In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. The separation of mineral from gangue is known as mineral processing, mineral dressing or ore dressing and it is a necessary and often significant aspect of mining. It can be a complicated process, depending on the nature of the minerals involved.
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. The ease with which the ore can be separated also plays an important part. Early mining ventures, with their relatively unsophisticated methods, often could not achieve a high degree of separation, so significant quantities of minerals found their way into the tailings dumps of mines. As the value of a mineral increases, or when new and cheaper means of processing the ore are introduced it has often become worthwhile to rework such old dumps to retrieve the minerals they still contain.
Minerals that were once thought of as gangue, and were dumped as tailings, may later find a commercial use. When this happens the old dumps are often reworked to extract the wanted mineral. For example, in copper mines in the 19th century the mineral arsenopyrite was dumped until arsenic became popular as an insecticide later in the century.
- An Elementary Outline Of Mechanical Processes, by G. W. Danforth. 1912; 49. Elimination Of Gangue