Abstract
To examine the availability of trace elements in pyrite for exploration, elevencore samples from the Kirishima geothermal field were analyzed for copper, nickel, cobalt and arsenic by electron microprobe. Among them, cobalt and arsenic gave interest informations. Cobalt contents of pyrite are relatively high in the lower Makizono lava of pyroxene andesite and the underlying Ebino formation of tuff breccia and tuffaceous shale, while they are remarkably low in the underlying Iino lava of pyroxen andesite. This suggests that, even in the well lacking the Ebino formation, cobalt contents give a key to identify the Makizono lava and the Iino one, both of which are petrographically similar to each other. Arsenic contents of pyrite are low in the KT-7 well of neutral hydrothermal solution, as compared with the KT-8 well of acidic solution. This implies that the increase ofoxygen activity resulted in the concentration of arsenic into pyrite as well as the decrease of pH.
