Silver Inclusions in zircon ,and gold and silver particles on the zircon surface from SK100 volcanic ash in the Uonuma Group, Niigata ..

Abstract

 Zircon crystals contaioned in SK100 volcanish ash layer of Uonuma Group  which is widely distributed in the Niigata Prefecture were closely examined. The zircon crystals have characteristically covered by glassy materials. The zircon crystals were examined mainly by SEM. Zircon crystals have inclusions of  melt phase whose composition is alkaline volcanic glass. Aatite ,plagioclase , and other minerals were also found as inclusion. In some zircon crystals, native silver grains were found in association with glassy materials. In addition, native gold and native silver grains were observed in the zircon surface and in the bubble hole of volcanic glass.  In the hole of the crack of zircon, many other small minerals were found, such as barite, chalcopyrite and Ni, Cr and Cu minerals, etc. From these observations, it could be said that the SK100 volcanic ash layer is very characteristic.