Open-pit mining , also known as open-cast or open-cut mining and in larger contexts mega-mining , is a surface mining technique that extracts rock or minerals from the earth.
59-464: The Rouchleau Mine is an abandoned open-pit mine within the Mesabi Iron Range at Virginia , Minnesota , United States. The mine, located on the east side of the city, is roughly 3 miles (4.8 km) long and .5 miles (0.80 km) wide; its deepest point is 450 feet (140 m) below its surface, making it one of the deepest mines in the range. Named for Louis Rouchleau, who explored
118-405: A decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of the fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into
177-860: A plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or the Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are
236-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving
295-410: A fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing the seismic shaking and tsunami hazard to infrastructure and people in
354-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear
413-447: 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
472-429: 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
531-599: A railroad car, and a visitor center. The attraction closed in 2015 due to United Taconite's planned expansion of its mine into the land the mineview occupied. The mine expansion forced U.S. Route 53 to relocate; the Minnesota Department of Transportation built a bridge over the Rouchleau Mine to carry the highway. The Thomas Rukavina Memorial Bridge opened in September 2017. The mine pit serves as
590-477: 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
649-450: 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
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#1732783978841708-406: Is 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 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
767-509: 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
826-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of
885-434: Is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas the brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when
944-401: 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
1003-559: 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
1062-463: The Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with a major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in
1121-668: 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
1180-594: 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
1239-418: 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
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#17327839788411298-427: The area for its mining potential, the mine was initially created as a shaft mine . It was converted to a pit mine by the 1930s due to improvements in open-pit mining technology and increasingly unstable terrain which made shaft mining unsafe. Ten companies have overseen mining operations at the Rouchleau Mine since it began operating in 1893. The majority owner has always been either present owner U.S. Steel or one of
1357-402: 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
1416-414: The crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of a hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through
1475-433: The direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between the fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as
1534-472: 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
1593-409: The fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of a non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body,
1652-459: The fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of
1711-465: The fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on the direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and
1770-451: The firm's predecessors. The mine has produced 300 million gross tons of iron ore since it opened; it was last mined in 1977. Since its closure, the mine became part of Mineview in the Sky, a local tourist attraction. Mineview in the Sky featured a viewing platform overlooking both the Rouchleau Mine and an active United Taconite mine; it also included a 240-ton mining truck, a production truck,
1829-428: The footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms
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1888-531: The footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other, is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near
1947-429: The geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in the gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of
2006-429: 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
2065-491: The implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering ,
2124-464: The largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining a fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where
2183-454: 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
2242-450: 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
2301-408: The miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In a reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of
2360-435: The most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to the original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to
2419-494: The opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by the fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and
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2478-411: The plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on
2537-446: 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
2596-407: 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
2655-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases
2714-423: The rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along a fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy
2773-404: 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
2832-412: 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
2891-446: The source of drinking water for Virginia, Minnesota . 47°30′42″N 92°31′20″W / 47.5115931°N 92.5221273°W / 47.5115931; -92.5221273 Open-pit mining 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
2950-404: The strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of the fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of
3009-416: The stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in the fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form
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#17327839788413068-400: The surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in a manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along
3127-442: The surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However, the term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and
3186-416: 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
3245-517: 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 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
3304-582: The vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess
3363-466: 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
3422-463: The world. Listed are the world's ten largest open-pit mines in 2015. Fault (geology) In geology , a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with the largest forming the boundaries between
3481-472: 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
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