mining and smelting centre, northern Chile. It lies near Calama at 9,350 feet (2,850 m) above sea level and is the largest open-pit mine in the world. Large-scale operations started in 1915. Tapping one of the world's largest-known copper deposits, it produces more than one-fourth of the nation's copper, which is carried by rail to Antofagasta, 140 miles (225 km) southwest, for export. Flotation and smelting facilities were installed in 1952; and expansion of the refining facilities in 1968 made 500,000-ton annual copper production possible in the late 1970s. Ores at nearby La Exótica are also mined. The controlling interest in these mines passed from foreign to Chilean hands in 1969; complete nationalization followed in the early 1970s. Pop. (2002) 10,465.