In the Shirataki mine the main ore deposit follows the plunge of an asymmetrical overturned anticline and is over 4, 000 m long. Several ore shoots are highly folded, and are nearly concordant with the structure of the enclosing schists. The various kinds of ores in the ore bodies include a massive or banded pyritic ore, impregnated ore, chalcopyrite-rich ore and apophyses. Many massive or banded pyritic ores show intense intraformational folding. The constituent minerals are pyrite, chalcopyrite, sphalerite, bornite, chalcocite, covellite, native silver, stromeyerite, tetrahedrite (?), an undetermined mineral (Rosagrau Kuferglanz?), hematite, magnetite, ilmenite, guartz, a carbonate mineral, green hornblende, albite, chlorite, garnet and epidote.
Chalcopyrite, sphalerite, quartz, a carbonate mineral and chlorite show "pressure shadow" features around some pyrite and magnetite crystals in impregnated ores. In a few apophyses ores stromeyerite is found among chalcocite and native silver, and a microtexture of bornite and chalcocite shows lamellar intergrowth and mutual boundaries that are probably of simultaneous origin in metamorphic differentiation process.
The field and microscopic features of this deposit are reasonably explained by the theory of sulphide syngenesis, later modified by regional metamorphism.

View full abstract

The ore-deposits of the Okuki and the Nebutoyama mine are composed mainly of copper and iron sulfides and are of the bedded type found within an older formation in Japan. The main ore minerals are pyrite and chalcopyrite. They often show various colloform textures.
Iron-titanium oxide minerals are commonly found associated with these sulfide minerals, though they are not abundant. Most of them rarely occur in the same layer with sulfide minerals. Magnetite, hematite and ilmenite are commonly present. These minerals show typical sedimentary occurrence .and are associated with fine magnetite grains and pyrite in colldform texture and are sometimes found with radiolarian fossils. However, exsolution texture between magnetite or hematite and ilmenite is commonly found associated with the textures suggesting their low temperature mineralization as previously described. Very small grains of chalcopyrite are generally closely associated with oxide minerals and, in some cases, in them. This seems to show that all of these metallic constituents were separated and crystallized from the mother solution almost simultaneously.
These textures have not been reported in many descriptions of similar ore-deposits in the highly metamorphosed area of Japan.
The writer concludes that the ore-deposits of the Okuki, the Nebutoyama and similar mines were derived from submarine volcanism in the Chichibu geosyncline. Some iron-titanium oxide and sulfide minerals were formed in the same high temperature conditions as in the pyroclastic rocks and. were then deposited in the bottom of the sea. However, the main sulfide minerals and perhaps some of the iron-titanium oxide minerals, precipitated from colloidal solution.

View full abstract

The Yonaihata mine is mining several massive bodies of gypsum with sphalerite, galena and chalcopyrite in a Miocene mudstone. The bodies are thought to belong to a type of Black Ore in Japan. They also contain, besides gypsum and sulphide minerals, small amounts of fluorite, calcite, barite and anhydrite. The gypsum bodies consist of massive or disseminated alabaster accompanied by veinlets of fibrous gypsum at their margin. The alabaster replaces calcite, fluorite, barite and anhydrite, and often penetrates the sulphide minerals in the form of veinlets. It suggests that the gypsum was formed by epithermal solutions at the latest stage of the mineralization. The ore solutions have replaced black mudstone more than tuffaceous mudstone which is inserted in this black mudstone. In this case, the tuffaceous mudstone plays the role of cap rock for ore bodies. The mudstones surrounding ore bodies are widely changed into clays by hydrothermal solutions. In the clay zone, an increase of magnesia and a decrease of silica compared with the original mudstones are conspicuous. The occurrence of magnesium chlorite and montmorillonite in the clay zone is ascertained from the results of X-ray powder photographs and differential thermal analyses.
The writers would like to emphasize that the deposition of gypsum is due to the breakdown of the chemical equilibrium by a change of physical conditions in the ascending solution as shown below.
For example,
Na₂SO₄+Ca(HCO₃)₂+H₂O CaSO₄⋅2H₂O+Na₂CO₃+CO₂
(gypsum)
In the formula, the reaction will progress toward the formation of gypsum, if the pressure of the environment decreases to allow the escape of CO₂ gas. By this consideration, it may be shown that ore bodies are formed only within the limits of a geological horizon in this mine.

View full abstract