100MPa、800℃下Mo和W在流体/花岗质熔体相间分配的实验研究

An experimental study on the partitioning of molybdenum and tungsten between granitic melt and coexisting aqueous fluid at 100 MPa and 800 ℃

利用"RQV-快速内冷淬火"(外加热冷封式)高温高压实验装置,在100 MPa、800℃条件下,以东秦岭地区出露的高钾钙碱性岩浆岩(合峪花岗岩)为实验初始物,实验研究了Mo和W在花岗岩-H2O、花岗岩-NaCl(KCl)-H2O及花岗岩-NaF-H2O体系流体/熔体相间的分配行为。实验结果表明,Mo比W更倾向于分配进入流体相(DM流o体/熔体>>DW流体/熔体),相对于纯水体系而言,流体介质中Cl和F的存在均有利于Mo和W向流体相迁移富集;随体系内Cl含量的不断增高,Mo和W的分配系数呈线性增大趋势;而在天然花岗岩可能含有的F含量范围之内,F含量的增高将阻碍Mo、W向流体相迁移;流体介质中Na/K(摩尔比)的变化对Mo和W的分配系数没有明显影响,表明体系碱质(Na或K)类型不是Mo和W在流体/熔体相间分配的主要影响因素。

An experimental study has been conducted to investigate the effect of fluid composition on the partitioning behavior of Mo and W between granitic melts and coexisting aqueous fluid at 100 MPa and 800 ℃. High-K, calc-alkaline granites of the East Qinling molybdenum belt were used as starting materials, and the system of granite-H2O, granite-NaCl（KCl）-H2O0 and granite-NaF-H2O were investigated. All runs were conducted in cold-seal Rapid-Quench pressure Vessels （RQV, a kind of ＂externally heated cold-seal pressure vessels＂） using water as a pressure medium. The results showed that molybdenum was more likely to distribute into the aqueous phase than tungsten （DMo^fluid/melt〉〉 DW^fluid/melt）. In contrast to pure water, the existence of Cl and F in the aqueous promotes the distribution of Mo and W into the fluid phase; The partition coefficients of Mo and W increases linearly with increasing Cl concentration, while the increase of F concentration, within the scope of natural granites, hinders Mo and W to move to the fluid phase. The variation of Na/K value （mole ratio） in the aqueous phase had little effect on the partition coefficients of Mo and W, which indicates that the alkaline type of the system was not the main factor that influences the partitioning behavior of Mo and W between granitic melt and coexisting aqueous fluid.