The Onta-Yamakuni gold area is located in the northwestern part of the Neogene Hohi volcanic zone, northern Kyushu. Hydrothermally altered volcanic rocks in the area host gold-bearing quartz veins and clay deposits. The Asahi mine as a well known gold mine has produced at least 0.3 tonnes of gold during 12 years from 1935 to 1953.
On the basis of alteration mineral assemblages, the gold area was divided into four zones, the chlorite zone which widely distributes in the central part, the mixed layer mineral zone which surrounds the chlorite zone, the smectite zone and unaltered zone. The smectite zone is subdivided into the inner quartz-smectite subzone and the outer cristobalite-smectite subzone. Gold-bearing quartz veins and sericitized rocks occur in the chlorite zone. Fluid inclusion studies on quartz and calcite indicate that the mineralization temperatures are 140-260°C in the Asahi gold deposit, and that the alteration temperatures are 220-270°C in the chlorite zone, and ca. 170°C in the mixed layer mineral zone.
Three unaltered volcanic rocks and four sericite separates from argillized andesites were dated with K-Ar method. The Dainichigatake Volcanic Rocks gave 4.49±0.20 Ma, consisting with the reported fission track ages (4.5-4.3 Ma). The Jogusan Andesite and the Bukunoyama Dacite gave 3.37±0.10 Ma'and 3.29±0.08 Ma, respectively, suggesting the later stage of volcanic activity in the southern part of the area. Sericite gave 3.67±0.08 Ma and 3.71±0.08 Main the Onta area and 3.77±0.09 Ma and 4.10±0.09 Ma in the Yamakuni area. The last one indicates the age of gold mineralization at the Asahi deposit. These newly obtained K-Ar ages and field observations strongly suggest that the hydrothermal alteration and gold mineralization occurred in the final stage of the volcanic activity in the Onta-Yamakuni area.

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Fluid inclusion study was performed to understand evolution of hydrothermal systems related to the very young granitic intrusives at depths in the Kakkonda and Nyuto geothermal areas, northern Honshu, Japan. The intrusives of the Kakkonda and Nyuto geothermal areas are 0.34-0.07Ma (KANISAWA et al., 1994) and 2.20-0.75 Ma (NEDO, 1992), respectively. Studied samples are igneous quartz in granitic rocks collected from each geothermal system. Fluid inclusions observed in the quartz are classified as follows; vapor-rich inclusion (Type V). liquid-rich inclusion (Type L), halite-bearing polyphase inclusion (Type P₁). X₁(Fe-chloride)-and halite-bearing polyphase inclusion (Type P₂), and X₁-, X₂(sylvite)-and halite-bearing polyphase inclusion (Type P₃).
Homogenization temperatures (Th) of the Type L inclusions from the Kakkonda geothermal system are above 330°C with salinities below 20wt.% (NaCI eq.). Most of the Type L inclusions show Th values from 330 to 350°C with salinities below 1 wt.%. Th of the Type P₁ and Type P₂ inclusions from the Kakkonda geothermal system are above 310°C with salinities between 35 and 75 wt.%. Th of the Type P₃ inclusions range from 380 to 510°C with salinities between 60 and 75 wt.% while Na/K mole ratio of the Type P₃ inclusions ranges from 1.2 to 2.3.
Th of the Type L inclusions from the Nyuto geothermal system range from 130 to 350°C with salinities below 3.5 wt.% except one inclusion of about 10 wt.%. The Type P₁ inclusion has not been observed in the Nyuto granitic rock. Th of the Type P₂ inclusions range from 560 to 620°C with salinities between 65 and 75 wt.%. Th of the Type P₃ inclusions range from 480 to 620°C with salinities between 75 and 85 wt.% while Na/K ratio of the Type P₃ inclusions ranges from 1.5 to 4.4.
The Th of the relatively low salinity Type L inclusions from each system correspond to the measured downhole temperatures, and the Type L inclusions are considered to have trapped geothermal fluids presently circulating in the each granitic intrusive. Conversely, the Type P₃ inclusions from each system are considered to have trapped hydrothermal fluids equilibrated with each granitic intrusives at high temperatures because the Na/K ratios of the Type P₃ inclusions are similar to the ratios of the fluids equilibrated with granitic rocks that have been experimentally determined by WHITNEY et al. (1985). The Type P₁ and Type P₂ inclusions have trapped fluids generated by mixing of highly saline fluids with low salinity fluids because the ranges in Th and salinity for the Type P₁ and Type P₂ inclusions are intermediate between those for the Type L inclusion and Type P₃ inclusion. The fluids circulating in the granitic intrusive of the Kakkonda geothermal system have continuously changed from highly saline fluid to low salinity fluid. However, hydrothermal activities of highly saline fluid and low salinity fluid for the Nyuto geothermal system might have occurred at different ages.

