Contrasting tectonic and magmatic signatures of convergent margin magmas associated with porphyry Cu versus iron oxide-copper-gold deposits

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Copper and gold, industrially and societally important metals, are commonly extracted from ore deposits formed at convergent plate margins, and can be found in the western Cordilleras of South and North American, including in Canada. Two important classes of such deposits, porphyry Cu±Mo±Au and iron oxide-copper-gold deposits (IOCG) have similarities but also important differences, and do not typically occur together in time and space. Both deposit types can be related to hydrothermal fluids exsolved from magmas, and seem to form by broadly similar processes. However, most current research treats the deposit types as unrelated, with distinct, and sometimes highly contrasting models for ore formation. In Chile, porphyry and IOCG deposits occur in close but not overlapping proximity. Excellent exposure and the well-constrained tectonic history of this region permit a high level of control on the geological context of these deposits. Our preliminary assessment of published data indicates that clear but subtle differences in their geochemistry can be observed, which correlate with documented changes in tectonic setting. In this proposal, we aim to probe more deeply into these geochemical contrasts by using minerals such as zircon, apatite, and Fe-Ti oxides to provide constraints on the fugacities of oxygen, sulfur, and water. We will test the hypothesis that one of the main differences between magmas associated with these two different deposit types is their sulfur content, which in turn reflects different magmatic sources and melting conditions. A better understanding of the contrasting tectonic and magmatic settings conducive to the formation of porphyry and IOCG deposits will inform and constrain exploration for such deposits in less well studied regions such as the Canadian Cordillera.