Open pit mining or open-cast mining or open-cut mining and strip mining is a method of extracting rocks and minerals from earth. Open Pit mining is used to differentiate it from the process that includes tunneling. Whenever the surface material is necessarily thin or not suitable for tunneling, in such case open pit mining is used.
In places where the surface material is thick and minerals occur in hard rocks, in such cases underground mining methods are used to extract the material. Quarries are the building materials and stones produced from open pit mines. The various open cast mining types such as quarries, borrows, placers, and strip mines are not considered distinct from open-pit mining. In some cases the increasing burden to produce large amount of ore makes mining uneconomic and it may also happen that all the mineral resources were exhausted. In such case, the mines are used to dump the solid wastes. A constant water control check is required to keep the mine pit from becoming a lake. Australia’s largest open cut gold mine is the Fimiston Open pit, also known as super pit. The Super pit extends south east edge of Kalgoorlie-Boulder, Western Australia and is located off the Goldfields Highway. Kalgoorlie Consolidate Gold Mines Pty Ltd owns Super pit, 50/50 by Barrick Gold Corporation and Newmont Mining Corporation. The mine employs 550 employees and produces around 850,000 ounces of gold per year. Initially the super pit comprises of a number of small underground mines. Alan Bond attempts to convert them into a single open pit mine but unable to complete this. Golden Mile Dolerite is an ancient shear in rock unit that produces ore lodes responsible for the occurence of Super pit. The Golden Mile extends over 2 km in width and 1 km in length and is a major produce of lodes.
Open pits are generally dug on vertical levels on benches and the benches are generally four to six metres in terms of interval, the benches that are created depends upon the size of the machines that are used. Shallow quarries do not make use of benches. To minimize the damage from the falling rocks most of the pits are dug on an angle less than vertical. Batter is the inclined section of the rock and the flat part is termed as perm or a bench. Rock bolts and cable bolts are used for providing the ground support.