Cu, Ni-bearing immiscible sulfide globules and pyrrhotite in scoria of Asama 2004 eruption: Sulfur-rich basalt magma injection and mixing

Abstract

During the 2004 eruption of Asama volcano, sulfur-rich basaltic magma repeatedly intruded into a felsic reservoir beneath the summit. Olivine phenocryst includes sulfur-rich mafic melt (S ≤ 2600 ppm) before the mixing. Olivine phenocryst also includes Cu and Ni-bearing heterogeneous sulfide globules and homogeneous Ni-rich pyrrhotite. In contrast, the major phenocrysts (ortho- and clinopyroxene, and plagioclase) include only homogeneous Cu,Ni-poor pyrrhotite. And these sulfides are also found to be scattered in the glassy groundmass. The melt inclusion and sulfide mineral data reveal that basaltic magma provides a large amounts of sulfur to the frontal volcanoes in central-northeastern Japan.