Open Pit Mining
Open Pit mining methods are a general process in opening up an ore-body so It can be later excavated from the topographic surface. The “Open Pit” is generally mined by using steps that are described as benches within the open pit mining method. Benches are commonly referred as horizontal slice of an open pit operation that are mined as a type of unit. These benches typically are considered to vary from 2 to 30-metres, with the other bench being reserved for selective mining, and larger benches for bulk mining. For the most part, benches can be even further subdivided into flitches if more selective mining is needed. Selective mining is whereby ore of high value is mined while the low-grade ore is left for future sustainability. This method typically is responsible for selecting the best ore in order to make good mill returns, leaving the low-grade ore in the mine.
The Excavation process in an open pit results in a cone shaped volume in which the benches become more smaller as the pit deepens. Walls of an open-pit mining operation are also left to be formed by cascading benches. The flat surface of an open bench remaining are generally confined to the pit wall as they are referred as berms. These berms are known to commonly create safe zones that are used in case of rock spalling away from the walls, and are also used for developing the haul roads ramp. These ramps are generally considered to be needed in order to access the bottom of an open pit mining project.
Methods like these depend on the nature of the geochemical characteristic of the rocks, and equipment selection. Stopes of the open pit walls are described by two angles. As the wall rocks becomes more geotechnical competent it results in providing a much more engineered steeper slope. A stope section of the pit wall is described by two angles of individual bench faces, and batters. Both of these types of angles are important for characteristics of open pits and together with the berm width and bench height. Its these types of selections that control the safety along with the economics of the “Open Pit” mining operation.
The depth of an “open pit” mining project is known to greatly vary from a few metres to kilometers. Pit depth largely depends on the geometry of the ore-body being excavated to the overall economics of the project. Its also the overall pit wall angle that remains one of most important selective controlling factors. Another important term in open pit mining operations is known to go by stripping ratio of the project. This general type of method is estimated as a ratio in tonnes of waste in the open pit to the tonnes of ore. One disadvantage of this parameter is that it does not take into account the value of the metal or mineral being mined as another parameter can be used for the limitation of stripping ratio.