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80-660: The BHP Mitsubishi Alliance (BMA) is an Australian coal mining company operating in Central Queensland . The largest coal producer in Australia, it is a joint venture with BHP and Mitsubishi each owning 50%. It was established in 2001. The BMA alliance operates five mines in the Bowen Basin : BMA also operates Moranbah Airport and part of the Hay Point Coal Terminal. It operated

160-705: A 70% increase over the 20 years since 1999. In 2018, the world production of brown coal (lignite) was 803.2 Mt, with Germany the world's largest producer at 166.3 Mt. China is most likely the second largest producer and consumer of lignite globally although specific lignite production data is not made available. Coal production has grown fastest in Asia, while Europe has declined. Since 2011, world coal production has been stable, with decreases in Europe and US offset by increases from China, Indonesia and Australia. The top coal mining nations are: Energy production from coal mining

240-467: A coal seam occurring near the top of a ridge or hill, the entire top is removed in a series of parallel cuts. Overburden is deposited in nearby valleys and hollows. This method usually leaves the ridge and hilltops as flattened plateaus. The process is highly controversial for the drastic changes in topography, the practice of creating head-of-hollow-fills , or filling in valleys with mining debris, and for covering streams and disrupting ecosystems. Spoil

320-405: A fourth of the world's energy. Coal extraction methods vary depending on whether the mine is an underground mine or a surface (also called an open cast) mine. Additionally, coal seam thickness and geology are factors in the selection of a mining method. The most economical method of coal extraction for surface mines is the electric shovel or drag line. The most economical form of underground mining

400-464: A fuel for extraction of iron from iron ore and for cement production. In the United Kingdom and South Africa , a coal mine and its structures are a colliery , a coal mine is called a "pit", and above-ground mining structures are referred to as a " pit head ". In Australia , "colliery" generally refers to an underground coal mine. Coal mining has had many developments in recent years, from

480-403: A greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. This equipment can include the following: Draglines which operate by removing the overburden, power shovels, large trucks in which transport overburden and coal, bucket wheel excavators, and conveyors. In this mining method, explosives are first used in order to break through

560-440: A land use condition is not equal to the original use. Existing land uses (such as livestock grazing, crop and timber production) are temporarily eliminated in mining areas. High-value, intensive-land-use areas like urban and transportation systems are not usually affected by mining operations. If mineral values are sufficient, these improvements may be removed to an adjacent area. Strip mining eliminates existing vegetation, destroys

640-440: A large dining-room table, but with hydraulic jacks for legs. After the large pillars of coal have been mined away, the mobile roof support's legs shorten and it is withdrawn to a safe area. The mine roof typically collapses once the mobile roof supports leave an area. There are six principal methods of underground mining: Coal is mined commercially in over 50 countries. 7,921 million metric tons (Mt) of coal were produced in 2019,

720-447: A method that currently accounts for about 60 percent of world coal production. In deep mining, the room and pillar or bord and pillar method progresses along the seam, while pillars and timber are left standing to support the mine roof. Once room and pillar mines have been developed to a stopping point limited by geology, ventilation, or economics, a supplementary version of room and pillar mining, termed second mining or retreat mining ,

800-447: A mine that contribute to this load: drilling , blasting, loading, and hauling . Waste rock is hauled to a waste dump. Waste dumps can be piled at the surface of the active pit, or in previously mined pits. Leftover waste from processing the ore is called tailings , and is generally in the form of a slurry . This is pumped to a tailings dam or settling pond, where the water is reused or evaporated. Tailings dams can be toxic due to

880-424: A new coal mine. Open pit Open-pit mines are used when deposits of commercially useful ore or rocks are found near the surface where the overburden is relatively thin. In contrast, deeper mineral deposits can be reached using underground mining. Open-pit mining is considered one of the most dangerous sectors in the industrial world . It causes significant effects to miners' health, as well as damage to

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960-429: A number of worked-out mines. After mining ends at a location, the mine area may undergo land rehabilitation . Waste dumps are contoured to flatten them out, to further stabilize them. If the ore contains sulfides it is usually covered with a layer of clay to prevent ingress of rain and oxygen from the air, which can oxidize the sulfides to produce sulfuric acid , a phenomenon known as acid mine drainage . This

