摘要: |
李家沟锂多金属矿床位于松潘–甘孜褶皱造山带东南缘,是近年来在区内发现的超大型锂多金属矿床,矿区内广泛发育花岗细晶岩脉。本文对花岗细晶岩脉进行了全岩地球化学测试、锆石U-Pb定年和Hf同位素分析,探讨其岩石成因及地质意义。花岗细晶岩锆石U-Pb加权平均年龄为200±2 Ma,属晚三叠世—早侏罗世。岩石具高硅(w(SiO2)=73.27%~75.14%)、富铝(w(Al2O3)=14.8%~15.25%)、富碱(w(Na2O+K2O)=4.86%~8.08%)、贫钙(w(CaO)=0.45%~1.45%)的特征,A/CNK值均大于1.1,属中钾–高钾钙碱性强过铝质S型花岗岩。微量元素表现出Rb、Th、U、K的正异常和Ba、Sr、P、Ti相对负异常。稀土元素显示轻稀土富集、重稀土亏损及弱的负Eu异常(δEu=0.68~0.81)。岩石中锆石εHf(t)值和对应的二阶模式年龄(tDM2)较为均一,分别为-6.36~-3.39和1424~1616 Ma。研究表明,花岗细晶岩脉形成的构造背景为松潘–甘孜洋(古特提斯支洋)闭合后的后碰撞造山阶段,源岩为古老地壳变杂砂岩。结合前人研究成果,认为锂矿化花岗伟晶岩与花岗细晶岩为同一源区不同源岩(变泥质岩和变杂砂岩)部分熔融的产物。 |
关键词: 锆石U-Pb-Hf同位素 S型花岗岩 后碰撞 古特提斯 李家沟锂多金属矿床 四川可尔因地区 |
DOI:10.19826/j.cnki.1009-3850.2022.09006 |
附件 |
投稿时间:2022-05-11修订日期:2022-06-27 |
基金项目:贵州省省级科技计划项目(黔科合基础-ZK[2021]一般204)、贵州省教育厅项目(黔教合KY字[2020]100)、遵义师范学院项目(遵师BS[2020]5号、遵师XM[2020]1号-01)、毕节市科学技术联合基金项目(毕科合字[2019]22号)联合资助 |
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Petrogenesis of granite aplite in the Lijiagou lithium polymetallic ore district in western Sichuan: constraints from geochemistry, zircon U-Pb geochronology and Hf isotope |
LUO Wei, PENG Jing, JIN Tingfu, YANG Bo, PANG Liangwu |
(1. College of Engineering and Technology, Zunyi Normal University, Zunyi 563002, China; 2. College of Mining Engineering, Guizhou University of Engineering Science, Bijie 551700, China; 3. Geochemical Exploration Brigade of Sichuan Provincial Geology & Mineral Resources Bureau, Deyang 618000, China) |
Abstract: |
The Super-large Lijiagou lithium polymetallic deposit is a newly discovered deposit in the southeastern margin of Songpan-ganzi Fold Orogenic Belt and has widespread outcrops of granite aplite veins. whole-rock geochemical analysis, zircon U-Pb dating and zircon Hf isotopic analysis for granite aplite are performed to explore its petrogenesis and geological significance. Zircons yielded weighted mean U-Pb age of 200±2 Ma for granite aplite, indicating that it was emplaced in the Late Triassic to Early Jurassic. The rocks exhibit high SiO2 concentration (73.27%~75.14%), high Al2O3 concentration (14.8%~15.25%), high total alkali concentration (4.86%~8.08%) and low CaO concentration (0.45%~1.45%) with A/CNK ratios >1.1, which are defined as median-K to high-K calc-alkaline strongly peraluminous S-type granites. Trace elements of the granite aplite show positive anomalies for Rb, Th, U, K and relative negative anomalies for Ba, Sr, P, Ti. The granite aplite display enrichment of LREE, depletion of HREE, and weak negative Eu anomalies (δEu=0.68~0.81). zircon εHf(t) values range from -6.36 to -3.39 with tDM2 varying from 1424 Ma to 1616 Ma. The study shows that the granite aplite veins were formed in the post-collision orogenic stage after the closure of the Songpan-Ganzi ocean (a branch of the Paleo-Tethys Ocean), and the source rocks are the ancient crustal meta-greywacke. Combined with the previous research results, it is considered that the lithium mineralized granitic pegmatites and the granite aplites are the products of partial melting of different source rocks (meta-argillite vs meta-graywacke) in the same source area. |
Key words: zircon U-Pb-Hf isotopes S-type granite post-collisional paleotethys Lijiagou Li polymetallic deposit Keeryin area in Sichuan |