引用本文: 郑范博, 王国光, 倪培. 2021. 花岗伟晶岩型稀有金属矿床流体成矿机制研究进展. 地质力学学报, 27(4): 596-613. doi: 10.12090/j.issn.1006-6616.2021.27.04.050 Citation: ZHENG Fanbo, WANG Guoguang, NI Pei. 2021. Research progress on the fluid metallogenic mechanism of granitic pegmatite-type rare metal deposits. Journal of Geomechanics , 27(4): 596-613. doi: 10.12090/j.issn.1006-6616.2021.27.04.050

随着战略性新兴产业的快速发展，稀有金属等关键金属资源的地位日益不可或缺。花岗伟晶岩是最重要的稀有金属矿床成因类型，该类型矿床的成矿流体特征和成因机制是矿床学的热门研究话题。文章主要对花岗伟晶岩型矿床的成矿流体特征和成矿机制进行了探讨。花岗伟晶岩型稀有金属矿床成矿流体普遍富集挥发分（B、P、F和H ₂ O）和成矿元素，具有低黏度、低成核率、强元素溶解能力和强迁移性。花岗伟晶岩型稀有金属矿床成矿流体形成温压条件存在争议，部分研究者认为形成于高温高压条件，也有研究者认为可能形成于过冷却条件下，温度可能低至350℃。花岗质岩浆高度结晶分异演化和富成矿元素地壳物质小比例深熔是形成成矿花岗伟晶岩的两种主要机制。流体不混溶和组成带纯化是岩浆热液演化过程中稀有金属进一步富集的重要手段。中国规模最大的甲基卡花岗伟晶岩型锂矿是研究该类矿床的理想实验室。

花岗伟晶岩型矿床 Abstract:

Strategic rare metals have irreplaceable important use to emerging industry development. Granitic pegmatite is the main source of rare metals, and their fluid characteristics and metallogenic mechanism are hot topics. This paper mainly focuses on fluid properties and metallogenic mechanism of granitic pegmatite-type rare metal deposits. Ore-forming fluids of the granitic pegmatite-type rare metal deposits are generally enriched in volatile (B, P, F and H ₂ O) and ore-forming elements, with low viscosity, low nucleation rate, but strong element solubility and mobility. The ore-forming fluids of the granitic pegmatite-type rare metal deposit were argued to be captured under the condition of high temperature and high pressure, or the temperature of as low as 350℃ under the condition of supercooling. The high crystallization differentiation evolution of granitic magma and the small proportion of crustal material rich in ore-forming elements are the two main mechanisms for the formation of ore-forming granitic pegmatite. Fluid immiscibility and constitutional zone refining are important means for further enrichment of rare metals in the process of magmatic hydrothermal evolution. The largest Jiajika granitic pegmatite-type lithium deposit in China is an ideal laboratory to study this kind of deposit.

Key words: granitic pegmatite-type deposit rare element ore-forming fluids metallogenic mechanism

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Representative photo of rare metal pegmatites showing graphic texture(The sample is a hand specimen from the Dahongliutan lithium deposit, Xinjiang)

Figure 2.

A complete section of a pegmatite dike from near Palomar Mountain, San Diego County, California, USA(29 cm-thickness; London, 2018 )

Figure 3.

Typical inclusions in the spodumene from the granitic pegmatite-type lithium-bearing ore. (a) Crystal-rich inclusion hosted in the spodumene from Jiajika; (b) CO ₂ -rich Fluid Inclusion Assemblage hosted in the spodumene from Jiajika; (c) Crystal-rich Fluid Inclusion Assemblage hosted in the spodumene from Jiajika; (d) Crystal-rich Fluid Inclusion Assemblage hosted in the spodumene from Dahongliutan

Figure 4.

Temperature versus H ₂ O concentration plot of the pseudo-binary silicate melt-H ₂ O system ( Thomas and Davidson, 2016 ).

Figure 5.

Temperature and pressure conditions of main pegmatite deposits in the world

Figure 6.

Schematic diagram of the relationship between granite and granitic pegmatite ( London, 2008 )

Figure 7.

Schematic diagram of the constitutional zone refining of granitic pegmatite magma( London, 2014 , 2018 ). (a) During the constitutional zone refining, the compatible components dissolve from the bulk melt and attach to the surface of the diagenetic mineral through the boundary layer. (b) Because the volatiles decrease the solid temperature and enhance the miscibility of the components, the excluded rare metal components are enriched in the boundary layer liquid. (c) Once the composition of the melt is exhausted, the boundary layer liquid will crystallize, resulting in a mutation in the composition of the growing minerals (mica, tourmaline)

Figure 8.

Distribution of major lithium deposits in the world

Figure 9.

Geological sketch of the Jiajika rare metal ore field( Huang et al., 2020 )