Fluid Flow Mapping at a Copper Leaching Operation in Arizona

At the San Manuel copper mine in southeastern Arizona, recovery of copper from the oxidized portion of this porphyry mineral resource is being achieved through a large in situ leaching operation using weak sulfuric acid solution. In the past, this activity was coordinated with open pit and underground mining, but in today's economic climate, only the in situ operation continues. The acid solution (20 grams per liter) is injected in wells un-pressurized at varying depths up to several hundred meters, usually at rates of only a few tens-of-gallons per minute. The copper-bearing pregnant leach solution (PLS) is recovered either in nearby recovery wells or in collection areas in the underground workings 350 m to 500 m (1200 to 1600 feet) below the surface. A thorough description of in situ mining in general as well as at San Manuel specifically can be found in Swan and Coyne (1992). Due to the economic efficiency of this mining method, the in situ operation at San Manuel has expanded from two test wells in the mid-1980s to more than 900 wells covering over 650,000 square meters of the open pit mine. Over the past twelve years, geophysical surveys have been useful in both planning and monitoring the expansion of the in situ field.