The Status of Lead Isotope Studies of Japan

Abstract

A brief review of lead isotope studies in Japan is made with particular reference to "kuroko" ore deposits. The lead isotopic evidence favors a continental crustal derivation for the lead in these deposits with possibly a component from subducted pelagic sediments. Supporting information is presented from the nature of the "green tuff" belt (abundant dacite and sparse basalt) and lead-rich nature of the ore. The question remains, however, whether the metals are derived from the immediate volcanics or the underlying volcanics or basement. A plan is briefly presented of lead isotope investigations to determine how important the "green tuff" is as a source of ore relative to the underlying volcanics or basement as accessed by deep penetration of ocean-water fluids along transverse fault and fracture zones.