On the Relationship between the Ore Deposit and fissure of the Yamato Mercury Mine

Abstract

The Yamato mercury mine is located in the central part of Nara Prefecture and one of the oldest mercury mines in Japan. The mine area is composed of plutonic rocks and mylonitic rocks of the post-Palaeozoic period, Tertiary quartz andesite and Quaternary sediments. The ore deposits of this mine are controlled by fissure systems such as EW and NW striking shear fractures, and WNW striking tentional fractures which are considered to be formed by the compression of WNW-ESE direction that is connected closely with the movement of the Median Tectonic Line. The ore deposits exist as a group of stringers, ore-pipe and pocket filling these fissure systems. The main Alterations of the country rocks are silicification, argillization, pyritization, carbonatization and chloritization. Ore shoots are formed where the fissures and veins cross, or where they dip at a low angle. It is considered that these ore shoots are controlled by structures of the fissures and the country rock.