Open-pit mining: Difference between revisions

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[[File:Ende Gelände 2017 CHB 23 (cropped).jpg|thumb|The giant [[bucket-wheel excavator]]s in the German Rhineland coal mines are among the world's biggest land vehicles.]]

'''Open-pit mining''', also known as '''open-cast''' or '''open-cut mining''' and in larger contexts '''mega-mining''',<ref>{{Cite web|last=Serafini|first=Paula|title=The Argentinian fight against 'mega mining'|url=http://theconversation.com/the-argentinian-fight-against-mega-mining-95672|access-date=2021-04-22|website=The Conversation|date=4 May 2018 }}</ref> is a [[surface mining]] technique ofthat extractingextracts [[rock (geology)|rock]] or [[minerals]] from the earth from an open-air pit, sometimes known as a [[Borrow pit|borrow]].

This form of [[mining]] differs from extractive methods that require tunnelling into the earth, such as [[long wall mining]]. 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 becausewhere the [[overburden]] 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, mineralsdeeper thatmineral have been found underground but are difficult to retrieve due to hard rock,deposits can be reached using a form of underground mining.<ref>{{Cite book|url=https://www.nap.edu/read/10318/chapter/5|title=Read "Evolutionary and Revolutionary Technologies for Mining" at NAP.edu|year=2002|doi=10.17226/10318|isbn=978-0-309-07340-0}}</ref>

[[File:Kittilä mine.jpg|thumb|Kittilä Gold Mine in [[Kittilä|Kittilä, Finland]] is the largest primary gold producer in Europe.<ref>{{cite web|url=https://www.avkvalves.eu/en/cases/water-cases/agnico-eagle-finland|title=Supplying more than 100 valves to the largest gold mine in Europe|publisher=AVK International|access-date=11 December 2023}}</ref><ref>{{cite web|url=https://www.mining.com/agnico-has-kittila-operating-permit-restored-expects-30000-oz-of-additional-production/|title=Agnico operating permit restored for Kittila mine in Finland|first=Jackson|last=Chen|publisher=Mining.com|date=27 October 2023|access-date=11 December 2023}}</ref>]]

This form of mining carries several risks to the health and safety of miners, and can have a significant negative impact on the environment.

Materials typically extracted from open-pit mines include:

{{div col|small=no}}

*[[Bitumen]]

*[[Clay]]

*[[Coal]]

*[[Copper]]

*[[Coquina]]

*[[Chromite]]

*[[Diamonds]]

*[[Gravel]] and [[Rock (geology)|stone]]

*[[Granite]]

*[[Gritstone]]

*[[Gypsum]]

*[[Limestone]]

*[[Marble]]

*[[Metal]] [[ores]], such as [[copper]], [[iron]], [[gold]], [[silver]] and [[molybdenum]]

*[[Phosphate]]

*[[Uranium]]

{{div col end}}

Open-pit mining is to be considered one of the most dangerous [[industrial sector|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.<ref>{{Cite journal|last1=Chen|first1=Jianping|last2=Li|first2=Ke|last3=Chang|first3=Kuo-Jen|last4=Sofia|first4=Giulia|last5=Tarolli|first5=Paolo|date=2015-10-01|title=Open-pit mining geomorphic feature characterisation|journal=International Journal of Applied Earth Observation and Geoinformation|volume=42|pages=76–86|doi=10.1016/j.jag.2015.05.001|issn=0303-2434}}</ref> Additionally, open-pit produces harmful [[pollutant]]s depending on the type of mineral being mined, and the type of mining process being used.

==Extraction==

{{missing information|section| the truck and shovel mining method with specific extraction steps: drilling into benches vertically, ammonium nitrate explosive deposition, blasting, removal of material from pit walls for extracting ore, horizontal? mine expansion due to extraction of ore from walls or bottom of the pit, creation of new pits during a mine's life|date=February 2025}}

[[File:Sunrise Dam Gold Mine open pit 11.jpg|thumb|alt=Refer to caption.|Note the angled and stepped sides of the [[Sunrise Dam Gold Mine]], Australia.]]

