花岗岩类矿床成矿流体形成过程的原位观测实验

花岗岩浆液态不混溶作用和饱和H₂O花岗岩浆的热液出溶作用是花岗岩类矿床成矿流体形成的重要机制。利用最新式热液金刚石压腔，开展了成矿流体形成机制的原位观测实验。在岩浆热液出溶过程的实验中，初始样品为各类硅酸盐和纯H₂O或LiCl水溶液，在H₂O饱和状态中，硅酸盐熔体珠不断分异出富H₂O的流体。花岗岩浆液态不混溶实验的初始样品为NaAlSi₃O₈-LiAlSiO₄-SiO₂-LiCl-H₂O。在硅酸盐完全重熔后的降温过程中，硅酸盐熔体珠分离出富H₂O熔体相和贫H₂O熔体相，压力的突然降低促进了相分离的发生。研究表明：岩浆热液的出溶作用发生在H₂O饱和的条件下，是岩浆的“第二次”沸腾作用，对花岗岩型稀有金属矿床的形成具有重要意义；花岗岩浆液态不混溶产生的富H₂O熔体易于结晶出粗大晶体，暗示岩浆液态不混溶作用可能是一些花岗伟晶岩形成的主要机制。两类成矿流体形成机制实验条件的差异表明，Li是花岗岩浆发生不混溶作用的重要因素。在今后的研究中，应把热液金刚石压腔的原位观测与微束分析技术结合，在高温高压状态下分析成矿元素的迁移和富集规律。

In Situ Observation of Separation Mechanism of Ore-Forming Fluid from Granitic Magma in Granite-Related Deposit

The liquid immiscibility and hydrothermal fluid exsolution from magma are the important separation mechanisms of ore-forming fluid from granite magma. At present, the understanding of the two mechanisms is mainly from researches of melt and fluid inclusions, or none-in-situ experiments. The newest hydrothermal diamond anvil-cell (HDAC) is used to observe the two processes in situ. In exsolution experiments with the initial sample of silicate and pure H₂O or LiCl dissolved aqueous fluid, the H₂O-rich fluid separated from H₂O-saturated silicate melt when H₂O is saturated in silicate melt. In the experiment of liquid immiscibility with the initial samples of NaAlSi₃O₈-LiAlSiO₄-SiO₂-LiCl-H₂O, the silicate melt balls can be separated into a H₂O-rich melt and H₂O-poor melt during cooling from homogeneous silicate melt. The sharp fall of pressure can induce the liquid immiscibility. These experimental results show that the hydrothermal fluid exsolution occurred in H₂O-saturated silicate melt is the second boiling of magma, and plays a great role in the mineralization of granite type deposit. The H₂O-rich melt separated from granite magma by liquid immiscibility can crystallize big and oriented crystals, suggesting that liquid immiscibility of granite magma is an important formation mechanism for granite pegmatite. The differences between the above two type experiments suggest that the element Lithium is an important factor for liquid immiscibility in granite magma. In the further research, we should combine the HDAC with microbeam analysis in order to analyze the enrichment process of metal element at high temperature and pressure.