Izu peninsula

Calcium silicates such as wairakite, epidote, prehnite, laumontite, and stilbite are common in the wall rocks of some Au-Ag deposits in the Izu peninsula. Epidote occurs as a gangue mineral coexisting with sulfides and quartz in some Cu deposits, but none of the other above-mentioned Ca and Mn silicates have been reported from these deposits. Laumontite is a common mineral in propylite, which is the host rock for Au-Ag deposits. Other zeolites such as mordenite and dachiardite are not generally common, but they are the main gangue minerals associated with Au-Ag minerals in the Ohnoyama and Awagano Au-Ag deposits. 

In the Izu Peninsula, located in the middle part of Honshu, more than 20 epithermal Au-Ag vein-type deposits have been mined. Large Au-Ag mines are located in the western part of the peninsula. The Seigoshi mine is the largest one. The country... 

Generalized stratigraphic succession in the Izu Peninsula and the area surveyed (Shikazono, 1985a)... 

The Izu Peninsula is mainly composed of pyroclastic and volcanic rocks of Tertiary-Quaternary age. The general geology of the peninsula has been well studied (Tayama and Niino, 1931), and thus, it is briefly described below. 

Few data on the chemical compositions of feldspars (albite, K-feldspar) are available. Fuji (1976) indicated that K-feldspar and albite in the propylite of west Izu Peninsula, middle Honshu are of nearly end member composition. Nagayama (1992) showed that K-feldspars in the Hishikari Au-Ag vein and in the host andesitic rock have different composition Na/K ratio of K-feldspars from the vein is lower than that from the host rocks. 

Figure 1.114 demonstrates that the deposits in northeastern Hokkaido, central Honshu, Sado Island and Kyushu deposits are Non-Green tuff type and those in southwestern Hokkaido, Northeast Japan (Tohoku), the Izu Peninsula, and San-in are Green tuff-type. 

Fujii, S. (1976) Petrology of metamorphic rocks of the Yugashima group, Izu Peninsula. Unpub. Masters Thesis, U. Tokyo. 

Shikazono, N. (1985a) Mineralogical and fluid inclusion features of rock alterations in the Seigoshi gold-silver mining district, western part of Izu Peninsula, Japan. Ghent. Geol, 213-230. 

Shikazono, N. and Aoki, M. (1981) Hydrothermal alteration and ore deposits in Izu Peninsula. J. Geol Soc. Japan, Guide Book, 1-20 (in Japane.se). 

Tayama, R. and Niino, H. (1931) Report on the geology of the Izu Peninsula. Saito-Hoonkai-gakuho, 13, 1-30 (in Japanese). 

The other opinion is that the mineralization is related to bimodal volcanism. For example, in west Izu Peninsula, epithermal Au-Ag vein type deposits (e.g., Seigoshi) are associated with basic intrusive rocks and acidic volcanic rocks. 

Ritterella tokioka Kott, a tunicate of the family Polyclinidae, collected from the Izu Peninsula 100 km southwest of Tokyo, on extraction and partitioning between a number of solvent systems followed by repeated chromatography, afforded another series of bis-steroidal pyrazine alkaloids, ritterazines A-M (26-38). Structures of these alkaloids were found to be related to the cephalostatins isolated from the hemichordate Cephalo-discus gilchristii. 

Kanroji, Y., and Tanaka, A. (1980). Calcium Chloride Springs on the Southwestern Coast of the Izu Peninsula, Japan. Onsen Kogakkai-shi 14(3), 88-97. 

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