Hard rock mining refers to various mining techniques used to excavate hard minerals such as those containing metals like gold, copper, zinc, nickel and lead or gems such as diamonds. In contrast soft rock mining refers to excavation of softer minerals such as coal, or oil sands.
Small hard rock crushers produce 100-300 tons of aggregate per hour, medium hard rock crushers 300-600 tons and large hard rock crushers 600-1,000 tons per hour. The biggest hard rock crushing plants can produce more than 2,000 tons of aggregates per hour. It takes 25,000-50,000 tons of aggregate to build an asphalt road that is one kilometer long and ten meters wide.
Mobile, semi-mobile and stationary hard rock crushing plants are in operation all around the world. Mobile crushing plants are built ready-mounted on their own travel gear. Semi-mobile crushing plants are moved from one location to the next as a piggyback load on separate haul units. Semi-mobile crushing plants are always to be recommended when there are long periods between changes of location. Each crushing plant comes ready to operate with its own feed hopper, feed conveyor, discharge conveyor and material transfer belt. The size and design of the crusher naturally depends upon the work that it is intended for.