| 滇黔相邻地区峨眉山玄武岩地球化学特征 及其成自然铜矿作用 | |
| Alternative Title | Geochemical characteristics of Emeishan Basalt and Mineralization of native copper deposit in junction area of Yunnan - Guizhou Province, China |
| 许连忠 | |
| Subtype | 硕士 |
| Thesis Advisor | 张正伟 |
| 2006 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 中国科学院地球化学研究所 |
| Keyword | 滇黔交界地区 峨眉山玄武岩 玄武岩铜矿 地球化学 同位素 有机质 |
| Abstract | 峨眉山玄武岩分布于云、贵、川三省。在滇黔交界处，二叠世玄武岩因为广泛发育自然铜矿化而具有重要的研究意义。本研究通过地质、地层和地球化学的方法探讨本区出露的峨眉山玄武岩的起源、成因和喷发时代，同时用同位素方法探讨玄武岩铜矿成矿。通过本次研究获得以下成果：
1 探讨了威宁二叠纪玄武岩的成因。通过主量和微量元素地球化学特征研究表明：玄武岩起源于微混染的 EMⅡ型富集地幔，岩浆端元矿物为石榴子石二辉橄榄岩。岩浆在上升过程中发生了辉石和橄榄石的分离结晶。微量元素 Rb 的强烈负异常，表明玄武岩形成后遭到了强烈的热液蚀变。
2 用恢复 Rb-Sr 古混合线定年方法确定了本区宣威组底部硅质页岩的成岩年龄为 255±12 Ma，首次确定了峨眉山玄武岩的喷发上限年龄。
3 玄武岩铜矿石铅同位素组成 206Pb/204Pb=18.078~18.923 ； 207Pb/204Pb=15.463~15.690；208Pb/204Pb=38.301~39.036。通过Pb同位素比较研究，矿石铅同位素组成与玄武岩岩石铅同位素组成相似，成铜物质可能来源于玄武岩的淋滤。
4 与玄武岩铜矿伴生的沥青和碳质δ13CPDB值变化在－32.3‰ ~－21‰之间，与自然界δC13储库生物成因的碳同位素组成相符，表明其为有机成因。铜矿石中方解石的碳氧同位素表现出明显的特殊性，以富δ18OSMOW和贫δ13CPDB 为特征，δ18OSMOW和δ13CPDB值分别为13.1‰~22.9‰ 和-32.3 ‰ ~ -13．5‰。不同矿床
碳同位素组成一致，暗示碳为同一来源，均为有机碳。
5 矿石中石英和方解石中流体包裹体的H-O同位素组成为：δ18O矿物-SMOW，14.3‰ ~18.9‰；δ18O水－SMOW，2.8‰ ~ 7.2‰； δ18D水－SMOW，-63.6‰ ~ -80.6‰。 其中流体包裹体均一温度为151 ~ 201℃。研究表明，成矿流体来源于建造水与玄武岩发生强烈的水-岩反应所形成的成矿流体。成矿流体通过对流循环方式从玄武岩中萃取成矿物质,有机质对成矿流体的还原和对成矿物质的吸附作用可能是成矿的重要机制。
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| Other Abstract | Emeishan Basalt spreads widely in Yunnan , Guizhou and Sichuan Province. There are variations between the different parts of the Emeishan Basalt. In the junction area of Yunnan and Guizhou Province , the basalt is special for far-ranging nature copper mineralization. This study focus on Emeishan basalt in the junctional area of Yunnan and Guizhou Province. Based on systematic studies on geological, stratigraphic and geochemical characteristics of the volcanic rocks and copper deposits hosted in the rocks, the composition of primary magma and their changes and
the time of volcanic activity have been discussed respectively in this paper. Isotope also has been proposed to explain the evolution of Emeishan basalt copper deposits. From this study, following achievements have been obtained:
1. Based on geochemical characteristics of major elements, trace elements and rare earth elements of the basalts, it is indicated that the primary magma of the basalts is derived from enrich mantleⅡ(EMⅡ) with little contamination, and the basalts end mineral composition is garnet lherzolite, and picrite and olivine fractional crystallization have been occured during magma ascent or emplacement. Intensive
activity of hydrothermal fluid has also been suggested to explain Rb’s intensive negative anomaly.
2. The age of the the shale, which overlays Emeishan Basalt Group, have been accessed by iterative reconstruction and regression of Rb-Sr binary isotope paleomixing line. This is different from conventional Rb-Sr dating. From the research, the shale’s model age of 255±12 Ma have been dated. This age indicates Emeishan basalts end-eruption happened before 255Ma. It not only supports the study of
paleomagnetism of stratum and stratum chronology but also Emeishan basalt main eruption time is nearly 258Ma. This study indicates Rb-Sr isotope chronology is applicable in Mesozoic stratum and 255Ma effectively constraints the upper limit time of Emeishan basalt.
3. 206Pb/ 204Pb , 207Pb/ 204 Pb and 208 Pb/ 204 Pb of minerals from copper deposits are generally from 18.078 to 18.923, from 15.463 to 15.690 and from 38.301 to 39.036, respectively. Pb isotopic compositions of the minerals resemble their host rocks-Emeishan basalt, which indicates the matter of basalt copper deposit originated from Emeishan basalt.
4. δ13CV-PDB of bitumen and carbonaceous matter from copper ore in basalts range from -32.3‰ to -21‰, conforming to the range of Sedimentary organic carbon and Biomass in Nature δ13C reservoirs, which suggested that carbon of the bitumen and the carbonaceous matter did not come from mantle source but bio-source. δ18OSMOW and δ13C PDB of calcite from copper ore are generally from 13.1‰ to 22.9‰ and from -32.3 ‰ to -13.5‰，respectively. It is special in that δ18O is rich while δ13C depleted. Different ore deposit has same carbon isotope composition respectively, which suggests the carbon comes from same source –organic carbon.
5. δ18O矿物-SMOW, 18OH2O- SMOW and δDV-SMOW of fluid inclusions in quartz and calcite from copper ore are from 14.3‰ to 18.9‰, from 2.8‰ to 7.2‰ and from -63.6‰ to-80.6‰ respectively ,with a medium-low temperature(151℃to201℃). All these data suggest that ore fluids are formed by intensive water-rock reaction of evolved formation water and Emeishan basalt. Fluids extracted copper from basalts in the way of convection, as well as the reduction and adsorption action of organic
matters are important mechanism to form copper deposit .
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| Pages | 78 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/42920512-1/10794 |
| Collection | 研究生 |
| Recommended Citation GB/T 7714 | 许连忠. 滇黔相邻地区峨眉山玄武岩地球化学特征 及其成自然铜矿作用[D]. 中国科学院地球化学研究所. 中国科学院大学,2006. |
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