In situ determination of sulfur speciation and partitioning in aqueous fluid-silicate melt systems

Abstract

Current knowledge of sulfur behaviour in magmas is based exclusively on ex situ analyses. Here we report the first in situ measurement of sulfur speciation and partitioning between coexisting aqueous fluids and silicate melts. These data were acquired using Raman spectroscopy in a diamond anvil cell at 700°C, 0.3-1.5 GPa, and oxygen fugacity in the vicinity of the sulfide-sulfate transition, conditions relevant to subduction zone magmatism. Results show that sulfate and sulfide are dominant in the studied systems, together with the S •− 3 and S •− 2 radical ions that are absent in quenched fluid and silicate glass products. The derived fluid/melt partition coefficients for sulfide and sulfate are consistent with those from available ex situ data for shallow crust conditions (<10 km), but indicate stronger partitioning of these sulfur species into the silicate melt phase with increasing depth. In contrast, both radical ions partition at least 10 times more than sulfate and sulfide into the fluid phase. Thus, by enhancing the transfer of sulfur and associated chalcophile metals from melt into fluid upon magma degassing, S •− 3 and S •− 2 may be important players in the formation of economic metal resources within the redox window of the sulfate-sulfide transition in subduction zone settings.

Gold speciation in hydrothermal fluids revealed by in situ high energy resolution X-ray absorption spectroscopy

“…1). As a result, to be fully successful in resolving chemical speciation, high-resolution spectroscopy should Hedenquist and Lowenstern 1994;Einaudi et al 2003;Kouzmanov and Pokrovski 2012), which are all favorable for S 3 •− (Colin et al 2020).…”

“…) has not been yet definitely recognized, despite the growing body of studies demonstrating that these sulfur forms are stable across a wide temperature (T) and pressure (P) range of acidic-to-neutral sulfate/sulfide-bearing hydrothermal-magmatic fluids associated with subduction zones (Pokrovski and Dubrovinsky 2011;Jacquemet et al 2014;Barré et al 2017;Schmidt and Seward 2017;Colin et al 2020). The lack of direct data on gold-sulfur radical ion interactions is mostly because the gold solubility pattern is a complex function of various fluid parameters such as acidity, chlorinity, redox, and S speciation.…”

“…DOI: https://doi.org/10.2138/am-2022-8008. http://www.minsocam.org/ temperature (<150°C) hydrothermal systems (e.g.,Bernd et al 1994), and of the S •− radical ion that is stable at closer-to-magmatic temperatures (>450-500°C;Pokrovski et al 2019;Colin et al 2020), as well of mixed-ligand species or alkali-ion pairs (e.g., Na-Cl-HS-S 3 ;Zajacz et al 2010), all of them potentially contributing to the exceptional mobility of the most inert metal of the PeriodicTable in sulfur-bearing planetary fluids. ACKNOWLEDGMENTS This work was funded by the French National Research Agency (grant RadicalS -ANR-16-CE31-0017) and the Institut Carnot ISIFoR (grant OrPet).…”

Species of Sulfur in Sour Gas Reservoir: Insights from In Situ Raman Spectroscopy of S–H2S–CH4–H2O System and Its Subsystems from 20 to 250°C

“…S species with intermediate valences, such as thiols, S, and S 3 − , have high reactivity, promoting the TSR reaction [8,[12][13][14]. S 3 can be stable at temperatures of up to 700°C [65]. Furthermore, it is especially important that S 3 can even be present at temperatures as low as 100°C in the (NH 4 ) 2 SO 4 -H 2 S-H 2 O system [14].…”

“…Magmatic-hydrothermal fluids are important for the formation of ores. Formation of polysulfide complexation can influence the transport and deposition of ore elements (e.g., As [83] and Au [65,84]) in magmatic-hydrothermal fluids. Thus, the effects of polysulfides on the formation of magmatic-hydrothermal deposits need to be explored further.…”