Sulfur content and sulfide minerals were examined on Cretaceous granitoids of the Kitakami Mountains. All but one (Akagane mine stock) belong to the magnetite series. The sulfur content increases with decreasing normative ab+or+qz, indicating that mafic magmas are much capable of dissolving sulfur than felsic magmas. The content goes up also to the following order: (i) calc-alkaline batholith and stock, (ii) alkaline stock and (iii) mineralized stock, especially of the ilmenite series. Sulfides of the magnetite-series rocks are largely pyrite and chalcopyrite, and rarely pyrrhotite. Other sulfides as arseno-pyrite, molybdenite and unidentified minerals, are present only locally. These sulfides may have been re-equilibrated during slow cooling of magmas but are considered ultimately magmatic in origin. Solubility of sulfur in the magnetite-series, calc-alkaline magmas may be as low as 40 ppm at a granodiorite composition, while that of the magnetite-series, alkaline magmas would be higher (_??_200 ppm). Ilmenite-series granodioritic melt of the Akagane mine stock seems to contain even more sulfur (_??_600 ppm). Sulfide mineral assemblage of the stock is the same as that of skarn deposits indicating that sulfur and copper of the ore deposits are largely magmatic in origin.
K-Ar ages have been determined on white micas from four Sangun pelitic schists in the Nishiki-cho and Toyoga-dake areas, Yamaguchi Prefecture. The dates from the Nishiki-cho area are 172 and 175 Ma, while those from the Toyoga-dake area are 264 and 274 Ma. They represent a wide range of time, 172 to 274 Ma, which is nearly identical with that of eight ages, 165 to 264 Ma, reported previously from the Sangun metamorphic rocks. The twelve available dates on the Sangun metamorphic rocks can be divided into two age clusters, an older age cluster around 260 Ma (middle Permian) and a younger cluster around 170 Ma (middle Jurassic). It is suggested that the two age clusters may coincide with the two stages of uplift for the Sangun metamorphic rocks. Namely, the age cluster around 260 Ma may indicate the event in which the Sangun metamorphic rocks were emplaced as nappes from the deep tectonic position of glaucophanitic metamorphism into a shallow tectonic position and the metamorphism had ceased. On the other hand, the age cluster around 170 Ma may represent an event related to the beginning of the formation of the pile nappe structure in which the Sangun metamorphic rocks tectonically overlie the Jurassic non-metamorphic equivalents of the Tamba Group.
The strata-bound sulfide deposits of the Taro mine are located in the outer belt of the Kitakami massif. On the basis of lead isotope data, it was proposed that the ore deposits of the Taro mine is regarded as the Kuroko-type deposits of the Mesozoic age (Sato and Sasaki, 1978, 1980). The Honko and the Shinkabu ore deposits at the Taro mine occur in the pelitic and psammytic sediments in the Harachiyama Formation consisting mainly of intermediate to acidic calc-alkaline lavas and pyroclastics. In this paper, a great deal is written about the features of ores of both stratiform ore deposits. The main minerals constituting the sulfide ores are pyrite, sphalerite, galena, chalcopyrite, and a small amount of pyrrhotite with quartz, calcite, sericite and chlorite as gangue minerals. Arsenopyrite occurs as accessory amounts. Tennantite and electrum are rarely observable. Barite, one of the main constituent minerals of the Cenozoic Kuroko-type deposit, is absent in the ore deposits at the Taro mine. FeS and MnS contents of sphalerites show large variations ranging from 3 to 21 and 0.2 to 12.5 mole percent, respectively. However, CdS content of sphalerites shows the limited variation ranging from 0.2 to 1.0 mole percent. FeS contents of sphalerites in the ores which has pyrite, are less than about 15 mole percent, and those in ores pyrrhotite is present, are more than about 20 mole percent. Ranging from 15 to 20 mole percent of FeS in sphalerites are common with regard to coexisting pyrite and pyrrhotite. Alabandite rarely occurs at the hanging wall side of the Honko deposit, and is associated with pyrrhotite, chalcopyrite and Mn-rich sphalerite containing about 12 mole percent of Mos. It is worthy of note that colloform texture, such as concentrically zoned, framboidal, pellet-like etc., locally exists in the ores from the marginal parts of the Honko and the Shinkabu stratiform ore deposits. In the Taro mining district, the Harachiyama Formation is intruded by granodioritic rock of the Neocomian age and by diabase sills. owever, it is probably certain that some of pyrrhotite from the Honko and the Shinkabu ore deposits are formed regardless of thermal effects of these intrusive rocks. Both ore deposits at the Taro mine are presumed to be formed under the lower fs2 and fo2 conditions as compared with the Cenozoic Kuroko depos-its, and the ore of pyrrhotite-sphalerite-chalcopyrite-alabandite assemblage is considered to be formed under the environmental condition of oxidation-reduction boundary and its vicinities.
K-Ar dating on hornblende from biotite-hornblende quartz diorite in northeastern part of the Kanto Mountains was carried out. The age of the quartz diorite is 251±8 Ma. The result, together with geological facts, supports the idea that island arc composed of granitic plutons was present between the Sanbagawa and the Ryoke metamorphic belts.