Accessory and Ore Mineralization of Schists from the Basement of the Yamal Peninsula (Zapadno-Yarotinsky Area, Western Siberia)
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The results of studying the mineralogy of metamorphic schists from the Pre-Jurassic base of the Arctic part of the West Siberian plate are presented. The accessory and ore mineralization of schists from the Zapadno-Yarotinsky license area located in the southern part of the Yamal Peninsula is studied. The schists was uncovered by the Zapadno-Yarotinskaya No. 300 well at a depth of 2762 m. Above the section, the metamorphic rocks are overlain by a young Meso-Cenozoic cover. The schists are mainly composed of quartz, plagioclase (albite), carbonates (dolomite and siderite), mica (muscovite) and chlorite (donbassite). The discovered accessory and ore minerals in the metamorphic schists of the Zapadno-Yarotinsky area can be divided into two groups. The first group includes minerals that were formed during the metamorphism of schists, or were preserved as detrital matter. These minerals include zircon, fluorapatite, and rutile as the most stable compounds. The remaining mineralization (pyrite, sphalerite, chalcopyrite, cubanite, galena, cobaltite, barite, xenotime-(Y), goyazite, synchysite-(Nd), native silver and copper) is clearly secondary and was formed as a result of superimposed metasomatic processes. Judging from the described mineralogy, the schists underwent changes as a result of superimposed propyllitization. The temperature range of this process is determined by the formation of cubanite in association with chalcopyrite at a temperature of 200-210 оС.Massif
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1958)
The regional metamorphism which produces glaucophanites can be regarded as metamorphism under low temperature and high pressure. It has been expressed by many authors including the present writer that the glaucophanites have no special characteristics in the chemical composition. However, it is evident from the statistical study of the available chemical data that the metamorphic rocks, especially the green schists in the glaucophanitic regional metamorphic terrains have generally higher content of Na2O and higher ratio of Fe2O3: FeO than the metamorphic rocks subjected to other types of regional metamorphism. These features are considered to be due to the soda-metasomatism and rather high water vapour pressure prevailing in some glaucophanitic regional metamorphic terrains.
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For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a black art. Because low-grade rocks are frequently fine-grained, contain a wide variety of low-temperature minerals with limited stability fields, and have high porosities and fluid contents they are not as readily understood as higher grade metamorphic rocks. For these rocks, few, if any, of the standard thermobarometers or thermobarometric datasets are applicable and the derivation of fluid evolution histories is complicated by the high concentration of, frequently reduced, fluids. Low-grade metamorphism, at T <400°C and P <4–5 kbar, spans the P – T interval between what may be erroneously termed ‘proper’ metamorphism and the field of diagenesis, although in reality there is no clear or sharp break between the diagenetic and metamorphic fields. As such, techniques relevant to the study of low-grade metamorphism span those of both the sedimentary and metamorphic fields. This …
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