Tracing fluid exsolution and hydrothermal alteration signature of the Mufushan Nb-Ta-(Li-Be-Cs) deposit, South China: An apatite perspective

Nuerkanati Madayipu, Huan Li, S. M. Elatikpo, M. Ghaderi, Rub'son N'nahano-Ruhindwa Heritier, Xiao-Jun Hu, Han Zheng, Qian-hong Wu
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Abstract

The appearance of hydrous magmas and the following separation of volatile-rich fluids through hydrothermal alteration are intricately linked to forming granitic rare-metal deposits, the principal source of worldwide Li, Be, Nb, Ta, and Cs production. The lack of mineralogical information from the developing magmatic-hydrothermal system has, however, prevented a thorough comprehension of these processes. Apatite occurs as an accessory mineral in the metasedimentary (schist)–magmatic (muscovite monzogranite)–pegmatite (ore-free/ore-bearing pegmatite) rocks in Mufushan Complex (MFSC) rare-metal ore field of the northeastern Hunan, South China, potentially providing insights into Nb-Ta-(Li-Be-Cs) mineralization. To demonstrate that apatite can potentially record the magmatic-hydrothermal evolution of metasedimentary-magmatic-pegmatite systems, this study presents a combined textural and geochemical study of apatite from the MFSC granitic pegmatite-type rare-metal mineralization. The MFSC apatite textures and compositions have changed (i.e., post-crystallization alteration) since it first crystallized. Apatite from the schist shows homogeneous rim or homogeneous textures with crack or inclusion (S-ap1) and patch core (S-ap2), indicative of a magmatic-hydrothermal origin. Apatite from the muscovite monzogranite (G-ap) displays altered and distinctive core-rim textures, with visible voids, mineral inclusions, and cracks, suggestive of overprinting of early-magmatism texture by hydrothermal fluid. However, compared to the S-ap1, S-ap2, and G-ap, the pegmatite apatite shows more complicated textures, i.e., P-ap1: homogeneous bright and dark areas, and P-ap2: replacement texture involving alteration rim, growth zonation, patchy, and complex zoning patterns. P-ap1 underwent early magmatism and weaker post-hydrothermal overprinting, P-ap2 reflects a magmatic-hydrothermal product. S-ap1 and S-ap2 yield lower intercept ages of 130.6 ± 1.8 Ma and 128.4 ± 3.8 Ma, respectively, which are consistent with the transitional age of magmatic-hydrothermal metallogenic environment in northeastern Hunan. The G-ap and P-ap1 yield older ages of 136.3 ± 2.8 Ma and 141.3 ± 6.7 Ma, respectively, which are corresponding to the age of magmatic early-stage (Nb-Ta)-mineralization within their uncertainty in the northeastern Hunan. The Sr isotopic composition of apatite provide evidence for the provenance of the MFSC batholith in the rare-metal metallogenesis of the Lengjiaxi Group. Therefore, we hypothesize that apatite in granitic rare-metal deposits within metasedimentary-magmatic-pegmatite systems might be employed as a viable proxy to explore fluid exsolution and hydrothermal alteration signature concerning its textures and geochemical fingerprints. Supplementary material: https://doi.org/10.6084/m9.figshare.c.7038699
追溯华南幕阜山铌钽(锂铍钴)矿床的流体溶出和热液蚀变特征:磷灰石视角
含水岩浆的出现以及随后通过热液蚀变分离出富含挥发性的流体与花岗岩稀有金属矿床的形成密切相关,花岗岩稀有金属矿床是全球锂、铍、铌、钽和铯生产的主要来源。然而,由于缺乏来自正在形成的岩浆-热液系统的矿物学信息,人们无法彻底了解这些过程。磷灰石作为一种附属矿物出现在中国湖南东北部幕阜山稀有金属矿区的变质岩(片岩)-岩浆岩(黝帘石单斜岩)-伟晶岩(无矿/含矿伟晶岩)岩石中,有可能为铌-钽-(锂-铍-铯)成矿提供启示。为了证明磷灰石有可能记录辉长岩-岩浆岩-伟晶岩系统的岩浆-热液演化过程,本研究对来自中福州花岗岩伟晶岩型稀有金属矿化的磷灰石进行了纹理和地球化学综合研究。自首次结晶以来,MFSC磷灰石的质地和成分发生了变化(即结晶后蚀变)。片岩中的磷灰石显示出均匀的边缘或均匀的纹理,带有裂缝或包体(S-ap1)和斑块核心(S-ap2),表明其来源于岩浆热液。来自蕈云母独居岩(G-ap)的磷灰石显示出改变了的独特岩心-岩缘纹理,具有可见的空隙、矿物包裹体和裂纹,表明热液对早期岩浆纹理的覆盖。然而,与S-ap1、S-ap2和G-ap相比,伟晶岩磷灰石的纹理更为复杂,即P-ap1:均质的亮暗区域,P-ap2:涉及蚀变缘、生长带状、斑块状和复杂分带模式的置换纹理。P-ap1经历了早期岩浆作用和较弱的热液后叠加作用,P-ap2则反映了岩浆-热液作用的产物。S-ap1和S-ap2的截距年龄较低,分别为130.6±1.8Ma和128.4±3.8Ma,与湖南东北部岩浆-热液成矿环境的过渡年龄一致。G-ap和P-ap1的年龄分别为136.3±2.8 Ma和141.3±6.7 Ma,在其不确定范围内与湘东北岩浆早期(Nb-Ta)成矿作用年龄相一致。磷灰石的Sr同位素组成为冷家溪组稀有金属成矿过程中中频闪长岩浴成岩的来源提供了证据。因此,我们推测花岗岩稀有金属矿床中的磷灰石可作为一种可行的替代物,用于探索流体外溶蚀和热液蚀变特征的质地和地球化学指纹。 补充材料:https://doi.org/10.6084/m9.figshare.c.7038699
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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