Editing Gangue (section)

{{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|æ|ŋ}})<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 &ndash; and thus a "tailing" at that time &ndash; 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 = 70–91
| 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 1700–1900| 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.