The fluorite from veins in the Takatori tungsten deposit, central Japan, has a distinct ⁸⁷Sr/⁸⁶Srr composition ranging from 0.7260 to 0.7270. This ratio is significantly higher than the initial ⁸⁷Sr/⁸⁶Srr ratio of the granitoids (0.7095-0.7136) in the Tsukuba and Yamizo areas probably related to the ore formation but rather approaching that of the wall sandstone (0.7250). Sr content in the wall sandstone composed mainly of quartz, feldspars (alkali feldspar+plagioclase) and sericite, shows a strong positive correlation with Na content, indicating that the Sr is mostly included in feldspars. The Sr content in the wall psammitic rocks decreases successively toward the vein from 200 ppm to several tens ppm with the increasing degree of sericitization of feldspars. Therefore, it is presumed that the Sr in the mineralizing fluid is essentially derived from feldspars in the nearby wall rocks through the sericitization.

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Microfossil data around Kuroko deposits of the Shakanai mine are re-examined, based on the recent development of fossil datum levels. It is indicated through the examination on the list of planktonic spieces among foraminiferan fossils described by OTAGAKI (1966) that the lower and middle horizons of M₂ mudstone overlying Kuroko deposits are correlated to BLOW'S (1969) N9. Nannofossils described in m³ mudstone by SASAKI and HIRAYAMA (1983) can be correlated to CN3 and CN4, not in accordance with their conclusion. The recent works on fossil datum levels assigned the boundary between CN3 and CN4, to 16.2 Ma in age and that between N8 and N9 to 15.2 Ma, respectively. Furthermore, the occurrence of planktonic foraminifera correlated to N7 has not been described from the relevant strata in the inner side of northeastern Japan arc.
It is concluded that m³ and M₂ mudstone beds deposited during periods between 16.5 and 15.5 Ma and between 15.2 and 14.7 Ma, respectively. Therefore, it is indicated that the Kuroko deposits in the Shakanai mine which occur beneath the M₂ mudstone bed, were formed about 15.2 Ma ago. The age is correlated to the middle Nishikurosawa in the Cenozoic standard stratigraphy of the Northeast Japan.

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Electrum-galena-sphalerite mineralization of the Jeoneui Au-Ag mine was deposited in three stages of quartz and calcite veins at temperatures between 350°and 180°C from moderate salinity fluids (4 to 14 wt%NaCI eq). Evidence of boiling indicates pressures of <150 bars, corresponding to depths of 700 and 1, 800m assuming lithostatic and hydrostatic loads. Au-Ag deposition was likely a result of boiling, coupled with declining temperatures. Sulfur isotope compositions of sulfides indicate an igneous source with a δ34S value near 4‰. Measured and calculated hydrogen and oxygen isotope values of ore-forming fluids suggest significant meteoric water involvement. Comparison of the Jeoneui Au-Ag deposits to similar shallow Cretaceous Au-Ag deposits and a deeper Jurassic Au system reveals an inverse relationship between depth and water-to-rock ratios in Korean Au-Ag vein deposits. This indicates significant differences in the postmagmatic evolutions of these granite-related gold-bear-ing hydrothermal systems and may be indicative of the manner in which Au and Ag are scavenged from cooling plutons.

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The Minamishiraoi deposits, one of the kuroko-type barite deposits located in southwestern Hokkaido, oc-cur in volcanic and pyroclastic rocks of Tertiary age, and are composed of barite ore body, silicified zone and argillized zone characterized by kaolin clay. This paper describes the occurrence of barite ores and the compositional variation in tetrahedrite-tennantite series mineral in them.
The barite ores are classified into three types: (1) grayish, sulfide-poor barite ore, which consists of major part of the barite ore body, (2) black, Cu·Pb·Zn·Fe sulfide-rich barite ore, which occurs as massive lens or cobble-size masses in the lower and/or marginal part of the barite ore body, (3) stockwork barite ore, which occurs in the silicified and argillized zones around the major barite ore body.
In the black barite and the stockwork barite ores, tetrahedrite-tennantite occurs widely as a common constituent mineral under microscope, with sphalerite, pyrite, galena, and chalcopyrite. On the other hand, the mineral occurs mainly within veinlets or cracks of barite in the grayish barite ore. Such texture suggests that the formation of the mineral could be later than the mineralization of sulfide minerals mentioned above.
The electron microprobe analysis of tetrahedrite-tennantite indicates that the chemical composition of the mineral varies extensively owning to the site substitutions between Cu-Ag, Fe-Zn-Hg, and As-Sb. It is noteworthy that the variations in chemical composition are closely related to the barite ore types. For example, the mineral from the black barite ore has wide substitutional range in (Fe↔Zn) and (As↔Sb) and nearly inverse relation between Zn and As contents is observed. These compositional variations are common even within a single grain of the mineral from the black barite ore.
The exchange of Fe and Zn between ore-forming solution and tetrahedrite-tennantite in the black barite ore is a function of physico-chemical conditions (e. g. oxygen fugacity and/or temperature). And it maybe infered that the com-positional variations of the mineral in the black barite ore might be caused by the variation of physico-chemical condi-tions owning to the change of sedimentary enviroment, the hydrothermal action related to kaolin alteration and/or the change of ore solution chemistry during barite mineralization.

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A system of fractures of EW direction which were filled with gold-bearing quartz veins occur in the Aikawa and Nyukawa Formations distributed in the Sado mine area.
The purpose of this study is to analyze the fracture system using three dimensional elastic-plastic finite element method. This computer simulation analysis was done by Virtual Basement Displacement method (VBD method) developed by one of us (K.K.).
The results of this study are as follows;
(1) Half-dome-shape uplifting of the basement at the central part of the arbitarily set-up tectonic system can produce observed vein pattern. State of dislocation of the veneer rocks is in harmony with that of the basement, but there is a tendency of decreasing dislocation toward upper level.
(2) The concentration of strain within the lower layer occurs near the central part of the mine. Shapes of isopleth of strain are elliptic and elongated to EW direction.
(3) Typical fracture systems in the central part of the mine area is a pair of conjugate faults of EW direction which are low-angle normal fault and high-angle reverse fault. The fracture systems are more distinct in the lower layer.
The concentration of strain and fracture systems shown by the simulation analysis fit well with the distribution and vertical variation of the observed fractures and vein systems of the mine area. Therefore this method is thought to be useful for exploration.

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Epithermal ore deposits hosted by volcanic rocks and formed by volcanic-related hydrothermal systems are becoming increasingly important gold producers in Circum-Pacific countries, with many recent discoveries. One such type of epithermal deposit, termed low sulfidation, is characterized by reduced sulfur. This deposit formed in an en-vironment analogous to many active geothermal systems; it is now recognized that in the low sulfidation system, gold precipitates from boiling fluids focussed into zones of high permeability. Exploring for this type of deposit can be greatly aided by detailed mapping of alteration. The other group of gold deposits reviewed here is characterized by relatively ox-idized sulfur, termed high sulfidation. They remain somewhat enigmatic because they are poorly studied exceptions be-ing Summitville, Colorado and El Indio, Chile. However, indications are that their formation is closely related to an acid magmatic fluid, with mineralization therefore more intimately associated with volcanism such as that at White Island, New Zealand than is the case for the low sulfidation type. Further exploration for this style of mineralization will be greatly assisted through integrated geologic and geochemical (particularly paragenetic) studies of this style of deposit and of active volcanic systems.

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