Tectonomagmatic controls on localization of porphyry copper deposits, Chile

Several of the world's largest porphyry copper deposits, including Chuquicamata and La Escondida, occur within the West Fissure Zone, an 800-km-long, N-S-trending corridor of strike-slip faults in northern Chile. Location within this corridor is controlled by intersection of the WFZ with oblique, NW-trending lineaments, which appear to mark deep-seated, long-lived discontinuities in the basement. It is argued that generation of porphyry mineralization at these loci in the Late Eocene-Early Oligocene is a function of: (I)suitable (translithospheric) structural framework; (2) stress field oriented in such a way as to impose tension or transtension on this framework; (3) voluminous shallow-level calc-alkaline plutonism: (4) appropriate oxidation state and contents of water and sulphur in the magmas to promote volatile exsolution prior to sulphur saturation during differentiation; and (5) supergene enrichment. Omission or ineffective operation of any one of these factors will reduce the efficiency of the ore-forming process, or prevent the formation of deposits altogether.