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Open-pit mining, also known as open-cast or open-cut mining and in larger contexts mega-mining, is a surface mining technique of extracting
rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...
or
minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed ...
from the earth from an open-air pit, sometimes known as a
borrow Borrow or borrowing can mean: to receive (something) from somebody temporarily, expecting to return it. *In finance, monetary debt *In language, the use of loanwords * In arithmetic, when a digit becomes less than zero and the deficiency is taken f ...
. This form of
mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...
differs from extractive methods that require tunnelling into the earth, such as
long wall mining Longwall mining is a form of underground coal mining where a long wall of coal is mined in a single slice (typically thick). The longwall panel (the block of coal that is being mined) is typically long (but can be upto long) and wide. Histo ...
. Open-pit mines are used when deposits of commercially useful ore or rocks are found near the surface. It is applied to ore or rocks found at the surface because the
overburden In mining, overburden (also called waste or spoil) is the material that lies above an area that lends itself to economical exploitation, such as the rock, soil, and ecosystem that lies above a coal seam or ore body. Overburden is distinct from tai ...
is relatively thin or the material of interest is structurally unsuitable for tunnelling (as would be the case for cinder, sand, and gravel). In contrast, minerals that have been found underground but are difficult to retrieve due to hard rock, can be reached using a form of underground mining. To create an open-pit mine, the miners must determine the information of the ore that is underground. This is done through drilling of probe holes in the ground, then plotting each hole location on a map. The information gained through the holes with provide an idea of the vertical extent of the ore's body. This vertical information is then used to pit tentative locations of the benches that will occur in the mine. It is important to consider the grade and economic value of the ore in the potential pit. Open-pit mines that produce
building material Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings. Apart from naturally occurring materials, many man-ma ...
s and dimension stone are commonly referred to as "
quarries A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envir ...
." Open-pit mines are typically enlarged until either the
mineral resource Natural resources are resources that are drawn from nature and used with few modifications. This includes the sources of valued characteristics such as commercial and industrial use, aesthetic value, scientific interest and cultural value. O ...
is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. When this occurs, the exhausted mines are sometimes converted to landfills for disposal of solid wastes. However, some form of water control is usually required to keep the mine pit from becoming a lake, if the mine is situated in a climate of considerable
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
or if any layers of the pit forming the mine border productive
aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...
s. In Germany and adjacent countries several former open pit mines have been deliberately converted into artificial lakes forming areas such as the
Lusatian Lake District The Lusatian Lake District (german: Lausitzer Seenland, dsb, Łužyska jazorina, hsb, Łužiska jězorina) is a chain of artificial lakes under construction in Germany across the north-eastern part of Saxony and the southern part of Brandenburg ...
, the
Central German Lake District The Central German Lake District (''German:'' Mitteldeutsches Seenland) is a group of artificial lakes that are the result of extensive open pit lignite mining. The area around Leipzig is sometimes separately marketed as the "Leipzig Lake Distri ...
or the Upper Palatinate Lake District. A particular concern in the formation of these lakes is
acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines or coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weathering ...
. Open-pit mining is to be considered one of the most dangerous sectors in the industrial world. It causes significant effects to miners' health, as well as damage to the ecological land. 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.


Extraction

Open-cast mines are dug on benches, which describe vertical levels of the hole. The interval of the benches depends on 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 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 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 the wall. In some instances additional ground support is required and
rock bolt A rock bolt is a long anchor bolt, for stabilizing rock excavations, which may be used in tunnels or rock cuts. It transfers load from the unstable exterior to the confined (and much stronger) interior of the rock mass. Rock bolts were first use ...
s, cable bolts and
shotcrete Shotcrete, gunite (), or sprayed concrete is concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique, first used in 1907 invented by Carl Akeley. It is typically ...
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
truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame constructi ...
s can drive, carrying
ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...
and waste rock.


Waste

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 is generally four main operations in a mine that contribute to this load: drilling, blasting, loading, and
hauling Haulage is the business of transporting goods by road or rail between suppliers and large consumer outlets, factories, warehouses, or depots. This includes everything humans might wish to move in bulk - from vegetables and other foodstuffs, to cloth ...
. 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 In mining, tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different to overburden, which is the waste rock or other material that overli ...
, and is generally in the form of a slurry. This is pumped to a
tailings dam A tailings dam is typically an earth-fill embankment dam used to store byproducts of mining operations after separating the ore from the gangue. Tailings can be liquid, solid, or a slurry of fine particles, and are usually highly toxic and po ...
or settling pond, where the water is reused or evaporated. Tailings dams can be
toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
due to the presence of unextracted sulfide
minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed ...
, some forms of toxic minerals in the
gangue In mining, gangue () is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body ...
, and often
cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
which is used to treat
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
ore via the cyanide leach process. If proper environmental protections are not in place, this
toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
can harm the surrounding environment.


Pollutants

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 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 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.


Hydrology in mining

Open pit mines operating in an area with heavy groundwater features may eventually face hydrology-related problems. This includes heaving and bursting of 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. Which includes groundwater and associated pressures that may be acting within the slopes. The reduction of groundwater related to pore pressures 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 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 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 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.


Untopping

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 a result of
room and pillar mining Room and pillar or pillar and stall is a variant of breast stoping. It is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars. To do this, "rooms" of ore are dug out ...
. 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 The existence of a slate industry in Wales is attested since the Roman period, when slate was used to roof the fort at Segontium, now Caernarfon. The slate industry grew slowly until the early 18th century, then expanded rapidly until the l ...
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 a number of worked-out mines.