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Based on a compilation of geological and geophysical data, a new hypothesis is proposed for the formation of epithermal Au-Ag deposits in the Hokusatsu region, Kyushu, Japan. Several Plio-Pleistocene stratovolcanos in a graben with anortheasterly trend would have the following feature of gravity data:a regional low anomaly (-10mgal) corresponds to the graben being filled with low density sediments, and areal high anomalies (+30mgal) in the reagional low gravity correspond to the center of andesitic stratovolcanoes.
In the Hokusatsu region, all stratovolcanic bodies are accompanied with one or more epithermal Au-Ag ore deposits. Veins of these deposits have a northeast orientation approximately perpendicular to the regional tensional stress orientation related to the opening of the Okinawa Trough.

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Some Pb-Bi-Sb-S minerals (Sb-cosalite, Sb-heyrovskyite, Sb-lillianite, Bi-boulangerite and unknown Pb-Bi-Sb-S mineral) occur in the Dunjeon gold mine of the Taebaegsan mining district, Korea. They tend to be relatively abundant in the galena-rich ores which are composed of galena, boumonite, tetrahedrite, pyrite, chalcopyrite, sphalerite and electrum. The average composition of sixteen analyses of Sb-cosalite is Pb;44.1, Bi;30.7, Sb;5.7, Ag;1.6, Cu;0.6 and S;16.7 wt.%, and its empirical formula calculated on the basis of S=5 atoms is Pb_2.08(Bi_1.41Sb_0.47)_1.88(Ag_0.15Cu_0.15)_0.27S₅. The average of sixteen analyses of Bi-boulangerite is Pb;55.5, Bi;6.5, Sb;19.3 and S;18.2 wt.%, and its calculated chemical formula on the basis of S=11 atoms is Pb_5.18(Bi_0.60Sb_3.10)_3.7S₁₁.The average chemical formulae of Sb-lillianite, Sb-heyrovskyite and unknown Pb-Bi-Sb-S mineral on the basis of S=6, S=9 and S=5 are Pb2.94(Ag_0.14Cu_0.15)_0.3(Bi_1.54Sb_0.40)_1.94S₆, Pb_5.84(Ag_0.15Cu_0.15)_0.3(Bi_1.52Sb_0.38)_1.9S₉ and Pb_2.12(Ag_0.08Cu_0.25)_0.34(Bi_0.76Sb_0.93)_1.69Fe_0.23S₅, respectively. The composition of Sb-cosalite, unknown Pb-Bi-Sb-S mineral and Bi-boulangerite are well correlated with the chemical formulae of synthetic Sb-cosalite (phase C), phase Y₁ to Y₂ solid solution and phase W given by CHANG et al. (1980), respectively. The 2PbS-Bi₂S₃-Sb₂S₃ system has revealed the substitution between Bi and Sb, because Sb content increases with decrease of Bi content. It is suggested that the maximum atomic rato of Bi/(Bi+Sb) is 0.75 for Sb-cosalite, 0.45 for unknown Pb-Bi-Sb-S mineral and 0.16 for Bi-boulangerite.

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Tectonodynamic force plays an important role in controlling the spatial distribution of ore deposits and the mineralization process such as water release from sediments, increase in temperature and pressure, activity of elements, transportation of ore solution, and accumulation of ore-forming elements. The ore deposit produced by the tectonodynamic force is termed as a tectonodynamic ore deposit. The recognition of this new type ore deposit is useful for better understanding the mineralization process and for establishing as an ore-exploration model. Some ore deposits of this type in China are described.

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K-Ar ages were measured on five whole-rock samples of felsic volcanics and clays from the Hiraki mine. The results are: (1) 70.0±1.5 Ma for the underlying Kamogawa rhyolite; (2) 68.9±1.6 Ma and 69.1±1.6 Ma for the least-altered and altered rhyolitic non-welded tuff (= ore horizon), respectively; (3) 67.6±1.5 Ma for the unconformably overlying rhy-olitic Hiraki welded tuff; (4) 63.8±1.5 Ma for clays from the fracture zone crosscutting the whole volcanic sequence. These ages are fairly consistent with the volcanostratigraphy in the mine area, indicating that various volcanisms and mineralization took place within a time span of a few million years in the latest Cretaceous to the earliest Tertiary Periods. The unconformity recognized, therefore, means a minor time-gap, not a long cessation of volcanism, at least in the Hiraki mine area.

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