In the Odate district, typical argillaceous and zeolitic alteration zones develop in the Miocene marine acidic tuffs surrounding Kuroko deposits (Pb-Zn-Cu sulphide ore) which were formed on the sea bottom of middle Miocene age by submarine exhalative activities. The ore deposits are enclosed by the sericite-chlorite zone which changes upward and laterally to the montmorillonite zone. These alteration zones were formed beneath the sea bottom by reaction of acidic tuffs and tuffaceous sediments with hydrothermal solution as the tuffs deposited. The zeolitic alteration zones extend distant from the ore deposits, and they are subdivided into the clinoptilolite-mordenite zone and the analcime-calcite zone. The letter was formed by reaction of acidic tuffs with interstitial solution which was enriched in Na⁺ and Ca⁺ migrating from the argillaceous alteration zones.
Native sulphur was discovered in the sericitized pumice tuff of the marine Shakanai Formation about 50 meters below the No.7 ore body of the Shakanai Mine.

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Peculiar stone characterized by "interlaced structure", tenacious feeling and beautiful grass green color, similar to nephrite jade was found in 1966 in Chisaka area, Hidaka Province, Hokkaido Japan. This stone has been called "Hidaka jade". The stone consists mainly of chrome-diopside, associated with small amount of uvarovite and pectolite. The stone is found as network veins cutting through the boundary between serpentinite and rodingite, both of which intruded into the Jurassic formations in the so-called Kamuikotan metamorphic belt. Alkali diabase composed of titan-augite and plagioclase with an ophitic texture is also found in the neighbouring area.
In some part of rodingite, fine veins consisting of grossularite and kämmererite are found. It is observed sometimes that kämmererite is replaced by chrome-diopside, retaining the original fibrous structure. For these observations the author led the following conclusions on the genesis of this "Hidaka jade".
In the sheared zone along the boundary between the serpentinite and rodingite, hydrothermal solution derived from rodingite or alkali diabase reacted with the chromite of the serpentinite, resulting the formation of kämmererite-grossularite vein and also uvarovite. Soda-rich deuteric solution derived from the alkali diabase produced pectolite. Later various metamorphic minerals, including chrome-diopside, have been formed by the low-grade metamorphism of the Kamuikotan belt. Chrome-diopside after kämmererite retained the original fabric of "interlaced structure", then became a jadelike precious stone. Therefore the author proposes to call this precious stone "chrome-diopside jade" or "Hidaka jade" after the locality name as a new variety of jade.

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Possible behaviours of the ascending ore-forming solution in seawater are discussed on the basis of two assumptions, namely, (1) chemistries of both the ascending solution and seawater can be approximated by simple aqueous NaCl solutions, and (2) factors except for the heat capacity are negligible in the calculation of the temperatures of the mixed brines between the ascending solution and seawater. Density of any mixed brines is then calculable if the salinity and the temperature of the ascending solution are given. From a series of calculations, the following conclusions are obtained.
(1) Four basic types are recognized in patterns of the density variation caused by the successive degree of mixing (Fig.3).
(2) Factors responsible for this distinction is the temperature and salinity of the ascending solution discharged into seawater (Fig.4).
(3) Depositional features and textures of the mineral deposits formed in submarine environments from these mixed brines should be largely different according to the type of brine (Table 2).
(4) Application of the hypothesis to the "Kuroko" deposits leads to a conclusion that a type IIb brine is responsible for the bed-type ore of this group of deposits.
Acknowledgement; I wish to thank Dr. Akira SASAKI for his helpful suggestions and constructive criticism during the preparation of this paper.

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[in Japanese]

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Polymetallic vein-type deposits of tin, tungsten, copper, zinc, lead, silver and gold are found at Akenobe (SAIGUSA, 1958; ABE, 1963; MURAOKA and IKEDA, 1968) and Ikuno (MARUYAMA, 1957; TANAKA et al., 1971). These are among the best-known of Japanese deposits and have been cited as type examples of a xenothermal deposit (e. g., PARK, Jr. and MACDIARMID, 1964). The ore deposits at both mines are quite similar in the assemblage of vein-forming minerals but differ in their host rocks. The host rocks at the Akenobe mine are Permo-Car-boniferous sedimentary rocks and the early Triassic dioritic rocks of the Yakuno mafic complex; while those of the Ikuno deposits are the Cretaceous rhyolitic pyroclastic rocks of the Ikuno group. No granitic rocks younger in age than the host rocks have been found very close to these deposits (Fig.1). However, a number of dikes, basaltic to rhyolitic in composition, have intruded before (especially at the Ikuno mine) and after (especially at the Akenobe mine) the mineralization.
There has been no definite evidence reported about the geologic age of the mineralization in and around these deposits. But most Japanese geologists have followed T. KATO (1927) in arguing for a late Tertiary metallogenic epoch (NISHIWAKI and WATANABE, 1956; SEKINE, 1956; TSUBOYA et al. 1956; SEKINE et al., 1960; TATSUMI et al., 1970; NAKAMURA, 1970). During the last five years, this conclusion has been questioned by some geologists studying the regional geology and ore deposits of the province, who have suggested rather a much older stage of late Cretaceous to Paleogene (e. g., IMAI, 1966; IMAI et al., 1970). This dispute came to the annual meeting of the Society of Mining Geologists of Japan in February 1967 when IMAI et al. (1967) presented a paper about the metallogenic province of the western Kinki district. In Imai's opinion the ore solution derived from a cryptobatholith of the late Cretaceous to Paleogene granitic rocks, similar rocks of which are widely distributed in the Inner Zone of Southwest Japan.
Such was the general climate of opinion about this subject when we began to collect specimens for isotopic dating. Direct dating of these deposits is difficult because of the lack of suitable minerals, either among the vein-forming material or alteration products. We finally decided therefore to determine the age of the post-ore dike by the potassium-argon method, which thus yields the minimum age of the mineralization.

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