Can various minerals be smelted together to produce copper alloys? The potential for cosmelting of different minerals to produce mixed alloys is expressed by subtracting the free energies of the reactants from the free energies of the reaction products. When the difference is highly negative, it is likely that cosmelting will work. After discussing the theory, the authors recount their experiments on cosmelting to produce the copper-arsenic alloys, tin bronzes, and brasses. The feasibility of cosmelting of the copper-nickel alloys has been demonstrated before. Sulfur can be a reducing element in cosmelting, and some of the cosmelts produced with sulfide minerals have extensive sulfides of various elements included in the metal, along with thick sulfide matte on the surface. A test smelt of malachite with galena yielded copper with a high lead content, present as lead sulfide in the interdendritic phase; the authors conclude that galena can simply dissolve in molten copper. Structures of the cosmelted alloys produced are nicely illustrated by metallographs.