[[File:Tagebau Garzweiler bei Otzerath Schaufelradbagger Januar2008.ogv|thumb|A bucket-wheel excavator extracting lignite from [[Garzweiler surface mine]] in Germany during 2008]]

ToMiners createtypically andrill open-pita mine, the miners must determine the informationseries of the ore that is underground. This is done through drilling of probetest holes into thelocate ground,an thenunderground plottingore each hole ___location on a mapbody. The information gained throughFrom the holesextracted withsamples, providethey ancan idea ofdetermine the vertical extent of the ore's body. This verticalhelps informationthem isdetermine thenthe usedlikely to pit tentative locations___location of the veins or benches thatof willore occurand inits thecommercial minevalue.<ref name=eb>{{Cite web|url=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopedia Britannica|access-date=2019-04-01}}</ref> It is important to consider the grade and economic value of the ore in the potential pit.<ref name=eb /> Open-pit mines that produce [[building material]]s and [[dimension stone]] are commonly referred to as [[quarries]].

Open-cast mines are dug on [[Bench (geology)|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.<ref name="Mark A. Prelas 1997 pp. 496">Mark A. Prelas; Galina Popovici; Louis K. Bigelow (23 September 1997). Handbook of Industrial Diamonds and Diamond Films. CRC Press. pp. 496–. {{ISBN|978-0-8247-9994-6}}.</ref> In contrast, many quarries do not use benches, as they are usually shallow.<ref> name="Mark A. Prelas; Galina Popovici; Louis K. Bigelow (23 September 1997). Handbook of Industrial Diamonds and Diamond Films. CRC Press. pp. 496–. {{ISBN|978-0-8247-9994-6}}.<496"/ref> 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.<ref name=eb /> 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.<ref name=eb />

Open-pit mines are typically enlarged until either the [[mineral resource classification|mineral resource]] is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic. When this occurs, the exhausted mines are sometimes converted to [[landfill]]s 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 (meteorology)|precipitation]] or if any layers of the pit forming the mine border productive [[aquifer]]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 [[Central German Lake District]] or the [[Upper Palatinate Lake District]]. A particular concern in the formation of these lakes is [[acid mine drainage]].

Open-cast mines are dug on [[Bench (geology)|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.<ref>Mark A. Prelas; Galina Popovici; Louis K. Bigelow (23 September 1997). Handbook of Industrial Diamonds and Diamond Films. CRC Press. pp. 496–. {{ISBN|978-0-8247-9994-6}}.</ref> In contrast, many quarries do not use benches, as they are usually shallow.<ref>Mark A. Prelas; Galina Popovici; Louis K. Bigelow (23 September 1997). Handbook of Industrial Diamonds and Diamond Films. CRC Press. pp. 496–. {{ISBN|978-0-8247-9994-6}}.</ref> 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.<ref name=eb /> 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.<ref name=eb />

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 [[Fault (geology)|fault]]s, [[Shear (geology)|shears]], joints or [[Foliation (geology)|foliations]].

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A haul road is usually situated at the side of the pit, forming a ramp up which [[truck]]s can drive, carrying [[ore]] and waste rock.<ref>G.E. Blight; A.B. Fourie; G.R. Wardle (1 January 1999). Geotechnics for Developing Africa: Proceedings of the 12th regional conference for Africa on soil mechanics and geotechnical engineering, Durban, South Africa, 25–27 October 1999. CRC Press. pp. 49–. {{ISBN|978-90-5809-082-9}}.</ref>

== After closure ==

Open-pit mines are typically enlargedworked until either the [[mineral resource classification|mineral resource]] is exhausted, or an increasing ratio of overburden to ore makes further mining uneconomic.{{cn|date=March When2024}} thisAfter occurs,open-pit themines exhaustedare minesclosed, they are sometimes converted to [[landfill]]s for disposal of solid wasteswaste. However, someSome 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 (meteorology)|precipitation]] or if any layers of the pit forming the mine border productive [[aquifer]]s. In Germany and adjacent countries severalSeveral former open-pit mines have been deliberately converted into artificial lakes, forming areas such as 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]].

