The Bureau of Mines studied copper-nickel minerals (mainly sulfides) of the Duluth Gabbro complex in north-eastern Minnesota to determine their response to selective high-temperature sulfatization techniques. The gabbro, containing 0.44 percent copper and 0.13 percent nickel, was ground to minus 325 mesh and sulfatized in a heated, rotating, stainless steel bench-scale retort. Tests demonstrated that over 95 percent of the copper and 80 percent of the nickel can be converted to water-soluble sulfates, depending upon the roasting conditions employed. Yield equations were developed using regres analysis for predicting the extraction of copper and nickel between the temperature limits of 520 deg. to 670 deg. C, the roasting time limits of 3 to 7 hours, and so2 limits of 10 to 40 percent in so2-air mixtures.