Using a computer model of the mine, excavation is carefully designed by the mining engineer. When constructing an underground mine, it must sink vertical or have inclined shafts or bore horizontal tunnels or adits to reach the mineral vein. Mine construction can take several years and employ several hundred people. Underground mining is virtually a world unto itself. Productive silver mines in Idaho are over a mile deep and require very specialized people and equipment.
Safety is paramount in the underground world.
Once the rock is loosened up by blasting, shovel operators selectively load ore into large trucks bound for the concentrating mill. The most common form of concentrator is the flotation mill. After being crushed, the ore passes through a series of large grinding mills. These giant drums reduce the rock to particles smaller than flour. These tiny particles are mixed with water and chemicals and sent through a series of flotation circuits.