==Impacts==

Open-pit mining is to be considered one of the most dangerous [[industrial sector|sectors in the industrial world]].,{{cnl|date=March It2024}} causesand can cause significant effectsharm to miners' health,. asIt wellcan asalso damagehave tosignificant thenegative ecologicalenvironmental landimpact, anddepending water.on Open-pitthe miningtype causesof changesmineral tobeing vegetation, soilmined, and bedrock,the whichtype ultimatelyof contributesmining toprocess changesbeing inused. surface hydrology, groundwater levels, and flow paths.<ref>{{Cite journal|last1=Chen|first1=Jianping|last2=Li|first2=Ke|last3=Chang|first3=Kuo-Jen|last4=Sofia|first4=Giulia|last5=Tarolli|first5=Paolo|date=2015-10-01|title=Open-pit mining geomorphic feature characterisation|journal=International Journal of Applied Earth Observation and Geoinformation|volume=42|pages=76–86|doi=10.1016/j.jag.2015.05.001|issn=0303-2434|hdl=11577/3159353|hdl-access=free}}</ref> Additionally, open-pit produces harmful [[pollutant]]s depending on the type of mineral being mined, and the type of mining process being used.

===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.<ref name=eb /> There are generally four main operations in a mine that contribute to this load: [[drilling]], blasting, loading, and [[hauling]].

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===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.<ref name=impact>{{Cite journal |last1=Huertas |first1=José I. |last2=Huertas |first2=María E. |last3=Izquierdo |first3=Sebastián |last4=González |first4=Enrique D. |title=Air quality impact assessment of multiple open pit coal mines in northern Colombia |journal=Journal of Environmental Management |volume=93 |issue=1 |pages=121–129 |date=January 2012 |pmid=22054578 |doi=10.1016/j.jenvman.2011.08.007|bibcode=2012JEnvM..93..121H }}</ref> These typetypes 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.<ref name=impact /> 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.<ref>{{Cite journal|last1=Abdul-Wahab|first1=Sabah|last2=Marikar|first2=Fouzul|date=2012-01-01|title=The environmental impact of gold mines: pollution by heavy metals|journal=Open Engineering|volume=2|issue=2|page=304|doi=10.2478/s13531-011-0052-3|bibcode=2012CEJE....2..304A|s2cid=3916088|issn=2391-5439|doi-access=free}}</ref>

===Deforestation===

Open-pit [[Nickel mine|nickel mining]] has led to environmental degradation and pollution in developing countries such as the [[List of mines in the Philippines|Philippines]] and [[List of mines in Indonesia|Indonesia]].<ref>{{cite news |last1=Rick |first1=Mills |title=Indonesia and China killed the nickel market |url=https://www.mining.com/web/indonesia-and-china-killed-the-nickel-market/ |work=MINING.COM |date=4 March 2024}}</ref><ref>{{cite news |title=Land grabs and vanishing forests: Are 'clean' electric vehicles to blame? |url=https://www.aljazeera.com/news/2024/3/14/land-grabs-and-cleared-forests-why-electric-vehicles-are-getting-a-bad-rep |work=Al Jazeera |date=14 March 2024}}</ref> In 2024, nickel mining and processing was one of the main causes of [[deforestation in Indonesia]].<ref>{{cite news |title=Indonesia's massive metals build-out is felling the forest for batteries |url=https://apnews.com/article/indonesia-nickel-deforestation-rainforest-mining-tesla-ev-184550cddf1df6aad8e883862ab366df |work=AP News |date=15 July 2024}}</ref><ref>{{cite news |title=EU faces green dilemma in Indonesian nickel |url=https://www.dw.com/en/eu-faces-green-dilemma-in-sourcing-nickel-from-indonesia/a-69681557 |work=Deutsche Welle |date=16 July 2024}}</ref> Open-pit [[Copper extraction|cobalt mining]] has led to [[Deforestation in the Democratic Republic of the Congo|deforestation]] and habitat destruction in the [[Mining industry of the Democratic Republic of the Congo|Democratic Republic of Congo]].<ref>{{cite news |title=How 'modern-day slavery' in the Congo powers the rechargeable battery economy |url=https://www.npr.org/sections/goatsandsoda/2023/02/01/1152893248/red-cobalt-congo-drc-mining-siddharth-kara |work=[[NPR]] |date=1 February 2023}}</ref>

===Safety===

Open-pit mining is considered one of the most dangerous [[industrial sector|sectors in the industrial world]].{{cnl|date=March 2024}} and can cause significant effects to miners' health.

