The Mineral Deposit of the Yamato Mercury Mine

Abstract

The Yamato Mercury Mine is located in Nara Prefecture, in central Japan, and is one of the oldest mercury mines in Japan. It was developed about 1, 300 years ago, but was inactive for a long time. Several years ago, it-was reopened, and it now produces 2 tons of mercury per month. The principal ore bodies of this mine are in two areas eastern and western, and all are controlled by a fissure system and an altered zone. The strikes and dips of the fissure systems that are closely connected with the ore deposits are as follows.
Strike
Dip
1.N30°—40°W SW35°—40°
2.N—S W30°—40°
3.N60°—80°W SW20°—30°
The main fissure system among those above mentioned is the sheared zone striking N30°—40°W. Others are formed by tensional stress acting on the foot wall side of the sheared zone, and are syngenetic with, that zone. On the hanging wall side of the sheared zone the fissure systems are parallel. The ore deposits exist as a group of stringers filling these fissure systems. The ore deposits are closely connected with the alteration of country rocks, so they are scarce in the weakly altered zone. The main alterations of the country rocks are silicification, argillization, and pyritization. Carbonatization and chloritization are weak.
Generally, the richer deposits are formed where the veins cross or where they dip at a low angle. Most of the faults crossing the veins are thrust faults.