SULFUR ISOTOPE FRACTIONATION AT THE MOVIN G OXIDATION FRONT UNDER HYDROTHERMAL CONDITIONS - AN ANALYSIS OF FIELD EVIDENCE

This paper presents a steady-state isothermal dynamic model for the ma ss transfer of sulfur and its isotopes at the oxidation front as it mi grates with the flow of oxygen-containing water through reduced rocks under hydrothermal conditions. The model incorporates H2S generation b y sulfate reduction and by the disproportionation of metastable sulfur compounds. The type of hydrothermal system to which this model is app licable is specified. The isotope characteristics of sulfides and sulf ates at certain stratabound barite-sulfide and sulfide deposits suppor t the concept that they were mineralized as the oxidation front moved through reduced rocks. The interpretation of the isotope data based on the model enabled the temperature at the final stage of sulfide redep osition to be established, the proportion of sulfide produced by dispr oportionation of metastable compounds to be determined, and the isotop e composition of the sulfur source to be estimated Some features of su lfur reactions near the oxidation front and the conditions favorable t o the deposition of gold and base metals within the resultant.