Extraction of copper from a porphyry ore by simulated in situ leaching techniques was investigated by the Bureau of Mines as a means of recovering copper from deeply buried sulfide deposits. Effects of adding sodium chloride and nitric acid separately to sulfuric acid leaching systems under oxygen pressure were studied on a bench scale to define conditions under which copper could be extracted more effectively from porphyry ores. Charges of ore, crushed to 3/8 inch, were leached under static conditions in the range of 25 deg. to 200 deg. C and in the range of 14 to 400 psig oxygen. Additions of sodium chloride or nitric acid to dilute sulfuric leachants were found to enhance dissolution of chalcopyrite markedly. Addition of 1 weight-percent-sodium chloride or 0.25 percent nitric acid increased copper extractions obtained at 80 deg. C with sulfuric acid alone by twofold and eightfold, respectively, under the test conditions. In addition, the na+ ion, along with the fe+3 and so4-2 ions, forms a crystalline natrojarosite. Precipitation of the codissolved iron as crystalline natrojarosite, or minerals closely related to jarosite, permits continuous contact of the leach solution with the particles of ore, purifies the pregnant solution with respect to iron, and redeposits the ferric iron contents as an innocuous mineral.