Hydrothermal alteration in the Kamikita Kuroko mineralization area have been examined by using samples from 16 drill holes and the field covering about 100km² in area. Four types of alteration (I-IV) are distinguished spatially, temporally, and mineralogically in this area. Alteration I may be related to the intrusion of quartz diorite bodies at 13 Ma. This alteration is composed of five mineral zones which are zonally arranged from the center to the periphery as follows: the biotite-actinolite (I₅) → the chlorite-epidote (I₄) → the corrensite-laumontite (I₃) → the smectite-zeolites (I₂) → the smectite (I₁) zones. Alteration II may be related to the Kuroko-type mineralization at 10 to 12 Ma. It comprises the K-feldspar, the illite-chlorite, and the mixed layer mineral zones which are arranged in turn from the stratigraphically lower to the upper parts. Alteration III was probably formed at almost same time or slightly later than the alteration II. The mineral assemblages of the laumontite and wairakite zones in the alteration III are similar to those in the higher-grade zones of alteration I, but the former is distinguished from the latter by the association of pumpellyite, prehnite, hedenbergite, or garnet. Alteration IV comprises the pyrophyllite-diaspore, the mixed layer mineral, and the alunite zones. The formation of the former two zones was at 6 Ma and the alunitization followed at 3 to 4 Ma.
Epidote, chlorite, or white mica is a common product in the higher-grade zones of all the types of alteration. These minerals were formed at approximately 200-300°C as inferred from comparison with the formation temperatures of the minerals in low-grade metamorphic environments and active geothermal fields. The compositional variability in these minerals, in addition to the difference in the mineral assemblages of each alteration, was caused by difference of geochemical conditions such as fugacities of CO₂ and O₂ and pH of solution.

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Asymmetric slip planes within a shear zone, echelon arrangements of extension fractures and those of shear fractures, and the two types of "cymoid loop": adjoining two shear fractures bridged by extension fractures and those bridged by shear fractures are common also for ore veins and vein systems. By estimating the stress orientation and the dependence of the fracturing mode on confining pressure, the distribution of ore bodies, including the depth and pitch of cymoid loops, can be effectively predicted.

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K-Ar age was determined to be 54.4 ± 2.7Ma for the alteration envelope of a quartz-calcite-molybdenite vein at the Nakatatsu mine. The sample for this study is composed of muscovite of which closure temperature is included by the range of the homogenization temperature of the fluid inclusion of quartz-calcite-molybdenite veins. Thus the age of 54.4Ma is considered to represent the timing of the molybdenum mineralization at the Nakatatsu mine.

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Feasibility studies on the Okuaizu geothermal field have been carried out to test the possibility of generating 65, 000kW of electricity. A production well, 87N-15T, drilled to a depth shows the highest productivity in the geothermal field. It produces geothermal fluid of high temperature (300°C at the well bottom ) and high salinity (Cl-: 15, 300-18, 500 mg/l).
A heavy metal precipitate containing high amounts of gold and silver(max: Au=116ppm, Ag=3.49%) was discovered inside the two=phase (vapor and water) pipeline in front of the separator where pressure and temperature drop from 60kgf/cm² and 275°C to 8.4kgf/cm² and 171°C.
The texture and mineralogy of the precipitates were examined as were the chemical properties of the fluid to the surface from the underground reservoir. The precipitates deposited in the pipe before the separator are dominated by sulfides, mainly tetrahedrite with subordinate amounts of sphalerite and galena. These minerals are minute in size and occur in intergrown aggregates. The gold is submicroscopic in size but seems to be included in the tetrahedrite and/or sphalerite. The silver is contained in tetrahedrite and galena. Computer calculations for the chemical properties of the reservoir fluid based on the data gathered from the separated water at the surface is as follows: Temperature=280°C, pH=4.08, logf(H ₂)=-3.11, Au=0.06ppb, HS^-=0.245 mg/l, Cl^-=13, 400 mg/l.

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