11. What is underground mining?
Mineral deposits which cannot be economically extracted by surface mining techniques may be mined by underground methods.
Underground (U/G) mining can be applied to orebodies of any description, from tabular to massive and pipes, from relatively shallow depth to ultra-deep. The deepest operating mines today, in South Africa, are exploiting gold reefs some 4,000m below surface.
U/G mining has two primary activities: Development and Stoping.
Development is the collective name for all the tunnels in a mine, used to reach an orebody and prepare it for stoping.
“Development” is used to describe both the process of mining tunnels, and also the actual tunnels created in the process.
Individual tunnels, while they are being mined, are called development ends and also development headings.
The end of a tunnel, whether it is still being developed or has stopped, is called the face.
The floor & roof of a tunnel are often called the footwall & hangingwall.
Stoping is the process of bulk extraction of the orebody which has been accessed and made available by development. The resulting excavations are called stopes.
Mechanized mining is underground mining in which mobile equipment is used, e.g. self-propelled machines (machines with an engine).
Mechanized mining may be trackless or semi-trackless.
In trackless mining, no vehicles which run on rails are used to move rock. In these mines, rock is moved by U/G dump trucks or, sometimes, conveyors.
In semi-trackless mining, mobile equipment is used which may include hydraulic drill rigs, loaders & other machines. However, close to the production areas the rock is tipped down orepasses and waste passes to a haulage level where it is trammed in locomotive-drawn cars running on tracks. This method combines mobile machines with rail-mounted cars.