@article{fdi:010054157,
  title = {{I}ron and sulphur isotopes from the {C}arajas mining province ({P}ara, {B}razil) : implications for the oxidation of the ocean and the atmosphere across the {A}rchaean-{P}roterozoic transition},
  author = {{F}abre, {S}. and {N}{\'e}d{\'e}lec, {A}. and {P}oitrasson, {F}ranck and {S}trauss, {H}. and {T}homazo, {C}. and {N}ogueira, {A}.},
  editor = {},
  language = {{ENG}},
  abstract = {{M}ineralogical analyses and major and trace element geochemistry combined with iron and sulfur isotopes were applied to banded iron formations ({BIF}s) and pyrite-bearing sandstones from the {C}arajas mineral province, {B}razil. {T}he {BIF}s belong to the 2.7 {G}a old {G}rao {P}ara {G}roup and show a rather simple mineralogy (hematite and quartz or cryptocrystalline silica). {T}heir {REE} + {Y} patterns suggest deposition under marine sub-oxic conditions. {F}e isotopes show highly positive values (delta {F}e-57({IRMM}-14) = 2.06 +/- 0.34% in average) which can be explained by the partial oxidation of {F}e2+ (aq) in the surface ocean, subsequent to the upwelling of deep anoxic seawater. {T}he resulting iron oxy-hydroxides likely formed in the shallow photic zone as a seasonal process and acquired highly positive iron isotope signature values consistent with a {R}ayleigh distillation model. {T}he pyrite-bearing sandstones belong to the {A}guas {C}laras {F}ormation of ({P}alaeoproterozoic) younger age and were cored at the base of the giant {A}zul manganese deposit. {D}iagenetic pyrite is characterized by positive delta {F}e-57({IRMM}-14) = 1.02 +/- 0.2%. and delta {S}-34({VCTD}) (11.97 +/- 0.12%) average values, that are different from values of modern marine biogenic pyrite. {R}esults likely indicate that dissolved sulfate was the limiting factor controlling biogenic pyrite formation at that time. {N}ear-zero {D}elta {S}-33 values (0.013 +/- 0.003%) indicate minimal mass-independent sulfur isotope fractionation ({MIF}-{S}), consistent with the 2.1 {G}a age previously obtained from the {A}guas {C}laras pyrites. {T}his result suggests deposition at a time when the oxygen partial pressure in the atmosphere was already high enough (10(-5) to 10(-2) {PAL}- or {P}resent {A}tmospheric {L}evel-) to hinder {MIF}-{S} by photochemical reactions. {I}ncidentally, this also confirms that the giant {M}n deposit of {C}arajas is in the same age range (2.1 +/- 0.2 {G}a) as other {M}n ores in {G}abon and {S}outh {A}frica, pointing to the importance of {M}n precipitation in {P}aleoproterozoic times.},
  keywords = {{BIF} ; {P}yrite ; {C}arajas ; {I}ron and sulphur isotopes ; {A}rchaean ; {P}alaeoproterozoic},
  booktitle = {},
  journal = {{C}hemical {G}eology},
  volume = {289},
  numero = {1-2},
  pages = {124--139},
  ISSN = {0009-2541},
  year = {2011},
  DOI = {10.1016/j.chemgeo.2011.07.019},
  URL = {https://www.documentation.ird.fr/hor/fdi:010054157},
}