Underground hard-rock mining

Soft-rock mining refers to the excavation of softer minerals, such as salt, coal, and oil sands.

Accessing underground ore can be achieved via a decline (ramp), inclined vertical shaft or adit.

Declines are often started from the side of the high wall of an open cut mine when the ore body is of a payable grade sufficient to support an underground mining operation, but the strip ratio has become too great to support open cast extraction methods.

Development mining is composed of excavation almost entirely in (non-valuable) waste rock in order to gain access to the orebody.

There are six steps in development mining: remove previously blasted material (muck out round), scaling (removing any unstable slabs of rock hanging from the roof and sidewalls to protect workers and equipment from damage), installing support or/and reinforcement using shotcrete or other supports, drill face rock, load explosives, and blast explosives.

Typically, long hole mining requires two excavations within the ore at different elevations below surface, (15 m – 30 m apart).

Ventilation is the primary method of clearing hazardous gases and/or dust which are created from drilling and blasting activity (e.g., silica dust, NOx), diesel equipment (e.g., diesel particulate, carbon monoxide), or to protect against gases that are naturally emanating from the rock (e.g., radon gas).

Holes are drilled into the back (ceiling) and walls and a long steel rod (or rock bolt) is installed to hold the ground together.

An orebody hosted in strong self-supporting rock may be mined by an open stoping method and an orebody hosted in poor rock may need to be mined by a cut and fill method where the void is continuously filled as the ore is removed.

These pieces of equipment may operate using diesel engines or electric motors, and resemble a low-profile front end loader.

Electrically powered LHD utilize trailing cables which are flexible and can be extended or retracted on a reel.