| 云南大丫口祖母绿颜色环带成因对多阶段成矿的指示意义 |
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| 引用本文： | 余晓艳,郑育宇,张婷雅,郭鸿舒,龙政宇,万佳鑫,张存.云南大丫口祖母绿颜色环带成因对多阶段成矿的指示意义[J].地学前缘,2020,27(5):116-125. |
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| 作者姓名： | 余晓艳 郑育宇 张婷雅 郭鸿舒 龙政宇 万佳鑫 张存 |
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| 作者单位： | 1.中国地质大学(北京) 珠宝学院, 北京 1000832.中国地质大学(北京) 地球科学与资源学院, 北京 100083 |
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| 基金项目： | 中央高校基本科研业务费专项资金项目(53200759514);中国地质调查局中国矿产地质志项目(DD20190379-88) |
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| 摘 要： | 云南大丫口祖母绿常出现颜色环带,且伴随明显成分变化,而目前颜色环带的成因仍存争议,相关的多阶段成矿假说尚缺少明确证据。文章通过电子探针和激光剥蚀电感耦合等离子质谱仪对大丫口祖母绿的颜色环带及黑色矿物包裹体进行主微量元素成分分析,并对不同类型岩脉祖母绿中流体包裹体进行显微测温分析,进而探讨祖母绿颜色环带成因与多阶段成矿的联系。成分测试结果表明,从浅绿白核部至绿色边部,V(970×10-6→10 077×10-6)、Rb(9.6×10-6→27.4×10-6)、Cs(535×10-6→3 108×10-6)、Fe(1 376×10-6→2 199×10-6)和Ga(4×10-6→14.7×10-6)等微量元素的含量急剧增加。结合绿色晶体边部中同生黑色富钒电气石包裹体的分布,有力证明了大丫口祖母绿颜色分带的形成与晶体的多阶段成矿有关。流体包裹体测试结果表明,含矿长石-方解石脉、含矿石英脉和伟晶岩-变粒岩接触带中矿物的流体包裹体盐度范围分别为3.39%~10.36%(NaCleq)、5.71%~12.29%(NaCleq)和8%~18.72%(NaCleq),指示了伟晶岩脉中祖母绿的多阶段结晶,且表明随结晶阶段演变,成矿流体的盐度逐渐升高。同时,成矿流体盐度升高也是晚期云英岩化阶段致色元素含量剧增的原因。
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| 关 键 词： | 云南祖母绿 主微量成分分析 流体包裹体 颜色环带成因 多阶段成矿 |
| 收稿时间： | 2020-04-12 |
The genesis of color zonation of emerald from Dayakou,Yunnan Province: implication for multi-stage mineralization |
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| YU Xiaoyan,ZHENG Yuyu,ZHANG Tingya,GUO Hongshu,LONG Zhengyu,WAN Jiaxin,ZHANG Cun.The genesis of color zonation of emerald from Dayakou,Yunnan Province: implication for multi-stage mineralization[J].Earth Science Frontiers,2020,27(5):116-125. |
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| Authors: | YU Xiaoyan ZHENG Yuyu ZHANG Tingya GUO Hongshu LONG Zhengyu WAN Jiaxin ZHANG Cun |
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| Institution: | 1. School of Gemology, China University of Geosciences(Beijing), Beijing 100083, China2. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China |
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| Abstract: | Color zonation with obvious composition variation often appear in emeralds from Dayakou, Yunnan Province, China. However, the origin of color zonation is still controversial, and there has been no reliable evidence for the related multistage mineralization hypothesis. In this study, we analyzed the main and trace elemental signatures of the Dayakou emerald with obvious color zonation by electron microprobe (EMP) and laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We also carried out microthermal analysis of fluid inclusions hosted within emerald and other associate minerals from different types of veins. The composition results showed that the trace elemental contents in emerald increased sharply from the light greenish white core to the green rim, yielding V((970-10077)×10-6), Rb((9.6-27.4)×10-6), Cs((535-3108)×10-6), Fe((1376-2199)×10-6) and Ga((4-14.7)×10-6); and the syngenetic black inclusions which only occur at the green crystalline rim were proved to be V-rich intermediate oxy-schorl-dravite. The above evidence strongly suggests that color zonation are formed from multistage crystalline mineralization. Furthermore, the microthermal analysis results showed that salinities of fluid inclusions hosted within minerals from the feldspar-calcite and quartz veins and pegmatite-granofel contact zones were 3.39%-10.36%, 5.71%-12.29% and 8%-18.72%(NaCleq), respectively, again indicating different mineralization stages in pegmatite veins and suggesting increasing parent fluid salinity with evolution of the mineralization stage. And the considerable variation of V concentration is also caused by increasing salinity at the greisenization stage. |
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| Keywords: | Yunnan emerald major and trace elemental analysis fluid inclusions origin of color zonation multistage mineralization |
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