Microanalyses were performed on principal ore minerals-pyrite and chalcopyrite-from the porphyry copper deposits of the Mamut Mine, East Malaysia. The result reveals that Ag and Mn are concentrated in chalcopyrite; and Mo, Ni, Co, Pb and Bi in pyrite. In general, the minor element variability in chalcopyrite is smaller than that in pyrite. Minor element abundances in pyrite and chalcopyrite vary with host rock types. The Ni composition of the sulfide minerals is likely due to mixing of Ni from the host rocks with Ni derived from the ore fluid.
Comparing the analytical data from the Mamut deposit with those from the Bingham deposit and the Santa Rita deposit, it can be pointed out that chalcopyrites in the former deposit are generally richer in Ag and poorer in Sn, Mo, Bi and As than in the latter deposits.

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In the Shakanai kuroko deposits are well developed so-called "gypsum zones" characterized by an abundance of gypsum and/or anhydrite. The purpose of this paper is to disclose their geological modes of occurrence and petrographical characteristics and thereby to provide some constraints in studies of their origin. Some of our conclusions are summarized as follows:
(1) The "gypsum zones" are always developed in close contact with or in the vicinity of the kuroko deposits, occurring generally in stratiform as a whole. Interpreting in a broad sense, it appears that they were primarily a sort of sedimentological stratum.
(2) Mineralogically, both anhydrite and gypsum of different morphological types such as alabaster, satinspar and celestite are recognized. Anhydrite and alabaster are the principal constituents and they occur usually as oval lumps of various size.
(3) The "gypsum zones" in general underlie the kuroko deposits to form a set of zonal arrangement. In some places, however, at least two sets of such zonal arrangement are known to be repeated spatially. This may be due either to repetitional mineralizations or to secondary deformation and dislocation of the pre-existing deposits formed by a single mineralization.
(4) Relative abundance of anhydrite to gypsum depends evidently on the burial depth at present, increasing signifi-cantly towards deeper levels. It is strongly suggested that gypsum was formed by hydration of anhydrite very recently, i.e., during Quaternary period.
(5) Between the "gypsum zones" and the kuroko deposits are sometimes interstratified economically workable "gypseous sulfide zones", which are similar in sulfide mineralogy to the kuroko deposits overlain. It appears that the "gypseous sulfide zones" were formed either by simultaneous deposition of sulfide minerals and a Ca-sulfate minerals or by later physical or chemical interactions between the pre-existing "gypsum zones" and kuroko deposits.

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Dunite, peridotite and pyroxenite of the Arakawa and Iwakura-yama bodies along the Hayachine tectonic belt in the Kamaishi mining district, Northeastern Japan, have been weakly to completely serpentinized. Magnetite and a variety of Fe-Ni(-Co) sulfides occur in these rocks, which have secondarily formed under serpentinization.
With the progress of serpentinization of the host rocks, mineral assemblages in the Fe-Ni-S-O system change as follows.
1. Arakawa body
Magmatic pyrrhotite-pentlandite→secondary hexagonal pyrrhotite-pentlandite-mackinawite.
2. Iwakura-yama body
Magmatic pyrrhotite-pentlandite→secondary monoclinic pyrrhotite-pentlandite-magnetite→secondary pentlandite-heazlewoodite-godlevskite-magnetite→secondary pentlandite-violarite-pyrite-magnetite, pentlandite-violarite-magnetite, pentlandite-violarite-inillerite-magnetite and violarite-millerite-magnetite.
Two kinds of violarites genetically different occur in the Hayachine ultramafic rocks, one which has replaced pentlandite under supergene condition and the other which is regarded to have formed in association with pentlandite, millerite and magnetite under the serpentinization. Violarite in the above assemblages is the latter one.
In present study, chemical analyses of the phases in each assemblage were carefully made by electron microprobe method, and a tentative low-temperature (about 200°C) phase diagrams of the Fe-Ni-S and Fe-Ni-S-O systems were drawn on the basis of the analytical data and the experimental studies so far reported. The chemical compositions of the violarite range from Fe_0.6 Ni_2.4S₄ to Fe_1.3 Ni_1.8 S₄, indicating that violarite-pentlandite tie line is stable at low temperature in the Fe-Ni-S system.
Projecting the Hayachine mineral assemblages onto the log Po₂-log Ps₂ diagram of the Fe-Ni-S-O system, it was revealed that both Po₂ and Ps₂ have gradually become lower during serpentinization reaction, and both higher in the process after that reaction. These phenomena can be interpreted from the viewpoints of supply of H₂O, formation of H₂ and desulfurization of magmatic sulfides.

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