At the first stage, the distribution of skarn zone has been surveyed by the geophysical magnetic prospecting.
Then, the existence of ore body in the skarn zone has been confirmed by twenty-five long vertical bore-holes on the ground surface.
On account of this result, more precise boring investigation has been done successively for every 100 meters level underground, and consequently exploration was carried out in the levels one by one.
Since 1955, 45, 170 meters of boring and 18, 000 meters of drifting have been carried out by us to confirm the dimension and the grade of the deposit, and eight million tons of ore reserves have been discovered.
On the other hand, these ores of the respective grades, transported from each drift and face, were sampled and analyzed more precisely on the pilot dressing plant having 200 t/day capacity.
These survey works contributed a great deal to our schedule for the future development of this deposit.

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The Akatani iron mine is situated in the western border of Iide mountainland. In the mine, the massive micaceous hematite deposits of hydrothermal replacement type are found mainly in the Paleozoic limestone, sometimes in liparite mass of the Neogene age. The deposits are considered to have been genetically related to the eruption of the liparite, being structurally controlled by the shape of liparite masses. The Bawarizawa "Shu" deposit, the largest in the mine, is developed in the limestone immediately below the lava of liparite and extends downward to the limestone in the immediate vicinity of the intrusive contact surfaces of the liparite dyke on both sides, which is connected to the upper lava flow.
The ore-shoot tends to occur at the depressed area, the "U shaped" part of the liparite against limestone.

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Cubanite, which seems to have been crystallized out directly from the ore solution, was discovered in abundance in some pyrometasomatic deposits such as Koyo, Hakki, Mihara and Saezaki mines. Tiny bands of the mineral were also discovered in the meso-hypothermal veins of the Daiei, mine. These Cubanite-bearing ores always contain veinlets or irregular lenticular masses of valleriite and exhibit many interesting exsolution textures among chalcopyrite, cubanite, pyrrhotite, sphalerite and valleriite.
Valleriite occurs commonly in tiny veinlets or irregular lenses about 4 to 170 microns in length and 3 to 10 microns in width, and is often arranged along the crystallographic structure of cubanite and chalcopyrite or along the crystal grains and mineral boundaries.
This paper deals with the paragenetic relations between valleriite and other Cu-Fe-S system minerals.

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Geologically, the northeastern part of the Shakotan Peninsula where, the Oe mine is located, is composed of acidic plutonic rocks, liparite, green tuff and igneous rocks.
Liparite covers the acidic plutonic rocks, and the green tuff, which can be divided into many beds, covers the liparite.
It can be observed that the igneous activities were followed by basaltic and andesitic igneous activities.
This area is characterized by the following geological features;
Folding-Shakotan dome, and Hachinaidake, Kamifutamata and Senzaizawa anticlines.
Faulting-Parallel fault group (Oe-Inakuraishi tectonic line) and Inaho-Taishu fault.
Many ore deposits. occur in the Shakotan Peninsula area. The central part of the ore deposits is chiefly composed of chalcopyrite, galena, zincblende veins, while the marginal parts are chiefly madee up fo manganiferous veins.
The Oe-Inakuraishi tectonic line belongs to one of the parallel fault groups, comprising a number of faults, some being parallel to the parallel faults having a strike of N 60°W, while others are parallel to the Kamifutamata anticline striking N 60°E.
The vein structure of the Oe mine is also affected by the direction of N 60°W and N 60°E, the direction of the faults and anticlines.
The above characteristics of occurrence of ore deposits and vein structures have been utilized for prospecting, and can be used also for future prospecting.

