Volcanic domes and gold mineralization in the Pueblo Viejo district, Dominican Republic

Abstract

Gold mineralization in the Pueblo Viejo district, Dominican Republic, is spatially and temporally related to a series of Early Cretaceous volcanic domes. Separate but overlapping hydrothermal cells, centered on the domes, together deposited more than 40 million oz. of gold, 240 million oz. of silver, 3 million tonnes of zinc, and 0.4 million tonnes of copper. Two principal deposits (Moore and Monte Negro) and a number of smaller deposits (Cumba, Mejita, Upper Mejita, Banco V, Arroyo Hondo I and II) have contributed ore since mining commenced in 1975. New geologic mapping has identified a series of previously unrecognized volcanic domes that vary from andesite to dacite in composition. A dacite porphyry dome intrudes epiclastic sediments in the Moore deposit and is surrounded by a baked contact metamorphic aureole. Crumble breccias of mixed epiclastic and pyroclastic origin mantle andesite domes in the Monte Negro, Cumba, and Mejita deposits. Epiclastic volcanic sediments surrounding each of the domes reflect the composition of the local source rock. Andesite domes of the Monte Negro deposit are surrounded by andesitic volcaniclastic sediments. Epiclastic sediments surrounding a dacite porphyry dome in the Moore deposit contain detrital quartz eyes and debris flows of dacite porphyry. A series of at least seven volcanic centers interfinger, overlap, and are interbedded with locally derived epiclastic sediments. Field relations indicate that volcanic dome emplacement, epiclastic sediment accumulation, hydrothermal alteration, and gold mineralization were coeval events. Domes were emplaced in a shallow subaqueous environment on the flanks of an emergent volcanic edifice. Hydrothermal cells responsible for gold mineralization are controlled by high-angle faults. These same faults influenced the emplacement of volcanic domes, an essential step in the development of gold ore in the Pueblo Viejo district.