1040-477: A result of room and pillar mining . Untopping removes the overburden from above this, opens up the mine from above, and then allows the previously 'trapped' minerals to be won. Untopping was a feature of Welsh slate workings in the 1930s and 2000s, where Martyn Williams-Ellis, manager at Llechwedd found that earlier Victorian workings could be kept profitable with the newly mechanised techniques for bulk excavation to extract their pillars, and more recently across

1120-589: A result of occupational exposures is coined occupational hearing loss . To protect miners' hearing, the US Mine Safety and Health Administration 's (MSHA) guidelines for noise place a Permissible Exposure Limit (PEL) for noise at 90 dBA time-weighted over 8 hours. A lower cutoff, 85 dBA, is set for a worker to fall into the MSHA Action Level which dictates that workers be placed into hearing conservation programs. Noise exposures vary depending on

1200-450: Is a crucial aspect of determining whether or not a geotechnical engineering design for open-pit slopes is attainable. Groundwater control systems, which include dewatering and depressurization wells, may also have a large impact on local groundwater. Because of this, an optimization-based version of the control system is required to ensure that local and regional hydro-geological impacts are within acceptable ranges. Open Pit depressurization

1280-575: Is accomplished by drilling holes into the overburden, filling the holes with explosives, and detonating the explosive. The overburden is then removed, using large earth-moving equipment, such as draglines , shovel and trucks, excavator and trucks, or bucket-wheels and conveyors. This overburden is put into the previously mined (and now empty) strip. When all the overburden is removed, the underlying coal seam will be exposed (a 'block' of coal). This block of coal may be drilled and blasted (if hard) or otherwise loaded onto trucks or conveyors for transport to

1360-427: Is commonly started. Miners remove the coal in the pillars, thereby recovering as much coal from the coal seam as possible. A work area involved in pillar extraction is called a pillar section. Modern pillar sections use remote-controlled equipment, including large hydraulic mobile roof-supports, which can prevent cave-ins until the miners and their equipment have left a work area. The mobile roof supports are similar to

1440-418: Is dedicated to mining activities until it can be reshaped and reclaimed. If mining is allowed, resident human populations must be resettled off the mine site; economic activities, such as agriculture or hunting and gathering food and medicinal plants are interrupted. What becomes of the land surface after mining is determined by the manner in which the mining is conducted. Usually reclamation of disturbed lands to

1520-516: Is highly concentrated in certain jurisdictions, which also concentrates much of the social and economic impacts of the industry to these regions. The industry directly employs over seven million workers worldwide, which, in turn, creates millions of indirect jobs. In several parts of the world, producers have reached peak coal as some economies shift away from fossil fuels to address climate change. A 2020 study found that renewables jobs could feasibly be created in these geographies to replace many of

1600-427: Is mostly used to generate electricity, and 75% of annual coal production is exported, mostly to eastern Asia. In 2007, 428 million tonnes of coal was mined in Australia. In 2007, coal provided about 85% of Australia's electricity production. In the fiscal year 2008/09, 487 million tonnes of coal was mined, and 261 million tonnes was exported. In the fiscal year 2013/14, 430.9 million tonnes of coal

1680-417: Is partially economically recoverable. Coal refuse is distinct from the byproducts of burning coal, such as fly ash . Piles of coal refuse can have significant negative environmental consequences, including the leaching of iron, manganese, and aluminum residues into waterways and acid mine drainage . The runoff can create both surface and groundwater contamination. The piles also create a fire hazard, with

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1760-593: Is placed at the head of a narrow, steep-sided valley or hollow. In preparation for filling this area, vegetation and soil are removed and a rock drain constructed down the middle of the area to be filled, where a natural drainage course previously existed. When the fill is completed, this underdrain will form a continuous water runoff system from the upper end of the valley to the lower end of the fill. Typical head-of-hollow fills are graded and terraced to create permanently stable slopes. Most coal seams are too deep underground for opencast mining and require underground mining,

1840-436: Is referred to as 'overburden' and is removed in long strips. The overburden from the first strip is deposited in an area outside the planned mining area and referred to as out-of-pit dumping. Overburden from subsequent strips is deposited in the void left from mining the coal and overburden from the previous strip. This is referred to as in-pit dumping. It is often necessary to fragment the overburden by use of explosives. This

