mine with the largest total production (approximately 29 million tonnes) of copper until the end of 2007 (excluding Radomiro Tomić). Despite over 90 years of intensive exploitation, it remains one of the largest known copper resources. Its open pit is the world's largest at long, wide and over deep and its smelter and electrolytic refinery (855,000 tonnes p.a.) are among the world's largest. Chuquicamata is also a significant producer of molybdenum. Chuquicamata is now amalgamated with the currently operational Radomiro Tomić mine to the north (on the same mineralized system), the still under development Alejandro Hales mine to the south (formerly Mansa Mina) and the recently discovered 'Toki cluster' of copper porphyries to form the "'Codelco Norte'" division of Codelco. Geology Chuquicamata belongs to the broad class of porphyry copper deposits. Practically, the entire Chuquicamata orebody is hosted by the Chuqui Porphyry Complex, made up of East, Fine Texture, West and Banco porphyries. These Cu-Mo porphyry systems formed during the Eocene-Oligocene and exhibit classic "zoned alteration-mineralization features. A regional fault zone gave rise to hydrothermal activity which concentrated metal and sulfide minerals. The West Fault is a major fault that separates Chuquicamata into western and eastern parts. This fault is part of the Cenozoic West Fault System in Chile, extending several hundred kilometers in a general north-south to northeast strike direction. The Chuqui Porphyry Complex lies in the mineralized east part of the pit. In contrast, the barren Fortuna Complex lies in the west part. A large proportion of the copper at Chuquicamata occurs in veins and veinlets filling faults and fault-related shatter zones. Pyrite is present everywhere, and chalcocite and covellite appears as both supergene and hypogene minerals. Molybdenite is conspicuous at Chuquicamata, almost all of it carried by quartz veins. Economic effects Copper mining has long been the most consistent Chilean export, and currently accounts for almost one-third of all foreign trade, down from a peak of almost 75%. Copper has been mined in the land area between central Chile and southern Peru since the colonial period, but it was not until the 20th century that copper reached the same level of importance as other mineral exports such as saltpeter or silver. Before World War I, saltpeter was collected from abundant deposits of caliche in the Atacama Desert, and Chile was the primary source of nitrates in the world. After the war, the world market for saltpeter, Chile's