Experimental Studies of the Solubility of Cassiterite and the Extraction of Tin from Granitic Melts

Experiments indicate that the solubility of cassiterite can be enhanced by increasing either acidity oralkalinity in hydrothermal solutions as a consequence of the duality of tin. The minimum solubility ofcassiterite is found in neutral solutions. F--and CL--coordination compounds of Sn can alternate withhydroxy coordination compounds with changing pH in the solutions. In this case. F;and Cl;andOH;can be substituted with each other. The dissolution reaction of cassiterite is of reducing nature. Hightemperature and acidic reducing environment are favorable for the dissolution of cassiterite and the trans-port of Sn;compounds in fluids or solutions. High--temperature fluoride and chloride fluids can alldissolve, extract and enrich Sn to form F;and /or Cl-coordination compounds, However, F plays amore important role than Cl. F-coordination compounds are more stable and efficient thanCl-coordination compounds during the transport and eririchment of Sn in melts or solutions. The solubili-ty of cassiterite and the amount of Sn extracted from granitic melt depend not only on T, P. pH and Eh inthe fluids or solutions, but also on the amounts of dissociated F;and Cl;in the fluids.