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Drilling

on November 14, 2007

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Open-pit mining

OPEN PIT MINING Open-pit mining, also known as opencast 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.

Tailings Disposal Methods

Tailings Disposal Methods Pond Storage There are many different subsets of this method. Large earthen dams may be constructed and then filled with the tailings. Tailings may be deposited into natural geographical depressions. Exhausted open pit mines may be refilled with tailings. In all instances, due consideration must be made to contamination of the underlying water table, amongst other issues. Dewatering is an important part of pond storage, as the tailings are added to the storage facility the water is removed - usually by draining into decant tower structures. The water removed can thus be reused in the processing cycle. Once a storage facility is filled and completed, the surface can be covered with topsoil and revegetation commenced. However, unless a non-permeable capping method is used water that infiltrates into the storage facility will have to be continually pumped out into the future.

Environmental and Social Considerations

Tailings in general, are often pointed at by environmentally active groups as evidence of the destruction that mining operations can wreak upon the planet. And to a degree, they have a valid point. In the past, non-environmentally friendly methods were the method of the day - profit at all costs being the main motivator. In todays modern mining environment, it is possible to find many mining operators continuing to engage in tailings disposal methods that are not environmentally friendly, particularly in developing nations where legislative requirements are far less than first world countries, and the need for quick cash overrules any environmental considerations. There is, however, a strong push from the leading mining houses and their design consultants to support the cessation of unsustainable tailings disposal practises. Unsustainable, in the sense that continuing to blatantly pollute the local environment damages a mining company's social license to operate, and by defa...

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