Distribution of minor elements (Ag, Co, Ni, Mn, Bi, Cr, Cd, Hg, In, Ga, Ge, Sb, As) in, some sulfide minerals from the Kuroko-type deposits of the Shakanai Mine, Akita Prefecture, has been investigated with atomic absorption spectroscopy. The specimens include 12 sphalerites, 7 galenas, 22 pyrites, 12 chalcopyrites and 1 tennantite. They were taken from various representative parts of the deposits, namely, black ores, yellow ores, siliceous ores, veins and gypsum ores, as well as from the hanging and footwall rocks. The results are summarized as follows:
(1) There is a general trend that Ag is concentrated in tennantite and galena; Cd, Mn and Ga in sphalerite; In in chalcopyrite; and Hg in tennantite and sphalerite.
(2) As to the distribution among the different parts of the deposits, concentrations of Mn, Ag and Hg are found to be relatively high in black ores, while Bi and In are predominant in yellow ores and siliceous ores.
(3) Cd and Fe in sphalerite are in the range of 0.1 - 1 wt% and Mn is in 0.008 - 0.1 wt%. Lattice constants of sphalerites were calculated by the function, a₀ = 5.4093 + 0.000456X + 0.0042 Y+ 0.00202Z, where X, Y and Z are the contents of FeS, CdS and MnS in mole percent and a₀, is in Angstroms (SKINNER, 1961). The calculated values show good agreement with those obtained by X-ray measurements, indicating that the lattice constant of sphalerite from this deposit varies mainly with the variation ;in Cd content rather than Fe and Mn contents.
(4) The colour of sphalerite from the deposits has no apparent correlation with the Fe content.

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The alteration of various degrees is recognized in the Miocene pyroclastic rocks in Nishiaizu District, Fukushima Prefecture. According to the assemblage of authigenic minerals, the Miocene pyroclastic rocks can be grouped into six zones as follows:
A) Clinoptilolite-mordenite zone,
B) Mordenite zone,
C) Analcime zone,
D) Montmorillonite zone,
E) Chlorite-sericite zone,
F) Gypsum zone.
These zones are distributed surrounding "Kuroko-type" ore deposits, alternately or successively from the gypsum zone or the chlorite-sericite zone in the central part to the clinoptilolite-mordenite zone in the marginal part as shown in 15 cross sections of Figs. 5 to 19. The writers interprete that this zonal distribution of alteration zones genetically relates to the "Kuroko-type" mineralization and later hydrothermal alterations.
Among the alteration zones, the analcime zone which may have been formed by concentration of sodium is a characteristic alteration zone around "Kuroko-type" ore deposits. In fact, typical Kuroko ore deposits are situated in the central part of the area where the analcime zone is distributed and is comparatively thick (Fig. 20). This fact may be usuful for exploration of "Kuroko-type" ore deposits.
Advantages of the analcime zone for an indicator of ore deposits are as follows:
1) Refering the previous works, it may be sure that there is a genetical, relation between the "Kuroko-type" mineralization and the formation of the analcime zone,
2) The determination of analcime by X-ray method is comparatively easier,
3) The analcime zone is distributed in favourable demensions for exploration.

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This paper describes basic stratigraphical data, geological structure, petrographical characters of sandstones, and relationship between Paleogene formations and their Upper Cretaceous basement rocks in the southern part of Shimoshima, Amakusa Coal-field, Kumamoto Prefecture. Unconformable features between the Paleogene Fukuregi Formation and the H-Formation, which includes the so-called Fukami Formation having been interpreted as of Tertiary, are recognized at some localities in the studied area. The time-gap is not clear because of scarcity of fossils to indicate definite ages. The formations below and above the unconformity, however, show considerable dissimilarities in geological structure. For instance, the Upper Cretaceous formations are controlled by the tectonic movement, to which the Asami dome structure might be attributed; while the Paleogene strata are only influenced by the movement to form the so-called Ittyoda synclinal structure. These facts indicate a considerable time-gap between two formations. Sandstones of the Cretaceous and Paleogene formations are dissimilar in the lithological characters. The formers are characterized by abundant rock fragments, particularly those of igneous rocks. The latters predominate in quartz (Fig.5).The Cretaceous sandstones contain garnet and epidote in greater quantities than the Paleogene ones. The results of the petrographical study are consistent with the geotectonic interpretation mentioned above.

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The Hokuroku district, which belongs to the "Green Tuff region" of Northeast Japan, is well known for distribution of the typical Kuroko deposits, as Kosaka, Shakanai, Hanaoka and others. The field examination and investigation of many drilling cores indicate that the district has a basin satructure of about 25 km (E-W) by 30 km (N-S). The ore deposits mainly occur along the east and west marginal parts within the basin.
During the Nishikurosawa and Onnagawa stages of the Miocene, the basin was formed in consequence with progressing volcanic activity and subsidence of surface materials at the same time. The acidic volcanisms accompanying Kuroko mineralization and other acidic to basic volcanism were most active along both the sides of the basin, where the basement rock had been sheared.
On the basis of Lehman's theory, the tectonic history was analyzed. A tension environment at the Nishikurosawa stage or later is responsible for the acidic volcanism (including Kuroko mineralization) of the Hanaoka and Kosaka mines areas. The volcanism at the late Onnagawa and Funakawa stages followed the zone of a maximum compression. Degree of subsidence in the Hokuroku basin seems largely dependent on the amount of erupted materials from the magma chamber.

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