| As a sediment formation, silicalite formation with a large sedimentary thickness is consist of siliceous rocks (cherts), mud stone/shale or callys, carbonatite and siltstone, and is charactered by enrichment in organic and bacterium-alga microbe. In addition, the cherts in siliclite formation, as an uppermost member, generally, possess many mineral products, such as Au, Se, U, V, P, Mn, PGE, barite and py etc). Thereupon, it is important to undertake study on the silicalite formation and cherts. This dissertation mainly focuses on two selenium-rich "silicalite formation" from Yutangba Selenium Deposit in Shuanghe(in Permian) and Ziyang Selenium-rich area in Southern Qinling(in the early Cambrian), respectively.Based on the petrochemistry, isotopic geochemistry, mineralogy and fluid inclusion, the Ph.D dissertation mainly focused on mineralization law, petrogenesis, sedimentary environment and fluid type of two areas, respectively, in addition, discussed the mineralogy, the composition of inclusions and physical chemistry characteristics of the selenium deposit in Yutangba, Hubei province. By studying, the main conclusions have been put forward as follows:1 The SiO2 content is 64.2%~95.84% and 63.62%-95.24% of two areas. Se contents analysis for the representative samples shows that the enrichment of selenium is strictly sedimentary strata-bound. With the exception of the Maokou Formation limestones, the samples with the Se contents higher than 80ug/g were all collected from the Lower Permian Maokou Formation siliceous rocks. The highest selenium's content is 278ppm of the siliceous rocks in Ziyang.2 For the trace elements, both of two areas have high Cu, Ni, V, As, Sb, Cr and U/Th (>1), Along with the projection in AI-Fe-(Cu+Co+Ni) ternary diagram, in U-Th, Zr-Cr and P2O5-Y relative diagram, both of two study areas' silicalitesamples fall into the hydrothermal field. In Yutangba selenium deposit, the REE content of siliceous rocks is Iow(38.9x10-6), and enriched in LREE. In Ziyang selenium-rich area, it is from (12.0-37.6)x10-6, In both of two areas, there exist Ce negative anomaly and Eu positive anomaly. They both show the character of hydrothermal genesis, the silicon and oxygen isotope composes are similar with the hydrothermal origin. Based on the Oxygen isotope fractionation equation of chert and water, the petrogenetic temperatures of the silicalites in two study areas are (46-72)C and (78.6-126.20)C.Geochemistrical characteristics of the selenium-rich cherts from Yutangba and Ziyang suggest that the silicalite resulted from hydrothermal sediment. In addition, the high Cr content, the brachiopodous biology fossil existing in Yutangba cherts, and the high Ba contents, the organic matter in Ziyang samples, together with the positive 13C for the cherts of Yutangba, and negative 13C for the cherts of Ziyang, all imply that the petrogenesis of the cherts is related with volcanism, however, during diagenetic process, biology may be an important role.3 The negative Sulfur isotope compositions of the pyrite in the cherts of Yutangba indicate that the selenium deposit was formed in an anoxic oceanic basin. However, the selenium of the cherts from Ziyang resulted from sea water due to the sulfur isotopic compositions.4 The study on the mineralogy suggests that there are four type forms for selenium existing in the deposits, such as native selenium, independent selenium minerals, isomorphism and organic adsorption. Native selenium minerals from the abandoned coal pile are the results of natural factors and anthropologic activities, instead of the slow combustion of the coal.5 Systematic studies on many multiform fluid inclusions including temperature, salinity and density have been conducted for the quartzes and calcites ofYutangba selenium deposit and Ziyang selenium-rich area, and the results show that most of fluid inclusions from two study areas are primary. The homogenization temperatures of the fluid inclusions from two study areas (Yutanba and Ziyang) are changeable fr...
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