In-situ measurements of iron isotopes by ion microprobe

Fe isotopes are extensively used in geochemistry studies, especially as proxy of biosignatures. We have developed the measurements of Fe isotopes by ion microprobe at Nancy, (France) using the procedure described by Whitehouse and Fedo (2007). Possible matrix effects were evaluated using different reference materials : the IRMM-014 Fe isotope standard, and in-house reference materials (pyrite, hematite, magnetite and siderite). These reference minerals were also measured by MC-ICP-MS (CRPG-Nancy). The influence of ion probe analytical parameters, i.e. presputtering time, primary intensity, was also tested. Under the established analytical conditions and with a 54Cr correction applied on 54Fe intensity, we obtained an external reproducibility better than 0.2‰ (1 sigma) depending of the reference materials. This reproducibility will allow us to apply in situ Fe isotope measurements in siderite and magnetite minerals of chert samples from Gunflint Iron Formation (1.88 Ga) to have informations about the redox conditions and the diagenetic history of these cherts. Whitehouse and Fedo (2007) Microscale heterogeneity of Fe isotopes in >3.71 Ga banded iron formation from the Isua Greenstone Belt, southwest Greenland. Geology, 35, 719-722.