1920-515: Is removed and overburden dumped to the side. Dust, vibration, and diesel exhaust odors are created (affecting sight, sound, and smell). Residents of local communities often find such impacts disturbing or unpleasant. In case of mountaintop removal , tops are removed from mountains or hills to expose thick coal seams underneath. The soil and rock removed is deposited in nearby valleys, hollows and depressions, resulting in blocked (and contaminated) waterways. Removal of soil and rock overburden covering

2000-712: Is still common, with 4,000 new cases of black lung every year in the US (4 percent of workers annually) and 10,000 new cases every year in China (0.2 percent of workers). The use of water sprays in mining equipment reduces the risk to miners' lungs. Build-ups of a hazardous gas are known as damps, possibly from the German word Dampf which means steam or vapor: Noise is also a contributing factor to potential adverse effects on coal miners' health. Exposure to excessive noise can lead to noise-induced hearing loss . Hearing loss developed as

2080-464: Is the long wall, which involves using two spinning drums with carbide bits that runs along sections of the coal seam. Many coals extracted from both surface and underground mines require washing in a coal preparation plant . Technical and economic feasibility are evaluated based on the following: regional geological conditions; overburden characteristics; coal seam continuity, thickness, structure, quality, and depth; strength of materials above and below

2160-401: Is the process of removing tensions or pressure from different areas of a mine. Depressurization helps to make open-pit mines more stable and secure. By using an integrated mine slope depressurization program the likelihood that mine plans can be achieved, and at an acceptable level of risk increase drastically. Depressurization allows considerable expansions of a mine, and can extend the life of

2240-559: Is then generally covered with soil , and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large-scale open-pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to

2320-435: Is used for both thermal and metallurgical coals . In New South Wales open casting for steam coal and anthracite is practiced. Surface mining accounts for around 80 percent of production in Australia, while in the US it is used for about 67 percent of production. Globally, about 40 percent of coal production involves surface mining. Strip mining exposes coal by removing earth above each coal seam. This earth to be removed

2400-616: The Gregory coal mine until March 2019, when it was sold to Japan's Sojitz Corporation . BMA owned the Blackwater and Daunia coal mines until it was sold to Whitehaven Coal in April 2024. Coal mining Coal mining is the process of extracting coal from the ground or from a mine. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as

2480-491: The Industrial Revolution , and coal provided the main source of primary energy for industry and transportation in industrial areas from the 18th century to the 1950s. Coal remains an important energy source. Coal is also mined today on a large scale by open pit methods wherever the coal strata strike the surface or are relatively shallow. Britain developed the main techniques of underground coal mining from

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2560-668: The Lusatian Lake District , the Central German Lake District or the Upper Palatinate Lake District. A particular concern in the formation of these lakes is acid mine drainage . Open-pit mines create a significant amount of waste. Almost one million tons of ore and waste rock can move from the largest mines per day, and a couple thousand tons moved from small mines per day. There are generally four main operations in

2640-594: The Philippines and Indonesia . In 2024, nickel mining and processing was one of the main causes of deforestation in Indonesia . Open-pit cobalt mining has led to deforestation and habitat destruction in the Democratic Republic of Congo . Open-pit mines operating in an area with heavy groundwater features may eventually face hydrology-related problems. This includes heaving and bursting of

2720-418: The mineral resource is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. After open-pit mines are closed, they are sometimes converted to landfills for disposal of solid waste. Some form of water control is usually required to keep the mine pit from becoming a lake. Several former open-pit mines have been deliberately converted into artificial lakes, forming areas such as

2800-812: The U.S., Examples include the Sago Mine disaster of 2006, and the 2007 mine accident in Utah 's Crandall Canyon Mine , where nine miners were killed and six entombed. In the decade 2005–2014, US coal mining fatalities averaged 28 per year. The most fatalities during the 2005–2014 decade were 48 in 2010, the year of the Upper Big Branch Mine disaster in West Virginia, which killed 29 miners. Chronic lung diseases, such as pneumoconiosis (black lung) were once common in miners, leading to reduced life expectancy . In some mining countries black lung

