The bedded manganese and manganiferous iron deposits in this area are distinctly strata-bound. The manganese deposits are concentrated in a lower Permian formation of the North Kitakami belt and in a middle Jurassic formation of the Iwaizumi belt, while the manganiferous iron deposits are in a Paleozoic formation of the Hayachine belt. The manganese deposits occur abundantly in the alternation zone of slate and chert, but rarely in chert dominant zone, implying that the depositional environment of these deposits may have been a moderately deep sea-floor of eugeosynclinal basin. The deposits are conformable to the wall rocks rich in banded chert, and large-scale deposits are often underlain by massive chert which is thought to have been a product of hydrothermal activity. The manganiferous iron deposits, whose occurrence is limited to schalstein zone, are also conformable to the wall rocks which comprise mostly banded and massive cherts. The source of manganese and iron in the ores and the source of silica of the banded chert are thought to be in submarine basic volcanism as well as in leaching from land and submarine volcanic rocks. Bedded cherts associated with the manganese and manganiferous iron deposits may have been deposited from soluble silica in sea water and hydrothermal solution either by chemical or biochemical reactions.
Both the manganese and the manganiferous iron deposits in this area suffered thermal metamorphism related to an early Cretaceous granitic activity. Original mineral phases in unmetamorphosed manganese ores are considered to have been manganese dioxide minerals, rhodochrosite with or without hausmannite, jacobsite, bementite, penwithite etc. The metamorphosed equivalents show a systematic mineralogical change corrcsponding to the metamorphic grades of the country rocks. Four grades of metamorphism, the chlorite-, biotite-, cordieriteand potash feldspar zones, all of which are identifiable in the metamorphic mineral assemblages of interbedded pelitic and psamitic sediments, are reflected in the manganese ores by the existence of rhodochrosite ore, braunite ore, manganese silicate-rich ore and manganiferous amphibole and pyroxene-bearing silicate ore, respectively. Original mineral species of the manganiferous iron ores seem to have included ferric oxide hydrate, iron carbonate, manganese oxides, manganese carbonate, amorphous silica, some hydrosilicates etc., and they have been converted to hematite, magnetite, rhodochrosite, rhodonite etc. in the metamorphosed ores.

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The studies of the Pre-Miyakoan (Lower Cretaceous) stratigraphy and geologic development of the Northern Kitakami Massif are reviewed. In the Northern Kitakami Massif, a thick sedimentary complex which attains a hundred thousand meters, consisting of shale, chert, sandstone and greenstone intercalating with lenticular limestone are extensively distributed. They were believed to be an "eugeosynclinal" deposits. The area is divided into three "tectonic belts", namely "Northern Kitakami Belt", "Iwaizumi Belt" and "Taro Belt" by the "Kuzumaki Tectonoic Line" and "Taro Tectonic Line" trending NNW-SSE from the west (Kano, 1958; Shimazu et al., 1970; Sugimoto, 1974a). The geologic age of them was believed to be Carboniferous to Permian, Triassic to Jurassic and Jurassic to Lower Cretaceous respectively, from the fossil evidence occurred from the lenticular limestones. And the above tectonic lines were regarded to have controled the eastward shift of the sedimentary basin. During the past decade, however, it has become accepted from the paleontological evidence of conodont that the many chert beds are Permian to Triassic in age (Toyohara et al., 1980; Murai et al., 1981, 1983, 1985, 1986) and of radiolalia from only one locality of "Taro Belt" that shale is Jurassic in age (Taketani and Minoura, 1984). The most of the paleontologically dated rocks of Permian and Triassic ages are now considered to be exotic blocks or sheets included in the Jurassic to Early Cretaceous clastic sediments. The strata of the Northern Kitakami Massif are presumably emplaced in a trench, where land-derived sandstone and shale and ocean-derived chert and limestone which covers the seamount constituents can encountered and be mixed together. So the sediments of the Northern Kitakami Massif can be taken as an accretionary body. The differences are recognized between the western area and eastern area devided by Iwaizumi Tectonic Line in the occurrence of the fossils and the compositions of the sandstone. The western area, Kuzumaki-Kamaishi Belt, is characterized by including the Permian to Triassic exotic blocks and by distributing of lithic-, plagioclase rich elastics, and the eastern area, Akka-Tanohata Belt, is characterized by including only Mesozoic exotic blocks and being composed of quartz and potash feldspar rich elastics which originated from granite. In the present, the significance of this "line" is obscure, but the "line" can be traced to the northward, which passes between the Kamiiso and Esashi-Katsurako districts of the Southwestern Hokkaido.

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