Open-pit mining: Difference between revisions

Revision as of 15:49, 5 August 2023

Revision as of 04:55, 12 August 2023

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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 because 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, minerals that have been found underground but are difficult to retrieve due to hard rock, 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>

Materials typically extracted from open-pit mines include:

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.<ref>{{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>{{Cite web|url=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopedia Britannica|access-date=2019-04-01}}</ref> Open-pit mines that produce [[building material]]s and [[dimension stone]] are commonly referred to as [[quarries]].

{{div col|small=yesno}}

*[[Bitumen]]

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]].

*[[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 pollutants[[pollutant]]s depending on the type of mineral being mined, and the type of mining process being used.

==Extraction==

[[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]]

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.<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>{{Cite web|urlname=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopediaeb Britannica|access-date=2019-04-01}}</ref> 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>{{Cite web|url=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopedia Britannica|access-date=2019-04-01}}</ref><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>{{Cite web|url=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopedia Britannica|access-date=2019-04-01}}</ref> 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>{{Cite web|url=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopedia Britannica|access-date=2019-04-01}}</ref>

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>{{Cite web|url=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopedia Britannica|access-date=2019-04-01}}</ref><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>{{Cite web|urlname=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopediaeb Britannica|access-date=2019-04-01}}</ref> 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>{{Cite web|urlname=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopediaeb Britannica|access-date=2019-04-01}}</ref>

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>

==WasteImpacts==

===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>{{Cite web|urlname=https://www.britannica.com/technology/mining|title=Mining|website=Encyclopediaeb Britannica|access-date=2019-04-01}}</ref> There are generally four main operations in 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.

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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 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 [[Gold cyanidation|cyanide leach process]]. If proper environmental protections are not in place, this toxicity can harm the surrounding environment.<ref>[http://ec.europa.eu/environment/waste/mining/index.htm "Mining Waste"] ''European Commission Environment'' (17 November 2011) accessed 19 December 2011</ref>

===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}}</ref> 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.<ref name=impact /> Furthermore, the pollutants affect flora and fauna in the areas surrounding open-pit mines.

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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 document |last1=Leech |first1=Simon |last2=McGann |first2=Matthew |title=Open Pit Slope Depressurization using Horizontal Drains – a Case Study |date=2008}}</ref>

Open Pit Depressurizationdepressurization 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}}</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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[[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%.

Materials typically extracted from open-pit mines include:

{{div col|small=yes}}

*[[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}}

==Largest open-pit mines==