Metallogenic features of Miocene porphyry Cu and porphyry-related mineral deposits in Ecuador revealed by Re-Os, 40Ar/39Ar, and U-Pb geochronology

Abstract

Mineralization and alteration events at ten Miocene porphyry Cu and porphyry-related epithermal mineral deposits in southern, central, and northern Ecuador were dated by means of molybdenite Re-Os, biotite and alunite 40Ar/39Ar, and titanite U-Pb geochronology. Most of these hydrothermal events show a spatio-temporal correlation with porphyry intrusion emplacement as constrained by zircon U-Pb ages. The total age range for these events spans the 23.5–6.1 Ma period, without displaying systematic along- or across-arc age distribution trends. While epithermal deposits tend to be spatially associated with volcanic rocks of a similar age, porphyry Cu deposits in Ecuador are frequently spatially associated with deeper-seated basement units and batholith-scale precursor intrusive systems assembled over ≥5 m.y. time periods. In most cases, formation of the porphyry Cu deposits is related to the youngest magmatic (-hydrothermal) event in a given area, postdating batholith construction at a regional scale. The majority of Miocene deposits occurs in southern Ecuador where areally extensive, post-mineralization (late Miocene to recent) volcanic sequences with the potential to conceal mineralization at depth are lacking. Only few Miocene deposits occur in northern-central Ecuador, where they mainly crop out in the Western Cordillera, west of the productive present-day volcanic arc. The surface distribution of post-mineralization arc volcanism reflects along-arc variations in subducting slab geometry. Porphyry Cu and epithermal deposits in Ecuador define a Miocene metallogenic belt broadly continuous with its coeval counterpart in northern-central Peru. Although both belt segments were formed in an overall similar tectonomagmatic and metallogenic setting, their respective metal endowments differ significantly.