Break time underground,
Colorado, ca. 1900
is the extraction of
valuable minerals or other
geological materials from the earth, usually from an
ore body,
vein or (
coal) seam. Materials recovered by mining include
base metals,
precious metals,
iron,
uranium,
coal,
diamonds,
limestone,
oil shale,
rock salt and
potash. Any material that cannot be grown through
agricultural processes, or created
artificially in a
laboratory or
factory, is usually mined. Mining in a wider sense comprises extraction of any
non-renewable resource (e.g.,
petroleum,
natural gas, or even
water).
Mining of stone and metal has been done since
pre-historic times. Modern mining processes involve
prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials and finally reclamation of the land to prepare it for other uses once the mine is closed. The nature of mining processes creates a potential negative impact on the environment both during the mining operations and for years after the mine is closed. This impact has led to most of the world's nations adopting regulations to moderate the negative effects of mining operations. Safety has long been a concern as well, though modern practices have improved safety in mines significantly.
History
Prehistoric mining
Since the beginning of civilization, people have used
stone,
ceramics and, later,
metals found on or close to the
Earth's surface. These were used to manufacture early
tools and
weapons, for example, high quality
flint found in northern
France and southern
England were used to create
flint tools. Flint mines have been found in
chalk areas where seams of the stone were followed underground by shafts and galleries. The mines at
Grimes Graves are especially famous, and like most other flint mines, are
Neolithic in origin (ca 4000 BC-ca 3000 BC). Other hard rocks mined or collected for axes included the greenstone of the
Langdale axe industry based in the
English Lake District.
The oldest known mine on archaeological record is the "Lion Cave" in
Swaziland. At this site, which by
radiocarbon dating proves the mine to be about 43,000 years old,
paleolithic humans mined mineral
hematite, which contained
iron and was ground to produce the red
pigment ochre. Mines of a similar age in
Hungary are believed to be sites where
Neanderthals may have mined
flint for weapons and tools.
Ancient Egypt
Ancient Egyptians mined
malachite at
Maadi. At first,
Egyptians used the bright green malachite stones for ornamentations and pottery. Later, between 2,613 and 2,494 BC, large building projects required expeditions abroad to the area of Wadi Maghara in order "to secure minerals and other resources not available in Egypt itself."
[Shaw, I. (2000). The Oxford History of Ancient Egypt. New York: Oxford University Press, p. 108.] Quarries for
turqoise and
copper were also found at "Wadi Hamamat, Tura, Aswan and various other Nubian sites"
on the
Sinai Peninsula and at
Timna.
Mining in Egypt occurred in the earliest dynasties, and the
gold mines of
Nubia were among the largest and most extensive of any in
Ancient Egypt, and are described by the Greek author
Diodorus Siculus. He mentions that
fire-setting was one method used to break down the hard rock holding the gold. One of the complexes is shown in one of earliest known maps. They crushed the ore and ground it to a fine powder before washing the powder for the
gold dust.
Ancient Greece and Rome
Agricola, author of De Re Metallica
Drainage wheel from Rio Tinto mines
Mining in Europe has a very long history, examples including the silver mines of
Laurium, which helped support the Greek
city state of
Athens. However, it is the
Romans who developed large scale mining methods, especially the use of large volumes of water brought to the minehead by numerous
aqueducts. The water was used for a variety of purposes, including using it to remove overburden and rock debris, called
hydraulic mining, as well as washing
comminuted or crushed ores, and driving simple machinery. They used hydraulic mining methods on a large scale to prospect for the veins of ore, especially a now obsolete form of mining known as
hushing. It involved building numerous
aqueducts to supply water to the minehead where it was stored in large
reservoirs and tanks. When a full tank was opened, the wave of water sluiced away the overburden to expose the bedrock underneath and any gold veins. The rock was then attacked by
fire-setting to heat the rock, which would be quenched with a stream of water. The
thermal shock cracked the rock, enabling it to be removed, aided by further streams of water from the overhead tanks. They used similar methods to work
cassiterite deposits in
Cornwall and
lead ore in the
Pennines. The methods had been developed by the Romans in
Spain in 25 AD to exploit large
alluvial gold deposits, the largest site being at
Las Medulas, where seven long aqueducts were built to tap local rivers and to sluice the deposits.
