The Cretaceous Takatori tin-tungsten deposit, Ibaraki Prefecture, Japan, is characterized by wolframite-bearing quartz veins. While tin-tungsten type deposits are usually considered to be produced by hydrothermal fluids from granitic magma, no granitic rocks have previously been described around the mine. Aplite veins are found in a diamond-drill hole located 350m west of No. 7 vein of the Takatori deposit. The drill hole is situated within the area of the mineralization. The aplite, composed of quartz (30-40%), K-feldspar (25-35%), plagioclase (25-40%) and muscovite (2-4%), characteristically contains small amounts of fluorite and topaz. The aplite samples are peraluminous and have high SiO₂ contents (76.4 to 76.9%), and high Ga contents. Judging from mode of occurrence and petrological characteristics, the aplite is intimately related to the formation of the tin-tungsten deposit. The presence of this aplite implies that the granitoid body that produced the aplite could be present at depth.
While the Takatori deposit was formed at about 71 Ma, ages of the Younger granitoids of the Yamizo mountains are slightly younger, ranging from 66 to 69 Ma. The mineralization also predates the intrusion of granitoids in the Tsukuba mountains, that have ages between 58 and 66 Ma. Therefore, the Takatori deposit was formed by granitic plutonism that is slightly older than these granitoids intrusions.

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From the mode of occurrence, texture, and mineral assemblage, granitic rocks in the Kashiwa-jima-Okinoshima district are classified into four groups; namely, the Tanijiri-type granodiorite (abbreviated to TGd), the Tanijiri-type granodiorite porphyry (TGdp), the Moshima-type medium-grained granite (MmGr), and the Moshima-type fine-grained granite (MfGr). The similarity of major and trace element chemistry of the TGd and TGdp, and of the MmGr and MfGr suggests that the petrogenetic processes operating were similar, respectively.
The Rb-Sr isotopic analyses of nine whole-rock samples of the Moshima-type granitic rocks (MmGr and MfGr) yield an age Rb-Sr of 16±2 Ma with an initial ₈₇Sr/₈₆Sr ratio of 0.70740± 0.00018. From the data of Nd and Sr isotopic ratios (Fig. 9) and of initial ₈₇Sr/₈₆Sr ratios and reciprocals of the strontium concentration (Fig. 10), it is suggested that the Tanijiri-type granodioritic rocks have been formed by mixing of an original S-type magma and sedimentary rocks of the Shimanto belt, while the Moshima-type granitic rocks have been formed by fractional crystallization of a S-type magma, which has been more felsic than the original S-type magma.
From the chemical composition of garnet in the TGdp, it is suggested that the original S-type magma of the Tanijiri-type granodioritic rocks may have been generated by the partial melting of metamorphic rocks of pelitic and psammitic origin at a depth of about 20km.
The TGdp shows a distinct porphyritic texture compared with the TGd. Minerals, such as plagioclase, orthopyroxene, cordierite, and biotite in the TGd have slightly wider range of solid solution compared with the minerals in the TGdp. Therefore, it is suggested that the petrogra-phical difference between the TGd and TGdp may have been caused by a difference in the ascent and cooling rate of their magmas.

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New K-Ar ages of hornblende in volcanic rocks from the type localities of the Shimonoseki Subgroup, upper half of the Kanmon Group are presented. The obtained ages are 105.2±3.3 Ma for andesite and 106.7±3.3 Ma for dacite. These data indicate igneous activity during Albian, late Early Cretaceous and support the age estimation by Shibata et al. (1978) based on stratigraphic and paleomagnetic evidences.

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Sakashita and Suzuran are two largest monogenetic volcanoes belonging to the Ueno basaltic rocks of Pliocene to Pleistocene age in Gifu Prefecture, central Japan. Bulk and mineral composi-tions of lavas from these two volcanoes are determined. They show petrographically and chemically remarkable heterogeneities. They are composed of (augite-) olivine basalt to basaltic andesite with 50.3-55.2 and 48.4-53.9 wt% SiO₂, respectively. Their compositions construct nearly straight trend lines in variation diagrams.
Three Fe-Mg zoning types of olivine are recognized. Type A is characterized by a nearly homogeneous broad core (Fo_82-88) and a highly-zoned narrow rim. Type C is unzoned from core to rim (Fo_64-77). Type B is normally zoned, an intermediate type between A and C. Core compositions of olivine phenocrysts with type A zoning are interpreted to be not affected by crystal-melt diffusion. Those with type C zoning result from obliteration of all zoning by diffusion. Chemical compositions of phenocrystic minerals indicate that olivine began to crystal-lize first in a stable magmatic environment, while existing phenocrysts of augite and plagioclase nucleated and grew later at lower temperatures than olivine.
Mixing calculations using the major-element compositions reveal that the chemical heter-ogeneities are caused by fractional crystallization of olivine, augite, plagioclase and Ti-magnetite, with a significant amount of accompanying assimilation of low-potassium acidic rocks. Based on the trace-element chemistry, however, the assimilant is requested to have peculiar chemical compositions enriched in Th, Sr, Ba, Zr, Nb etc., but highly depleted in K and Rb compared with normal acidic rocks distributed in the vicinity of the Ueno basaltic rocks.

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Andesites from the Yubari Coal field and the Umaoi Hill, east of the Ishikari Depression, Hokkaido, were dated by K-Ar method and their major and trace elements and isotope chemistries were determined. The rock spiecemens were collected from the andesitic dyke intruding into the late Eocene Poronai Formation in the Yubari Coal Field, and from the tuff breccia and lava of the Umaoiyama Agglomerate Unit in the Umaoi Hill.
The Umaoiyama Agglomerate Unit have been considered to be middle Miocene in age. All the obtained ages are, however, within the range from 19 to 20 Ma. Thus, the Unaoiyama Agglomerate Unit can be correlated with the lower Miocene strata in the Yubari Coal Field, namely the Takinoue Formation. It can also be correlated with the subsurface andesitic layer at the depth of 2, 465-2, 526m in the westward Ishikari Depression. On such stratigraphical grounds, it is suggested that the andesites from the Yubari Coal field and the Umaoi Hill may represent the eastern end of the volcanics at 19-20 Ma.
The andesites from the studied areas show little difference in major and trace elements, and isotope chemistry from those of the back-arc side of the NE Japan arc at around 20 Ma. The andesites have higher LILE and lower HFSE contents compared with the contemporaneous WPB-type basaltic rock. It suggests that they are not the differentiation products of the WPB-type basalt magma. They might be originated from the metasomatized mantle by the subduction component. Alternatively, crustal component might have participated in the generation of the andesitic magma.

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