Ages and isotope evolution of the Agua Rica Cu-Au porphyry-epithermal deposit, NW Argentina

Abstract

The link between porphyry-epithermal deposits and continental-arc magmatism is widely accepted, but in flat-slab settings the source of metals is still debated. The Central Andes region hosts numerous important mineral deposits within the flat-subduction zone including the world-class Agua Rica Cu-Au (Mo) porphyry-epithermal deposit, which is associated with the Farallón Negro Volcanic Complex. The suite of mineralization at Agua Rica includes a porphyry-Cu phase, an associated epithermal assemblage and a supergene enrichment overprint. The main mineralization is considered to be related to the Trampeadero and Seca Norte dacite porphyry intrusions, for which U-Pb SHRIMP zircon ages are 6.09 ± 0.17 and 5.81 ± 0.32 Ma to 5.41 ± 0.25 respectively. Rhenium-Os dating of pyrite from the Trampeadero porphyry yielded an isochron with an age of 5.85 ± 0.42 Ma, and molybdenite yielded a model age of 5.61 ± 0.03 Ma. The Seca Norte body was responsible for the main porphyry-style mineralization, while the older Trampeadero porphyry served as a host rock. Magmatic-hydrothermal activity at Agua Rica commenced at approximately the same time as it was ending in other parts of the volcanic complex.Pb isotope signatures of sulfide samples from Agua Rica indicate a significant addition of crustal material to a mantle source. Neogene magmatism in the area is likely related to the subduction of the Juan Fernández Ridge, which was subjacent to the deposit by the time of the porphyry intrusions. Upper crustal MASH (mixing, assimilation, storage, and homogenization) in the melting zone above the slab is inferred as the source of the shallow magma reservoir beneath the Farallón Negro Volcanic Complex.