Spain was one of the most important mining regions, but all regions of the
Roman Empire were exploited. They used
reverse overshot water-wheels for dewatering their deep mines such as those at
Rio Tinto. In Great Britain the natives had
mined minerals for millennia , but when the
Romans came, the scale of the operations changed dramatically. The Romans needed what Britain possessed, especially
gold,
silver,
tin and
lead. Roman techniques were not limited to surface mining. They followed the ore veins underground once opencast mining was no longer feasible. At
Dolaucothi they stoped out the veins, and drove
adits through barren rock to drain the stopes. The same adits were also used to ventilate the workings, especially important when
fire-setting was used. At other parts of the site, they penetrated the
water table and dewatered the mines using several kinds of machine, especially
reverse overshot water-wheels. These were used extensively in the
copper mines at
Rio Tinto in Spain, where one sequence comprised 16 such wheels arranged in pairs, and lifting water about . They were worked as treadmills with miners standing on the top slats. Many examples of such devices have been found in old Roman mines and some examples are now preserved in the
British Museum and the
National Museum of Wales.
Medieval Europe
Mining in the
Medieval period is best known through the work
De Re Metallica (1556) of
Georg Agricola, who described many different mining methods then used in German and Saxon mines. Use of water power in the form of
water mills was extensive; they were employed in crushing ore, raising ore from shafts and ventilating galleries by powering giant
bellows.
Black powder was first used in mining in
Selmecbánya,
Kingdom of Hungary (present-day
Banská Štiavnica,
Slovakia) in 1627. This allowed blasting of rock and earth to loosen and reveal ore veins, which was much faster than fire setting. In 1762, the world's first mining academy was established in the same town.
The mining of tin was important in
Cornwall and Devon throughout the medieval period.
North and South America
In
North America there are ancient, prehistoric
copper mines along
Lake Superior.
[Lankton, L. (1991). Cradle to Grave: Life, Work, and Death at the Lake Superior Copper Mines. New York: Oxford University Press, p. 5-6.][West, G.A. (1970). Copper: its mining and use by the aborigines of the Lake Superior Region. Westport, Conn: Greenwood Press.] "Indians availed themselves of this copper starting at least 5000 years ago,"
and copper tools, arrowheads, and other
artifacts that were part of an extensive native trade network have been discovered. In addition,
obsidian,
flint, and other minerals were mined, worked, and traded.
While the early French explorers that encountered the sites made no use of the metals due to the difficulties in transporting it,
the copper was eventually traded throughout the continent along major river routes. In
Manitoba, Canada, there also are ancient
quartz mines near Waddy Lake and surrounding regions.
In the early colonial history of the Americas, "native gold and silver was quickly expropriated and sent back to Spain in fleets of gold- and silver-laden galleons" mostly from mines in Central and South America.
Turquoise dated at 700 A.D. was mined in
pre-Columbian America; in the Cerillos Mining District in
New Mexico, estimates are that "about 15,000 tons of rock had been removed from Mt Chalchihuitl using
stone tools before 1700."
Mining in the
United States became prevalent in the 19th century. As with the
California Gold Rush in the mid 1800s, mining for minerals and precious metals, along with
ranching, was a driving factor in the
Westward Expansion to the Pacific coast. With the exploration of the West, mining camps were established and "expressed a distinctive spirit, an enduring legacy to the new nation;" Gold Rushers would experience the same problems as the Land Rushers of the transient West that preceded them. Aided by railroads, many traveled West for work opportunities in mining. Western cities such as
Denver and
Sacramento originated as mining towns.
