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A nearly dormant copper sulfide pilot-scale experimental leach containing 8.7 tons of ore was injected with oxygen to determine the effect on the copper leaching rate. Prior treatment of the uncrushed 0.25 percent copper, mine-run stripping material consisted of 461 days of acid ferric sulfate leaching to extract 47 percent of the total copper. The permeability of the bed had decreased and the percolation rate decreased from an initial 20 gallons per square foot per day to 0.8 gallon, and copper extraction had nearly stopped. After injecting oxygen into the ore column and leaching for 30 days, the percolation rate was increased to 6 gallons per square foot per day. In an additional 298 days of leaching, an additional 40.7 percent of the copper was extraced. The improved leaching after the use of oxygen is attributed to stimulated bacterial action, better oxidation, and increased permeability.