2880-624: The US Department of Labor's Mine Safety and Health Administration (MSHA) show that between 1990 and 2004, the industry cut the rate of injuries by more than half and fatalities by two-thirds. But according to the Bureau of Labor Statistics , even in 2006, mining remained the second most dangerous occupation in America, when measured by fatality rate . These numbers, however, include all mining activities, and oil and gas mining contribute to

2960-673: The United States and proposed mines under development. The coal mining industry employs almost 2.7 million workers. The History of coal mining goes back thousands of years, with early mines documented in ancient China, the Roman Empire and other early historical economies. It became important in the Industrial Revolution of the 19th and 20th centuries, when it was primarily used to power steam engines, heat buildings and generate electricity. Coal mining continues as an important economic activity today, but has begun to decline due to

3040-402: The areas surrounding open-pit mines. Open-pit gold mining is one of the highest potential mining threats on the environment as it affects the air and water chemistry. The exposed dust may be toxic or radioactive, making it a health concern for the workers and the surrounding communities. Open-pit nickel mining has led to environmental degradation and pollution in developing countries such as

3120-581: The coal mining jobs as part of a just transition ; however, renewable energy was not suitable in some of the geographies with high concentrations of miners, such as in China, which is far and away the leading coal-mining nation. Coal refuse (also described as coal waste, rock, slag, coal tailings, waste material, rock bank, culm, boney, or gob ) is the material left over from coal mining, usually as tailings piles or spoil tips . For every tonne of hard coal generated by mining, 400 kg (880 lb) of waste material remains, which includes some lost coal that

3200-497: The coal preparation (or wash) plant. Once this strip is empty of coal, the process is repeated with a new strip being created next to it. This method is most suitable for areas with flat terrain. Equipment to be used depends on geological conditions. For example, to remove overburden that is loose or unconsolidated, a bucket wheel excavator might be the most productive. The life of some area mines may be more than 50 years. The contour mining method consists of removing overburden from

3280-863: The coal resource may cause burial and loss of topsoil, exposes parent material, and creates large infertile wastelands. Soil disturbance and associated compaction result in conditions conducive to erosion. Soil removal from the area to be surface-mined alters or destroys many natural soil characteristics, and reduces its biodiversity and productivity for agriculture. Soil structure may be disturbed by pulverization or aggregate breakdown. Top 10 hard and brown coal producers in 2012 were (in million metric tons): China 3,621, United States 922, India 629, Australia 432, Indonesia 410, Russia 351, South Africa 261, Germany 196, Poland 144, and Kazakhstan 122. Coal has been mined in every state of Australia, but mainly in Queensland, New South Wales and Victoria. It

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3360-409: The deposit being mined, the mineral being mined, and the size of the machinery that is being used. Generally, large mine benches are 12 to 15 metres thick. In contrast, many quarries do not use benches, as they are usually shallow. Mining can be conducted on more than one bench at a time, and access to different benches is done with a system of ramps. The width of each bench is determined by the size of

3440-429: The developed world. Modern coal mining in the US has an average 23 deaths per year due to mine accidents (2001–2020). However, in lesser developed countries and some developing countries, many miners continue to die annually, either through direct accidents in coal mines or through adverse health consequences from working under poor conditions. China , in particular, has the highest number of coal mining related deaths in

3520-455: The disruptive activities of blasting, ripping, and excavating coal. Stripping of overburden eliminates and destroys archeological and historic features, unless they are removed beforehand. The removal of vegetative cover and activities associated with the construction of haul roads, stockpiling of topsoil, displacement of overburden and hauling of soil and coal increase the quantity of dust around mining operations. Dust degrades air quality in

3600-424: The early days of men tunneling, digging, and manually extracting the coal on carts to large open-cut and longwall mines. Mining at this scale requires the use of draglines , trucks, conveyors , hydraulic jacks , and shearers. The coal mining industry has a long history of significant negative environmental impacts on local ecosystems, health impacts on local communities and workers, and contributes heavily to

3680-424: The ecological land and water. Open-pit mining causes changes to vegetation, soil, and bedrock, which ultimately contributes to changes in surface hydrology, groundwater levels, and flow paths. Additionally, open-pit produces harmful pollutants depending on the type of mineral being mined, and the type of mining process being used. Miners typically drill a series of test holes to locate an underground ore body. From

