The environmental impacts of mining vary with the type of mineral and the kind of mine. However mining is inherently a destructive activity involving the taking of a non-renewable resource. Some environmental damage is inevitable in any mine; the goal should be to minimize the extent of the impacts.
Mining impacts can be sub-divided for convenience into four categories: the effects of the mine itself, the disposal of mine wastes, the transport of the mineral, and the processing of the ore which often involves or produces dangerous materials. These activities may take place at the same site, in which case the impacts are combined, or they may be separated by considerable distances. The effects of each are discussed separately here.
Direct impact of the mine
Many mines are at the surface (sometimes called open cast mines). They may consist of a great hole in the ground (most copper mines), strip mining along the tops of ridges (nickel in New Caledonia), the digging out of ore in pits and sheets across a large surface (phosphates), or a pit or hillside excavation (rock and sand quarries). With such mines, the land surface over a considerable area is destroyed, and what is left behind may be unstable, producing landslides, erosion, siltation, and polluted water. Such land is generally useless after the mining ends, and may continue to cause environmental problems long after the mine has closed.
When the mine is beneath the surface and is composed of tunnels, the disturbance is usually localized at the mine entrance unless there are later cave-ins or some interference with ground-water supplies.
The drilling of oil wells may cause some local environmental effects from the machinery and drilling muds used, and there is a slight risk of blow-outs or accidental breakage leading to oil spillage, but once the well is in operation, there is generally little further effect.
Any kind of mine may cause some water pollution through water drained or pumped from the mine.
Disposal of mine wastes
In most mining operations, a great deal of waste rock and tailings must be moved to reach the ore. In addition to rock covering the ore or mixed in with the ore, there may be low grade ores that are not worth treating. The disposal of these wastes from the mine often causes more environmental damage than the mine itself. The problems come both from the enormous quantities of rock to be disposed of, and the fact that some mine wastes may be toxic to plants or cause water pollution as water drains through them.
The dumping of these wastes may affect more land surface than the mine. Waste dumps are subject to erosion, and are difficult to stabilize or revegetate. It is sometimes even necessary to build dams to hold the wastes back. Inadequately contained mine wastes have damaged or destroyed rivers and agricultural land and caused heavy flooding. In some mines the wastes are intentionally washed in to a river so that they will be carried away to the sea, with severe effects on the river, its valley, and the sea coast at the river mouth.
Transport of ores
Mines are usually located in remote areas, requiring the transport of the mineral in some form from the mine to a port where it can be shipped to its markets. The infrastructure for the transport of large quantities of heavy material may involve roads, railroads, pipelines and conveyor belts, the construction and operation of which may have considerable environmental impacts, particularly since the terrain crossed is often difficult. Major port facilities and storage areas are also generally required.
Ore treatment or refining
Since transportation cost in island regions are very high, and are related to the bulk of the material, there is a strong incentive for at least some treatment of the ore to concentrate it if not refine it completely. This generally requires large industrial installations and the further production of wastes to be disposed of. Furthermore, ore treatment often requires dangerous chemicals like mercury or cyanide, or strong acids or alkalis, and the metals being treated may themselves be toxic. Some are even known to accumulate in food chains, threatening human food supplies. Even if the wastes are treated, there usually is some spillage, and there is always the risk of accidents.
Special impacts in coastal areas
Where mines occur in coastal areas, or mine wastes are released there, additional environmental impacts can be expected on sensitive coastal resources. Corals and other forms of life on the bottom generally require clear water for growth, and are easily smothered by any input of tailings or other sediment. Dredging and other forms of coastal mining thus both destroy the immediate site and affect a much larger area through the sediment stirred up in the water. Removing sand and gravel from the beach or lagoon bottom can also cause beach disappearance and serious coastal erosion. Copper and other toxic materials from mines may kill most marine life in the vicinity of treatment and shipping facilities.
Mines as development projects can create employment and provide a significant source of national income and foreign exchange. However, as a development based on a non-renewable resource, mines are only viable for a limited period and are then abandoned, requiring the writing off of all the capital investment involved. Many islands have mining ghost towns and rusting equipment that are the only remaining signs of brief periods of prosperity. When the mine closes, there is generally no one left to be legally or financially responsible for the long-term effects. Those costs are left to the government and people. Often all that remains of the mine are the environmental problems and large areas of ruined land on islands that can ill afford to waste limited land resources.
The solution to such long-term problems is to build environmental controls and provision for rehabilitation into the project from the beginning.