waste rock
Waste rock is rock that has to be moved to reach the ore but does not contain enough valuable mineral to be worth processing. It is usually piled up on the surface near the mine.
Technically: Waste rock is material excavated during mining that does not meet the cut-off grade required for processing and is therefore discarded, typically to surface dumps. It is distinguished from tailings by the fact that it has not been milled: it remains coarse-grained and has not been subjected to processing reagents. Where waste rock contains sulfide minerals, oxidation upon exposure to air and water can generate acid mine drainage, making the geochemical characterisation of waste rock a standard component of environmental assessment.
Mining