Experimental studies of the solubility of cassiterite and the extraction of tin from granitic melts

Abstract

Experiments indicate that the solubility of cassiterite can be enhanced by increasing either acidity or alkalinity in hydrothermal solutions as a consequence of the duality of tin. The minimum solubility of cassiterite is found in neutral solutions. F- and CL-coordination compounds of Sn can alternate with hydroxy coordination compounds with changing pH in the solutions. In this case, F^- and Cl^- and OH^- can be substituted with each other. The dissolution reaction of cassiterite is of reducing nature. High temperature and acidic reducing environment are favorable for the dissolution of cassiterite and the transport of Sn²⁺ compounds in fluids or solutions. High-temperature fluoride and chloride fluids can all dissolve, extract and enrich Sn to form F^- and /or Cl-coordination compounds, However, F plays a more important role than G. F-coordination compounds are more stable and efficient than Cl-coordination compounds during the transport and enrichment of Sn in melts or solutions. The solubility of cassiterite and the amount of Sn extracted from granitic melt depend not only on T, P, pH and Eh in the fluids or solutions, but also on the amounts of dissociated F^- and Cl^- in the fluids.