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In situ Raman spectroscopy identification of the S (sub 3) (super -) ion in S-rich hydrothermal fluids from synthetic fluid inclusions

Nicolas Jacquemet, Damien Guillaume, Antoine Zwick and Gleb S. Pokrovski
In situ Raman spectroscopy identification of the S (sub 3) (super -) ion in S-rich hydrothermal fluids from synthetic fluid inclusions
American Mineralogist (May 2014) 99 (5-6): 1109-1118

Abstract

The chemical forms of sulfur in geological fluids control the behavior of this element and associated base and precious metals in magmatic, hydrothermal, and metamorphic environments. However, these forms are insufficiently known at elevated temperature (T) and pressure (P). In this study, sulfur speciation in model aqueous solutions of thiosulfate and sulfur ( approximately 3 wt% of total S) was examined by in situ Raman spectroscopy on synthetic fluid inclusions at T-P-pH-redox conditions typical of porphyry Cu-Au-Mo deposits. Fluid inclusions were entrapped at 2 kbar and 600 or 700 degrees C in quartz that served as a container for the high T-P fluid. Then, the inclusion-bearing quartz samples were re-heated and examined by Raman spectroscopy as a function of T and P (up to 500 degrees C and approximately 1 kbar). At T < 200 degrees C, all fluid inclusions show sulfate (SO (sub 4) (super 2-) + or - HSO (sub 4) (super -) ) and sulfide (H (sub 2) S + or - HS (super -) ) in the aqueous liquid phase and elemental sulfur (S (sub 8) ) in the solid/molten phase; these results agree both with thermodynamic predictions of sulfur speciation and the common observation of these three S forms in natural fluid inclusions. At T > 200-300 degrees C, in addition to these S species, the S (sub 3) (super -) ion was found to appear and grow with increasing temperature to at least 500 degrees C. The formation of S (sub 3) (super -) is rapid and fully reversible; its Raman signal disappears on cooling below 200 degrees C, and re-appears on heating. These new data confirm the recent findings of S (sub 3) (super -) in similar aqueous solutions at P of 5-50 kbar and T > 250 degrees C; they suggest that S (sub 3) (super -) may account for some part of dissolved sulfur and serve as a ligand for chalcophile metals in fluids from subduction zones and related Cu-Au-Mo deposits. This work demonstrates that in situ approaches are required for determining the true sulfur speciation in crustal fluids; it should encourage future spectroscopic investigations of natural fluid and melt inclusions at high temperatures and pressures close to their formation conditions.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 99
Serial Issue: 5-6
Title: In situ Raman spectroscopy identification of the S (sub 3) (super -) ion in S-rich hydrothermal fluids from synthetic fluid inclusions
Affiliation: Universite de Toulouse, Geosciences Environnement, Toulouse, France
Pages: 1109-1118
Published: 201405
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 83
Accession Number: 2014-048831
Categories: General geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201427
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