Formed over millions of years, coal is found in underground formations know as ‘coal seams’. There are two mining methods used for extracting coal: Surface Mining and Underground Mining.

Surface Mining:

If coal seams are located closer to the earth’s surface then the most economical way to extract coal is through Surface Mining. Recovery rates are higher and the coal mines are safer.

There are two types of Surface Mining techniques:

Strip Mining: In Strip Mining, the overburden, comprising rock, vegetation and soil, above the coal seam is removed in strips. Once the seam is exposed, various mining equipment is used to extract the coal. Mining is carried out in a series of parallel and shallow strips and, when complete, the overburden is replaced. If the original land is barren, as a responsible mining practice, afforestation programmes are implemented on the restored land.

Strip Mining in a coal mine is suitable for relatively flat terrains where the overburden is not too thick and the coal is more accessible.

Open Pit Mining: This type of mining is ideal for coal deposits which are deeper and where the terrain is hilly or mountainous.

Like in Strip Mining, the overburden is removed first. Then a deep pit is dug to reach the coal below. Open Pit mines are dug on benches which are at four to sixty-meter intervals. The benches create vertical levels, resembling steps, and have slightly inclined walls to minimize damage from falling rocks.

A haul road is located at the side of the pit so that trucks can transport coal and waste rock out of the mine to ports for shipping.

Underground Mining

When coal deposits are found at considerable depth below the earth’s surface, Underground Mining is used to extract coal. Underground Mining is more expensive than Surface Mining as it requires more specialized equipment and is often more labour intensive.

To access the underground coal, vertical shafts are drilled through the Earth’s surface. These shafts enable the movement of miners, equipment and coal. There are three types of Underground Mining and the extraction method depends on the thickness and depth of the coal seams.

Room & Pillar Mining: Leading out from the shafts, a series of grid-like tunnels known as ‘rooms’ are created directly into the coal seam while leaving pillars of coal to support the mine’s roof. The pillar size is critical as it ensures that the mine’s roof does not collapse. In this type of mining, the coal seams are usually shallow and allow for efficient recovery of coal from the coal mine.

Longwall Mining: In this method extremely long rectangular walls of coal are cut using shearing machines along the surface of the coal seam. Hydraulic supports are used to hold up the roof. Once an area has been mined, the roof supports are removed and the roof is allowed to collapse safely. Longwall Mining is highly efficient and allows higher recover rates of coal than Room & Pillar Mining. However, the use of specialized machinery makes it more expensive.

Highwall Mining: This is often described as a hybrid form of mining because it combines aspects of Surface as well as Underground Mining.

When no more Surface Mining can be carried out in a mine, specialized remote-powered equipment is used to drill into exposed coal seams which lie at the base of the highwall of an open pit coal mine. A highwall mining machine drives a cutter into the coal seam. A conveyor system is integrated into the machine to extract and move the coal to the entry point of the mine from where it can be transported where needed. The entire operation is precisely monitored by just three to four personnel from the machine’s cabin.

Highwall Mining is an economical way to extract coal reserves locked up in a pit’s highwall.

As the global mining industry strives to become more efficient, coal mines in South Africa are committed to making optimum use of resources and adopting more responsible mining practices.