Mining methods and procedures
Steps of mine development
The process of mining from discovery of an ore body through extraction of minerals and finally to returning the land to its natural state consists of several distinct steps. The first is discovery of the ore body, which is carried out through
prospecting or
exploration to find and then define the extent, location and value of the ore body. This leads to a mathematical
resource estimation to estimate the size and
grade of the deposit. This estimation is used to conduct a pre-feasibility study to determine the theoretical economics of the ore deposit. This identifies, early on, whether further investment in estimation and engineering studies is warranted and identifies key risks and areas for further work. The next step is to conduct a
feasibility study to evaluate the financial viability, technical and financial risks and robustness of the project. This is when the mining company makes the decision to develop the mine or to walk away from the project. This includes mine planning to evaluate the economically recoverable portion of the deposit, the
metallurgy and ore recoverability, marketability and payability of the ore concentrates, engineering concerns, milling and infrastructure costs, finance and equity requirements and an analysis of the proposed mine from the initial excavation all the way through to reclamation. Once the analysis determines a given ore body is worth recovering, development begins to create access to the ore body. The mine buildings and processing plants are built and any necessary equipment is obtained. The operation of the mine to recover the ore begins and continues as long as the company operating the mine finds it economical to do so. Once all the ore that the mine can produce profitably is recovered,
reclamation begins to make the land used by the mine suitable for future use.
Mining techniques
Mining techniques can be divided into two common
excavation types: surface mining and sub-surface (underground) mining. Mining targets are divided into two general categories of materials:
placer deposits, consisting of valuable minerals contained within river gravels, beach sands, and other unconsolidated materials; and
lode deposits, where valuable minerals are found in veins, in layers, or in mineral grains generally distributed throughout a mass of actual rock. Both types of ore deposit, placer or lode, are mined by both surface and underground methods.
Processing of placer ore material consists of gravity-dependent methods of separation, such as sluice boxes. Only minor shaking or washing may be necessary to disaggregate (unclump) the sands or gravels before processing. Processing of ore from a lode mine, whether it is a surface or subsurface mine, requires that the rock ore be crushed and pulverized before extraction of the valuable minerals begins. After lode ore is crushed, recovery of the valuable minerals is done by one, or a combination of several, mechanical and chemical techniques.
Some mining, including much of the
uranium mining and mining for rare earth elements being done today, is done by less-common methods, such as
in-situ leaching: this technique involves digging neither at the surface nor underground. The extraction of target minerals by this teqhnique requires that they be soluble, e.g.,
potash,
potassium chloride,
sodium chloride,
sodium sulfate and
uranium oxide which dissolve in water.
Surface mining is done by removing (stripping) surface vegetation, dirt, and if necessary, layers of bedrock in order to reach buried ore deposits. Techniques of surface mining include;
Open-pit mining which consists of recovery of materials from an open pit in the ground,
quarrying or gathering building materials from an open pit mine,
strip mining which consists of stripping surface layers off to reveal ore/seams underneath, and
Mountaintop removal, commonly associated with coal mining, which involves taking the top of a mountain off to reach ore deposits at depth. Most (but not all) placer deposits, because of their shallowly-buried nature, are mined by surface methods.
Landfill mining finally are sites where
landfills are excavated and processed.
Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits. Ore, for processing, and waste rock, for disposal, are brought to the surface through the tunnels and shafts. Sub-surface mining can be classified by the type of access shafts used, the extraction method or the technique used to reach the mineral deposit.
Drift mining utilizes horizontal access tunnels,
slope mining uses diagonally sloping access shafts and
shaft mining consists of vertical access shafts. Other methods include
shrinkage stope mining which is mining upward creating a sloping underground room,
long wall mining which is grinding a long ore surface underground and
room and pillar which is removing ore from rooms while leaving pillars in place to support the roof of the room. Room and pillar mining often leads to
retreat mining which is removing the pillars which support rooms, allowing the room to cave in, loosening more ore. Additional sub-surface mining methods include
Hard rock mining which is mining of hard materials,
bore hole mining,
drift and fill mining,
long hole slope mining,
sub level caving and
block cavingMachinery
Gold-bearing gravels are shoveled into a trommel at the Blue Ribbon placer mine, Alaska.
Heavy machinery is needed in mining for exploration and development, to remove and stockpile overburden, to break and remove rocks of various hardness and toughness, to process the ore and for reclamation efforts after the mine is closed. Bulldozers, drills, explosives and trucks are all necessary for excavating the land. In the case of
placer mining, unconsolidated gravel, or
alluvium, is fed into machinery consisting of a hopper and a shaking screen or
trommel which frees the desired minerals from the waste gravel. The minerals are then concentrated using
sluices or jigs. Large
drills are used to sink shafts, excavate stopes and obtain samples for analysis.
