@article{PAR00008106,
  title = {{F}irst experimental determination of iron isotope fractionation between hematite and aqueous solution at hydrothermal conditions},
  author = {{S}aunier, {G}. and {P}okrovski, {G}. {S}. and {P}oitrasson, {F}ranck},
  editor = {},
  language = {{ENG}},
  abstract = {{A}lthough iron isotopes provide a new powerful tool for tracing a variety of geochemical processes, the unambiguous interpretation of iron isotope ratios in natural systems and the development of predictive theoretical models require accurate data on equilibrium isotope fractionation between fluids and minerals. {W}e investigated {F}e isotope fractionation between hematite ({F}e2{O}3) and aqueous acidic {N}a{C}l fluids via hematite dissolution and precipitation experiments at temperatures from 200 to 450 degrees {C} and pressures from saturated vapor pressure ({P}-sat) to 600 bar. {P}recipitation experiments at 200 degrees {C} and {P}-sat from aqueous solution, in which {F}e aqueous speciation is dominated by ferric iron ({F}e-{III}) chloride complexes, show no detectable {F}e isotope fractionation between hematite and fluid, {D}elta {F}e-57(fluid-hematite) = delta {F}e-57(fluid) - delta {F}e-57(hematite) = 0.01 perpendicular to 0.08 parts per thousand (2 x standard error, 2{SE}). {I}n contrast, experiments at 300 degrees {C} and {P}-sat, where ferrous iron chloride species ({F}e{C}l2 and {F}e{C}l+) dominate in the fluid, yield significant fluid enrichment in the light isotope, with identical values of {D}elta {F}e-57(fluid-hematite) = -0.54 + 0.15 parts per thousand (2{SE}) both for dissolution and precipitation runs. {H}ematite dissolution experiments at 450 degrees {C} and 600 bar, in which {F}e speciation is also dominated by ferrous chloride species, yield {D}elta {F}e-57(fluid-hematite) values close to zero within errors, 0.15 +/- 0.17 parts per thousand (2{SE}). {I}n most experiments, chemical, redox, and isotopic equilibrium was attained, as shown by constancy over time of total dissolved {F}e concentrations, aqueous {F}e-{II} and {F}e-{III} fractions, and {F}e isotope ratios in solution, and identical {D}elta {F}e-57 values from dissolution and precipitation runs. {O}ur measured equilibrium {D}elta {F}e-57(fluid-hematite) values at different temperatures, fluid compositions and iron redox state are within the range of fractionations in the system fluid-hematite estimated using reported theoretical beta-factors for hematite and aqueous {F}e species and the distribution of {F}e aqueous complexes in solution. {T}hese theoretical predictions are however affected by large discrepancies among different studies, typically +/- 1 parts per thousand for the {D}elta {F}e-57({F}e(aq)-hematite) value at 200 degrees {C}. {O}ur data may thus help to refine theoretical models for beta-factors of aqueous iron species. {T}his study provides the first experimental calibration of {F}e isotope fractionation in the system hematite-saline aqueous fluid at elevated temperatures; it demonstrates the importance of redox control on {F}e isotope fractionation at hydrothermal conditions.},
  keywords = {},
  booktitle = {},
  journal = {{G}eochimica et {C}osmochimica {A}cta},
  volume = {75},
  numero = {21},
  pages = {6629--6654},
  ISSN = {0016-7037},
  year = {2011},
  DOI = {10.1016/j.gca.2011.08.028},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00008106},
}