渔塘坝硒矿床地球化学特征及其成因

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	渔塘坝硒矿床地球化学特征及其成因
其他题名	The Geochemistry of Yutangba Selenium deposit and its Origin
	姚林波
	2002
学位授予单位	中国科学院地球化学研究所
学位授予地点	中国科学院地球化学研究所
学位名称	博士
学位专业	地球化学
关键词	渔塘坝地球化学微量元素稀土元素稳定同位素
摘要	在湖北恩施市双河乡渔塘坝,下二叠茅口组顶部的合碳硅质岩段硒的异常富集形成了硒的独立矿床,该矿床自发现以来,大多集中在环境和矿床地质方面的研究,还未有系统的地球化学证据解释其成因.该文通过地球化学手段,以硒的存在形式、地球化学和富集机制为主线,对渔塘坝硒矿床的地球化学进行初始的研究,首次提供了有关渔塘坝硒矿床较全面的地球化学证据,包括硒的存在形式和矿物组合、硒矿石岩石化学特征和分类、微量和稀土元素特征、稳定同位素组成(Si、O和S)、有机地求化学特征,并对渔塘坝硒矿床的成因做了可靠而全面的阐述.
其他摘要	In the carbonaceous cherts at the top of the Lower Permian Maokou Formation limestones at Yutangba, Shuanghe Town, Enshi, Hubei Province, the element Se is so abnormally enriched as to have formed an independent Se deposit. Since the discovery of this deposit, great efforts have been devoted to research on its geology and geological setting, but no systematic geochemical evidence has yet been found for its origin. The present paper is focused on the origin of the seleniferous layers in terms of their petrochemical composition, existing forms of selenium in the ore, REE and trace element characteristics, Si, 0, S isotopic composition, organic geochemistry, and Se enrichment mechanism, in conjunction with the tectonic background of sedimentation and the features of the rocks, in an attempt to shed much more light on the origin of the Yutangba Se deposit. Geotectonically this mining district is located ,in the northeastern sector of the Upper Yangtze Platform of the Yangtze Paraplatform, The mining district lies in the middle part of the N-W flank of the Shuanghe syncline, with the. synclinal axis extending NEE. The Triassic Daye Formation limestones are developed in the core and the Permian strata on both flanks. Fault structures are less developed. The Yutangba seleniferous layer consists of the Lower Permian Maokou 'Formation carbonaceous cherts, in pseudo-conformable contact with the Maokou Formation limestones and in parallel unconformable contact with the overlying Wujiaping Formation. The seleniferous layer is generally a suite of black thin-layered carbonaceous cherts and the cherts are the typical bedded cherts with horizontal bedding and laminated structure. The seleniferous cherts and shale are the main ore type of the Yutangba Se deposit. The ores contain as much Se as 842 x 10"6 on average. The minerals in the ore are composed dominanlly of amorphous quartz, chalcedony, carbon and hydromica, accounting ior y /% of the total; other minerals include pyrite, pyrrhotite, selenium minerals (chalcomenite, klockmannite, krutaite, native selenium), apatite, xenotime and so on. The chemical composition of the ores contain mainly SiO2, Corg (organic carbon) and Al2O3, which account for 89.17% of the total. SiO2 is 67.86%, Corg 15.73%, AI2O3 5.58%, Mn 0.04%, TFe 0.57%, P2O50.35% and S 0.35 on average, with K content being higher than that of Na because of the occurrence of illite in the samples. In addition, the contents of Ca and Mg are not high. The seleniferous layer is characterized by well developed horizontal bedding and laminated bedding, reflecting an anoxic or oxygen-poor marine-facies sedimentary environment. Relatively high carbon contents indicate that biological activities were involved in the formation of the seleniferous layer. Existing forms of selenium in Yutangba ores include: (1) independent Se minerals: mainly presents in native selenium, basically absorbed in organic matters or other microminerals, and rarely appears klockmannite, chalcomenite, krutaite, etc. in the ores, (2) isomorphism: Se substitutes S in different amounts and forms Se-bearing pyrite. The ratios of SiO2/MgO, SiO2/Al2O3, and SiO2/ (K20+Na20) in the cherts of this area are close to those of bio-chemically sedimentary cherts. As can be seen in the corresponding SiO2-AI2O3, SiO2-MgO and SiO2- (K20-t-Na20) diagrams, the data pointsof the Yutangba cherts all fall within the field of bio-chemically sedimentary cherts. Al/(A1+Fe+Mn) ratios in the cherts of this area are relatively high, averaging 0.67. So it can be ruled out that the Yutangba cherts are of hydrothermal sedimentation origin, and instead they should be of normal bio-chemical sedimentation origin with the involvement of some terrigenous materials. The Yutangba seleniferous ores are characterized by an element association of Se-Mo-Bi-V-Cd-Cr-Ag-Sb-U, with Se being abnormally enriched. In addition, the average values of Mo and V are coming up to the industrial requirements. The V/(V+Ni), V/Cr and U/Th ratios indicate that the seleniferous layers were formed in an anoxic environment. The Yutangba seleniferous ores are low in S REE and are characterized by distinctive fractionation between HREE and LREE, and LREE enrichment, moderate negative Ce and Eu anomaly. The comparability in the characteristics of trace element between Yutangba ore and Emeishan flood basalts in southwestern China reveals in the close ratios Zr/Nb, Zr/Hf, Rb/Nb etc. and LREE enrichment type. Negative Ce and Eu anomaly may be inherited from Emeishan basalts. All these evidences suggest that basalt effusion could provide abundant ore-forming materials for Se mineralization. The samples are characterized by relatively heavy Si isotope enrichment, and insignificant variations in 6 30Si value within the range of 0.5‰～1.2‰. Theδ18O is within the range of 21.6～27.8‰, and -3.14‰ ～-13.08% for the 34S. Stable isotope studies provide further evidence for view point of the Yutangba seleniferous ores are of bio-sedimentation origin. The content of organic carbon(Corg) in the ores is within the range of 3,85～43.9%( 15.5% on average), and the concentration of asphaltum "A" remains low in chert-type and shale-type ores. The ratios Pr/Ph(
页数	91
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3618
专题	研究生_研究生_学位论文矿床地球化学国家重点实验室
推荐引用方式 GB/T 7714	姚林波. 渔塘坝硒矿床地球化学特征及其成因[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,2002.

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