Underground mining, also known as underground mining, consists of digging or blasting tunnels and shafts into the earth’s crust to reach buried ore bodies. Ore deposits and tailings are brought to the surface for processing at local processing plants.
Hard rock versus soft rock mining requires different underground mining methods and this should be considered when choosing the right mining method.
Three different types of access tunnels are used to extract ore:
- Drift mining: uses horizontal access tunnels.
- Slope mining: uses access shafts with a diagonal inclination.
- Shaft mining: uses vertical access shafts.
Below are the main types of underground mining methods:
- Room and pillar mining. Room and pillar mining consists of clearing a room of ore, but leaving the pillars in place to support the weight of the ceiling until the ore is cleared from the face.
- Retreat mining. Retreat mining follows chamber and pillar mining and is the process of removing the pillars from the room, thus extracting the remaining ore. This process is done strategically and can be extremely dangerous as the mine collapses in on itself during the removal process.
- Shrinkage mining. Shrinkage mining, also known as sub-floor mining, is used to extract minerals from steep ore bodies. Pillars are excavated and then backfilled at different sub-levels. The host rock between the backfilled holes is then excavated using the same process.
- Sub-level open stoping. Sub-level open pit mining, also known as blast hole mining or longwall mining, is used when a solid rock body is present and no structural support is required to extract the ore. Drill holes are drilled and the host rock is blasted in sections to an open pit. This method is used to extract lead and iron.
- Cut-and-fill mining. The cut-and-fill mining is carried out by working horizontal strips from the bottom of the ore body to the top. Before moving to the next level, drifts are mined and backfilled. This method is used for soft host rocks.
- Sublevel caving. Sublevel caving is used to mine the footwall of an inclined ore body. This method mines from the top down and uses blasting to extract the ore, which leads to the destruction of the bedrock.
- Block caving. Block caving undermines massive ore bodies and creates voids under the loosened rock. The ore falls apart in the voids and is transported to the crusher through the ore passages. During mining, the surface of the mine deflects as the ore is removed. This method is used for massive but weak ore bodies and has a more complex preparation process than other mining methods.