The discovery of Iron Knob and Iron Monarch near the western shore of the Spencer Gulf in South Australia combined with the development by the BHP metallurgist, A. D. Carmichael, of a technique for 'separating zinc sulphides from the accompanying earth and rock' led BHP 'to implement the startlingly simple and cheap process for liberating vast amounts of valuable metals out of sulphide ores, including huge heaps of tailings and slimes up to' 40 feet high.