佐渡鉱山の地質鉱床

抄録

A number of gold-silver mines on Sado Island, Onomi, Takachi, Kanoura, Kitaebisu, Sado and Tsurushi mines, belong to the type classified as epithermal fissure-filling deposits. These mines are situated on the western slope of the Osado mountain range of the Island.
The Sado mine, the largest gold producer in Japan ever since its opening in ancient age, consists of very many Au-Ag quartz veins which filled fissures in the lower Miocene formations.
Main vein fissures are intimately related to the movement of the second order fractures trending east-west. These fractures are formed by the NE-SW trending master fractures, with a wider mineralized zone by virtue of many branch and parallel veins.
The developments of vein fissures are observed more prominently in brittle rocks such as shale and bedded fine tuff than in the massive pyroclastic rocks and lava flows.
The ore shoots are formed mostly in the lower Aikawa formation surrounding the rhyolite dome which lies in the deeper part of the mine area.
Recent prospecting works based on the re-analysis of structural patterns of the mineralized areas have proved the existence of promising new veins, and this will contribute to the revival of the Sado mine, which has been idle for fifteen years.