Flotation of oxidized copper ores

The method of recovering copper by froth flotation from an aqueous pulp of an ore containing both sulfide and oxidized minerals of copper which comprises subjecting an aqueous pulp of the ore to a first froth flotation operation in the presence of a collector for sulfide copper minerals, thereby producing a concentrate containing a large proportion of the sulfide copper minerals, then subjecting the residual ore pulp to a further operation which comprises continuously monitoring the EMF of the pulp, adding a water-soluble sulfide to the pulp in an amount from 0.05 to 7 pounds contained sulfur per ton of ore whenever and for so long as the pulp EMF rises above about -30 millivolts with reference to a silver-silver chloride standard electrode and discontinuing such addition whenever such EMF becomes less than about -30 millivolts, and thereafter subjecting the pulp to a second froth flotation operation in the presence of a collector for copper sulfide minerals, thereby producing a concentrate containing much of the remaining sulfide copper minerals and a substantial part of the oxidized copper minerals of the ore.