Asarco/Freport Santa Cruz joint venture for copper

The United States Bureau of Mines in cooperation with the Santa Cruz Joint Venture will undertake a copper mining research project at a deep, low-grade copper deposit located seven miles west of Casa Grande, Ariz.

The Santa Cruz Joint Venture is owned 50-50 by subsidiaries of Asarco Inc and Freeport-McMoRan Gold Company.

The project will test a process for in situ, or in place mining of copper deposits that are too deep for open-pit mining and too low-grade for conventional underground mining methods.

In situ mining technology involves injecting dilute acid solutions under pressure into the pores and fractures of ore-bearing rock. The solution, which travels through the rock, dissolves the copper and carries it to a recovery well. The copper-laden liquid is then pumped to the surface and copper is recovered by solvent extraction and electromining.

The research project is expected to span several years, and its initial year will involve injecting and recovering fresh water to establish permeability, flow rate and direction of movement of solutions, as well as hydrologic studies and data gathering for environmental permits. Santa Cruz deposit

The Santa Cruz orebody is considered an excellent candidate for in situ mining. The deposit is estimated to contain 800 million tons averaging 0.4% copper oxide with internal higher grade zones. The deposit is located between 1,400 and 2,600 feet below the surface.

Mr. A. R. Raihl, Santa Cruz Joint Venture project manager, said “in situ mining could enhance the competitive position of copper producers if the field test at the Santa Cruz site develops the technology and expertise necessary to produce copper commercially.”

Jon K. Ahlness, technical project officer for the Bureau of Mines, said, “It is hoped that development of in situ technology will make it possible to produce metal more efficiently and with minimum environmental disruption from deposits previously considered uneconomic. If successful, in situ mining may open to development about a dozen large copper oxide deposits in Arizona,” he added.

The Bureau of Mines’ Mining Technology Program has produced a 454-page technical manual detailing in situ mining procedures. Asarco Incorporated

Asarco Inc. is one of the world’s leading producers of nonferrous metals, principally copper, silver, lead, and zinc. Asarco operates or has interests in mines in the United States, Australia, Peru, Mexico and Canada. In addition to mining and treating ore from its own mines, Asarco is a custom smelter and refiner of nonferrous metal ores mined by other companies.

Freeport-McMoRan Gold Company’s principal business includes the mining, milling and processing of gold in Nevada and exploration for precious metals throughout the United States and Canada. Freeport believes that the in situ copper mining research project could benefit its ongoing precious metals activities.

The Santa Cruz project is expected to be a model government- industry cooperative research program to test innovative technology. “The economic benefits of in situ mining could further improve the competitive position of U.S. copper toward foreign-produced copper. A healthy copper industry acts to reduce trade deficits,” said Arizona state Senator, Dennis DeConcini.