Mining

Ore is extracted from the ground using one of two basic forms of mining - opencut (or open-pit) and underground mining. Geologists use the results of their drilling samples to develop a model of the mineralisation. Engineers use this model to help them determine which mining methods will be most effective at each site.

Open Cut Mining

Opencut mining is used when the orebody is close to the surface and not covered by a lot of overburden (rock that does not contain mineralisation). Some shallow ore deposits may be located in rocks soft enough to be removed with excavators or back-hoes instead of blasting.

Underground Mining

Deeper deposits (sometimes called deposits, reefs or lodes) covered in layers of hard rock are accessed and extracted via drill and blast methods. Underground mining is a far more complex and costly process than open cut mining, with more complicated safety, access, ground support (to avoid the risk of mine shaft collapse), ventilation and transportation issues to address.

Access, or the way that the miners are going to get to the orebody, is based on the understanding of the how the mineralisation occurs at depth and the costs associated with mining the orebody. Access can be gained by vertical or inclined shafts, horizontal tunnels (called adits) or downward sloping tunnels (called declines).

Mine planning cannot occur without a good understanding of the orebody, how it is predicted to occur and the surrounding country rocks (the unmineralised rocks). To achieve this the orebody is modelled by geologists from the results of initial drilling from the surface and then more closely spaced drilling and geological mapping underground. Geologists, engineers and surveyors work closely together to plan how the underground mining will occur.

Ground support will also be considered during the mine planning stage. Depending on the rock type, structure and conditions of mining, there may be a chance of rock falls or voids (holes) created underground. The competency (how well it holds together) of the rock being mined will determine how large a void may be created and what ground support methods will be necessary to maintain a safe working environment.

Fresh air is drawn into the underground mine through the entrance (adit) but this air has limited reach. Adequate ventilation throughout the mine is ensured by the provision of a fan drawing fresh air through the mine through a separate shaft from the surface. This air is pumped through to areas that are actively mined.

Mining Methods

A process called stoping is used to extract ore from the surrounding rock. Once the area being mined has been drilled to a depth and pattern predetermined by engineers and geologists, explosives are detonated in each drill hole to break up the rocks in and around the ore bodies into small pieces that can easily be bogged (dug out), loaded into trucks and taken to the surface for processing (extraction of ore).

Investigate the resource From Exploration to Rehabilitation - the Life of a Gold Mine for further information about exploration and the techniques used to discover minerals.