The layered cupriferous pyritic deposits of the Shimokawa mine have a characteristically simple geological structure, where the foot-wall consists of thick spilitic and diabasic rocks with numerous thin intercalations of graywackes and slaty rock, and the hanging wall consists of slaty rocks.
These basic rocks were previously regarded as dyke swarms intruding the Hidaka. formation at high angles, and the deposits as epigenetic ones having replaced the sheared slaty rocks near the boundary with the basic rocks.
Recent underground and surface geological studies have revealed that some of the basic rocks are subaqueous lava flows with a pillow structure, and the ore deposits rest on the uppermost spilite flows intercalated with thin sedimentary layers. Immediately after the end of the ore deposition, when no sedimentary cover was existent yet, diabase sheets intruded between the ore body and the foot-wall, often branching into the ore body forming a distinct chilled margin.
These facts clearly indicate that the deposits are one of the most typical syngenetic sedimentary-exhalative deposits originated from a spilitic magma.

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The geology and ore deposits of the Ishizu mining district are described with special reference to the form and structural control of the ore deposits.
The rocks occurring in the district are chiefly andestic lavas and pyroclastic rocks ejected from the Kusatsu-Shirane volcano. These rocks can be generally classified into five groups, namely, from older to younger, Matsuozawa, Aoba, Komenasi, Motoshirane, and Sessyo groups. The first two are found in the older caldera and the others are in the younger caldera which formed above the former.
The ore deposits of the mine are found mainly in the Matsuozawa group and in the lower part of the Aoba group. The mineralization of sulfur ore is closely associated with the ejection of these lava groups, i.e., after the formation of the older caldera the ejection of lavas of the Matsuozawa group took place and the ore solution ascended through the weak part of the bottom of the caldera, and the mineralization became active on account of the ejection of the lavas of the Aoba group, and then became weak rapidly but not simultaneously with the formation of the younger caldera. And, after the ejec-tion of the lavas of the Motoshirane group which flowed into the younger caldera, there occurred weak fumarolic activities which, however, ceased before the ejection of the lavas of the Sessyo group.
The ore deposits show a bedded form and belong to the so-called Ishizu-Numajiri type. In the upper part of the ore deposits, the ore gradates into wall rocks with dissemination, but in the lower part the ore forms pipes concentrated in the small centers along the weak zone.
The ore deposits are controlled by the following structural factors ; a) fissure groups trending N 10°W and N 40°W, b) distribution and form of the Middle lava, which is a member lying in the center of the succession of the Matsuozawa group and seemingly acting as a cap rock, c) two beds of tuff-breccia trending N 40-50°E, which are the members of the same group and apparently playing an important role in diffusion of the ore solution.
Prospecting of the ore deposit was carried out based on the above-mentioned structral factors. Great attention was paid to the results of the investigations by means of boring, with special interest in the above factors, because of the charactor of the ore deposits under cover.

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The natural gas of the Miyazaki gas field is of the water-drive type, reserved in the sandstone and conglomerate of the Tano formation. The chief source of the gas is Tano and upper formation, which contain a great deal of mollusks and foraminiferas. The permeability of reservoir rocks is low, but that calculated from the amount of lift water is high. The S.P. and R curves of the electric logs show that the rocks are compact and massive.
The reservoir rocks of this gas field, therefore, abound in fissures and cracks, with minor faults which resulted from folding.

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In the Chugoku province, there are many tungsten and molybdenum deposits closely associated with the igneous activities ranging in age from late Mesozoic to early Tertiary. The molybdenum deposits are distributed especially in the northern part of this province, i.e. the San-in province. The molybdenum deposits of the Daito district are located about 20km southwest of Matsue city, Shimane prefecture. They are now the most productive deposits of molybdenum in Japan.
The present paper briefly discusses the relations of the molybdenum deposits of this district to the igneous intrusives and the origin of these deposits in the light of field observations as well as laboratory works.
The results obtained are as follows:
(1) The rocks occunrring in the Daito district are many intrusives of various rock types and related metamorphic rocks.
(2) The most important deposits (Honko and Hinotani deposits of the Daito mine, Kamitani, Honko and Namera deposits of the Seikyu mine, and Honko deposits of the Higashiyama mine) are all situated around the margin of the Rengeji biotite granite and/or near the contact between this granite and the Kawai hybrid rocks serving as the cap-rock of the granite. The deposits seem to be closely related to the Rengeji biotite granite.
On the other hand, the Minamiko deposits of the Seikyu mine are located in the Kawai hybrid rocks that are the cap-rock of the Ouchidani biotite granite ; the deposits are believed to be closely related to this granite.
(3) The molybdenum deposits are hydrothermal molybdenite quartz veins, 10 to 100cm thick, generally 100m long in the dip direction, and 250m long in the strike direction. Molybdenite and quartz are common essential vein minerals, and other minerals such as biotite, plagioclase, adularia, epidote, galena, sphalerite, pyrite, ankerite and calcite are also found as accessory minerals.
(4) The country rocks adjacent to the veins are rather strongly altered. The alteration zone commonly comprises two transitional zones, namely, sericitized zone (in places, silicified zone is recognized) and chloritized zone, from the inner side toward the outer side. In the sericitized zone, about 10cm wide, feldspar and biotite are markedly replaced by aggregates of sericite and quartz. In the chloritized zone, about 10cm or more wide, feldspar is slightly replaced by sericite and calcite, and biotite is completely converted into aggregates of chlorite and pyrite.

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Depth of formation is evaluated on some subvolcanic hydrothermal veins in Akita Prefecture, Northeastern Japan mainly based on isopach maps of Tertiary formations in the area questioned. There are two opinions on the age of metallogenesis in the province ; late Nishikurozawa stage to very early Onnagawa stage (A) or late Funagawa stage to very early. Tentokuji stage (B), both belonging to Neogene. Estimated depth of formation is about 200 meters for the uppermost parts of the veins developed in the Osarizawa, Ani, Miyatamata and Tazawa mines, and about 250-300 meters for those in the Akarimata and Tatemata mines, if we assume that those veins were formed during the A age. The depth is, however, evaluated as several to ten hundreds meters, if we choose the B age instead of the A. In the district near the Tazawa mine, no sedimentation occurred during the Funakawa and Tentokuji stages. Then, the depth of formation of the veins in the mine is clearly defined as 150-300 meters regardless of its age of formation is A or B.

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