3760-472: The environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence , to prevent access, and it generally eventually fills up with ground water . In arid areas it may not fill due to deep groundwater levels. In Germany, the world's largest producer of lignite (virtually all of which these days is mined open-pit), the former mines are usually converted to artificial lakes . To mitigate

3840-480: The equipment being used, generally 20–40 metres wide. Downward ramps are created to allow mining on a new level to begin. This new level will become progressively wider to form the new pit bottom. Most walls of the pit are generally mined on an angle less than vertical. Waste rock is stripped when the pit becomes deeper, therefore this angle is a safety precaution to prevent and minimize damage and danger from rock falls. However, this depends on how weathered and eroded

3920-402: The extracted samples, they can determine the extent of the ore. This helps them determine the likely location of the veins or benches of ore and its commercial value. Open-pit mines that produce building materials and dimension stone are commonly referred to as quarries . Open-cast mines are dug on benches , which describe vertical levels of the hole. The interval of the benches depends on

4000-571: The fatalities occurring in the first half of the 20th century. 3,242 died in 1907, the worst year ever; in 2020 there were five. Open cut hazards are principally mine wall failures and vehicle collisions; underground mining hazards include suffocation, gas poisoning, roof collapse, rock burst , outbursts , and gas explosions. Firedamp explosions can trigger the far more dangerous coal dust explosions, which can engulf an entire mine. Most of these risks are greatly reduced in modern mines, and multiple fatality incidents are now rare in most parts of

4080-457: The genetic soil profile, displaces or destroys wildlife and habitat, alters current land uses, and to some extent permanently changes the general topography of the area mined. Adverse impacts on geological features of human interest may occur in a coal strip mine. Geomorphic and geophysical features and outstanding scenic resources may be sacrificed by indiscriminate mining. Paleontological, cultural, and other historic values may be endangered due to

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4160-399: The global environmental crises, such as poor air quality and climate change . For these reasons, coal has been one of the first fossil fuels to be phased out of various parts of the global energy economy . The major coal producing countries, though, such as China , Indonesia, India and Australia , have not reached peak production, with production increases replacing falls in Europe and

4240-450: The immediate area, has an adverse impact on vegetative life, and constitutes health and safety hazards for mine workers and nearby residents. Surface mining disrupts virtually all aesthetic elements of the landscape. Alteration of land forms often imposes unfamiliar and discontinuous configurations. New linear patterns appear as material is extracted and waste piles are developed. Different colors and textures are exposed as vegetative cover

4320-460: The late 18th century onward, with further progress being driven by 19th-century and early 20th-century progress. However, oil and gas were increasingly used as alternatives from the 1860s onward. By the late 20th century, coal was, for the most part, replaced in domestic as well as industrial and transportation usage by oil , natural gas or electricity produced from oil, gas, nuclear power or renewable energy sources. By 2010, coal produced over

4400-404: The majority of fatalities. Coal mining resulted in 47 fatalities that year. One study, though, has suggested that hazards of modern mining are now more accretive with workers facing long-term health impacts, such as sleep deprivation, that build up over time. Strip mining severely alters the landscape, which reduces the value of the natural environment in the surrounding land. The land surface

4480-461: The method of extraction. For example, a study has found that among surface coal mine operations, dragline equipment produced the loudest sound at a range of 88–112 dBA. Within longwall sections, stageloaders used to transport coal from the mining face and shearers used for extraction represent some of the highest noise exposures. Auxiliary fans (up to 120 dBA), continuous mining machines (up to 109 dBA), and roof bolters (up to 103 dBA) represent some of

4560-454: The mine by 10 to 15 years. One technique used in depressurization is annealing. Annealing is the slow heating and cooling of a metal, alloy or glass. This slow heating and cooling relieves the internal stress of surrounding areas. Annealing will increase a material's workability and durability, which overall increases open-pit mine safety. When groundwater pressures cause problems in open-pit mines, horizontal drains are used to aid in accelerating

