Copper is most commonly present in the earth’s crust as copper-iron-sulfide and copper sulfide minerals, e.g. chalcopyrite (CuFeS2), bornite (CusFeS4) and chalcocite (Cu2S). The concentration of these minerals in an ore body is low. Typical copper ores contain from 0.5% Cu (open pit mines) to 1 or 2% Cu (underground mines). Pure copper metal is produced from these ores by concentration, smelting and refining. Copper also occurs in oxidized minerals (carbonates, oxides, hydroxy-silicates, sulfates), but to a lesser extent. Copper metal is usually produced from these minerals by hydrometallurgical methods. Hydrometallurgy is also used to produce copper metal from chalcocite, Cu2S.