| 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 |
| 投稿时间：2025-04-18 修订日期：2025-05-26 点此下载全文 |
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| 基金项目:科技部重点研发计划项目（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”（202219）、东华理工大学博士启动基金（DHBK2019307）、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（2022NRE-LH-17） |
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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。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。LA-ICP-MS测试结果显示，与含铍花岗伟晶岩中磷灰石相比，富锂者的磷灰石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为带正铕异常的右倾斜线，富锂者的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219～218Ma，代表了伟晶岩脉的侵位冷凝时间。该锂铍矿带是印支晚期的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来自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，岩浆的水含量有所增加，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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| The Ages, in Situ Geochemical Characteristics and its Geological Significances of Apatite in Be-bearing and Li-rich Granitic Pegmatites from Chakabeishan Metallogenic Belt, Northern Qaidam basin |
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| Abstract:Apatite is a effective "black box" of magmatic and hydrothermal process due to its strong stability and diversiform components. Chaka Beishan lithium beryllium metallogenic belt is a granitic pegmatite type rare metal metallogenic belt, which is discovered in recent years. However, there has no granite relevant to the pegmatite been found, in the eastern part of Zongwulong tectonic zone where the Chakabeishan metallogenic belt located in. And the accurately emplacement age, detailed magmatic process and genetic mechanism of granitic pegmatite need to be studied deeply. In this paper, the primary magmatic apatite from beryllium bearing granitic pegmatites in Chaka Beishan ore block and lithium rich granitic pegmatites in Edanggang ore block are selected for in-situ U-Pb dating, major and minor elements analysis. EMPA analysis results show that the apatite in beryllium bearing and lithium rich granitic pegmatites are fluorapatite, with average F content of 3.86% and 3.81%, Cl content of 0.01% or below the detection limit, high FeO and MnO content, and with average Fe2+/Mn2+(pfu) value of 0.10 and 0.19, respectively. LA-ICP-MS test results show that apatite in lithium rich pegmatite has higher U content, lower Th/U (about 0.05) and lower Sr content compared to apatite in beryllium bearing granitic pegmatite. The chondrite normalized REEs distribution curves of apatite from beryllium bearing granitic pegmatite are right oblique lines with positive europium anomaly, and the curves of apatite from lithium rich pegmatite are "M" type with four grouping effect. The crystallization ages of apatite in beryllium bearing and lithium rich granitic pegmatite are 219-218Ma, it’s the emplacement and condensation age of pegmatite. The ChakaBeishan granitic pegmatite type lithium beryllium ore belt is formed by highly evolved granitic magma, which is formed from partial melting of metamorphic sedimentary rocks, under the background of post collision to intra-plate extension in the late Indosinian, they have characteristics of LCT type pegmatite. The magma from the same source area makes the beryllium bearing granitic pegmatite in Chakabeishan ore block and the lithium rich granitic pegmatite in Edanggang ore block in different evolution stages. The water content of magma increased, and the temperature and oxygen fugacity decreased during the evolution of granitic pegmatite magma from beryllium bearing stage to lithium rich stage. |
| keywords:Northern margin of Qaidam Basin Northern mountain of Chaka granitic pegmatite Lithium beryllium ore Apatite U-Pb age In situ geochemistry Magmatic process |
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