K-Ar ages of Hosokura Pb-Zn and Sado Au-Ag vein-type deposits, north eastern part of Japan

Abstract

One sample of adularia from the Hosokura Pb-Zn vein-type deposits gives a K-Ar age of 5.8±0.2 Ma. This age is quite younger than that of the host rocks (Hosokura formation) of Daijima to Nishikurozawa (early to middle Miocene).
Two samples of adularia from the different veins of the Sado Au-Ag mine give the K-Ar ages of 14.5±0.5 Ma. and 13.4±0.5 Ma. These ages are 25-15 m. y. younger than those of the host rocks (Odate and Aikawa formation).
Summary of the ages of the vein-type deposits and those of the host rocks in the Green tuff region previously studied, including the present data on the Hosokura and Sado deposits, suggests that almost all of the vein-type mineralization in the Green tuff region of north eastern part of Japan took place after the Nishikurozawa stage (14-16 Ma.). This implies that the ages of the vein-type mineralization were later than and/or similar to that of the Kuroko mineralization.