Underground Mining Methods

Generally, orebodies are either vein-type, massive or tabular in shape. This, together with ore thickness and regularity, will influence the mining method selected.

Vein-type orebodies usually dip steeply, allowing ore to fall to a lower mining level where it can be loaded. The orebodies are usually narrow and often irregular, so care must be taken to avoid mining barren wall rock. They are most sucessfully mined by small-scale-underground stoping.

Massive orebodies are large and usually have an irregular shape. Underground bulk mining methods, with large stopes, are best suited to this type of orebody.

Tabular orebodies are flat or generally dipping and the ore, having nowhere to fall, must be handled where it is blasted. Thicknesses of the orebodies vary. Room-and-pillar mining is normally used to extract the ore. Depending on the thickness and lateral extent of the ore, these types of deposits tend to be moderate- to high-tonnages producers.

The strength of the ore and the rocks surrounding an orebody also influence the method (and therefore the costs) used to mine the orebody. Openings may be supported or self-supported. Some supported openings are held up by backfill, waste rock or aggregate placed in the openings shortly after they are mined out. Others are held up by timber sets, supports made of timber or steel, although this kind of mining is costly and is little used today. 

Self-supported openings stand up with little artificial support. The walls and pillars are of sufficient strength to carry the weight of rock above them and the horizontal stresses in the rock caused by tectonic forces — although the miner may help them along with rock bolts and screening. In massive orebodies, it is common to plan for the mining of pillars. This is done by backfilling the mined-out stopes to provide the necessary support when the pillars are mined.