Gangue

Deaf rock, also called mass, tailings (especially in hard coal mining), overburden, intermediate (in open pit mining), segregation or secondary rock (in ore mining), refers in miners' language to rock that cannot be used.

In order to mine ore deposits, it is unavoidable to remove the surrounding rock as well. In addition, numerous shafts are necessary for mining operations in order to reach the ore veins. Coal seams are also usually not sharply defined, or there is also waste rock that is produced during the mining process. The tailings then have to be separated from the coal in the coal washing plant.

Similarly, in opencast mining, the overburden must first be removed in order to access the coal. This means that each mining operation produces waste rock, which is then stored in waste rock piles. Some of this material is used again to backfill the shafts or the opencast pits. In ore mining, the art of the miners requires that, if possible, a clean separation of ore and waste rock is ensured during the mining process in order to obtain a low slag content during the smelting process. Depending on the value and availability of the metal to be extracted, an ore content of more than 50 % for iron ores down to a few ppm for gold, for example, is worthwhile.

Old rock dumps will be partially reprocessed at a later date, as ores contained in them that cannot be separated using the former methods can now be extracted economically.

Waste rock, waste rock, waste rock or other waste rock is not to be confused with gangue. While waste rock has to be removed to get to the ore itself, after which it is directly stockpiled without further processing, gangue is the part of the ore that cannot be used and is only separated from the economically interesting ore minerals in the ore processing plant.