Oro en depósitos ecuatorianos: morfología, composición y paragénesis del oro nativo y refractario en depósitos primarios y secundarios

Abstract

Abstract: This research aimed to characterize the morphology, mineral associations, textures, and chemical composition of gold from primary and secondary deposits in Ecuador using reflectedlight petrography and SEM-EDS microanalysis. Samples were collected from the Zaruma Portovelo mining district (El Oro Province), the Nambija skarn deposit, and alluvial deposits from the Zamora River (Zamora Chinchipe Province). Results showed that gold from primary deposits exhibits predominantly anhedral morphologies, close associations with quartz, calcite, and pyrite, and fracture-filling textures with sulfide-hosted inclusions. In contrast, alluvial gold displays subrounded to rounded particles with abrasion features produced by prolonged fluvial transport. SEM-EDS analyses distinguished native and refractory gold, identified compositional variations within Au Ag alloys, and provided evidence to interpret the paragenetic evolution of the mineralization. The integration of petrographic observations and geochemical data improved the understanding of the genesis of the studied gold deposits and provided mineralogical criteria useful for mineral exploration and resource evaluation.