Mineral processing involves the processes used to manipulate the particle size of solid raw materials and to separate valuable materials from materials of no value, referred to as gangue.
Tailings (the materials left over after the removal of the uneconomic fraction (gangue) of the ore) also provide some of the archaeological evidence from Otago gold mine sites.
Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Palaeoproterozoic age limestones in Sweden's Persberg mining district.