4640-450: The mine floor due to excessive uplift pressure. A groundwater control system must be installed to fix problems caused by hydrology. The formation of an appropriate open-pit slope design, changes throughout the life of a mine. It is based mainly on an ever-increasing understanding of the rock mass conditions, including groundwater and associated pressures that may be acting within the slopes. The reduction of groundwater related to pore pressures

4720-465: The mining workforce. in 2015 US coal mines had 65,971 employees, the lowest figure since EIA began collecting data in 1978. However, a 2016 study reported that a relatively minor investment would allow most coal workers to retrain for the solar energy industry. Coal mining has been a very dangerous activity and the list of historical coal mining disasters is long. In the U.S., 104,895 coal miners were killed in mine accidents since 1900, 90 percent of

4800-469: The noisiest equipment within continuous mining sections. Exposures to noise exceeding 90 dBA can lead to adverse effects on workers' hearing. The use of administrative controls and engineering controls can be used to reduce noise exposures. Improvements in mining methods (e.g. longwall mining), hazardous gas monitoring (such as safety-lamps or more modern electronic gas monitors), gas drainage, electrical equipment , and ventilation have reduced many of

4880-590: The open pit methods, due to thickness of the seam 20–25 metres (60–90 feet). Coals occurring below 90 m (300 ft) are usually deep mined. However, there are open pit mining operations working on coal seams up to 300–460 metres (1,000–1,500 feet) below ground level, for instance Tagebau Hambach in Germany. When coal seams are near the surface, it may be economical to extract the coal using open-cut , also referred to as open-cast, open-pit, mountaintop removal or strip, mining methods. Opencast coal mining recovers

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4960-421: The operation reaches a predetermined stripping ratio (tons of overburden/tons of coal), it is not profitable to continue. Depending on the equipment available, it may not be technically feasible to exceed a certain height of highwall. At this point, it is possible to produce more coal with the augering method in which spiral drills bore tunnels into a highwall laterally from the bench to extract coal without removing

5040-408: The overburden. Mountaintop coal mining is a surface mining practice involving removal of mountaintops to expose coal seams, and disposing of associated mining overburden in adjacent "valley fills." Valley fills occur in steep terrain where there are limited disposal alternatives. Mountaintop removal mining combines area and contour strip mining methods. In areas with rolling or steep terrain with

5120-425: The potential to spontaneously ignite. Because most coal refuse harbors toxic components, it is not easily reclaimed by replanting with plants like beach grasses. The use of sophisticated sensing equipment to monitor air quality is common and has replaced the use of small animals such as canaries, often referred to as " miner's canaries ". In the United States, the increase in technology has significantly decreased

5200-446: The presence of unextracted sulfide minerals , some forms of toxic minerals in the gangue , and often cyanide which is used to treat gold ore via the cyanide leach process . If proper environmental protections are not in place, this toxicity can harm the surrounding environment. Open-pit mining involves the process of disrupting the ground, which leads to the creation of air pollutants. The main source of air pollutants comes from

5280-407: The problem of acid mine drainage mentioned above, flooding is often done with the water of nearby rivers instead of using groundwater alone. In some cases, calcium oxide or other basic chemicals have to be added to the water to neutralize the pH -value. Gold is generally extracted in open-pit mines at 1 to 5 ppm (parts per million) but in certain cases, 0.75 ppm gold is economical. This

5360-399: The risks of rock falls, explosions, and unhealthy air quality. Gases released during the mining process can be recovered to generate electricity and improve worker safety with gas engines . Another innovation in recent years is the use of closed circuit escape respirators , respirators that contain oxygen for situations where mine ventilation is compromised. Statistical analyses performed by

5440-404: The rocks are, and the type of rocks involved. It also depends on the amount of structural weaknesses occur within the rocks, such as a faults , shears , joints or foliations . The walls are stepped. The inclined section of the wall is known as the batter, and the flat part of the step is known as the bench or berm. The steps in the walls help prevent rock falls continuing down the entire face of

5520-418: The seam for roof and floor conditions; topography, especially altitude and slope; climate; land ownership as it affects the availability of land for mining and access; surface drainage patterns; groundwater conditions; availability of labor and materials; coal purchaser requirements in terms of tonnage, quality, and destination; and capital investment requirements. Surface mining and deep underground mining are