==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, including 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.<ref name=depressurization>{{Cite documentweb |url=https://www.imwa.info/docs/imwa_2008/IMWA2008_035_Leech.pdf|work=International Mine Water Association |last1=Leech |first1=Simon |last2=McGann |first2=Matthew |title=Open Pit Slope Depressurization using Horizontal Drains – a Case Study |date=2008}}</ref>

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.<ref name=depressurization /><ref>{{Cite journal|author=Stephen P. White|author2=Ashley L. Creighton|author3=Paul F. Bixley|author4=Warwick M. Kissling|date=August 2004|title=Modeling the dewatering and depressurization of the Lihir open-pit gold mine, Papua New Guinea|journal=Geothermics|volume=33|issue=4|pages=443–456|doi=10.1016/j.geothermics.2003.09.011|bibcode=2004Geoth..33..443W }}</ref> 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.<ref>{{Cite journal|author=S. Mohan|author2=P.K. Sreejith|author3=S.K. Pramada |date=July 1, 2007|title=Optimization of Open-Pit Mine Depressurization System Using Simulated Annealing Technique|journal=Hydraulic Engineering|volume=133|issue=7}}</ref> 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.<ref name=depressurization />

==Untopping==

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==Rehabilitation==

{{main|Land rehabilitation#mine rehabilitation}}

[[File:New_Antelope_Rochelle_Coal_MineNew Antelope Rochelle Coal Mine.png|thumb|alt=A reclaimed area next to an active mine is now grassy hills.|A loadout station and reclaimed land at the [[North Antelope Rochelle Mine|North Antelope Rochelle]] open-pit [[coal]] mine, in [[Coal mining in Wyoming|Wyoming]], [[United States]]]]

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]].<ref>Walter Geller; Helmut Klapper; Wim Salomons (6 December 2012). Acidic Mining Lakes: Acid Mine Drainage, Limnology and Reclamation. Springer Science & Business Media. {{ISBN|978-3-642-71954-7}}.</ref> This 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.<ref>Vasudevan Rajaram; Subijoy Dutta; Krishna Parameswaran (30 June 2005). Sustainable Mining Practices: A Global Perspective. CRC Press. pp. 207–. {{ISBN|978-1-4398-3423-7}}.</ref> 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]] 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.<ref>[http://www.dmp.wa.gov.au/documents/mine_rehab.pdf "MINE REHABILITATION"] ''Department of Mines and Petroleum'' (October 2006) accessed 19 December 2011</ref> 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 lake]]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]] or other basic chemicals have to be added to the water to neutralize the [[pH]]-value.

{{Clear}}

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==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 in 2015.<ref>{{Cite web|author=Mining Global|date=September 9, 2015|title=Top 10 Largest Open Pit Mines in the World|url=https://www.miningglobal.com/top-10/photos-top-10-largest-open-pit-mines-world}}</ref>

{{div col|small=yes}}

*1. [[Bingham Canyon Mine]] - UtahUnited States

*2. [[Mir Mine]] - Eastern Siberia, Russia

*3. [[Super Pit Gold Mine]] - Australia

*4. [[Big Hole]] - South Africa

*5. [[Diavik Diamond Mine]] - Canada

*6. [[Hull–Rust–Mahoning Open Pit Iron Mine]] - MinnesotaUnited States

*7. [[Grasberg Mine]] - Indonesia

*8. [[Chuquicamata]] - Chile

*9. [[Udachnaya Pipe]] - Siberia, Russia

*10. [[Escondida]] - Chile

{{Div col end}}

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==See also==

* {{annotated link|Artisanal mining}}

* [[Rheinisches Braunkohlerevier]]

* {{annotated link|Closure problem#Applications|Closure problem}} applied to open-pit mines for optimal extraction (not related to closing the mine)

* {{annotated link|Cut (earthmoving)}}