Rehabilitation

After mining finishes, the mine area may undergo
land rehabilitation Land rehabilitation as a part of environmental remediation is the process of returning the land in a given area to some degree of its former state, after some process ( industry, natural disasters, etc.) has resulted in its damage. Many projects ...
. 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 Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
to prevent access of
rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...
and
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
from the air, which can oxidize the sulfides to produce sulfuric acid, a phenomenon known as
acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines or coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weathering ...
. This is then generally covered with
soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...
, 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 the environment. The dumps are usually fenced off to prevent
livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animal ...
denuding them of vegetation. The open pit is then surrounded with a
fence A fence is a structure that encloses an area, typically outdoors, and is usually constructed from posts that are connected by boards, wire, rails or netting. A fence differs from a wall in not having a solid foundation along its whole length. ...
, to prevent access, and it generally eventually fills up with
ground water Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
. In arid areas it may not fill due to deep groundwater levels. Instead of returning the land to its former natural state, it may also be reused, converting it into recreational parks or even residential/mixed communities. In Germany, the world's largest producer of lignite (virtually all of which is mined open pit these days), the former mines are usually converted to
artificial lake A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...
s. To mitigate 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 Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ...
or other basic chemicals have to be added to the water to neutralize the pH-value.


Typical open cut grades

Gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
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 was achieved by bulk
heap leaching Heap leaching is an industrial mining process used to extract precious metals, copper, uranium, and other compounds from ore using a series of chemical reactions that absorb specific minerals and re-separate them after their division from other e ...
at the
Peak Hill mine Peak or The Peak may refer to: Basic meanings Geology * Mountain peak ** Pyramidal peak, a mountaintop that has been sculpted by erosion to form a point Mathematics * Peak hour or rush hour, in traffic congestion * Peak (geometry), an (''n''-3)-d ...
in western
New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...
, near Dubbo, Australia.
Nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
, generally as laterite, is extracted via open-pit down to 0.2%.
Copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
can be extracted at grades as low as 0.11% to 0.2%. Materials typically extracted from open-pit mines include: * Bitumen *
Clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
*
Coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
*
Copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
* Coquina * Chromite *
Diamonds Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, bu ...
* Gravel and
stone In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...
*
Granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...
* Gritstone *
Gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...
*
Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
*
Marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorphose ...
*
Metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
ores, such as
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
,
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
,
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
,
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
and molybdenum *
Phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
*
Uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...


Largest open pit mines

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 the world. Listed are the world's ten largest open pit mines. *1.
Bingham Canyon Mine The Bingham Canyon Mine, more commonly known as Kennecott Copper Mine among locals, is an open-pit mining operation extracting a large porphyry copper deposit southwest of Salt Lake City, Utah, in the Oquirrh Mountains. The mine is the largest m ...
- Utah *2.
Mir Mine The Mir mine (russian: кимберлитовая алмазная трубка «Мир» ''kimberlitovaya almaznaya trubka "Mir"''; English: kimberlite diamond pipe "Peace"), also called the Mirny mine, is an open pit diamond mine located in ...
- Eastern Siberia, Russia *3.
Super Pit Gold Mine The Fimiston Open Pit, colloquially known as the Super Pit, was Australia's largest open cut gold mine until 2016 when it was surpassed by the Newmont Boddington gold mine also in Western Australia. The Super Pit is located off the Goldfields ...
- Australia *4.
Big Hole The Kimberley Mine or Tim Kuilmine ( af, Groot Gat) is an open-pit and underground mine in Kimberley, South Africa, and claimed to be the deepest hole excavated by hand, although this claim is disputed. History and size The first diamonds he ...
- South Africa *5.
Diavik Diamond Mine The Diavik Diamond Mine is a diamond mine in the North Slave Region of the Northwest Territories, Canada, about northeast of Yellowknife. Description Diavik Diamond Mine is an industrial complex set in a remote, subarctic landscape. It consis ...
- Canada *6.
Hull–Rust–Mahoning Open Pit Iron Mine The Hull–Rust–Mahoning Open Pit Iron Mine in Hibbing, Minnesota, United States, is the largest operating open-pit iron mine in Minnesota. The pit stretches more than long, wide, and deep. It was established in 1895 and was one of the worl ...
- Minnesota *7.
Grasberg Mine The Grasberg mine has one of the largest gold mining, reserves of gold and copper extraction, copper in the world. It is located in Mimika Regency, Central Papua, Indonesia near Puncak Jaya. It is operated by PT Freeport Indonesia (PTFI, ''s ...
- Indonesia *8.
Chuquicamata Chuquicamata ( ; referred to as Chuqui for short) is the largest open pit copper mine in terms of excavated volume in the world. It is located in the north of Chile, just outside Calama, at above sea level. It is northeast of Antofagasta and ...
- Chile *9.
Udachnaya Pipe The Udachnaya pipe (russian: тру́бка Уда́чная, literally ''lucky pipe'') is a diamond deposit in the Daldyn- Alakit kimberlite field in Sakha Republic, Russia. It is an open-pit mine, and is located just outside the Arctic ...
- Siberia, Russia *10.
Escondida Escondida is a copper mine at elevation in the Atacama Desert in Antofagasta Region, Chile. Geology The Escondida deposit is one of a cluster of porphyry coppers in an elongated area about 18 km north–south and 3 km east–west a ...
- Chile


See also

* * Rheinisches Braunkohlerevier * applied to open-pit mines for optimal extraction (not related to closing the mine) * * * *


References


External links


The biggest, deepest and deadliest mines in the world

Deepest open pit mines
{{DEFAULTSORT:Open-Pit Mining Open-pit mines Surface mining