5600-565: The seam in a pattern following the contours along a ridge or around the hillside. This method is most commonly used in areas with rolling to steep terrain. It was once common to deposit the spoil on the downslope side of the bench thus created, but this method of spoil disposal consumed much additional land and created severe landslide and erosion problems. To alleviate these problems, a variety of methods were devised to use freshly cut overburden to refill mined-out areas. These haul-back or lateral movement methods generally consist of an initial cut with

5680-412: The slope depressurization process. Which helps to prevent large scale slope failure in the mine. Horizontal drains are used to lower pore pressure by reducing groundwater head, which enhances slope stability. A form of open-cast quarrying may be carried out as 'untopping'. This is done where a previous underground mine is becoming uneconomic or worked-out, but still leaves valuable rock in place, often as

5760-432: The spoil deposited downslope or at some other site and spoil from the second cut refilling the first. A ridge of undisturbed natural material 15 to 20 ft (5 to 6 m) wide is often intentionally left at the outer edge of the mined area. This barrier adds stability to the reclaimed slope by preventing spoil from slumping or sliding downhill. The limitations of contour strip mining are both economic and technical. When

5840-556: The strong contribution coal plays in global warming and environmental issues, which result in decreasing demand and in some geographies, peak coal . Compared to wood fuels , coal yields a higher amount of energy per unit mass, specific energy or massic energy, and can often be obtained in areas where wood is not readily available. Though it was used historically as a domestic fuel, coal is now used mostly in industry, especially in smelting and alloy production, as well as electricity generation . Large-scale coal mining developed during

5920-476: The surface or overburden, of the mining area. The overburden is then removed by draglines or by shovel and truck. Once the coal seam is exposed, it is drilled, fractured and thoroughly mined in strips. The coal is then loaded onto large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used. Most open cast mines in the United States extract bituminous coal . In Canada, Australia, and South Africa, open cast mining

6000-416: The transportation of minerals, but there are various other factors including drilling, blasting and the loading and unloading of overburden. These type of pollutants cause significant damage to public health and safety in addition to damaging the air quality. The inhalation of these pollutants can cause issues to the lungs and ultimately increase mortality. Furthermore, the pollutants affect flora and fauna in

6080-524: The two basic methods of mining. The choice of mining method depends primarily on depth, density, overburden, and thickness of the coal seam; seams relatively close to the surface, at depths less than approximately 55 m (180 ft), are usually surface mined. Coal that occurs at depths of 55 to 90 m (180 to 300 ft) are usually deep mined, but in some cases surface mining techniques can be used. For example, some western U.S. coal that occur at depths in excess of 60 m (200 ft) are mined by

6160-466: The wall. In some instances additional ground support is required and rock bolts , cable bolts and shotcrete are used. De-watering bores may be used to relieve water pressure by drilling horizontally into the wall, which is often enough to cause failures in the wall by itself. A haul road is usually situated at the side of the pit, forming a ramp up which trucks can drive, carrying ore and waste rock. Open-pit mines are typically worked until either

6240-441: The world, with official statistics claiming that 6,027 deaths occurred in 2004. To compare, 28 deaths were reported in the U.S. in the same year. Coal production in China is twice that in the US, while the number of coal miners is around 50 times that of the US, making deaths in coal mines in China 4 times as common per worker (108 times as common per unit output) as in the US. Mine disasters have still occurred in recent years in

6320-524: Was achieved by bulk heap leaching at the Peak Hill mine in western New South Wales , near Dubbo , Australia . Nickel , generally as laterite, is extracted via open-pit down to 0.2%. Copper can be extracted at grades as low as 0.11% to 0.2%. Open-pit mining is a common method to extract minerals and samples from the Earth. Due to being cost-effective, this method is very popular and is used all over

6400-531: Was mined, and 375.1 million tonnes was exported. In 2013/14, coal provided about 69% of Australia's electricity production. In 2013, Australia was the world's fifth-largest coal producer, after China, the United States, India, and Indonesia. However, in terms of proportion of production exported, Australia is the world's second largest coal exporter, as it exports roughly 73% of its coal production. Indonesia exports about 87% of its coal production. A court in Australia has cited climate change in ruling against

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