For any particular ore deposit, and at any particular point in time, the concentration of the wanted mineral(s) in the gangue material will determine whether it is commercially viable to mine that deposit.

In particular, oxidation of pyrite, a common gangue mineral,[4] is one of the main sources of acid mine drainage.

For example, in 2002, about 130 million tons of gangue were produced per year from coal mining in China.

The estimated cost of such projects would be up to 4 billion yuan, but would be expected to save just over 4 million tons of standard coal per year.