Trace elements in sulfide minerals from the Tsuchikura mine were determined spectroscopically. Ore deposit of this mine is one of the cupriferous pyrite deposits occurring in the Paleozoic formations and consists of many ore bodies of various sizes. Samples for analysis were systematically collected from several representative ore bodies. It is found that the frequency distribution of the Co contents in sulfide minerals has two peaks at a range of 1000-2000 ppm and about 300 ppm, but the content of Co in a single ore body is nearly constant The Ni content of sulfide minerals ranges from 15 to 250 ppm with an average of 77 ppm and shows less-marked distribution as compared with Co Contents of the other trace elements in the sulfide ores and their correlation coefficient are shown in Tables 1 and 3 Some elements (As, Mo, Tl, Ag and otheis) detected in sulfide minerals from the Kuroko-type deposits were detected in the sulfide minerals from this mine as well. On the basis of these data and the geological evidences a possible syngenetic submarine exhalative or submarine hydrothermal origin of the Tsuchikura deposit is suggested

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Glassy two-pyroxene andesite, which distributed in the vicinity of Bonten-yama, was subjected to intense alteration, presumably originated from solfataric activities.
The altered rocks consist mainly of silicified and pyrophyllitized parts, which occur in irregular shapes, bounded with each other.
The silicified part is composed dominantly of microcrystalline quartz grains, though it looks like porous breccia. The pyrophyllitized part, which assumes white clay appearance, are mostly composed of pyrophyllite, diaspore and quartz, associated with small amounts of rutile, alunite and iron minerals (hematite and goethite).
Porphyritic texture of original andesite are not preserved in either of the altered part.
Seeing from the chemical compositions of the original. and altered rocks, it seems that the type of alteration in Bonten-yama is characterized by acid leaching process at high temperature. From the geological features, it is likely that the deposits were formed near the surface during the alteration.

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On the basis of field observations with K-Ar dating on biotite, this paper summarizes discussions of the igneous activities and source granites for three major molybdenum deposits of the Daito molybdenum area. The dating on a few granite masses showed a younger age, 36 to 49 million years, though some of them are batholith-forming granites which had been correlated with those dated as around between 50 and 80 million years in the other parts of the Sanin and Sanyo Districts in the previous studies. Since molybdenum deposits show a distinct local distribution from south (Median Line side) to north, i. e., barren in the Ryoke foliated granites associated with the Median Line, a small scale concentration with tungsten minerals in the Sanyo District, and strong molybdenum concentration in the Sanin District, the biotite ages are plotted across the Median Line (Fig.2). The molybdenum province is located in the youngests among the granites of late Cretaceous to early Tertiary (Chugoku Batholith). Although the Miocene granite among the granites has been reported by some geologists in the Daito area, according to the writer's field work and dating results, the granite is the latest facies (Paleogene) of the Chugoku Batholith.
It has been a puzzling question which granitic masses had brought the ore-fluid that made the major three molybdenum deposits, Daito, Seikyu, and Higashiyama mines. Three possibilities may be considered. They are, 1) the post-intrusive activity of the porphyritic granite (Gp), 2) ascending ore-fluid through steeply dipping faults from a hidden cupola, and 3) molybdenum ore-fluid from aplitic rocks within the present host rocks. Statistically speaking, 10 of very small deposits except Bushoji (though the total production of only about 38 tons molybdenum concentrates) among 111 molybdenum deposits in Japan, are located in intruded rocks near granite masses. This means that major number of the deposits and major quantity of the molybdenum are embedded in granites. Similar geological relations can be observed in such world major deposits as Climax, Questa, Emdako, and porphyry copper deposits. Furthermore, molybdenite occurs in ranging from aplite and pegmatite to hydrothermal deposits. It appears that molybdenum is concentrated (possibly in the quadrivalent state) in a residual magma (probably a hydrothermal granitic magma), and vesiculated and seperated from the melt in the situation where the magma is intruded, and then precipitated. If the molybdenum ore-fluid would have been derived from a much deeper horizon through the chilled crust of the intrusive body (ore bringer), we should have known molybdenum deposits filling a fault or the like in, for example, sedimentary rocks afar from granite masses. Considering these aspects the writer prefers tentatively the third possibility as the genesis of the molybdenum deposits in the Daito area. Finally a history of the igneous activities of this area is schematically presented in Figure 6.

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