Modelling the thermodynamics Sulfur in Silicate Melts

The sulfur partitioning between silicate melt, sulfide and fluid phase has been studied in numerous experimental studies motivated by better capturing ore deposit processes, planetary sciences, volacanology and high temperature industrial slag practices. Recently, empirical models aiming at predicting the sulfur content at sulphide saturation has been developed for geochemical purposes, while models defining fluid-melt partitioning have long been developed for industrial and volcanological applications. Here, fluid-melt-sulfide partitioning data have been parameterized into a new thermodynamic framework. The experimental database we used cover the temperature / pressure intervals 750-1750°C / 1 atm-8 GPa. The melt composition ranges from felsic to ultramafic and oxygen fugacity is restricted to conditions more reduced than FMQ+1, i.e. low fractions of sulfate ions in the silicate melts. This new model allows melt sulfur content and sulfur fugacity at sulphide saturation to be calculated. Calculation for sulphide under-saturated conditions can also be performed. The chemical potential of sulfur can be predicted for a large range of melt compositions and conditions relevant to magmatic processes on Earth and elsewhere. Some applications to degassing at sulphide saturated conditions will be shown.