Since 1960, the pyrophyllite-kaolinite (Roseki) deposits of the Chugoku region, the Inner Zone of Southwest Japan, have been investigated by Dr. Kinosaki, former professor of Hiroshima University, and his co-workers. Many fundamental data on the geology, hydrothermal alteration, and mineralogy for the development and utilization of the Roseki deposits and their products have been accumulated. That is, almost all of the Roseki deposits were formed in roughly concordant with the bedding planes of the tuff intercalated with lucustrine sediments and acidic volcanics during the Upper Cretaceous Period. The extensive reactions between host rocks and sulfuric acid solutions gave rise to a zonal arrangement of the hydrothermal minerals. The main constituent minerals, excluding pyrophyllite and kaolinite, are different in each Roseki district, such as those of Mitsuishi, Shokozan, Abu, and so on. The variations of the alteration zonings and main mineral assemblages may reflect the difference in the host rocks and the physico-chemical conditions of formation of the Roseki deposits. Such fundamental data as 1) stratigraphic control, 2) vertical zoning and 3) effect of host rock composition, were successfully applied to the exploration in the past years. A few case studies are described in this paper.

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The formation process of the Toyoha deposits is discussed from considerations on geological environment, mineral association and on the result of fluid inclusion studies. It is well known that mineralization at the Toyoha deposits is divided into two stages, the earlier and the later ones. More than 15 veins are arranged in major three directions, E-W, NW-SE and N-S. Most of the veins of E-W system are earlier ones, while those of NW-SE and N-S systems were formed by the later mineralization. Pyrite, sphalerite and galena are common and abundant minerals throughout two stages. In the earlier stage, arsenopyrite is found at eastern lower part (Harima), whereas hematite increases towards western upper side (Chikugo, Tajima). In the later one, pyrrhotite and graphite associated with tin and tungsten minerals occur at eastern and southeastern areas (Sorachi, Izumo), while carbonates and Sb-minerals are found at western and northwestern areas (Soya, Oshima).
Temperature and salinity of fluid inclusions have a decreasing tendency from Izumo to Soya, and from Harima to Tajima. From these evidences together with the existence of heat source at southeastern deeper zone, the model for the formation of the Toyoha deposits is proposed. By this model, the consistent explanation for the occurrence of overall minerals in the mine has become possible. The model also leads to some important suggestions for exploration.

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By means of fluid inclusions in minerals, this study examines common features that characterize the ore fluids responsible for the Neogene mineralization in the Green Tuff region of Japan. The main conclusions are summarized as follows:
1) All the inclusions investigated belong to simple two-phase (liquid>gas) type without having daughter minerals such as halite or CO₂-rich liquid at room temperature.
2) When heated, they always showed the expansion of liquid phase and the final disappearance of vapor phase.
3) The density of ore fluids was above the critical density 0.8 to 0.9 g⋅cm^-3, and mostly was not in boiling condition. Some of the inclusions, especially in some Kuroko deposits, however, might have been trapped in or very close to boiling condition.
4) Most mineralization probably took place in a temperature range from 200°to 250°C.
5) According to the published freezing data, the salinity of the inclusion fluids (i.e., ore fluids) is as low as 0 to 10 wt.% NaCl equivalent (mostly less than several wt.%), which may suggest the participation of circulating meteoric waters in the Neogene ore formation.
6) From the reported data on fluid inclusions, almost all hydrothermal ore deposits can be generally classified into three groups; (i) a group characteriezd by high temperature and high salinity ore fluids (e.g., porphyry copper deposits), (ii) a group characterized by low temperature and high salinity ore fluids (e.g. Mississippi Valley-type deposits), and (iii) a group characterized by low to intermediate temperature and low to intermediate salinity ore fluids (e.g., Neogene ore deposits in Japan). Moreover, it is worthwhile to mention that many other hydrothermal ore deposits are located within a region between group (i) and group (ii), whether they are closely associated with or not with granitic intrusives (e.g., Taishu Pb-Zn veins; Providencia Pb-Zn-Ag ore deposits, Mexico).

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Carbonaceous matters separated from the Cretaceous-Paleogene shales in the central part of AmakusaShimoshima, Kumamoto Prefecture, were examined by X-ray diffraction and vitrinite reflectance.
Reflectance values progressively change from 2.2% of the Paleogene sample to 3.5% of the Cretaceous one harmonizing with the result of X-ray experiment. A continuous transition of experimental values from the Paleogene to the Cretaceous may not indicate a great amount of accumulation of sediments above the uppermost horizon of the Cretaceous sequence observed today.
High reflectivity of the present samples lead us to the conclusion that the sediments in this area were kept under the high temperature condition since the Tertiary age, although the cause which brought about such condition will have to be clarified hereafter.
X-ray diffraction and vitrinite reflectance will successfully help the studies of diagenetic and low-grade metamorphic alteration of sediments when they will be used together in future work.

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