The so-called "Akashiro" silica stone in Japan is a sort of silica rock which is composed of reddish chert fragments and white cementing vein quartz. It has been mined for the domestic use in Japan as a refractive raw material of high quality, for steel industry. It forms thick lenticular and/or massive deposits of various dimensions mostly in the areas of Chichibu geosynclinal terrain of younger Palaeozoic and older Mesozoic eras. The deposits are mostly overlying submarine basalt lave flows and underlie thick bedded cherts of more or less limited horizons in the whole sequence of the formations. The geological occurrences as well as petrographical features of the deposits indicate that they are the products of submarine hydrothermal activities which started subsequent to the outflow of the basalt lavas on the ocean floor, and grew in parallel to the formation of the bedded chert.
Under the most probable assumption, consequently, that the finest clayey fractions of the sediments including both bedded chert and clayslate were accumulated at the same rate throughout the concerned period corresponding to respective known thickness of the sediments in the terrain, the rate of thickning of the bedded chert can be calculated. It gives a time interval of the rhythmus at about n×10² years for the deposition of the single unit bed. Calculating from the thickness of the silica stone deposit and the average thickness-about 4.8 cm-of the single unit bed of the bedded chert, the growing time of the deposits can be estimated at n×10³ - n×10⁴ years, and probably less than n×10⁵ years.

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Emery ore can be classified into two types; corundum-spinel emery and spinel-free corundum emery. In this study paragenetic relationships of Fe-Ti oxides and Fe-Al oxides in emery ores from the Shin-Kiura mine, Matsubase, Peekskill and Naxos are described and are explained in terms of oxidation-reduction conditions during the formation of the ore.
In corundum-spinel emery the most abundant Fe-Ti oxide mineral is ilmenite while smaller amount of magnetite is some-times also present. In spinel-free corundum emery, on the other hand, titanohematite is invariably present either as hemo-ilmenite or ilmeno-hematite. Martitized magnetite is also present in spinel-free ores from the Shin-Kiura mine and Naxos.
Such paragenetic relationships indicate that spinel-free emery was formed under more oxidizing conditions compared with spinel bearing emery.

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The Kurosawa mine is located in the western part of Fukushima Prefecture, and is well known as one of the "Kuroko" type deposits in this area.
In this mine, there are four ore deposits named as Sanjin, Shirouma, Daiei, and Tadamigawa, all of which occur within the Upper Oshio Formation (correlated to Onnagawa stage of Miocene age) and are closely associated with submarine rhyolitic volcanism. Two major stages of mineralization are responsible for the ore deposits. The earlier mineralization brought forth the former two ore deposits, which lie on the slope of the lava dome or rhyolite-1. The later mineralization is responsible for the latter two ore deposits, which are relatively rich in gypsum ore and lie on the rhyolite-3 lava dome.
The present study provides with the following additional knowledge on the geology of Sanjin deposits;
1. The flow structure of the rhyolite lava dome (rhyolite-1) shows a radial configuration spatially.
2. The ore-bodies of the Sanjin deposit lying on the volcanic breccia beds are present on the slope of the lava dome and also in the troughs located on the foot of the dome.
3. Breccia like ores were formed probably by slumping processes during and/or immediately after the ore deposition.
4. Two distinct alteration facies can be recognized in the footwall volcanic breccia, i.e., argillization zone in the vicinity of lava dome and silicification zone surrounding the above. The author suggests that the silicification is essentially due to the reprecipitation of silica, which might have been leached out from the argillization zone.

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Mangetite derived from post-ore dacitic tuff in the Kamanai copper deposit area, Miyagi Prefecture, Japan, carries high values of several metallic elements. In this paper the authors describe that the high metallic values influence the interpretation of analytical results stream sediment samples in geochemical prospecting. They recommend that magnetite should be separated from the samples in the sample preparation stage.

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