Ore grades Copper mining in the United States

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average grade of united states copper ore, , of concentrating ore (data usgs)


from start of copper mining in michigan copper district, ore has been divided 2 classes. rock higher copper content smelter ore, called direct shipping ore, , required no treatment before going smelter. rock less copper called milling ore, or concentrating ore, , required crushing , separation of ore minerals waste rock produce copper concentrate, sent smelter.


because metallic minerals have higher specific gravities gangue (waste) minerals, concentrating milling ore done in various gravity classifiers. michigan copper mines used buddles. later copper mining used improved gravity-classification machinery, including jigs, vanners, , wilfley tables.


a revolutionary development in american copper mining took place when mining engineer daniel cowan jackling conceived of mining huge low-grade copper ore body @ bingham canyon, utah, using steam shovels in big open pit. steam shovels had been used in iron mines of mesabi range, in minnesota, had not been used in copper mining. jackling incorporated utah copper company in 1903, , in 1906 began excavating. start, bingham canyon mine 1 of leading copper-producing mines in world, , returned profit mining ore less 2 percent copper. mining open-pit model using large-scale mechanization copied other mines, in ely, nevada (1908), santa rita, new mexico (1910), , ajo, arizona (1917). entire output of these mines low-grade milling ore. open-pit mining of porphyry copper deposits adopted worldwide.


in 1910s , 1920s, copper mills adopted froth flotation method, had been developed in australia. whereas old gravity methods of concentration, using jigs , wilfley tables recovered 60 80 percent of copper in ore, froth flotation recovered 90 95 percent. bingham canyon mill installed froth flotation in 1918.


large-scale mining of low-grade orebodies became predominant, , amount of direct-shipping ore mined fell drastically in first half of 20th century, , 1960, contribution of direct-shipping ore insignificant. improvements in low-cost mining , ore processing allowed average ore grade of milling ore decline.








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