| 滇东南长安金矿晚始新世正长斑岩岩石地球化学、成岩时代及其地质意义 |
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| 关键词:syenite porphyries rock-forming age Lu-Hf isotope Chang'an gold deposit |
| 基金项目:中国地质调查局地质调查项目(编号: DD20190011; DD20201165);中国地质科学院基本科研业务费专项(编号: JKY202011) |
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| Lithogeochemistry, Rock-forming Age, and Geological Implications of Late Eocene Syenite Porphyries in the Chang'an Gold Deposit, Southeastern Yunnan |
| The Chang'an gold deposit in southeastern Yunnan is located in the southern section of the Ailaoshan orogenic belt. The main exposed magmatic rocks in the mining area are syenite porphyries, which are often associated with gold ore bodies. The formation age and magmatic evolution of the syenite porphyries have important indicative significance for the study of the Chang'an gold deposit. In this study, syenite porphyry samples were selected for petrology, geochemistry, zircon U-Pb, and Hf isotope studies. Studies have shown that syenite porphyries have a SiO2 content of 68.00%–70.43% and a total alkali content (K2O+Na2O) of 8.15%–8.76%. It belongs to the sub-alkaline series of strong peraluminous rocks with the characteristics of S-type granites. The ΣREE is in the range of 71.52×10–6–76.43×10–6, with a low content and large degree of differentiation between light and heavy rare earth elements. The rare earth elements distribution curve has right-leaning characteristics, with δEu (0.81–0.86) weak negative anomalies and δCe (1.15–1.33) weak positive anomalies. The spider plot of trace elements is right-leaning, with enrichment of large ion lithophile elements such as Rb, Ba, Th, K, and depletion of highfield-strength elements, along with negative anomalies of Nb and Ta. The zircons of the pluton developed oscillating belts with a high Th/U ratio. The zircon 206Pb/238U analysis points are distributed in point groups with a weighted average of (34.7±0.3) Ma, indicating that the pluton was formed in the late Eocene. The zircon εHf(t) ranges from –2.65 to 2.02, single-stage Hf model ages (TDM) range from 629.95 Ma to 821.54 Ma, and two-stage Hf model ages (TDMC) range from 1 378.52 Ma to 1 801.25 Ma, suggesting that the plutons were formed as a result of remelting of ancient crustal components with a small number of mantle-derived materials. The rocks have adakite characteristics and were formed in a post-collisional tectonic setting. |
| ZHANG Yao-yao,CHEN Xuan-hua,ZHANG Da,MO Xuan-xue,SHAO Zhao-gang,ZHAO Ze-nan,LI Xing-jian.2022.Lithogeochemistry, Rock-forming Age, and Geological Implications of Late Eocene Syenite Porphyries in the Chang'an Gold Deposit, Southeastern Yunnan[J].Acta Geoscientica Sinica,43(6):817-831. |
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