The marine paleobathymetry and paleotopography of the Kuroko deposits are reconstructed, based on foraminiferal assemblages occurring in bore holes of the Hokuroku district, Akita Prefecture, Northeast Japan.
Judging from the fossil planktonic foraminiferal assemblages, Hokuroku district was predominated by a subtropical water mass during the time of. the Kuroko deposition. Correlating the benthonic foraminiferal assemblage of the Hokuroku district with those of present-day subtropical Kuroshio area, the paleobathymetry of the Kuroko deposits is inferred to range from 500 to 2, 500 meters. Reconstructed submarine topography indicates the existence of a ditch-like depression at that time.
Arenaceous foraminiferal assemblages distributed in the Hokuroku district may have inhabited in an extraordinary acid water condition which was caused by the dissolution of volcanic gas supplied from the sea bottom.
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Many kaolin deposits (Komaki halloysite deposit, Kodachi kaolin deposit, Toyosaka halloysite deposit, etc.) occurring in granitic rocks are found in Hiroshima and Shimane Prefectures. These deposits are hydrothermal in origin, and comparatively small in size. They are distributed along a notheast-southwest line.
The mode of occurrence and mineralogy of Kodachi kaolin deposit are given as related to its genesis in this paper. It is located at Jinushidaira, Miyoshi city, Hiroshima Prefecture, Southwest Japan. This area is composed of biotite granite and rhyolite rock both inferred to be of Cretaceous age. The main constituent minerals of the deposit are kaolinite and halloysite associated with a small amount of illite, according to X-ray diffraction and electron microscopic observations (TEM and SEM). It is divided into two zones on the basis of the clay mineral assemblages; one is kaolinite zone which is composed of kaolinite with a small amount of illite, and the other is halloysite zone which is composed of halloysite and associated kaolinite. It seems that the boundary of these two zones is inherited from notheast-southwest trending fault or sharp boundary.
Many green-clay veins (ca.1mm-10cm in width) consisting of illite, kaolinite and halloysite are observed in the clay deposit. In the kaolin zone, they are composed of illite and kaolinite, while in the halloysite zone, of illite and halloysite. Some brownish clay veins (ca. 50-100 cm in width) consisting of kaolinite and goethite are found in the halloysite zone.
Many white and green-clay veins (ca. 1 mm-20 cm in width) are observed in the host granite of this deposit. These constituent minerals are kaolinite, halloysite and a small amount of illite. Kaolinite in one of the green-clay veins has the lath and platy shapes and is considered to be pseudomorph after illite.
It is considered on the basis of these observations that the clay minerals of the deposit and those of the clay veins in the host granite of the deposit are formed by the same hydrothermal activites. The general sequence of formation of clay minerals in this district may be considered as follows: illite→kaolinite or halloysite+kaolinite.

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Mineralization factor (f) is defined here as a ratio (r/t) of the amount of an element (r ton) concentrated as the mineral deposits in a definite volume (or mass) of crust to the total amount of the element (t ton) in the crust. The factors of some metallic elements were tentatively calculated for selected areas including Japanese Islands and North American continent using published data on the reserves or resources of the elements. The factors vary to some extent in different regions and for different elements, but, generally speaking, are in order of 10 ^-4 to 10 ^--5 in Japanese Islands and 10 ^-5 to 10 ^-7 in North American continent for most of the metallic elements (Fig. 1 and Tab. 3). If it is justified to assume the general mineralization factor (F) for all the metallic elements concerned in the upper continental crust to be 10 ^-4-4 to 10 ^-5 based on the existing data, the total amount of the specific metallic element (R ton) concentrated in the mineral deposits of the upper continental crust is given by the following equation: R=M×n×A×10^-6×F, where M is total mass (ton) of the continental crust, n estimated ratio of mass of upper continental crust where mining operations are assumed in future to total mass of the continental crust (here assumed to be 0.2 or 0.3, which corresponds to about 7 to 10km in depth from the surface), A crustal abundance of the element (ppm) in the continental crust, and F general mineralization factor in the upper continental crust. Table 5 and Figure 3 show the results obtained. Some considerations on the results are also given.

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The Nansatsu plateau is largely covered by Quaternary pyroclastic flow deposits. The Shimanto supergroup of Mesozoic to Paleogene age, the Nansatsu group of Neogene age and the post-Nansatsu volcanics of Quaternary age are distributed around the plateau and make a semibasin structure which is open southwards. Gold-bearing massive silicified rocks are hosted in the Nansatsu group and partly in the post-Nansatsu volcanics, and make small hills in the periphery of the plateau because of their resistance to erosion.
Ministry of Agriculture, Metal Mining Agency of Japan (MMAJ), Gold Mining Promotion Corporation (GMPC), Mitsui Kushikino Mining Co., Miyauchi Akeshi Mining Co. and Kasuga Mining Co. conducted integrated water and mineral resources explorations, using geological survey, drilling, electric surveys and gravimetric surveys in the Nansatsu plateau during a period of about 7 years starting in 1969.
The authors re-examined the data of these surveys, and estimated the shallow geological structure based on the results of drilling and electric survey in the plateau. The gravimetric data were treated with the manual dataprocessing technique, which was proposed by TERASHIMA & TSUCHIYA (1976a·b) and TERASHIMA & YOSHIZAWA (1976), after a revision to make it applicable to the geological circumstances of the area, and with the threedimentional simulation technique proposed by CORDELL & HENDERSON (1968) in order to compare the results each other.
On the basis of the local gravimetric anomalies on the plateau, many faults or shear zones are considered to be developed parallel and perpendicular to the caldera-like structure which is situated on the south coast of the plateau. Moreover, the paleo-hills of the pre-pyroclastic flow deposits and the dome structure of the low resistivity, which includes the gold-bearing massive silicified body, are in parallel and perpendicular to the caldera-like structure on the plateau. These facts may indicate that there is some mutual relation between the silicification accompanied by the gold mineralization and the tectonic movement accompanied by volcanic activities.
Through such discussions, it was proved that the manual filtering operation is very useful to explain a reasonable geological structure. Moreover, even in the case of electric surveys, the authors pointed out that the method of interpretation and data-processing is very important to clarify the detailed two-layered structure in the area which is covered by pyroclastic flow deposits.

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Applicability of oxygen isotope geothermometers to sulphate minerals from the Kuroko deposits has been discussed by utilizing oxygen isotope fractionation factors determined for the anhydrite-water and barite-water systems together with the existing isotopic data and models. The oxygen isotopic calibration for the anhydrite-water system has recently been revised. The depositional temperature of the anhydrite-gypsum ore-body at the Shakanai mine is estimated to be about 200°C or so assuming direct precipitation of anhydrite from sea water. At these temperatures about 50% of calcium sulphate originally dissolved in the Miocene sea water was precipitated to form the ore-body. The total volume of sea water required to produce a known amount of the anhydrite-gypsum ore-body was calculated. Barite in the black ore from the Shakanai mine may have been precipitated at temperatures considerably lower than 250°C which is widely accepted as the depositional temperature of the black ores based on the sulphur isotopic data. However, this discrepancy remains to be studied in the future, because the number of oxygen isotopic data of barite and ore solutions is very limited.

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