Trams are used to transport miners, minerals and waste. Lifts carry miners into and out of mines, as well as moving rock and ore out, and machinery in and out of underground mines. Huge trucks, shovels and cranes are employed in surface mining to move large quantities of overburden and ore. Processing plants can utilize large crushers, mills, reactors, roasters and other equipment to consolidate the mineral-rich material and extract the desired compounds and metals from the ore.
Extractive metallurgy
The science of
extractive metallurgy is a specialized area in the science of metallurgy that studies the extraction of valuable metals from their ores, especially through chemical or mechanical means.
Mineral processing (or mineral dressing) is a specialized area in the science of metallurgy that studies the mechanical means of crushing, grinding, and washing that enable the separation (extractive metallurgy) of valuable metals or minerals from their
gangue (waste material). Since most metals are present in ores as oxides or sulfides, the metal needs to be
reduced to its metallic form. This can be accomplished through chemical means such as
smelting or through electrolytic reduction, as in the case of
aluminum.
Geometallurgy combines the geologic sciences with extractive metallurgy and mining.
Environmental effects
Iron hydroxide precipitate stains a stream receiving acid drainage from surface coal mining.
Environmental issues can include
erosion, formation of
sinkholes, loss of
biodiversity, and contamination of soil,
groundwater and
surface water by chemicals from mining processes. In some cases, additional forest logging is done in the vicinity of mines to increase the available room for the storage of the created debris and soil. Besides creating environmental damage, the contamination resulting from leakage of chemicals also affect the health of the local population. Mining companies in many countries may be required to follow environmental and rehabilitation codes; however, in many areas regulation is not enforced, and mining companies have encouraged
self-policing.
[Moody R. (2007). Rocks and Hard Places. Zed Books.] In 1992 a Draft Code of Conduct for Transnational Corporations was proposed at the
Rio Earth Summit by the UN Centre for Transnational Corporations (UNCTC), but the Business Council for Sustainable Development (BCSD) together with the International Chamber of Commerce (ICC) argued successfuly for self-regulation instead. This was followed up by the Global Mining Initiative which created of the
International Council on Mining and Metals, an industry organization which works to self-regulate the mining industry internationally.
[ The mining industry has provided funding to various nonprofit groups, which have been subsequently less inclined to fight for the rights of indigenous people. ]
Ore mills generate large amounts of waste, called tailings, which are perhaps their largest environmental burden. For example, 99 tonnes of waste are generated per tonne of copper, with even higher ratios in gold mining. These tailings can be toxic. There are various ways to store tailings (see tailings article). The mining industry has argued that submarine tailings disposal (STD) is ideal; although the practice is illegal in the United States and Canada, it is used in the developing world.
Certification of mines with good practices occurs through the International Organization for Standardization (ISO) such as ISO 9000 and ISO 14001, which certifies an 'auditable environmental management system'; this certification involves short inspections, although it has been accused of lacking rigor.[ Certification is also available through Ceres' Global Reporting Initiative, but these reports are voluntary and unverified. Miscellaneous other certification programs exist for various projects, typically through nonprofit groups.] Regulations and World Bank relationship
The World Bank has been involved in mining since 1955, mainly through grants from its International Bank for Reconstruction and Development, with the Bank's Multilateral Investment Guarantee Agency offering political risk insurance. Between 1955 and 1990 it provided about $2 billion to fifty mining projects, broadly categorized as reform and rehabilitation, greenfield mine construction, mineral processing, technical assistance, and engineering. These projects have been criticized, particularly the Ferro Carajas project of Brazil, began in 1981. The bank established mining codes intended to increase foreign investment, in 1988 solicited feedback from 45 mining companies on how to increase their involvement.
