An experimental study of tin partition between melt and aqueous fluid in F/Cl-coexisting magma

In order to investigate the formation mechanism of tin ores associated with F-bearing granite, an experimental study of tin partition between F-bearing granitic melt and coexisting HCl-bearing aqueous fluid was conducted at 850°C and 100MPa with fo2 approaching NNO. Geochemical behavior of tin was traced by changes in starting solid materials with different alumina saturation index ASI, in F content and in starting fluids of various HCl concentrations. The results show that D Sn increases with ASI of melt and peraluminous melt is favorable for tin partition into aqueous fluid in the F/Cl-coexisting system. Aqueous fluid of higher HCl concentrations is advantageous for enrichment of tin. Furthermore, chlorine contents in glass run products correlate positively with F and Cl contents in the magma. In the F/Cl-coexisting system, granitic melts with high F contents (> ～1 wt%) could extract and enrich tin in the melt which can serve as a reservoir for the formation of tin ores. However, the partition coefficient of tin would increase significantly when F contents in the melt were below 1 wt%. Therefore, the decrease of F contents is favorable to the partition of tin into aqueous fluid with high HCl contents, thus promoting deposition of hydrothermal tin ores. Supported jointly by National Basic Research Program of China (Grant Nos. 2007CB411404 and 2007CB411408), National Natural Science Foundation of China (Grant Nos. 40373020 and 40503007), and “Western Light” Project of the Chinese Academy of Sciences