Some dolomitic skarns in the Kamineichi area, Iwate Prefecture, were formed by contact metamorphism associated with emplacement of the Miyako granodiorite in Early Cretaceous age. The characteristic features of the fluid forming the dolomitic skarns were investigated on the basis of mineral assemblages of the dolomitic skarns, homogenization temperatures and salinities of fluid inclusions in calcite and quartz, and carbon and oxygen isotopic ratios of calcite and dolomite.
The Dainikadokami, Neichi, Nejo, Kebaraichi and Kadokami dolomitic skarns occur in recrystallized limestone intercalated with metamorphosed mudstone and chert. The apparent distances from the Miyako granodiorite to the dolomitic skarns are 0 km (almost contact) for the Dainikadokami and Neichi, 0.1 km for Nejo, 0.9 km for Kebaraichi and 1.3 km for Kadokami dolomitic skarns. The major mineral assemblages of the dolomitic skarns are calcite-dolomite-forsterite±spinel, and calcite-tremolite-diopside. The formation temperature of dolomitic skarns was estimated to be around 530°C from the mineral assemblage and chemical composition of calcite coexisting with dolomite. The homogenization temperatures of fluid inclusions in calcite range from 300 to 500°C with a peak around 460°C and from 100 to 325°C with a peak around 220°C. The salinities of the inclusion fluids are divided into 30 wt% equivalent NaCl and from 8.4 to 3.7 wt% equivalent NaCl. Based on the for-maion temperature of dolomitic skarns around 530°C and homogenization temperature of fluid inclusions in calcite around 460°C, the formation pressure was estimated to be from 1.0 to 0.7 kb. The fluid of 30 wt% equivalent NaCl was formed by phase separation of fluid having salinity from 8.4 to 3.7 wt% equivalent NaCl around 0.7 kb and 550°C. The trap temperature of fluid having the homogenization tempterature around 220°C is estimated to be around 280°C at 0.7 kb. The fluid was predominant in hydrothermal stage, in which ore minerals such as pyrrhotite and chalcopyrite were precipitated in the dolomitic skarns of the area.
The ranges of carbon and oxygen isotopic ratios of calcite from the dolomitic skarns in the area are 0.6 to 0.1 ‰ and 24.6 to 23.5 ‰ for the Dainikadokami, 0.2 to -1.7 ‰ and 23.8 to 20.4 ‰ for the Neichi, -1.5 and 17.8 ‰ for the Nejo, -2.3 to -2.9 ‰ and 16.5 to 13.6 ‰ for Kebaraichi and 0.1 to -1.0 ‰ and 23.3 ‰ for Kadokami dolomitic skarns. The oxygen isotopic ratios of calcite in the area were divided into higher oxygen isotopic ratios (23.3 to 24.6 ‰) and lower oxygen isotopic ratios (13.6 to 17.8 ‰). These carbon and oxygen isotopic ratios are lower than those of unaltered dolomite rocks (4.5 to 3.9 ‰ for carbon and 26.0 to 25.7 ‰ for oxygen), are higher than those of calcite from Japanese skarn deposits.

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The Hida metamorphic rocks intercalate many beds of limestone around 3 to 30% of the total thickness in each area, and this feature is distinct from other major metamorphic belts in Japan. The limestone in the complex is completely crystalline under the amphibolite to granulite facies metamorphism.
It was partly deformed by later mylonitization at the late Permian to Triassic age, and further thermally recrystallized by the intrusion of the early Mesozoic and late Cretaceous to Paleogene granitoids. This complex history is printed on the occurrences, style of folding, mineral compositions and particularly on the texture of crystalline limestone. The limestone in the eastern region is thinned and higly deformed by close to tight folds showing pinch and swelling, characterized by very fine-grained blastomylonitic to ultramylonitic texture, whereas the limestone in the western region is weakly deformed and has the largest scale in total thickness and length of beds having very coarse-grained granoblastic to gneissic and mortar textures. In contrast, the limestone in the central region is similar to the eastern region in the scale of beds and style of folding, but exhibits coarse-to medium-grained typical granoblastic texture without any mylonitic nature, and has higher temperature mineral assemblage such as wollastonite-calcite-quartz.
The limestone is partly dolomitic including dolomite, olivine, clinohumite, serpentine, phlogopite, graphite, clinopyroxene, tremolite and Mg-rich colourless amphiboles, and associated with calc-silicate rocks consisting of quartz, calcite, plagioclase, K-feldspar, wollastonite, grossular, scapolite, epidote, clinopyroxene, hornblende and prehnite. X-ray analyses of powdered samples and microscopic observations on stained specimens reveal that most parts of limestone are free from dolomite except very small thready particles in calcite. The dolomitic parts are found sporadically in the central and western regions of the complex, in which parts, the dolomite compositions are usually 1 to 10 wt.%, but rarely reaching 50 to 90 wt.%. The geological characteristics of limestone in the Hida complex are discussed in comparison with the Paleozoic reef-formed limestone of other areas in Japan.

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Mineralogical and microtextural features of Lake Superior-type banded iron-formations(BIFs)from the Hamersley group(2.5Ga), western Australia, are reported. BIBs samples are divided into five types according to their colors and mineralogy; black(maginetite, quartz, hematite, ankerite), gray(quartz, magnetite, riebeckite, stilpnomelane), yellow(quartz, magnetite, stilpnomelane), red(quartz, hematite, magnetite) and white(quartz) ones.
In thin sections, striking elliptical textures(30-40μm in diameter)with hematite core and quartz rim are exclusively recognized in red BIFs. Scanning electron microscopic observation of the red BIFs reveals that the hematite core is composed of aggregates of filamentous and tube-like materials, 1-7μm in length. These microtextures are very similar to those preserved in modern hydrothermal sediments and soils formed by biomineralization. Mineralogical and microtextural evidence suggests that the biomineralization is responsible for the elliptical textures and that the formation of the Hamersley BIFs is likely to be related to the biological activity of Precambrian era.

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Exploration of mineral resources should be conducted taking their geneses into consideration. Although coal is historically one of the most mined and utilized mineral resources, it has often been explored without regard to its genesis, probably due to the abundant occurrence in the thin surface layer of the Earth's crust. Not only modern, improved and systematic coal exploration is required for a large field within a limited period, but also it is necessary to investigate the depositional environments which controlled the deposition of coal beds, by analyzing all available geologic data. Recent studies on the genesis of coal beds and coal-bearing formations have been concerned mainly with the following four themes.
(1) Studies on modern peat deposits in tropical or temperate zones.
(2) Studies on modern delta and fluvial deposits.
(3) Basin analysis by means of depositional modeling.
(4) Sedimentary structures in coal beds reflecting original materials of coal.
It is concluded that peat deposits of geologic age were formed similar to modern peat deposits, contradicting the for-est-swamp concept. In the past, genesis of coal-bearing formations was explained by the cyclothem concept. The cyclic nature of both marine and non-marine deposits was observed in the Pennsylvanian coal-bearing formations that were deposited on a platform and was termed cyclothem. The origin of the cyclothem was interpreted to be predominantly a result of eustatic movement caused by change of sea water level, regional tectonics and climatic change. However, subsequent studies have revealed evidence against this interpretation so that the cyclicity of the cyclothem is not considered to have a stratigraphic significance because of poor correlation except for a few limestone beds. The development of most coal basins has been satisfactorily explained by delta and fluvial models, in particular the formation of the Appalachian Basin. Coal basins unrelated to deltaic depositional systems are some intermontane lacustrine coal basins in graben or orogenic belts.

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