Keith Nicholl's idea that the word "gangue" refers only to waste rock discarded underground was of interest to me as, having worked some years in an underground copper mine in India and then later at the open-cast Marampa iron ore mine in Sierra Leone, and then in my Mining Magazine days having visited around 140 mines in some 40 countries, I had never come across this idea.
Waste rock, I have always thought, is disposed of underground or, in the case of an open-pit mine, to waste dumps, whereas gangue is that part of the crude ore delivered to the mill for processing, the plant producing concentrates containing the valuable minerals, while as much of the gangue minerals as possible are despatched to the tailings dump or used as backfill underground.
Intrigued, I have looked in some of my books to see what their definitions might be.
In Peele's Mining Engineers Handbook, Third Edition, Tenth Printing (1963), Section 10, page 6, in the article written by Alan. M. Bateman, Professor of Economic Geology at Yale University, in discussing Metalliferous Deposits, he says they comprise the Ore Minerals (metallic) and Gangue Minerals, usually discarded, although some may be used (he quotes rock gangue as road metal; fluorspar for flux; quartz for abrasive; calcite for soil dressing). Ore, he says, is a mixture of ore minerals and gangue, from which metals may be extracted at a profit.
Arthur F. Taggart's Handbook of Mineral Dressing (Sixth printing 1956) Section 1, Page 1 defines "crude" as a mixture of minerals as they occur in the earth's crust; "ore" as a solid crude containing a valuable constituent in such amounts as to constitute a promise of possible profit in extraction, treatment and sale. The valuable constituent, he says, is ordinarily called "valuable mineral" or often just "mineral" while the associated worthless material is called "Gangue".
In "Mineral Processing Technology" 5th Edition (1992) by Barry A. Wills, at that time Principal Lecturer, Camborne School of Mines, he says on p6 "Most ores are mixtures of extractable minerals and extraneous rocky material described as gangue".
I find it interesting that two of these books containing definitions of the word "gangue" are about mineral processing, i.e. what on earth do you do with the stuff which has been dug out of the mine?? Crude ore, as delivered to the mill, contains valuable minerals and gangue. What is disposed of underground is, I would say, waste rock.
Tony Brewis
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