Copper is extracted from sulfide ores or concentrates by electrolysis in a cell having separate anode and cathode sections, and having an intermediate liquid copper-mercury alloy electrode between the anode and cathode sections. For example, 10 g of chalcopyrite containing 19.8 pct Cu and 24 pct S was slurried with 0.49 L of CuSO4-FeSo4 solution containing 16 g/l Cu and 43 g/l Fe and placed in the anode compartment of the divided electrolytic cell. The catholyte was 0.22 L of CuSO4 solution containing 31 g/l Cu. The intermediate alloy electrode contained 14 pct Cu and 84 pct Hg and was maintained at 92 deg C by means of a hot plate during the electrolysis at a cathode current density of 40 a/ft2, 7.1 V, for 9.5 A-h. Six grams of deposit were obtained, which contained 12 pct Hg. 5.5 g of residue was recovered from the anolyte slurry. It contained 0.23 pct Cu and 26.8 pct S, with 1.92 pct free S. After electrolysis the anolyte contained 12 g/l Cu and 46 g/l Fe, and the catholyte contained 24 g/l Cu. The results of this experiment show that 99 pct of the Cu was leached from the chalcopyrite source material in a CuSO4-FeSO4 anolyte and deposited from the CuSO4 catholyte after migration through the liquid Cu-Hg alloy intermediate electrode. Comigration of Fe was nil.