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.

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The Ohori mine is located about 15 kilometers east of the city of Shinjo, Yamagata Prefecture, in a steep mountain, about 700 meters above sea level. This mountain is mainly formed of Miocene pyroclastic rocks and their lava flows, such as altered andesite and its tuff, green tuff breccia, rhyolitic tuff, rhyolitic breccia and muddy tuff, all of which are intruded by granitic rocks, plagiorhyolite and dolerite. Two types of ore deposits, a bedded type and a vein type, are found in the mine.
The bedded type, named the Kaninomata deposit, has been formed by metasomatic replacement of a calcareous bed inserted in rhyolitic breccia. The ore consists of sphalerite, chalcopyrite, pyrite and. galena intimately accompanied by wollastonite, bustamite, garnet, diopside, rhodonite, epidote, quartz, calcite and rhodochrosite. The chemical composition of the garnet is given as (Ca2.81 Mn0.26 Mg0.12 Fe''0.02)3.21 (Al.50 Fe'''0.45)1.95 (Si2.89 Ti0.04)2.93 O12.00, with a unit cell lattice constant of 11.885A. Also, the molecular formula of bustamite is (Ca0.44 Mn0.50 Fe0.03 Mg0.08)1.05 Si0.98 O3.00. The appearance of wollastonite, diopside, garnet and bustamite indicates that the early stage of mineralization of the Kaninomata deposit was under high temperature. Metasomatism under such high temperature is very rare in the Tertiary formations in Japan. The ore texture of the sulphide minerals produced in the late stages of mineralization, however, is simple, and unmixing textures are not observed.
The vein type deposit named the Nakanomata deposit, mainly fills fractures in dolerite that has intruded muddy tuff and rhyolitic tuff. The ore consists of chalcopyrite, sphalerite and pyrite with gangue minerals such as quartz, epidote, calcite, chlorite and sericite. It seems to belong to the common type of shallow-seated veins deposited in the Miocene formation in northeastern Japan.
The bedded Kaninomata deposit is often penetrated by veinlets composed of chalcopyrite, sphalerite, pyrite and quartz, which are thought to have been formed at same time as the Nakanomata vein deposit. Thus, the mineralization of the Kaninomata deposit seems to be earlier than that of the vein type, and probably was emplaced by ore-forming fluid derived from subvolcanic magma that formed the Tertiary granite and diorite in this area.

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Altered zones are developed around the Yamabuki Deposit of the Hanawa Mine, Akita Prefecture.
Copper contents rise logarithmically from the outer to the inner parts of the zone, and the distribution behaviour of copper is similar to that of heavy metals in the altered zones of several mines indicated in previous papers.
Close correlation of copper to both silver and lead is pointed out.

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The question of whether the basic rocks in the core of the fold in the Okuki mine (the cupriferous pyrite deposit) are intrusive or effusive is discussed in relation to the genesis of the ore deposit.
The writer describes the petrographic characters of the gabbro found in the core of the fold. The gabbro is distinctly intrusive.

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