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Effect of salinity, pressure and temperature on the solubility of smithsonite (ZnCO3) and Zn complexation in crustal and upper mantle hydrothermal fluids

DOI: 10.1016/j.chemgeo.2021.120320 DOI Help

Authors: Stefan Farsang (University of Cambridge) , Marion Louvel (WWU Münster) , Angelika D. Rosa (European Synchrotron Radiation Facility) , Monica Amboage (Diamond Light Source) , Simone Anzellini (Diamond Light Source; CEA) , Remo N. Widmer (Empa) , Simon A. T. Redfern (Nanyang Technological University; Center for High Pressure Science and Technology Advanced Research, Beijing)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemical Geology , VOL 52

State: Published (Approved)
Published: May 2021
Diamond Proposal Number(s): 21869

Abstract: Modelling the reservoirs and fluxes of Zn in Earth's crust and mantle requires data on the solubility of its mineral hosts and ores in coexisting fluids, as well as on the complexation of Zn in these fluids as a function of fluid composition, pressure, and temperature. However, due to experimental challenges, the availability of such data is limited to pressures below 1 GPa, which are only representative of upper crust conditions. Here, we report the effects of salinity (0–4.5 m total Cl), pressure (0.5–6 GPa) and temperature (25–400 °C) on the solubility of smithsonite (ZnCO3) and speciation of Zn in aqueous fluids. Solubilities at mineral-fluid equilibria and Zn speciation in the coexisting aqueous fluids were determined in situ at high pressure-temperature conditions by synchrotron X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) using resistively heated diamond anvil cells (RH-DAC). The solubility of smithsonite increases with salinity, pressure, and temperature. In agreement with previous studies, conducted at lower pressures (below 1 GPa), we observed a gradual transition from octahedral hydrated [Zn(H2O)6]2+ to tetrahedral hydrated and chlorinated [Zn(H2O)4-nCln]2-n (n = 1–4) complexes with increasing salinity and temperature. Our results suggest that these tetrahedral complexes remain stable under the conditions relevant to cold slab dehydration. This change of coordination further enhances the solubility of smithsonite in Cl-rich fluids and provides a likely mechanism for the efficient uptake of Zn by slab-derived fluids.

Journal Keywords: Zinc speciation; Smithsonite; Solubility; Subduction zone fluids; Deep Earth; High pressure; High temperature; Salinity; Synchrotron XRF; XAS; DAC

Subject Areas: Earth Science, Chemistry

Instruments: I20-EDE-Energy Dispersive EXAFS (EDE)

Other Facilities: BM23 at ESRF

Discipline Tags:

Chemistry Earth Sciences & Environment Geochemistry Geology Mineralogy

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS)