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Our Mining Process |
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| OUR MINING PROCESS Open-pit mines look simple, but every pit needs to be tailor-made. First and foremost, the pit walls have to stay up, so a rock-mechanics engineer The size and location of the first bench of any open-pit mine is critical. It is excavated well into the waste rock surrounding an orebody. And since each successive bench is smaller than the last one taken, the depth to which the pit can be mined is determined by the size and location of the first cut or bench. The amount of waste rock mined relative to the amount of ore mined is called the stripping ratio. In most cases, this ratio is high for the first bench and decreases steadily with each successive bench. A stripping ratio of 3 to 1 means that during the life of the pit, there will be three times as much waste rock mined as ore. To be profitable, an open-pit mine must be designed so that the cost of mining the waste rock does not exceed the value of the ore. The main cost advantage of open-pit mining is that the miners can use larger and more power shovels and trucks — the equipment is not restricted by the size of the opening it must work in. This allows faster production, and the lower cost also permits lower grades of ore to be mined. Open-pit mining, also known as open-cast mining and open-cut mining, refers to a method of extracting rock or minerals from the earth by their removal from an open pit or borrow. The term is used to differentiate this form of mining from extractive methods that require tunneling into the earth. Open-pit mines are used when deposits of commercially useful minerals or rock are found near the surface; that is, where the overburden (surface material covering the valuable deposit) is relatively thin or the material of interest is structurally unsuitable for tunneling (as would be the case for sand, cinder, and gravel). For minerals that occur deep below the surface—where the overburden is thick or the mineral occurs as veins in hard rock— underground mining methods extract the valued material. Open-pit mines that produce building materials and dimension stone are commonly referred to as quarries. People are unlikely to make a distinction between an open-pit mine and other types of open-cast mines,[citation needed] such as quarries, borrows, placers, and strip mines. Open-pit mines are dug on benches, which describe The walls are stepped. The inclined section of the wall is known as the batter, and the flat part of the step is known as the bench or perm. The steps in the walls help prevent rock falls continuing down the entire face of the wall. In some instances additional ground support is required and rock bolts, cable bolts and shotcrete are used. De-watering bores may be used to relieve water pressure by drilling horizontally into the wall, which is often enough to cause failures in the wall by itself. A haul road is situated at the side of the pit, forming a ramp up which trucks can drive, carrying ore and waste rock. Ore which has been processed is known as tailings, and is generally a slurry. This is pumped to a tailings dam or settling pond, where the water evaporates. Tailings dams can often be toxic due to the presence of unextracted sulfide minerals, some forms of toxic minerals in the gangue, and often cyanide which is used to treat gold ore via the cyanide leach process. After mining finishes, the mine area must undergo rehabilitation. Waste dumps are contoured to flatten them out, to further stabilise them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to produce sulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to the environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence, to prevent access, and it generally eventually fills up with ground water. In arid areas it may not fill due to deep groundwater levels. Environmental and health issues 3.0 PRINCIPLES OF RECLAMATION Best practices in reclamation planning and management Mining operations are temporary land use activities and should be conducted with understanding and respect for the environment. Use of reclamation planning and environmental management that aims for sustainability is encouraged in all aspects of reclamation planning, design and implementation. Plans must be science-based, comprehensive in scope and mitigate against safety hazards and environmental effects. Applied principles of ecological restoration A central purpose in reclamation planning should be to promote the ecological integrity of Compatibility in land use, land cover and landscape design Surface mining also has the potential to visually impact natural scenery, open landscape Public consultation and Informed decision-making Considerations related to backfilling include: |