| 云南姚安Au-Pb-Ag矿床含矿富碱岩浆岩地球化学特征及岩石成因 |
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| 引用本文： | 罗晨皓,周晔,沈阳.云南姚安Au-Pb-Ag矿床含矿富碱岩浆岩地球化学特征及岩石成因[J].地球科学,2019,44(6):2063-2083. |
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| 作者姓名： | 罗晨皓 周晔 沈阳 |
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| 作者单位： | 1.中国地质大学地球科学与资源学院, 北京 100083 |
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| 基金项目： | 国家重点研究发展计划2016YFC0600310中国地质调查局地质调查项目DD20160024-07 |
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| 摘 要： | 通过锆石U-Pb定年、全岩主微量元素、Sr-Nd-Pb和锆石Hf同位素测试, 对滇西姚安Au-Pb-Ag矿床含矿正长斑岩和粗面岩的地球化学特征进行了分析, 系统探讨了其岩浆起源和演化过程.正长斑岩和粗面岩的锆石U-Pb年龄分别为33.8±0.42 Ma和33.9±0.60 Ma, 它们与同时代滇西镁铁质火山岩和煌斑岩具有相似的稀土和微量元素配分模式和Sr-Nd-Pb同位素组成, 而与区内同时代加厚地壳来源的富碱埃达克质岩石存在Sr-Nd-Pb-Hf同位素组成的明显差异.全岩SiO2与主微量元素关系指示正长斑岩和粗面岩总体上可由矿区内同时代的基性岩浆岩分异演化而来, 表明它们与这些基性岩浆岩起源相似, 较高的Rb/Sr(≥ 0.1)和较低的Ba/Rb(< 20)比值, 指示其源区为富金云母富集地幔, 较低的εHf和古老的模式年龄暗示源区的交代富集发生在中元古代.姚安富碱岩浆活动与矿化关系密切.正长斑岩和粗面岩较滇西镁铁质火山岩和煌斑岩具有稍高的初始Pb同位素组成, 暗示岩浆可能遭受了地壳混染, 从而提高了母岩浆中的金属含量, 增强了岩浆成矿潜力; 适中的氧逸度利于Au富集; 角闪石分离结晶和较多黑云母发育指示母岩浆含水量较高, 利于成矿流体的形成.这些特征综合起来为矿化发育提供了有利条件.
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| 关 键 词： | 姚安 富碱岩浆岩 岩浆源区 岩石成因 Au-Pb富集 岩石学 矿床 |
| 收稿时间： | 2018-10-20 |
The Geochemical Characteristics and Petrogenesis of the Mineralized AlkaliRich Magmatic Rock in Yao' an Au-Pb-Ag Deposit,Yunnan Province |
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| Abstract: | Newly-determined zircon U-Pb ages, whole rock major and trace elements, Sr-Nd-Pb and zircon Hf isotope data, are used to firstly examine the geochemical characteristics of the ore-related syenite porphyry and trachyte in the Yao' an Au-Pb-Ag deposit, western Yunnan, and then to systematically discuss the origin and evolution processes of the parental magmas in this paper. The zircon U -Pb ages of the syenite porphyry and trachyte in the Yao' an Au -Pb -Ag deposit respectively are 33.8±0.42 Ma and 33.9±0.60 Ma. And their patterns of trace elements and REE, and the Sr-Nd-Pb isotopes, are very similar to the contemporary mafic volcanic rocks and lamprophyre from the western Yunnan, but obviously different from the contemporary alkali-rich adakitic rocks in the western Yangtze craton. The relationships of SiO2 contents with major and trace element contents of the whole-rocks indicate that magmas for the syenite porphyry and trachyte could be formed by differentiation of the contemporary mafic magmas in the diggings. This implies that syenite porphyry and trachyte may have similar source to the mafic magmas. High Rb/Sr(≥ 0.1) and low Ba/Rb(< 20) ratios of the syenite porphyry and trachyte indicate that they were derived from a metasomatized enriched mantle source with abundant phlogopite. And the low εHf and the old model age of the rocks indicate that the metasomatism of the source region might happen in Mesoproterozoic. The alkali-rich magmation in Yao' an is closely related with the mineralization. The syenite porphyry and trachyte of Yao' an have a higher initial Pb isotopic composition than the mafic volcanic rocks and lamprophyre from the western Yunnan, which implies that some degrees of the crustal contamination might occur during evolution process of the magmas which could increase the metal contents of the magma and enhance the mineralization potential of the magmas. The moderate oxygen fugacity of the magmas in favour of the Au enrichment. And the obvious fractional crystallization of hornblende and the formation of abundant biotite indicate that the primary magmas were very hydrous, which facilitated the formation of oreforming fluids. All of these features could provide advantageous conditions for the mineralization in the Yao' an deposit. |
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