(1)(a) the barren rock in a mine; (b)(2) the ore deposit that is too low in grade to be of economic value at the time, but can be stored for later processing if it becomes economically feasible; (4) rock with insufficient amounts of economically valuable elements to warrant its extraction, but which has to be removed to allow physical access to the ore. Waste rock is typically blasted into smaller particles to allow its removal by truck and shovel. Disposal occurs in subaerial or subaqueous surface dumps or backfill to open pit or underground workings. In heap leaching, spent ore is sometimes referred to as 'spoils', 'gob', or 'rejects', terms which also can apply to waste materials from density separation and the wash plant.