An Arizona state agency has awarded the environmental permit required for the Santa Cruz project to proceed.
The $22-million operation, situated 7 miles west of Casa Grande, is an in situ copper mining research project managed by the U.S. Bureau of Mines and wholly owned subsidiaries of Asarco (NYSE) and Freeport-McMoRan (NYSE). The partners are testing a technique for mining certain resources without excavating rock or disturbing land surfaces. The technique, besides minimizing the impact to the land and surrounding environment, has the potential to yield high-quality copper (at a low cost) from deep, low-grade or uneconomic deposits.
The permit was awarded following five years of research and analysis, the conclusion of which is that the proposed facility will not seriously affect the environment or ground water quality.
The next step will be the construction of a solvent extraction-electrowinning (SX-EW) plant, which should be completed within a year.
Asarco hopes then to test the in situ mining technique over the next one to four years. The test (to be carried out at 1,600 ft. below surface) will involve injecting a diluted solution of sulphuric acid into undisturbed granitic rocks that contain soluble copper oxide mineralization. The copper-bearing solution will then be pumped to surface, and the copper will be recovered at an SX-EW plant.
Another procedural clearance — the environmental assessment — is near completion and should be released by the Bureau of Mines in December.
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