The discovery of Iron Knob and Iron Monarch near the western shore of the Spencer Gulf in South Australia, combined with the refinement, by BHP metallurgists A. D. Carmichael and Leslie Bradford, of the froth flotation technique for separating zinc sulphides from the accompanying gangue and subsequent conversion (Carmichael–Bradford process) to oxides of the metal, allowed BHP to economically extract valuable metals from the heaps of tailings up to 40 feet high at the mine site.