Although open-cast mining is the most economic and safest method of exploiting reserves of coal and minerals which lie just below the surface, it presents serious disadvantages. Large earth-moving equipment strips the over-burden and stacks it in a bank parallel with the cut and the uncovered ore is then fragmented, loaded and transported from the pit. This process disfigures the surface of the land, and in the absence of reclamation, leads to permanent scars. The process buries the vital topsoil, disrupts drainage patterns, destroys the productive capacity of agricultural and forest land, as well as impairing their aesthetic and social value. It may also poison rivers and totally disrupt ecosystems.
Open-cast mining began on a large scale during WWII as part of an emergency measure.
The limiting depth at which underground mining becomes profitable has deepened constantly and opencast mining dominates in the recovery of many raw materials. At the end of the 1980s, 70-90% of the world's exploitable iron, copper, phosphate, asbestos, bauxite, manganese and lignite was extracted in opencast mines. Nearly all materials for construction were recovered from opencast mines and in the case of hard coal and uranium, a substantial share of approximately 25-30% was workable by opencast mining techniques. In the OECD countries, strip mining of coal is practised on a large scale in Germany, Australia and the USA, and on a smaller scale in the UK, Canada, Ireland and Greece. Over 500,000 acres in the eastern USA have been stripped for coal, of which only half have been restored to close to their original state. About 50% of the coal produced in the USA comes from surface mines. So far only 1 million of the 54 million acres of government owned land containing coal have been leased for mining. Reclamation is very expensive and mining deeper coal reserves would considerably increase the cost of energy. Open-cast mining is an estimated 30% cheaper than deep mining, thus providing an economic incentive for those concerned mostly with costs. In 1984, it cost £27.55 to produce a tonne of open-cast coal in the UK, and in 1990, the cost increased only to £27.60.
The Scottish Opencast Action Group works with a number of village communities in the south of Scotland who are protesting the development of opencast coal mining operations around villages in the region. They claim the huge environmental scars left on the landscape by opencast mining undermine the value of houses in villages and have a depressing effect upon local communities. While many of these villages were originally based around village coal mine operations, local protestors claim the small fraction of jobs created by the opencast sites only creates further division within communities between those benefiting from the employment and the rest of the community forced to live with the consequences. The protestors further warn of health risks from opencast works, a claim supported by local doctors who report an increase in chest complaints, asthma and respiratory illness.
Since opencast mining has many advantages compared with underground mining it will gain in significance in the future. The mining losses are low in opencast mining operation. In general, 90% or more of a mineral deposit can be recovered. Furthermore, the large quantities - in opencast mines these amount to far more than 100,000 tons per day – necessary for economical raw material treatment cannot be produced from underground operations even in the case of maximum mechanization. Finally, the mechanization of all opencast operations with high equipment capacity and the working conditions in the open pit decrease staff requirements. In times when it is more and more difficult to find suitable labour to work in underground mines, this is a great advantage of opencast mining technology.