First of all you should calculate the δ34SH2S values. If your calculated δ34SH2S isotopic values of ore fluids for sulfides continue to display a considerable range this heterogeneity of the δ34SH2S values can be explained by isotopic disequilibrium due to varying fO2-pH conditions (Williams-Jones et al., 1992).  Alternatively it can be attributed to mixing of two different sourced-ore fluids. The first source could be  magmatic sulfur  and the second was seawater (as δ34SH2S ≈ 20.0 per mil, Claypool et al., 1980; Rozanski 1985; Compton et al. 1999; Mandernack et al., 2003).

Stellios Tombros

 Dear Tombros

Many thanks for your answer.

The temperature of fluids is

Here are two relevant publications to answer your questions, let me know if you cannot download them and I can attach a pdf-version:

Machel HG, Krouse HR, Sassen R (1995) Products and distinguishing criteria of bacterial and thermochemical sulfate reduction. Appl Geochemistry 10:373–389. doi: 10.1016/0883-2927(95)00008-8

Moreira NF, Walter LM, Vasconcelos C, et al (2004) Role of sulfide oxidation in dolomitization: Sediment and pore-water geochemistry of a modern hypersaline lagoon system. Geology 32:701–704. doi: 10.1130/G20353.1

Thanks Nicole for your hepl.

Cheers

Nejib

As noted above, you do not need two sulphur sources to get those contrasting values in a single ore body - in fact they would be common, and one would not expect the del values of the sulphides to be the same as the del values of the sulphates. A simple reduction process involving sea water sulphate (there are a few such different mechanisms, organic and inorganic ) would give that. As implied in one answer what you need to calculate is the del value of the fluid from which they precipitated, and this could well be similar to the del value of the barite.