Iron Oxide Cu-Au Monograph - Volume 3, Abstract

The Mesozoic iron oxide-copper-gold (IOCG) mineralisation of the southern Perúvian and northern Chilean coastal belt has emerged as one of the major exploration targets in the Central Andes in the last two decades. These Mesozoic Andean IOCG deposits were formed during two mineralising epochs, i.e., Middle to Late Jurassic (170 to 150 Ma) and Early Cretaceous (130 to 110 Ma), with the major copper-rich IOCG deposits being confined to the Early Cretaceous belt. Early studies of some IOCG centres supported a magmatic-hydrothermal model for both copper-rich IOCG deposits and broadly contemporaneous copper-poor "Kiruna-type" iron-oxide-apatite magnetite deposits. However, more recent evidence from field investigations, geochronology, fluid inclusions and stable isotopes, show that in the major Central Andean deposits, e.g., Raúl-Condestable and Mina Justa in southern Perú, and La Candelaria-Punta del Cobre and Mantoverde in northern Chile, the incursion of evaporite-sourced basinal brines, or seawater, may be a prerequisite for economic copper mineralisation. Moreover, some of the copper-poor massive magnetite deposits could be interpreted as a being the product of iron oxide melts, although many have been classified as magmatic-hydrothermal replacement without evidence of the involvement of external fluids. Therefore, the copper-rich IOCG and copper-poor massive magnetite deposits could represent different ore-forming process, although they may both be temporally associated with the same regional magmatism. Ore modelling for both the Middle to Late Jurassic and Early Cretaceous metallogenic epochs of the Central Andes is reconstructed.