The origin of Zn isotope fractionation in sulfides

Toshiyuki Fujii (1) , Frédéric Moynier (2, 3) , Marie-Laure Pons (4) , Francis Albarède (4)

1 Research Reactor Institute
2 Department of Earth and Planetary Sciences [St Louis]
3 McDonnell Center for Space Sciences
4 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement

Isotope fractionation of Zn between aqueous sulfide, chloride, and carbonate species (Zn(2+), Zn(HS)2, Zn(HS)(3)(-), Zn(HS)(4)(2-), ZnS(HS)(-), ZnCl(+), ZnCl(2), ZnHCO(3)(+), and ZnCO(3)) was investigated using ab initio methods. Only little fractionation is found between the sulfide species, whereas carbonates are up to 1 parts per thousand heavier than the parent solution. At pH > 3 and under atmospheric-like CO(2) pressures, isotope fractionation of Zn sulfides precipitated from sulfidic solutions is affected by aqueous sulfide species and the delta(66)Zn of sulfides reflect these in the parent solutions. Under high P(CO2) conditions, carbonate species become abundant. In high PCO(2) conditions of hydrothermal solutions, Zn precipitated as sulfides is isotopically nearly unfractionated with respect to a low-pH parent fluid. In contrast, negative delta(66)Zn down to at least -0.6 parts per thousand can be expected in sulfides precipitated from solutions with pH > 9. Zinc isotopes in sulfides and rocks therefore represent a potential indicator of mid to high pH in ancient hydrothermal fluids.

Mots clés: 1 ATM PRESSURE; AQUEOUS-SOLUTION; ZINC ISOTOPES; CARBONIC-ACID; BISULFIDE COMPLEXES; NMR-SPECTRA; NACL MEDIA; CHEMISTRY; RAMAN; IONIZATION

Domaines: Géochimie; Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux

Toshiyuki Fujii, Frédéric Moynier, Marie-Laure Pons, Francis Albarède. The origin of Zn isotope fractionation in sulfides. Geochimica et Cosmochimica Acta, 2011, 75 (23), pp.7632-7643. ⟨10.1016/j.gca.2011.09.036⟩. ⟨insu-00674540⟩