花岗伟晶岩中锂辉石和透锂长石产出特征及其形成条件

锂辉石(Spd)和透锂长石(Ptl)是富锂花岗伟晶岩中重要的锂铝硅酸盐矿物，查明锂辉石和透锂长石的形成条件和演化过程对进一步揭示花岗伟晶岩型锂矿床形成机制具有重要意义。锂辉石和透锂辉石通常产于伟晶岩的中间带或者核部，但两者结晶温度压力条件存在差异：透锂长石形成于高温低压条件，锂辉石在相对低温高压条件下稳定，两者随温度压力条件改变可发生相互转换。当温度降低时，透锂长石可以转换为锂辉石和石英(Qtz)集合体(SQI)，而当压力升高时，锂辉石和石英集合体又可以转换为透锂长石。精确厘定锂辉石和透锂长石的相互转换温度压力条件，可以揭示富锂伟晶岩形成演化的P-T轨迹。本文基于近年来关于锂辉石、透锂长石等相关研究成果，总结了其产出特征和形成条件，认为：(1)在富锂伟晶岩体系内，锂铝硅酸盐矿物的结晶主要受温压条件控制，与熔体成分关系较小，锂辉石和透锂长石稳定温压范围为400~680℃、160~400MPa；(2)锂辉石在岩浆出溶流体晚期演化而成的偏碱性流体叠加作用下，先后发生钠化/钾化、白云母化和锂绿泥石化等蚀变作用；(3)温度越高、铝饱和指数(ASI)越小，H₂O的含量越多，锂在熔体中的溶解度更大；(4)锂辉石和透锂长石的结晶实验，指示了伟晶岩的快速结晶过程，其结构的形成受过冷却度的影响，高温高压实验表明5% H₂O含量(不饱和条件)和50~130℃的过冷却度范围是伟晶结构形成的最佳条件；(5)岩浆中CO₂、Li元素含量对富锂伟晶岩结晶体系的酸碱度调节、降低岩浆液相线、降低熔体粘度和增加水合簇分子等方面起到了关键作用。未来，原位高温高压实验技术(如热液金刚石压腔)等分析技术的应用，将对研究花岗伟晶岩型稀有金属矿床成矿机制提供更为直接可靠的实验依据。

The occurrence characteristics and formation conditions of spodumene and petalite in granitic pegmatite

Spodumene (Spd) and petalite (Ptl) are important lithium-aluminosilicate minerals in Li-rich granitic pegmatite. It is of great significance to find out the formation conditions and evolution process of spodumene and petalite for further indicating the formation mechanism of granite-pegmatite type lithium deposit. Spodumene and petalite are usually occurred in the intermediate zone or core of pegmatites, but formed in different temperature and pressure conditions. The former one is formed at high temperature and low pressure, whereas the latter one is stable at relatively low temperature and high pressure, and the two can be converted with the change of temperature and pressure conditions. When the temperature decreases, the petalite can be converted into spodumene and quartz (Qtz) intergrowths (SQI), or when the pressure increases, the spodumene and quartz intergrowths (SQI) can be converted into petalite. The P-T trajectory of the formation and evolution of Li-rich pegmatite can be revealed by accurately determining the temperature and pressure conditions of the mutual conversion between spodumene and petalite. Based on recent research results on spodumene and petalite, this paper summarizes the production characteristics and formation conditions, and concludes that: (1) In the Li-rich pegmatite system, the crystallization of lithium-aluminosilicate minerals is mainly controlled by temperature and pressure conditions, and less relevant with the melt composition. The stable temperature and pressure range of spodumene and petalite is 400~680℃ and 160~400MPa; (2) Under the superposition of exsolution alkaline fluid, the hydrothermal alteration process of the late spodumene occurred albitization/potash feldspathization, muscovitization and lithium chloritization successively; (3) The higher the temperature, the less the aluminum saturation index (ASI), and the more H2O content may increase the solubility of lithium in the melt; (4) The crystallization experiments of spodumene and petalite indicate the rapid crystallization process of pegmatite, and the formation of its texture is influenced by the degree of cooling. High temperature and pressure experiments show that 5% H2O content (unsaturated condition) and 50~130℃ undercooling degree range are the best conditions developing the pegmatitic texture; (5) The content of CO2 and Li in magma plays a key role in regulating pH, reducing liquidus and melt viscosity, and increasing hydration cluster molecules in the crystallization system of Li-rich pegmatite. In the future, the application of in-situ high temperature and high pressure experimental techniques (such as hydrothermal diamond anvil cell) will provide more direct and reliable experimental basis for researching the metallogenic mechanism of granitic pegmatite rare metal deposits.