Geology, alteration and geochronology of the Cerro Vetas Porphyry Deposit, Middle Cauca Belt, Colombia

Abstract

The Cerro Vetas porphyry deposit is part of the Titiribi District of the Middle Cauca porphyry-epithermal belt of western Colombia. The Cerro Vetas porphyry stock hosting the deposit consists of an early syn-mineral quartz-diorite intruded by a later -post-mineral quartz-monzodiorite, with intrusion and contact breccias. These units intrude Cretaceous basement metabasalts and schists, the Oligocene-Miocene Amagá Formation, and Miocene age volcanic andesites, intercalated within the Amagá Formation. Two phases of potassic alteration are recognized - biotite-dominant in the quartz-diorite and K-feldspar in the quartz-monzodiorite. The biotite alteration is overprinted by weak to moderate phyllic alteration in the upper 100 m of the deposit. Below 100 m, the phyllic alteration assemblages are constrained to structural zones. An overprinting and grade destructive, calcic-sodic alteration (actinolite + albite ± magnetite) affects both porphyry phases. Mineralization is dominated by a chalcopyrite-native gold-pyrite assemblage associated with biotite alteration that is hosted in a truncated stockwork in the apical portion of the deposit with metal ratios typical of Au-rich Au-Cu porphyry deposits. The intrusive phases that host the deposit were dated via U-Pb in zircon laser ablation inductively coupled plasma-mass spectroscopy (LA-ICP-MS) to 7.65-7.24 Ma, thus consistent with other deposits in the Middle Cauca belt. The lithological, alteration and stratigraphic relationships identified at the deposit suggest that the Cerro Vetas porphyry and related deposit formed at a depth equal to or slightly less that 1 km with a portion of it eroded.