The Environmental Impacts of Mining and Quarrying

The Environmental Impacts of Mining and Quarrying This unpublished prĂŠcis catalogs the environmental impacts commonly associated with mining and quarrying and notes opportunities for increasingly responsible attitudes to the environmental implications of such operations and reclamation of mined land.

Olivier Serrat 02/07/1994

1 Introduction 1.

In the course of history, mankind has discovered and learned to use an increasing number of substances. Today, industry depends heavily on some 80 minerals such as aluminum and iron, which are in relatively plentiful supply, and chromium, manganese, cobalt, and platinum, which are relatively scarce. These are extracted from the earth's crust and processed for their final use.

Most minerals, such as petroleum, metal ores, and raw diamonds, are processed to yield metals and other elements and compounds. A few, such as sand and gravel, are used as they are found.

For example, minerals are used to make irrigation pipes, fertilizer, and machinery; to build transport systems; and to produce household goods.1 Because minerals are naturally occurring solid inorganic substances, they are usually regarded as nonrenewable resources.2 2.

Although minerals are present in varying amounts throughout the earth's crust, commercial exploitation will take place where they occur in sufficiently concentrated form. In such cases, the main methods of extraction of such reserves will include deep mining, dredging, and open-pit mining.

Environmental Impacts Commonly Associated with Mining and Quarrying 3.

Deep mining refers to the extraction of deep-lying mineral resources such as coal from subsurface workings. It usually involves driving a vertical shaft from the surface to the level of the mineral deposits, which are then accessed by means of horizontal tunnels. Although deep mining is a dangerous operation, its environmental effects are limited to the winding machinery, waste heaps, and possible subsidence.3,4 4.

Underwater deposits are exploited by dredging in rivers, lakes, or shallow offshore waters.

Although dredging activities constitute smaller-scale operations, large quantities of sand and gravel are nevertheless obtained by dredgers, that is, ships that scrape sand from the bottom of shallow parts of the sea or rivers. While dredging destroys the ecosystem on the sea or river floor, it may also alter the way in which the tide and currents move sand along the coastline, causing beaches to erode and sandbars to form.

5.

Open-pit mining, including quarrying, is a far more extensive activity which involves digging a large void open to the air.5 The term is used when there is no return of backfill into the void. Significant adverse environmental effects from open-pit mining activities can occur and, for clarity, may be classified under those that may arise as a result of a mining project's location, those that may arise during mining operations, and those linked to the aftermath of mining. The main environmental impacts of deep mining and dredging were treated above and it is to the more serious and widespread impacts of open-pit methods of mineral exploitation that the following sections refer.6 1

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The importance of minerals in modern life can be gauged from the amount of energy used to produce them. In the United States, about 20 percent of all energy used serve to extract and process minerals.

Mineral deposits are formed so slowly by geological processes that mankind cannot influence their formation.

The rock waste from deep mines, known as tailings, is usually dumped on the surface to form unsightly slag heaps.

Tailings often contain toxic materials and, when water runs off heaps of tailings into nearby fields and rivers, can poison the soil and create water that is unfit for irrigation or human consumption. Landslides of waterlogged tailings can also occur.

Deep mining can even cause earthquakes. However, the danger of subsidence can be eliminated by allowing underground workings to collapse in a controlled manner or by pumping concrete into the former tunnels.

The open surface excavation of mineral resources such as slate, granite, sand, and gravel is usually referred to as quarrying.

On the one hand, the economics of large-scale open-pit mining enables extraction of minerals of lower grade than

2

A.

Environmental Problems Due to Project Location

6.

The environmental problems due to a mining project's location may include: (i) changes in the hydrology of waterways intercepted by the project, which can result in: (a) creating or intensifying local flooding problems, and (b) affecting aquatic ecology including fishery; (ii) resettlement of families displaced by the project; (iii) encroachment into forests and swamplands; (iv) encroachment on historical or cultural monuments, buildings, and areas; (v) conflicts in water supply rights; and (vi) regional flooding and drainage hazards.

7.

Because of the environmental problems linked to a mining project's location, sites which should be avoided include: (i) areas where human settlements are found; (ii) areas where mining may cause safety problems concerning, for example deep water and unstable waste heaps; (iii) areas where important transport links would be affected; (iv) areas of scenic beauty or high visibility; (v) areas where the land could be used for better purposes; and (vi) areas of historical or cultural interest.

B.

Environmental Problems During Mining or Quarrying

8.

The environmental problems occurring during mining operations may include: (i) occupational health and safety, for example from blasting; and (ii) environmental pollution from: (a) contaminated mine drainage waters, which may have unforeseen effects on marine or freshwater habitats and require treatment, (b) silt runoff, (c) noise and vibrations, (d) fugitive emissions of dust and fumes from haulage vehicles or rock-crushing equipment, (e) possible effects on the surrounding flora and fauna from dust and desiccation, (f) visual intrusion, (g) traffic generation, particularly with regard to use of heavy vehicles, and (h) mineral processing.

C.

The Aftermath of Mining and Quarrying

9.

Nowadays, new discoveries are usually of relatively low grade ores, often at considerable depth below the surface of the earth. As a result, enormous quantities of rock have to be excavated to obtain useful amounts of the mineral. In the long term, therefore, one of the main environmental concerns about mining and quarrying is the potential scar left on the landscape.

Because open-pit mining involves the digging of vast pits or the removal of whole mountain tops, increasing pressure has been put on the mining industry to deal with waste heaps, mine and quarry voids, lakes (these are formed when excavations extended below the water table and/or collected surface water), and tailing lagoons.

Environmental Benefits of Surface Mining 10.

At least in higher-income countries, mining companies now have an increasingly responsible attitude to the environmental implications of their operations and reclamation of mined land is given high priority. After working, care is taken to recreate topographical features and to plant trees and hedgerows. When sites are not returned to agricultural use, they can, for example, provide land for housing and other urban developments, or be converted into valuable community facilities at either reduced or no initial cost to local authorities.

would be possible in deep mining. Consequently, the great majority of large mines are worked as open-pit operations. On the other, the seriousness of environmental impacts from open-pit mining operations arises from the nature of such operations.

3 Conclusion 11.

Some of the worst environmental effects associated with economic activity in the past were produced by mining. By its very nature, surface mining causes severe disturbance to the surface of the earth and, with associated activities, is undoubtedly detrimental to human, animal, and plant life. If, however, after taking into account a wide range of economic, social, and environmental factors, surface mining is deemed necessary, losses to the quality of both the natural and man-made landscape during extraction can be minimized. Handled correctly, surface mining can have even have beneficial effects.

The views expressed in this prĂŠcis are those of the author and do not necessarily reflect the views and policies of the Asian Development Bank, or its Board of Governors or the governments they represent.