This paper describes the skarns of the Nippo, Shinyama (8D and 4D-7D) and Tengumori deposits at the Kamaishi iron-copper mine, and compares each other. These deposits are situated on the west flank of the Ganidake igneous complex, and are arranged from north to south. Zonal arrangements of the skarns are as follows:
Nippo
diorite Pl Ga Cpx limestone hornfels Cpx Cpx
Shinyama 8D
diorite Pl Ep Ga Cpx limestone Cpx Cpx Cpx
Shinyama 4D-7D
dioriteporphyry Pl Ep Ep Ga Ga Cpx limstone Amp Amp Cpx Cpx
Tengumori
sandstone Ep Ep Ga Cpx Ga limestone Amp Cpx Cpx (I) Cpx (II)
(Pl: plagioclase, Ep: epidote, Ga: garnet, Amp: amphibole, Cpx: clinopyroxene)
Based on the phase equilibria in the system CaO-MgO-AL₂O₃-SiO₂-H₂O-CO₂ and CaO-Fe-AL₂O₃-SiO₂-H₂O-CO₂-O ₂, it is concluded that this variation in zonal arrangement is attributable to the difference in the forma-tion temperature (Nippo: 540-490°C, Shinyama 8D: 490-440°C, Shinyama 4D-7D: 440-400°C and Tengumori: 400-360°C at 1 kbar and XCO₂=0.02). The formation temperature increases northward. Based on this conclusion, the inversion temperature of isotropic-anisotropic garnet is estimated to be between 400 and 440°C. The temperature gradient is considered to be provoked by diorite to diorite porphyry which belongs to the Ganidake igneous complex.

View full abstract

Neogene stress field in Hokkaido has been analyzed, based on the strikes of ore veins. The ore veins formed during the period from late Middle Miocene to Recent are taken into account. Those of E-W and ENE-WSW directions are predominant in both northeast and southwest Hokkaido.
The major veins of thirteen representative mines are formed in the conjugate shear fractures, that is, E-W or ENE-WSW dextral and NW-SE sinistral. The estimated stress field is NW-SE or WNW-ESE compressional and parallel to the direction of the subducting Pacific Plate, even at ore-forming period. The predominance of E-W and ENE-WSW dextral shears might be related to the oblique subduction of the Pacific Plate.

View full abstract

The stability relationships of zunyite, AL₁3Si ₅O ₂0F ₂(OH, F) ₁₆Cl, were determined at P_f=1kb and T=300-600°C in solutions with constant HCl=1M but different HF=0.1 to 20M. The products of stoichiometric oxide mix seeded with natural zunyite in respective solutions at 400°C were used as starting materials. The stability field of zunyite is rather limited; it is stable in a solution with HF concentrations no more than 2M. In 1M HF solution, zunyite is stable up to 450(5)°C and is replaced by topaz at higher temperatures. It appears to remain stable at the same temperature range in solutions with HF as low as 0.1M. In solution with HF concentration of 3M, topaz is stable at temperature above 470(5)°C. At lower temperatures topaz is accompanied by AlF3 phase. This assemblage is also stable at higher temperatures in solutions with HF concentrations up to 10M. In solutions with high HF con-centrations, quartz+AlF ₃ become stable. The rare occurrence of zunyite compared to topaz is the consequnce of stringent chemical conditions aside from temperature. Both F and Cl are indispensable for the mineral and yet higher F activities destabilize it. The occurrence of zunyite as a massive body in altered felsic volcanics reported elsewhere is thus indicative of unusual solution behavior and physico-chemical condition during the alteration.

View full abstract

Propylite is widely developed in the Tertiary volcanic districts of Japan. In particular, it occurs typically in Toi-Seigoshi mining area, Idzu Province (Peninsula) Japan, where many epithermal gold-silver veins are found. KATO (1931) asserted that propylitization of the andesite in this area consists essentially in the formation of albite or potash albite at the expense of original lime-soda feldspars. According to him, the gold-silver mineralization began with the propylitization of andesites, succeeded by formation of gold-silver veins.
The writer has studied the propylites in this area and also in the Kushikino mining area of the southern Kyushu district.
The gold-silver veins of the Seigoshi mine occur both in propylite complex (Yugashima Miocene Formation) and in intruding dolerite or basic andesite dike (Fig. 1). The dolerite or basic andesite of the dike was subjected to weak or no propylitization. The propylitization of propylite complex and dike rocks is not controlled by the vein fissures. The writer concludes that the propylitization has no direct relation with the vein formation. It would be formed by autohydration or deuteric alteration.
The writer recognizes that the feldspar of propylite in this area is intermediate or basic plagioclase. It was replaced by orthoclase within 20-25m from the gold-silver veins. It has been confirmed by the microscopic observation, staining method of potassium in the uncovered thin section, electron microprobe and X-ray diffraction (Fig. 2, 3).
It is certain, I think, that albite or potash albite recognized by KATO in this area corresponds to orthoclase stated above. The formation of orthoclase would be closely related to vein deposition.
The plagioclase in dolerite or basic andesite is also replaced by orthoclase along the veins. The formation of orthoclase, i.e. potassium metasomatism is stronger in the propylite than in the dolerite-basic andesite dike. It would be due to the fact that before the intrusion of the dike potassium metasomatism began along the same fissure as the dike and continued during the dike formation and the vein deposition.
The formation of orthoclase is also recognized in the propylite adjoining the gold-silver veins of the Kushikino mining area, southern Kyushu (Fig. 4).
In the Kushikino mine, the potash feldspar zone grades into the sericite-montmorillonite (or mixed layers of both minerals) zone at the upper parts of the vein (Fig. 5).

View full abstract