东华理工大学核资源与环境国家重点实验室邹少浩团队以华南江西省松树岗矿床为例，以该矿床的石英结构和化学特征定性了Nb–Ta的成矿过程。该项研究成果发表在2024年6月22日出版的《地球化学学报》上。

团队研究人员利用CL和LA-ICP-MS的研究方法，对松树岗黄玉—钠长石花岗岩、石英—云母伟晶岩、石英—长石伟晶岩和石英—萤石伟晶岩中的石英多样性进行了研究，以限制Nb和Ta的富集机制，并寻找稀有金属矿床的石英地球化学指标。来自黄玉—钠长石花岗岩，石英—云母伟晶岩，石英—长石伟晶岩和石英—萤石伟晶岩的石英，在阴极发光显微镜下显示出许多深色CL条纹，斑块和一系列愈合的裂缝——像被照亮的复杂画布。这些结构表明，岩石在地壳深部压力作用下破裂，并经历了后期热液交代和石英充填作用。

石英—萤石伟晶岩中的石英存在有限的斑块或裂缝，但具有明显的生长带，说明这一阶段石英形成过程中的熔体流体成分变化较大，受机械破碎的影响较小。石英的LA-ICP-MS分析表明，从黄玉—钠长石花岗岩、石英—云母伟晶岩、石英—长石伟晶岩到石英—萤石伟晶岩，石英中的Al和Li之间存在正相关关系，表明Al主要通过与Li的电荷补偿置换机制进入石英晶格。

然而，研究数据偏离了石英中理论的Li：Al质量比约为1:3.89，表明在富水的岩浆环境中H⁺和Li之间可能存在竞争。黄玉—钠长花岗岩的石英富含K、Na元素，石英—萤石伟晶岩的石英富集萤石，石英中Ca含量低，进一步说明这些岩石受热液交代作用的影响。从黄玉—钠长石花岗岩到石英—萤石伟晶岩，石英中Al、Li、Ge含量和Al/Ti、Ge/Ti、Sb/Ti比值逐渐升高，而Ti含量逐渐降低，反映了岩浆的高度演化，可富集稀有金属元素。根据黄玉—钠长石花岗岩、石英—云母伟晶岩、石英—长石伟晶岩和石英—氟石伟晶岩的石英CL结构和微量元素特征，结合岩石的钠长石化和钾长石化，研究人员认为松树岗Nb–Ta矿化可能受岩浆结晶分异和流体交代作用的共同作用。研究将松树岗岩体中的石英与世界上已知的花岗岩型和伟晶岩型稀有金属矿床中的石英进行比较，发现松树岗伟晶岩与LCT型伟晶岩具有相似之处。结合前人的研究，Ge/Ti>0.1和Ti<石英中10ppm、Al、Li、Ge、Sb、K、Na含量及Al/Ti、Sb/Ti比值有可能成为其他地区花岗岩类花岗质Nb-Ta矿床的有力勘探标志。

附：英文原文

Title: Unveiling Nb–Ta mineralization processes: Insight from quartz textural and chemical characteristics in the Songshugang deposit, Jiangxi Province, South China

Author: Zhang, Hengsong, Zou, Shaohao, Chen, Xilian, Xu, Deru, Wang, Zhilin, Zhang, Yongwen, Wang, Hua

Issue&Volume: 2024-06-22

Abstract: The Songshugang deposit is a large Ta–Nb deposit in South China, with Ta–Nb mineralization associated genetically with the granite and pegmatite. A diversity of quartz from topaz–albite granite, quartz–mica pegmatite, quartz–feldspar pegmatite, and quartz–fluorite pegmatite at Songshugang was studied by CL and LA–ICP–MS in order to constrain enrichment mechanisms of Nb and Ta and to find geochemical indicators of quartz for rare metal deposits. Cathodoluminescence image illuminates a canvas of complexity, the quartz from topaz–albite granite, quartz–mica pegmatite, quartz–feldspar pegmatite, and quartz–fluorite pegmatite, exhibits numerous dark CL streaks, patches, and a series of healed fractures. These textures suggest that the rocks were fractured because of deep crustal pressure, and underwent later hydrothermal metasomatism and quartz filling. The quartz from quartz–fluorite pegmatite present limited patches or fractures but distinct growth bands, indicating that the melt fluid composition during the formation of quartz at this stage varies greatly and is less affected by mechanical fragmentation. The LA–ICP–MS analysis of quartz shows that there is a positive correlation between Al and Li in the quartz from topaz–albite granite, quartz–mica pegmatite, quartz–feldspar pegmatite, to quartz–fluorite pegmatite, indicating that Al mainly enters the quartz lattice through charge compensation substitution mechanism with Li. However, our data deviate from the theoretical Li:Al mass ratio of~1:3.89 in quartz, indicating that there may be competition between H+ and Li in a water-rich magmatic environment. The quartz from topaz–albite granite is enriched in K and Na elements, and the quartz from quartz–fluorite pegmatite is enriched in fluorite with a low Ca content in quartz, further elucidating that these rocks were subjected to hydrothermal metasomatism. From topaz–albitite granite to quartz–fluorite pegmatite, Al, Li and Ge content and Al/Ti, Ge/Ti, Sb/Ti ratios in quartz gradually increased, but Ti content gradually decreased, reflecting the high evolution of magma, which can enrich rare metal elements. Based on the characteristics of quartz CL textures and trace elements in topaz–albite granite, quartz–mica pegmatite, quartz–feldspar pegmatite, and quartz–fluorite pegmatite, combined with the albitization and K-feldspathization of rocks, it is suggested that the Nb–Ta mineralization in Songshugang may be influenced by the combined action of magmatic crystallization differentiation and fluid metasomatism. By comparing the quartz in the Songshugang pluton with the quartz in the granite type and pegmatite type rare metal deposits recognized in the world, the Songshugang pegmatite share similarities with the LCT-type pegmatite. Combined with previous studies, the Ge/Ti>0.1 and Ti<10 ppm, as well as Al, Li, Ge, Sb, K, Na contents and Al/Ti, Sb/Ti ratios in quartz have the potential to be a powerful exploration marker for identifying granite-like pegmatitic Nb–Ta deposits in other places.

DOI: 10.1007/s11631-024-00705-2

Source: https://link.springer.com/article/10.1007/s11631-024-00705-2