The LeadtZinc Concentrator at Mount lsa treats all the lead-zinc-silver ore from the Mount Isa Mine and some of the ore from the Hilton Mine. This concentrator was commissioned in June 1966 and total lead-zinc-silver ore treatment was transferred from the Mount rsa's original No 1 Concentrator in May 1967. Plant capacity is around 5 x 106 t/y.There have been three phases of major plant modifications since commissioning:1. replacement and upgrading of the flotation section in 1979; 2. upgrading of the crushing plant and installation of a heavy medium hydrocyclone plant in 1983 for ore preconcentration, and; 3. doubling ball milling capacity and a further upgrading of the flotation section in 1992.Other developments have included the installation of flotation columns and Jameson cells.The evolution of milling practice since 1955 has been reported by Davey and Slaughter (1970), Bartrum, Dobrowolski and Schache (1977), Fiedler and Munro (1984) and Espinosa-Gomez el al (1989).Lead concentrate is smelted in Mount Isa while zinc concentrate and bulk concentrate (locally called Low Grade Middlings or LGM) are railed to Townsville and shipped to custom electrolytic zinc plants and ISP smelters.