FRACTIONATION OF SULFUR ISOTOPES DURING LABORATORY SYNTHESIS OF PYRITE AT LOW-TEMPERATURES

The reaction products and the accompanying sulfur isotope fractionations during the reaction of H2S with goethite in aqueous media at 22-24°C for periods from 0.5 hr to 65 days were studied. Fine-grained pyrite formed within two days and was isotopically 0.8‰ lighter than the H2S source. After 65 days reaction time the pyrite had nearly the same isotopic value as the H2S. Aqueous precipitation of pyrite from H2S and goethite at room temperature involved three major steps, namely: (1) the rapid oxidation of H2S and reduction of Fe3+ during which elemental S is formed; (2) the formation of acid-volatile sulfides and the disappearance of elemental S; and (3) the formation of pyrite at the expense of acid-volatile sulfides. © 1979.