1985 Volume 35 Issue 189 Pages 57-65
The Kamioka Pb-Zn deposits are pyrometasomatic and hydrothermal replacements in Hida metamorphic rocks. The ore is divided into two types: The early "Mokuji" ore that is skarn-type ore with hedenbergite and epidote and the later "Shiroji" ore with quartz and calcite. Sericite occurs in the Shiroji ore or as an alteration product in the wall rock of the Shiroji. K-Ar ages of five sericite samples were determined to be 65.3, 65.1, 66.1, 67.5 and 63.8 Ma. The results show that the Shiroji mineralization took place near the end of Cretaceous. The Mokuji mineralization may be not much older than the Shiroji.
Recent finding of metamorphic skarn accompanied by pyrrhotite and sphalerite and crystalline limestone containing primary sphalerite and pyrrhotite suggests that the initial concentration of metals in this area can be traced back to a period prior to the Hida metamorphism. The K-Ar ages of sericites represent the time when the deposits took the present form.
