New Cornelia mine

The New Cornelia mine is a currently inactive open-pit copper mine in Pima County, Arizona, United States. It was the only productive mine in the Ajo mining district, and is located just outside the town of Ajo, which was built as a company town to serve the New Cornelia miners. The roughly circular pit is one and a half miles across at its widest point, and 1,100 feet deep at the center.

Native Americans had long mined surface exposures of copper veins near the New Cornelia for pigments: red copper oxide and green copper carbonate. Spanish miners are known to have excavated test shafts in the area by 1750, but the amount of copper produced is not known. Americans claimed the location in 1854 and shipped a few loads of selected ore to Swansea, Wales, but high transportation charges left little or no profit, and the mine was abandoned.

Development of the property was delayed because of its remote location in the Sonoran Desert. The low-grade copper ore could not be economically shipped to a smelter, and had to be concentrated at the site. The Cornelia Copper Company was organized by businessmen from St. Louis in 1900 to develop the property. However, early owners fumbled in their search for a suitable treatment process, and fell victim to "process men". In 1906 the owners contracted with Fred McGahan to build his unique "vacuum smelter" to treat the ore. The following year the company had McGahan indicted for obtaining money under false pretenses. It then arranged with another inventor to build facilities to treat the ore by the unproven "Anderson Process", which proved just as useless as McGahan’s process. A United States Geological Survey author later described these processes as "... among the most bizarre ever to have been floated in American mining." Mining commentator Horace Stevens wrote:

The company reorganized as the New Cornelia Mining Company. In 1911, the Calumet and Arizona Mining Company, which already had a major operation in Bisbee, took an option to buy 70 percent of New Cornelia stock. Calumet and Arizona confirmed the existence of a large copper carbonate orebody, and exercised the option. It then found a practical way to treat the ore, and located a sufficient source of water several miles north. A pilot plant began operation in 1915, and a railroad connection via Gila Bend was completed in 1916.

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