IOCG Deposits: A Cordilleran Perspective

During the latter part of the Phanerozoic, numerous iron oxide(-Cu-Au) (IOCG) systems formed in parts of the Cordillera of North and South America. They occur in diverse tectonic and magmatic settings with considerable variety in deposit associations and characteristics. Although there are general patterns, there is no simple, all-encompassing descriptive model; a comparison with the diversity of epithermal and other oreforming systems is informative. Observations on many districts demonstrates that IOCG systems are clearly distinct in character and origin from magmatic hydrothermal systems (e.g., porphyries) although they may overlap in space and time. Ongoing field-based studies in Chile and the USA illustrate this spectrum of deposit styles and the overlap with other types. Useful predictive tools follow from the data and a sound understanding of geologic processes. Based on these results, Cordilleran IOCG systems result from voluminous flow of highly saline, metal-rich, sulfur-poor fluids in the upper crust. Typically, flow is magmatically driven and dominated by non-magmatic fluid sources. Unlike the case for typical porphyry Cu systems, concentration of Cu in IOCG systems requires favorable circumstances, notably an independent source of sulfur. In the Cordillera, overlap with marine volcano-sedimentary sequences may be a key contributing factor to Cu-Au productivity. IOCG, American Cordillera, characteristics, genesis