By William Ascarza Special to the Arizona Daily Star
Mining has played a significant role in the history of Pinal County. Early mining dates back more than 1,000 years, as Native Americans mined chrysocolla using large diabase hammers for jewelry and trade.
More concentrated and successful mining efforts followed, beginning with the Silver King Mine. It was discovered by an Army soldier named Sullivan in 1873 and rediscovered two years later by a mining party led by Mason, Benjamin Regan, William H. Long and Isaac Copeland, who inaugurated it the Pioneer mining district.
The Silver King Mine became known for its exceptionally rich ore. A steadfast producer until implementation of the Sherman Act, which demonetized silver in 1893, the mine’s total production from 1875 to its decline in the 1920s was around $6.5 million in period values. By that time it reached a depth of 714 feet.
The Ray Mine was originally worked by the Mineral Creek Mining Co. in 1880 and greatly improved by Daniel C. Jackling under his organization of the Ray Consolidated Copper Co. It conducted extensive churn drilling and underground exploration with emphasis on shrinkage and block caving methods.
By 1955, the mine converted to open pit methods. At present, the Ray Mine produces 250,000 tons of ore daily. Concentrates have been sent to the Asarco smelter at Hayden for 110 years. At 1,000 feet in height, the smelter is the tallest free-standing structure in Arizona.
The Florence area has been known for a lucrative copper deposit that has yet to be developed. Hidden for many years by an alluvial layer, it took multiple sessions of diamond drilling to reveal copper oxide mineralization undertaken by the Continental Oil Company (Conoco). Underground mining recovered 31,700 tons of oxide materials and 16,900 tons of sulfide material.
Magma Copper Co. acquired the property in the 1990s and determined through a feasibility study the best option to recover copper was through in-situ leaching and SX-EW (solvent extraction and electrowinning).
Mineral recovery through in-situ mining is less impactful to the environment than regular mining processes with no open cuts, waste dumps, tailings or ore removal. It involves dissolving copper below the surface into a liquid and pumping it to the surface afterward.
The mine is currently owned by Taseko Mines Limited, which is involved in the permitting process to bring the mine into production. Projected life of the mine is 20 years with an annual production of 85 million pounds of copper.
As of 2021, more than 544 registered mines are known to exist in Pinal County. Pinal County will no doubt continue to develop its mineral resources over the next decade and beyond as it has done in the past 150 years, serving to meet the growing need worldwide for copper production.
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