Consists of roasting matte carrying copper, lead, gold, and silver at a very low temperature, forming copper sulfate and oxide, but not silver sulfate. This product is leached with dilute sulfuric acid for copper. The resulting solution is treated with calcium chloride, and the copper is precipitated as subchloride by passing SO₂through the solution. The cuprous chloride is then reduced to cuprous oxide by milk of lime, regenerating calcium chloride, and the cuprous oxide is smelted.