Abstract

Three distinct porphyry copper subbelts are defined in the Colombian Andes: (1) a western subbelt emplaced during the early to middle Eocene in an oceanic domain, underlain by ophiolitic basement, along the western side of the Western Cordillera; (2) a composite eastern subbelt generated during the Middle Jurassic to earliest Cretaceous in a continental domain, underlain by elements of the Guyana Shield, along the eastern side of the Central Cordillera and the western side of the Eastern Cordillera; and, between the two, (3) a central subbelt formed in the early to late Miocene at the contact of the oceanic and continental domains along the Cauca-Patia depression and its flanks.K-Ar geochronometry undertaken as part of this study provided preferred minimum ages of: 54.7 + or - 1.3 m.y. for Murindo, 48.1 + or - 1.0 m.y. for Acandi, and 42.7 + or - 0.9 m.y. for Pantanos-Pegadorcito in the western subbelt; 166 + or - 4 m.y. for Mocoa, 166 + or - 4 m.y. for Dolores, 144 + or - 3 m.y. for California, and 131 + or - 2 m.y. for Infierno-Chili in the eastern subbelt; and 17.4 + or - 0.4 m.y. for Piedrasentada in the central subbelt.The porphyry copper prospects are associated with dacite to tonalire porphyry stocks, which in the western and eastern subbelts intruded batholiths emplaced perhaps 15 to 30 m.y. earlier but which in the central subbelt are isolated within metamorphic or sedimentary host rocks. The porphyry copper systems exhibit a variety of alteration patterns, with potassium silicate and sericitic alteration important in the highest grade prospects and propylitization predominant in low-grade occurrences. None of the prospects displays significant supergene enrichment. Although porphyry coppers in the continental domain tend to be more molybdenum rich than those in the oceanic domain, gold-rich prospects occur in both settings, as do major lode gold deposits.The Jurassic and Miocene subbelts are interpreted to have been emplaced during eastward subduction at Andean-type continental margins, whereas the western Eocene subbelt could have been generated in either a modified Andean-type setting or in an intraoceanic island arc prior to its accretion to the continental edge.

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