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Open-pit mining refers to mining in the open space with mining, loading and transportation equipment according to the occurrence conditions of ore deposits. Some deposits are large in scale, shallowly buried, and even exposed on the surface. For this type of deposit, as long as the overlying rock layer and part of the surrounding rock are stripped off, useful minerals can be directly excavated from the surface without digging into a large number of shafts and tunnels, which are suitable for open-pit mining.
With the development of mining technology, the range suitable for open-pit mining is getting larger and larger. About two-thirds of the world's solid mines use the open-pit mining method. Compared with underground mining, open-pit mining has the following characteristics:
According to the experience of metal mines construction in the world, it generally takes only 2 ~ 4 years to build a large open-pit mine, and only 3 ~ 4 months for a small mine, while it takes at least double the time to build an underground mine of the same size.
Open-pit mining can use large or extra-large, high-efficiency mechanical equipment, which is conducive to the realization of mining mechanization, thereby greatly improving the mining intensity. And the labor productivity is 2 to 10 times higher than underground mining.
Due to the large range of open-pit mining operations, it is conducive to mechanized mining and reduces mining costs. Generally speaking, the cost of open pit mining is lower than that of underground mining by 200% to 300%.
In metal open-pit mine, the ore loss rate is generally 3% ~ 5% and dilution rate is generally 5% ~ 8%. While in underground mining, the ore loss rate is generally 15% ~ 25% and dilution rate is 3% ~ 20%. Therefore, open pit mining is beneficial to the full recovery of mineral resources. Especially for some high-temperature, flammable and watery ore bodies, open-pit mining is more adaptable and flexible.
Open-pit mining is not threatened by hazards such as harmful gas and roof, and its labor intensity is low.
Because open-pit mining is an open operation, it is greatly affected by the climate, and severe weather such as heavy rain and heavy snow may affect the mining operation.
Because of the large-scale mechanical equipment used in open-pit mining, the large amount of infrastructure stripping, and the large amount of land requisitioned by the mine, often lead to large initial investment in infrastructure.
During the mining process, the dust of drilling and blasting, loading, transportation, discharge and other operations is relatively large, and the carbon monoxide emitted by the transportation vehicle will escape into the atmosphere. Under the effect of rain, the harmful components of waste rock yard flow into rivers, lakes and farmland, polluting the air, water and soil, which will endanger people's health, affect the growth of crops, animals and plants, and destroy the ecological environment.
Although open-pit mining has some disadvantages, it has obvious advantages in economy, technology and safety. As long as conditions permit, open-pit mining should be given priority, which is also the general trend of mines in the world. After the mining is completed, the ecological restoration and reconstruction of the mined-out area should be done in accordance with relevant national environmental standards.
While open-pit mining cannot replace underground mining. When the mining conditions are constant, with the increase of the open-pit mining depth, the amount of rock stripping increases rapidly. It's not economically reasonable to use open-pit mining continually after reaching a certain depth. In this case, it should be transferred to underground mining. Especially for deposits with deep burial and deep extension, generally only suitable for underground mining.