The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists

Sepiolite is a very rare mineral in Japan and only one occurrence has been reported hitherto. The sepiolite from the Oeyama nickel mine would be speculated to attribute its formation to the reaction between serpentine rock and supergene water descending along fissures in the rock, considering from its occurrence; and it has been confirmed to be a variety of sepiolite exhibiting a very low crystallinity and giving an irregularity of the structure on the X-ray patterns as compared to that of typical one, further it would being considered also to be an incipient stage of the crystallization process from β-sepiolite to α-sepiolite described in the literature, judging from microscopical observation, electron micrographs, chemical analysis data, thermobalance curve, differential thermal analysis curve and X-ray data.

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So-colled Tertiary Granites, intruded at Miocene age as the form of stock or dyke in northeastern Japan can be characterized as follows;
1) The intrusive bodies have variable facies respectively. They change in texture from holocrystalline to hyaline. Many of them vary their chemical compositions from intermediate to acidic, and a few from basic through intermediate to acidic.
2) Alterations such as chloritization, albitization, sericitization, carbonitization, epidotization and pyritization of the body are seen remarkably even if any mineralization is not observed in the body. These alterations are observed more distinctly in the marginal part of it.
3) Gold bering chalcopyrite•galena•sphalerite deposits are seen in connection with the Tertiary Granites. There are some examples of veins which might be formed under the xenothermal condition.
In this paper, some problems concering these characteristics are presented. The author suggests that it had better regard the intrusive body as a complex derived from volcano-plutonism.

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