What are the differences between open-cut and underground mining?
Open Cut Mining
There are many differences between open cut and underground mining.
When minerals and deposits are found close to the surface and spread across a large distance, the best way to mine is to use the open cut mining method.
In this process, the area is cleared of all topsoil and vegetation, this material is stockpiled and used later when rehabilitating the area once mining is finished.
Next the waste rock layer is removed and a pit is dug into the ground to reach the mineral seam. A sloping road is created for transporting the unprocessed mineral out of the pit.
Explosives are used to break up the ore which is then scooped into large haul trucks by front end loaders or large electric shovels and transported to a processing plant.
The mineral is extracted from the ore and the material remaining (known as tailings) is deposited in a tailings dam and covered with clay, topsoil and vegetation.
Once the mine has been depleted and all work has been completed, the leftover rock and soil will either be covered with topsoil and revegetated to create new landforms, or it can be used to fill and re-vegetate the pit.
Sometimes the pit is used as a storage area for water or for other uses after consultation with the local community.
Underground Mining is generally used for areas where the mineral seam is too far underground for open cut mining to be of use.
A tunnel, called a decline, is created to allow workers and machinery to reach the location of the minerals. Stope mining is used for most hard rock mining of minerals such as copper, silver, lead and zinc.
Stopes are large openings or rooms connected by tunnels in which miners drill and blast the ore. A pillar or wall is left between each room (stope) to prevent the mine from collapsing. After drilling and blasting, the ore is removed using remote controlled vehicles or boggers.
One of the main pieces of equipment used in this room and pillar type of stope mining, is a machine called a Continuous Miner which breaks the coal seam mechanically by using a long rotating drum which has picks around the outside, it is then transported to the surface using a combination of shuttle cars and conveyor belts.
Long Wall Miners are another piece of machinery, sometimes remotely controlled, which can be used after the Continuous Miner has cleared the tunnel and roadways. This technique uses tunnels which are about 1500m long and 250m apart. The unit moves along the coal face allowing the roof over the area behind the face to collapse, after it has finished its 1500m journey, it is moved to a new location.
When the Long wall Miner is used, the roof of the tunnel is reinforced using large hydraulic jacks connected to the machine, as a measure to maintain the safety of workers and machinery in the underground environment. Remote controlled Longwall Miners are now used in many Australian mines.
Open Cut and Underground Mining