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The Sekizen ore deposit is situated at about 7 km east from the Besshi main ore deposit, both pyritic deposits occurring in the Sambagawa crystalline schist region.
The geological setting of the district in question is composed of spotted black schist, spotted quartz schist, spotted green schist and spotted epidote-hornblende schist, These crystalline schists are characterized by the remarkable presence of albite porphyroblasts, and the metamorphic grade of the rocks seems to correspond to the epidote-amphibolite facies. These rocks are intruded by small lenticular serpentinites which. are often found near the lenticular ore bodies.
Stratigraphically the horizon of the deposit belongs to the upper part of the Minawa formation in the Yoshinogawa group, and is found apparently 500m above the horizon of the Besshi main ore deposit.
The following remarkable features of the ore deposit, which must have been caused by the metamorphic action, are well observed:
(1) The structure of the ore bodies is concordant with that of country rocks, and intense intraformational folding is well observed in many parts of ore shoots.
(2) In some parts of the ore bodies fracture cleavage is often found in compact ores; the fracture cleavage may have been formed by the differential movement which acted upon the country rocks and ores of different competency.
(3) Under the microscope, biotite and green hornblende around ore minerals seem to have been formed in equilibrium relation with the ore minerals during metamorphic processes, because biotite and green hornblende with some ore minerals are not replaced by chlorite, epidote and sericite. In some ores stilpnomelane is associated with biotite as gangue minerals.
(4) In some ores quartz and chlorite occur as the "pressure shadow" around pyrite crystals.
(5) Oriented. structure of lamellar pyrrhotite which is observed under the ore microscope may have been caused by the formation and growth under stress.
(6) Ordinary ores of the deposit consist of pyrite, chalcopyrite, and considerable amounts of sphalerite, pyrrhotite, magnetite and hematite, associated with small amounts of valleriite, bornite, chalcocite, tetrahedrite (?), galena and native gold.
Valleriite occurs in exsolution-like form in chalcopyrite grains of pyrrhotite-rich parts, while blebs of chalcopyrite are found in some sphalerite crystals. These microscopic features may suggest the temperature condition which prevailed in the ore bodies. in question during the metamorphic processes.
The lenticular ore bodies are often accompanied by schistose serpentinites and actinolitic rocks, and such association is said to be useful as a guide to discovery of new ores.
Field evidences and microscopic features of the deposit may thus suggest the syngenetic origin of the deposit which was modified later by the regional metamorphism.

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A theme of high-speed excavation of the rock entry in the coal mines has been much discussed for the purpose of reducing production cost.
The Robbins Tunnel Boring Machine, which has driven a circular 26-foot, 9-inch tunnel through shale at Oahe Dam in South Dakota, U.S.A., at a rate of 12 feet an hour without benefit of explosives, was introduced to Japan in 1956.
Although the remarkably high efficiency of this machine had been proved in the Oahe Dam project, we are rather sceptical whether similar results would be expected in Japan as well, we take into account a considerable difference in the rock formation and its physical characteristics in U.S.A. and Japan.
We, therefore, experimented the application of this machine to the rocks collected from various local mines (mostly from our own mines) and also to the sample shale from Pittsburgh (similar to the shale at Oahe Dam which proved to be suitable for economic cutting in U.S.A.), as well. as the sample graywacke from New York which proved unsuitable for economic cutting, particularly in view of its drillability.
In case of rotary drilling by means of such a specific machine as Robbins Tunnel Boring Machine in which the rotation speed as well as shape of bit and thrust have been standardized, the drilling rate of rocks depends mainly on the physical characteristics of rocks, especially abrasiveness and indentation hardness.
We have examined physical characteristics of these rock samples, in cooperation with Mining Division of Resources Research Institute, Agency of Industrial Science and Technology of the Japanese Government. We have sorted these rocks into two different groups, namely:
(1) rocks suitable for economic cutting
(2) rocks unsuitable for economic cutting.
This classification was based on the above test by us and also on the result of operation of Robbins Tunnel Boring Machine in several projects in U.S.A.
Our conclusion is that the Robbins Tunnel Boring Machine is not suitable for economic cutting of Tertiary sandstone and conglomerate which mainly constitute the rock entry of coal mines of our company.
However, with the improvement of the cutting mechanism and the material of bits, this machine may become applicable in future to more kinds of rocks and to wider extent even in Japan.

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