Hi Taofik. Interesting, yet I think you may have some difficultly with this. The fractionation of sulphur isotopes during degassing are typically quite small (possibly within analytical uncertainty) and the degree of biologically-mediated sulphate reduction is extremely variable. I think when considering these options, you should dicuss the implications of both processes and note which is more likely given the geological setting you are working in. Other elements or rations (perhaps S/Se ratios) might help you make an informed decision
