The Bureau of Mines investigated separating copper-nickel mattes to recover a copper-rich fraction suitable for processing by conventional copper metallurgical processes and a nickel-rich fraction suitable for processing in a hydrometallurgical nickel circuit. Distribution of cobalt and precious metals between the copper and nickel fractions was also determined. A matte containing 65 pct cu, 9 pct ni, 4 pct fe, and 20 pct s was separated into a copper fraction that comprised 80 pct of the matte weight and contained 70 pct cu and < 1.5 pct ni, plus a nickel fraction that contained 40 pct ni and 30 pct cu. Recoveries of copper and nickel into their respective fractions were 90 pct and 87 pct. These results were obtained in a laboratory flotation cell at a matte grind of 90 pct minus 500 mesh and a ph of 12.4, Using 1.7 Pounds dpg (diphenyl-guanidine) per ton of matte as collector and frother. Magnetic separation was used to remove metallic iron-nickel alloy from the copper fractions. Distribution of cobalt was about 70 pct to the nickel fraction and 30 pct to the copper fraction. Silver reported predominately to the copper fraction, while au, pt, and pd were essentially entirely recovered in the nickel fraction.