| 柴北缘茶卡北山成矿带含铍与富锂花岗伟晶岩中磷灰石年龄、原位地球化学特征及其地质意义 |
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| 引用本文：康利刚,赵如意,王登红,李积清,凤永刚,李凯旋,梁婷,李善平,李正辉,石煜,王成辉,邵恒博,兰华平.2026.柴北缘茶卡北山成矿带含铍与富锂花岗伟晶岩中磷灰石年龄、原位地球化学特征及其地质意义[J].地球学报,47(3):644-666. |
| DOI：10.3975/cagsb.2025.072221 |
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| 基金项目:本文由国家重点研发计划项目(编号: 2021YFC2901902)、中国核工业地质局项目“柴达木盆地阿拉尔?苏干湖地区铀矿资源调查评价与勘查”(编号: 202219)、东华理工大学博士启动基金(编号: DHBK2019307)和中国铀业有限公司-东华理工大学核资源与环境国家重点实验室联合创新基金项目(编号: 2022NRE-LH-17)联合资助。 |
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| 中文摘要:磷灰石具有较强的稳定性和组分多变性, 是良好的岩浆-热液作用“黑匣子”。茶卡北山锂铍成矿带是近几年新发现的花岗伟晶岩型稀有金属成矿带。然而, 成矿带所在的宗务隆构造带东段尚未发现与之同期的花岗岩, 花岗伟晶岩的侵位时代、岩浆过程和成因机制有待开展精准、深入的研究。本文选取茶卡北山矿段含铍花岗伟晶岩和俄当岗矿段富锂花岗伟晶岩中的原生岩浆磷灰石开展原位U-Pb定年和地球化学分析。电子探针X射线显微分析仪(EMPA)分析结果显示, 含铍和富锂花岗伟晶岩中的磷灰石都是氟磷灰石, F含量平均值分别为3.86%和3.81%, Cl含量为0.01%或低于检测限, FeO和MnO含量较高, Fe2+/Mn2+(pfu)平均值分别为0.10和0.19。激光剥蚀电感耦合等离子体质谱法(LA-ICP-MS)测试结果显示, 与含铍花岗伟晶岩中磷灰石相比, 富锂花岗伟晶岩中的磷灰石U含量更高、Th/U更低(0.05左右), Sr含量更低。含铍花岗伟晶岩中磷灰石的球粒陨石标准化稀土元素配分曲线图呈正铕异常的右倾斜线, 富锂花岗伟晶岩中磷灰石的稀土元素为具有四分组效应的“M”型。茶卡北山成矿带含铍和富锂花岗伟晶岩中磷灰石的结晶时代为(216.29±3.14) Ma, 代表了伟晶岩脉的侵位冷凝时间。该花岗伟晶岩是在印支晚期后碰撞到板内伸展构造背景下, 由变质沉积岩部分熔融形成的花岗质岩浆, 经高度演化分异而成, 具有富Li-Cs-Ta(LCT)型伟晶岩特征。茶卡北山矿段含铍花岗伟晶岩和俄当岗矿段富锂花岗伟晶岩的岩浆是同一源区的岩浆在不同演化阶段的产物, 从含铍向富锂演化过程中, 岩浆的含水量有所增加, 温度和氧逸度都在降低。 |
| 中文关键词:柴达木盆地北缘 茶卡北山 花岗伟晶岩 锂铍矿 磷灰石 U-Pb年龄 原位地球化学 岩浆过程 |
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| Ages, in Situ Geochemical Characteristics, and Its Geological Significances of Apatite in Be-bearing and Li-rich Granitic Pegmatites from the Chakabeishan Metallogenic Belt, Northern Qaidam Basin |
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| Abstract:Apatite is an effective “black box” of magmatic and hydrothermal processes owing to its strong stability and diversiform components. The recently discovered Chakabeishan lithium–beryllium metallogenic belt is a granitic pegmatite-type rare-metal belt. However, no granite relevant to pegmatite has been found in the eastern part of the Zongwulong tectonic zone, where the Chakabeishan metallogenic belt is located. Moreover, the accurate emplacement age, detailed magmatic processes, and genetic mechanisms of granitic pegmatites need to be studied in depth. In this study, primary magmatic apatite from beryllium-bearing granitic pegmatites in the Chakabeishan ore block and lithium-rich granitic pegmatites in the Edanggang ore block were selected for in-situ U-Pb dating and major and minor element analyses. The Electron Probe X-ray Micro-Analyzer analysis results show that the apatite in beryllium-bearing and lithium-rich granitic pegmatites is fluorapatite, with average F contents of 3.86% and 3.81%, Cl contents of 0.01% or below the detection limit, high FeO and MnO contents, and average Fe2+/Mn2+(pfu) values of 0.10 and 0.19, respectively. The Laser Ablation Inductively Coupled Plasma Mass Spectrometry test results show that apatite in lithium-rich pegmatite has a higher U content, lower Th/U (approximately 0.05), and lower Sr content than apatite in beryllium-bearing granitic pegmatite. The chondrite-normalized REEs distribution curves of apatite from beryllium-bearing granitic pegmatite present as right oblique lines with a positive europium anomaly, and the curves of apatite from lithium-rich pegmatite present as “M”-type with the four-grouping effect. The crystallization age of apatite in beryllium-bearing and lithium-rich granitic pegmatite was (216.29±3.14) Ma, which is the emplacement and condensation age of pegmatite. The Chakabeishan granitic pegmatite-type lithium beryllium ore belt was formed by highly evolved granitic magma originating from the partial melting of metamorphic sedimentary rocks under the background of post-collision to intra-plate extension in the Late Indosinian, and had characteristics of Li-Cs-Ta type pegmatites. Magma from the same source area formed beryllium-bearing granitic pegmatite in the Chakabeishan ore block and lithium-rich granitic pegmatite in the Edanggang ore block at different evolution stages. The water content of the magma increased and the temperature and oxygen fugacity decreased during the evolution of granitic pegmatite magma from the beryllium-bearing stage to the lithium-rich stage. |
| keywords:northern margin of Qaidam Basin Chakabeishan granitic pegmatite lithium beryllium ore apatite U-Pb age in situ geochemistry magmatic process |
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