First evidence of the trisulfur radical ion S3- and other sulfur polymers in natural fluid inclusions
Résumé
Sulfur plays a key role in numerous processes occurring in the Earth's crust. However, its speciation in deep and hot geological fluids remains poorly constrained. Here, we used quantitative in-situ Raman spectroscopy on natural fluid inclusions from deep sedimentary environments where thermochemical sulfate reduction (TSR) occurred to determine the sulfur speciation at temperatures representative of their entrapment conditions (100–300 °C). Results unambiguously demonstrate the presence of the trisulfur ion S3− and other polymeric S species (Sn2− ± Sn0) at temperature (T) > 100 °C, whereas only sulfide and sulfate were detected at 25 °C. From 200 to 300 °C, sulfate and sulfide, the two dominant S species, contribute to 41 ± 9% and 59 ± 9% of the mean total dissolved S concentration ([Stot] = 0.25 mol/kgH2O = 0.8 wt%), respectively. The S3− concentration accounts for 0.2 to 3% of Stot in this T range, with a maximum recorded concentration of 2.9 × 10− 2 mol/kgH2O (2780 ppm) at 300 °C. This observation implies that the TSR process occurs under physico-chemical conditions that enhanced the stability of S3− and other polymeric S species. This conclusion has important consequences for the genesis of base metal sulfide deposits and sour gas fields where reduced sulfur originates from TSR.
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Barré et al. First evidence of S3 Chem Geol 2017_HAL.pdf (1.29 Mo)
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