Estudio Petrográfico y Mineralógico del Arco volcánico Macuchi asociado a depósitos minerales en la Cordillera Occidental del Ecuador : caracterización petrográfica de la roca caja en el VMS-Skarn de Rome Gold.

Abstract

The Macuchi block, located at Western Cordillera in Ecuador, is composed of volcanosedimentary and volcanic rocks dating from the Paleocene to the Eocene and is known for hosting significant volcanogenic massive sulfide (VMS) mineral deposits, such as El Domo, La Plata, Macuchi, and the Rome Gold mineral prospect. This study provides a detailed petrographic characterization of the host rock lithologies at Rome Gold through the analysis of hand samples and thin sections of rocks taken from the concession and its surroundings. The petrographic analysis results in four main lithology types: tuffs (lithic and crystalline), quartz diorites, andesites, and skarn. The lithic tuffs show volcaniclastic, andesitic fragments and minor plagioclase and quartz crystal fragments. The crystalline tuffs contain a higher proportion of plagioclase, amphibole and significant silicification. The quartz diorites exhibit phaneritic texture with plagioclase alteration to clays and amphibole to chlorite. The andesites have a porphyritic texture with phenocrysts altered to clays and epidote. The skarn contains epidote, quartz, garnet, calcite, wollastonite, and chlorite. These lithologies exhibit similar characteristics to those reported in previous studies of the Macuchi Formation. Additionally, intense silicification, chloritization, and the presence of sulfide minerals were observed, which are consistent with descriptions of other VMS deposits associated with the Macuchi arc.