The supergene alteration of pentlandite to violarite has been investigated mainly by the ore microscope and electron microprobe on nickel (-copper) sulphide ores from the following localities. (1) Marbridge mine, Quebec, Canada, (2) Falconbridge mine, Ontario, Canada, and, (3) Kimcheon nickel prospect, Republic of Korea. In addition, some Japanese serpentinites which contain opaque minerals involving the above two sulphides have been examined. As a result, the present authors have observed the significant textural relationships under the ore microscope, showing all stages of the replacement of pentlandite by violarite from incipient to essentially complete. The results obtained from this study may be summarized as follows:
1) The selective replacement of pentlandite by violarite in nature may depend upon the usual development of cleavage or parting in pentlandite and the similarity of crystal structure between the two minerals. The latter may be ascribed to the ease of convertion of π-phase to thiospinel phase, resulting from the cubic close-packed array of sulphur atoms.
2) The zonal structure which may appear after etching of the polished surfaces by HNO₃solution, is confined to the grains of violarite, the cores of which are occupied by the relicts of pentlandite, showing the intermediate stage of violaritization.
3) Electron microprobe study has shown that the zonal structure which consists of four zones in the Kimcheon material, is a reflection of compositional heterogeneity. The violarite-like minerals in these four zones are usually characterized by the higher Fe/Ni atomic ratio than FeNi ₂S₄ composition, and each zone is different in the Fe/Ni ratio. Especially, the innermost narrow zone (Zone I) which is in direct contact with pentlandite relict, is "extremely iron-rich" close to Fe₂NiS ₄ composition.
4) In general, as far as the end products of violaritization of pentlandite, in which homogenization of chemical composition has completed, are concerned, the removal of iron. is more conspicuous than that of nickel.
5) Despite the careful study of the supergene ores, bravoite which is pseudomorphous after pentlandite has not been confirmed. The natural occurrence of secondary bravoite after pentlandite as already described by RAMDOHR remains some doubts.

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Pyrite, chalcopyrite and sphalerite assemblage is the majority of regional metamorphosed ores of the Fudotaki deposit of the Hitachi mine. By contact metamorphism, pyrrhotite is formed from pyrite (desulfurization of pyrite) in the Fujimi and Irishiken deposits of the same mine.
In contact metamorphosed ores, monoclinic pyrrhotite+hexagonal one having 47.3-47.5 atomic % Fe with or without pyrite assemblages are frequently observed. The hexagonal pyrrhotite is sometimes composed of two or three phases with different Fe contents. Polytypes and Fe contents of pyrrhotite may reflect the T-fs ₂ environments of the retrogressive metamorphism. Euhedral (sometimes porphyroblastic) pyrite coexists frequently with pyrrhotite. This association may indicate that these two minerals were once in equilibrium at the climax of the contact metamorphism. FeS contents of sphalerite are generally higher in the rims by 1-3 mole % than those in the central parts of grains. Exsolution dots of chalcopyrite and/or pyrrhotite are always observed in sphalerite. Adding the amounts of exsolved dots to measured FeS contents, the FeS contents of sphalerite associated with pyrite and pyrrhotite become to 18-20 mole % FeS in the rims of grains, which correspond to those on pyrite-pyrrhotite-sphalerite solvus occurring below 600°C. Thus the exsolution dots may have appeared with decreasing temperature along the monoclinic pyrrhotite-hexagonal pyrrhotite fs ₂ buffer.
The desulfurization of pyrite by the contact metamorphism is not so strong in the Fujimi and Irishiken deposits of the Hitachi mine, showing the marked contrast to that in levels deeper than 26 L of the Besshi deposit, where the desulfurization is nearly complete. The marked difference of FeO/MgO ratios for silicates of rocks close to the massive ores between the Hitachi and Besshi deposits may explain this contrasted desulfurization. FeO contents for silicates become, in effect, poorer along the desulfurization of pyrite in the Besshi deposit. A role of Fe-Mg silicates for acceptor of sulfur was suggested.
The appearance of exsolution dots in sphalerite in the Fujimi and Irishiken deposits, and the non-appearance of them in levels deeper than 26 L of the Besshi deposit may be due to the contrasted T-fs ₂, environment in the retrogressive metamorphisms between these two deposits.

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Fluid inclusions in quartz from the Inari copper vein group of the Ani mine, Akita prefecture were studied. The filling and freezing temperatures of fluid inclusions were measured in silicon oil cell of the dual-purpose device which was designed by authers and were found to be useful for both heating and freezing measurements of the same inclusion in a single set of operation. The heating rate was controlled by a program controller.
To obtain relationship among the freezing temperature, heating rate and size of inclusion, the melting temperature of ice of distilled water enclosed in glass capillaries having various diameters were measured. The result show that the deviations from the true melting temperature of ice caused by various heating rates and sizes of inclusion, should not be ignored. In the present study, the heating rate was 0.3°C/min. in which the deviation of melting temperature is almost regardless of the size of inclusion.
Filling temperatures of fluid inclusions in quartz and adularia from the ore veins, and in quartz from diorite and dacite, were within the range from 150°C to 300°C. These results agree approximately with those obtained from various vein type deposits in Japan. On the other hand, salinities of most inclusions were within the range from 18 to 22 weight percent NaCl equivalent concentration. With only one exception of vein of the Taishu mine, these highly saline inclusions are not yet reported in the vein-type deposits in Japan. It is assumed from the occurrence of highly saline inclusions in vein quartz and the geological setting of the Ani mine that the formation of ore solution were genetically related to the granitic rocks intruded into the Tertiary systems in the Ani mineralised area.

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