In conventional dump leaching of porphyry mine strip wastes, many years are required to extract up to 20 percent of the copper from the contained sulfide minerals. Furthermore, none of the molybdenum, gold, or silver in the strip wastes is recovered by current leaching practices. Breaking the rock during mining operations liberates and concentrates some of the metal values in the fines. Research show that upgraded fines can be screened from mine wastes and froth floated for early recovery of copper, molybdenum, gold, and silver. For example, screening a dump sample assaying 0.35 percent copper as chalcopyrite removed about 20 percent of the copper as minus-1/4-inch material that analyzed 0.6 percent copper. About 35 percent of the molybdenum and 20 percent of the gold and silver also reported in the fines. Crushing the mine dump sample to minus-3 inch before screening increased the distribution of copper and molybdenum in the minus-1/4-inch screen fraction to 28 and 50 percent, respectively. Similar results were obtained by screening fines from two other large samples of mine waste dump materials. Flotation studies established that the enriched minus-1/4-inch fines from the three dump samples could be effectively concentrated. Comparative testing revealed that the combination of froth flotation of fines and acid-ferric sulfate leaching of the coarser fraction enabled doubling the recovery of copper over direct leaching of the samples. In addition, significant amounts of molybdenum, gold, and silver were recovered by flotation.
Soc. Min. Eng. AIME, Feb. 15-19, 1970, Preprint No. 70-B-102