James Colquhoun was a principal pioneer of porphyry copper production methodologies and among the first to realize profits from the processing of porphyry ores. During the 1890s at Arizona Copper Company’s Morenci, Arizona operations, Colquhoun was the first to apply sulfuric acid leaching successfully to oxide and sulfide copper ores, the first to apply aqueous gravity concentration at porphyry copper production scales, and the first to inaugurate bulk mining, concentrating, leaching, and cement-copper recovery methods. During his 24 years at Morenci, James Colquhoun made enduring contributions to the world copper industry.
Born in England and educated mainly in Scotland and Ireland, Colquhoun (pronounced Coh-hoon) sailed from Glasgow at age 25 to fill a position with the Scottish-owned Arizona Copper Company in what would become known as the Morenci District. His talents swiftly propelled him into the superintendence of metallurgy. By 1889, he was General Manager at Morenci, and in 1892, with appealing ideas in the face of serious cost/profit problems, he became General Manager of the entire Arizona Copper Company.
James Colquhoun was confident even in the early 1890s that copper oxide minerals could be leached with sulfuric acid and the soluble copper precipitated on scrap iron. In a July 1892 letter concerning an evaluation visit by young John Hays Hammond, he wrote, “I laid bare my proposal to concentrate and leach the low-grade porphyry ore of the Metcalf.” This is the first known use of the words ”porphyry ore.” Colquhoun described the ore as “white porphyry . . . streaked and spotted with black sulphides, very much as if it had been sprinkled over with pepper,” a fine layman’s description of the supergene-chalcocite-enriched, quartz-sericite-pyrite-altered Morenci quartz latite porphyry.
Acid, concentrating, and leach plants built to James Colquhoun’s design were soon completed at Morenci. From November 1893, leaching of porphyry ores was ongoing. Some 3 billion tons of such ore has been a mainstay of Morenci production for more than a century. Colquhoun’s success with oxide minerals led him in 1896 to initiate successfully acid dissolution of chalcocite from low-grade pyritic ores and recovery of the dissolved copper. As early as 1901, he also brought standard gauge railroads and electrolytic refining to Morenci.
Profitability is a key measure of mining success, and Colquhoun more than passed the test. Under his direction, Arizona Copper’s profits increased 1,000% from 1893 to 1896 and almost quadrupled again by 1903. Phelps Dodge Corporation acquired Arizona Copper in 1921, and Morenci remained a mainstay of Phelps Dodge production throughout the 20th century. The mine is continuing in that role in the early years of the 21st century. James Colquhoun’s achievements were nothing short of epic, especially when one recalls that in the 1890s extractive metallurgy was in its infancy, and the Morenci District was at the outer edge of idea exchanges. His brilliant work set the stage for modern bulk mining of copper.