In 1992 the bank began to push for privatization of government-owned mining companies with a new set of codes, beginning with its report The Strategy for African Mining. In 1997, Latin America's largest miner Companhia Vale do Rio Doce (CVRD) was privatized. These and other movements such as the Philippines 1995 Mining Act led the World Bank to publish a third report (Assistance for Minerals Sector Development and Reform in Member Countries) which endorsed mandatory environment impact assessments and attention to the locals. The codes based on this report are influential in the legislation of developing nations. The new codes are intenteded to encourage development through tax holidays, zero custom duties, reduced income taxes, and related measures.[ The results of these codes were analyzed by a group from the University of Quebec, which concluded that the codes promote foreign investment but "fall very short of permitting sustainable development". The observed negative effect of natural resources on economic development is known as the resource curse.]Mining industry
While exploration and mining can sometimes be conducted by individual entrepreneurs or small business, most modern-day mines are large enterprises requiring large amounts of capital to establish. Consequently, the mining sector of the industry is dominated by large, often multinational, mostly publicly-listed companies. See Mining Companies for a list.
However, what is referred to as the 'mining industry' is actually two sectors, one specializing in exploration for new resources, the other specializing in mining those resources. The exploration sector is typically made up of individuals and small mineral resource companies dependent on public investment. The mining sector is typically large and multi-national companies sustained by mineral production from their mining operations. In addition to these two sectors, various other industries such as equipment manufacture, environmental testing and metallurgy analysis also rely on and support the mining industry throughout the world.Corporate classifications
Mining companies can be classified based on their size and financial capabilities:
- Major companies are considered to have an adjusted annual mining-related revenue of more than US$500 million, with the financial capability to develop a major mine on its own.
- Intermediate companies have at least $50 million in annual revenue but less than $500 million.
- Junior companies rely on equity financing as their principal means of funding exploration. Juniors are mainly pure exploration companies, but may also produce minimally, and do not have a revenue of US$50 million.
Safety
Danger sign at an old Arizona mine.
Abandoned mine entrance in
Yorkshire, England
[ For this reason, the MHSA requires that workers have gas detection equipment in groups of miners. It must be able to detect common gases, such as CO, O2, H2S, and % Lower Explosive Limit. Additionally, further regulation is being requested for more gas detection as newer technology such as nanotechnology is introduced. High temperatures and humidity may result in heat-related illnesses, including heat stroke which can be fatal. Dusts can cause lung problems, including silicosis, asbestosis and pneumoconiosis (also known as miners lung or black lung disease). A ventilation system is set up to force a stream of air through the working areas of the mine. The air circulation necessary for the effective ventilation of a mine is generated by one or more large mine fans, usually located above ground. Air flows in one direction only, making circuits through the mine such that each main work area constantly receives a supply of fresh air.]
Since mining entails removing dirt and rock from its natural location creating large empty pits, rooms and tunnels, cave-ins are a major concern within mines. Modern techniques for timbering and bracing walls and ceilings within sub-surface mines have reduced the number of fatalities due to cave-ins, but accidents still occur. The presence of heavy equipment in confined spaces also poses a risk to miners, and in spite of modern improvements to safety practices, mining remains dangerous throughout the world.Abandoned mines
Abandoned mine in Nevada.
Hearing loss
Miners utilize equipment strong enough to break through extremely hard layers of the earth's crust. This equipment, combined with the closed workspace that underground miners work in, can cause hearing loss.[ ] For example, a roof bolter (commonly used by mine roof bolter operators) can reach sound power levels of up to 115 dB.[ Combined with the reverberant effects of underground mines, a miner without proper hearing protection is not only at a high risk for hearing loss,][ but is also going against OSHA standards.] Records
As of 2008, the deepest mine in the world is TauTona in Carletonville, South Africa at 3.9 kilometers
The deepest open pit mine in the world is Bingham Canyon Mine in Bingham Canyon, Utah, United States at over 1,200 meters. The largest and second deepest open pit copper mine in the world is Chuquicamata in Chuquicamata, Chile at 900 meters, 940,600 tons of copper and 17,700 tons of molybdenum produced annually.
The largest underground mine: El Teniente, in Rancagua, Chile, 2,400 kilometers of underground drifts, 418,000 tons of copper yearly. The deepest borehole in the world is Kola Superdeep Borehole at 12,262 meters. This, however, is not a matter of mining but rather related to scientific drilling. See also
