Unusual Mineralization in Basaltic Andesites of the Submarine Esmeralda Volcano (Mariana Island Arc)

The results of studies of a basaltic andesite sample (complicated by the mineralized fracture and voids, as well as fracture and gas voids filled with secondary mineralization) dredged on the submarine Esmeralda Volcano are presented. A detailed comparative study of the mineral composition of the substance lining the fracture, the near-fracture space, and the basaltic andesite part unaffected by secondary alterations made it possible to discover the presence of a mineral assemblage, which is atypical for the unaltered volcanic rocks, in the submarine Esmeralda Volcano. In the intra-fracture space and adjacent basaltic andesite zones, wide variation ranges of the plagioclase composition are recorded; isomorphism in the Fe–Ca pyroxene series is studied; REE oxides, hydroxides, and fluorohydroxides are studied; and variability in the composition of minerals of the magnetite–hematite series is shown. Tectonic movements in the previously formed basaltic andesites likely promoted the emergence of permeable zones, through which new portions of the melt leaked. In a limited space, high fluid gas saturation, temperature, and pressure fostered the extraction of metal compounds from the melt and host rocks.