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{{Short description|Commercially worthless material that surrounds a wanted mineral in ore}} [[File:Cassiterite - Mt Bischoff mine, Waratah, Tasmania, Australia.jpg|thumb|right|Crystals of [[cassiterite]], a commercially valuable [[ore mineral]], in a matrix of [[quartz]], the gangue]] [[File:Zinkblende-banderz badgrund hg.jpg|thumb|Banded Zn-Pb [[ore]] sample with [[sphalerite]] (brown) and (silver-grey) [[galena]] as main [[ore mineral]]s and (white) [[calcite]] as main gangue mineral]] '''Gangue''' ({{IPAc-en|g|Γ¦|Ε}})<ref>{{Cite web|title = gangue: definition of gangue in Oxford dictionary (American English) (US)|url = http://www.oxforddictionaries.com/us/definition/american_english/gangue|archive-url = https://web.archive.org/web/20130505063121/http://oxforddictionaries.com/us/definition/american_english/gangue|url-status = dead|archive-date = May 5, 2013|website = www.oxforddictionaries.com|access-date = 2016-02-06}}</ref> 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 that are displaced during [[mining]] without being processed, yet relative to the concept of [[tailings]] (rock already stripped of valuable minerals) as what is originally regarded as gangue – and thus a "tailing" at that time – may prove valuable and worth processing or reprocessing at a later time. The separation of valuable mineral from gangue minerals is known as [[mineral processing]], mineral dressing, or ore dressing. It is a necessary, and often significant, aspect of mining. It can be a complicated process, depending on the nature of the minerals involved.<ref>A number of historical examples are detailed in: {{cite book | last = Hardesty | first = Donald L. | title = Mining Archaeology in the American West: A View from the Silver State | publisher = University of Nebraska Press | year = 2010 | pages = 70β91 | url = https://www.questia.com/library/120074649/mining-archaeology-in-the-american-west-a-view-from | access-date = 2017-08-28 | archive-date = 2016-03-07 | archive-url = https://web.archive.org/web/20160307222833/https://www.questia.com/library/120074649/mining-archaeology-in-the-american-west-a-view-from | url-status = dead }}</ref> For example, [[galena]], an ore of lead, is usually found in large pieces within its gangue, so it does not normally need extensive processing to remove it; but [[cassiterite]], the chief ore mineral of [[tin]], is usually disseminated as very small crystals throughout its gangue, so when it is [[Underground mining (hard rock)|mined from hard rock]], the ore-bearing rock first needs to be crushed very finely,<ref>{{cite book| last1 = Palmer| first1 = Marilyn| authorlink1 = Marilyn Palmer| last2 = Neaverson| first2 = Peter| title = Industry in the Landscape 1700β1900| publisher = Routledge| location = New York| year = 1994| page = 77| url = https://www.questia.com/library/103382951/industry-in-the-landscape| access-date = 2017-08-28| archive-date = 2016-03-10| archive-url = https://web.archive.org/web/20160310001800/https://www.questia.com/library/103382951/industry-in-the-landscape| url-status = dead}}</ref> and then has to be subjected to sophisticated processes to separate the ore. For any particular ore deposit, and at any particular point in time, the concentration of the wanted mineral(s) in the gangue material will determine whether it is commercially viable to mine that deposit. The ease with which the wanted mineral(s) can be separated from gangue minerals also plays an important part. Early mining ventures, having relatively unsophisticated methods, often could not achieve a high degree of separation, so large quantities of minerals found their way into the [[tailings|waste mineral]] dumps of mines. As the value of a mineral increases, or when new and cheaper means of processing the ore to extract the wanted mineral(s) are introduced, it may become worthwhile to rework such old dumps to retrieve the wanted minerals they still contain. ==Environmental impact of gangue minerals in mine tailings== [[File:Naturkundemuseum Berlin - Gediegen Gold in Quarz, Eagles Nest Mine, Placer County, Kalifornien, USA.jpg|thumb|[[Native metal|Native]] [[gold]] partially contained within a quartz gangue, visible at lower left.]] {{Main|Acid mine drainage}} Gangue minerals, once separated by [[mineral dressing]] processes of (most of) the valuable [[ore mineral]]s and dumped in [[mine tailings]] may be a significant environmental impact. In particular, oxidation of [[pyrite]], a common gangue mineral,<ref>Clout, J.M.F., Manuel, R.J. (2015) Mineralogical, chemical, and physical characteristics of iron ore. In: Iron ore, mineralogy, processing, and environmental sustainability, p. 45-84.</ref> is one of the main sources of [[acid mine drainage]].<ref>Blowes, D. W., Ptacek, C. J., Jambor, J. L., & Weisener, C. G. (2003). The geochemistry of acid mine drainage. In B. S. Lollar (Ed.), Environmental geochemistry (Vol. 9, pp. 149β204). Oxford: Elsevier.</ref><ref>Dold, Bernhard (2014). Evolution of Acid Mine Drainage Formation in Sulphidic Mine Tailings, Minerals, v. 4, p. 621-641.</ref> ==Re-use== [[Tailings|Waste minerals]] that were once disgarded as gangue are sometimes salvaged and used commercially. For example, in [[copper]] mines in the nineteenth century the mineral [[arsenopyrite]] was dumped until [[arsenic]] compounds became popular as [[insecticide]]s later in the century. Starting in the second half of the 20th century the environmental benefits of [[recycling]] gangue gained prominence. For example, in 2002, about 130 million tons of gangue were produced per year from [[Mining industry of China#Coal|coal mining in China]]. This, mixed with the 60 million tons of coal mud also produced, could be used for power generation; and the coal mining gangue could be combined with [[coal fly ash]] to produce building materials. The estimated cost of such projects would be up to 4 billion [[Chinese yuan|yuan]], but would be expected to save just over 4 million tons of standard coal per year.<ref>{{cite book| last1 = Murray| first1 = Geoffrey| last2 = Cook| first2 = Ian G.| title = Green China: Seeking Ecological Alternatives| publisher = Routledge| location = New York| year = 2002| pages = 149β150| url = https://www.questia.com/library/102233537/green-china-seeking-ecological-alternatives| access-date = 2017-08-28| archive-date = 2016-03-24| archive-url = https://web.archive.org/web/20160324222248/https://www.questia.com/library/102233537/green-china-seeking-ecological-alternatives| url-status = dead}}</ref> ==See also== * {{annotated link|Froth flotation}} * {{annotated link|Magnetic separation}} * {{annotated link|Vanning}} * {{annotated link|Extractive metallurgy}} * {{annotated link|Mineral processing}} ==References== {{Reflist}} ==Further reading== * ''An Elementary Outline Of Mechanical Processes'', by G. W. Danforth. 1912; 49. Elimination Of Gangue {{Extractive metallurgy}} {{Authority control}} [[Category:History of mining]] [[Category:Ore deposits]]
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