Further Studies on Size Distribution of Siderophile Element Concentrations in Black Magnetic Spherules from Deep Sea Sediments

Abstract

(Co/Fe), (Ir/Fe) and (Au/Fe) ratios in magnetic iron spherules in deep sea sediments, whose sizes range from 16μm to 1440μm, were determined by instrumental neutron activation analysis. The following conclusion can be drawn from this work, together with the data obtained by a previous work for a narrow size region (100-440μum). Decreasing ratios of the respective element were commonly observed with increasing size of the spherules. In the intermediate size region (approximately 50-500μm), these ratios can be interpreted with the thermally degenerated compositions of metal phases of chondrites and iron meteorites. In the largest size region (>500μm), the spherules were so entirely oxidized that Co, Ir and Au components could hardly be detected. In the smallest size region (<50μm), we have many spherules, which had extremely high values of the ratios. The inner nucleus grains or nuggets of iron spherules, in which refractory or volatile elements were highly concentrated, is an available candidate for these spherules.