Intense biogeochemical iron cycling revealed in Neoarchean micropyrites from stromatolites

SIMS Iron Isotope Measurements of the Balmat Pyrite Reference Material: A Non‐Unique δ56Fe Signature

“…The number of microscale δ 56 Fe analyses in pyrite, measured either by SIMS and/or LA-MC-ICP-MS, has increased drastically over the last 10 years (Agangi et al 2015, Czaja et al 2018, Decraene et al 2021a, Decraene et al 2021b, Dupeyron et al 2023, Galić et al 2017, Harazim et al 2020, Liu et al 2022, Marin-Carbonne et al 2020, Marin-Carbonne et al 2014, Nishizawa et al 2010, Virtasalo et al 2015, Virtasalo et al 2013, Yoshiya et al 2012, Yoshiya et al 2015a, Yoshiya et al 2015b, Zhang et al 2022a, Zhang et al 2022b, Zheng et al 2018. The pioneering work of Whitehouse and Fedo (2007) developed and proposed to use natural pyrite originating from the Balmat deposit (Adirondack Mountains, New York) as a Fe reference material for SIMS measurements.…”

“…Indeed, over Earth's history the overall pyrite bulk δ 56 Fe variability ranges between ‐4 and +1‰, allowing SIMS δ 56 Fe investigation at the pyrite population level (e.g., Decraene et al . 2021b, Harazim et al . 2020, Whitehouse and Fedo 2007) and/or internal grain scale (e.g., Marin‐Carbonne et al .…”

“…However, in situ δ 56 Fe measurements by secondary ion mass spectrometry (SIMS) and/or laser ablation coupled to a multi-collector inductively coupled plasma-mass spectrometer (LA-MC-ICP-MS) are becoming more common for samples displaying large isotopic fractionation such as observed in pyrite, where the typical SIMS analytical precision for pyrite is around 0.20‰ (2s, Decraene et al 2021a). Indeed, over Earth's history the overall pyrite bulk δ 56 Fe variability ranges between -4 and +1‰, allowing SIMS δ 56 Fe investigation at the pyrite population level (e.g., Decraene et al 2021b, Harazim et al 2020, Whitehouse and Fedo 2007 and/or internal grain scale (e.g., Marin-Carbonne et al 2014). Interestingly, Dupeyron et al (2023) compiled available microscale δ 56 Fe and found an overall wider isotopic variability, i.e., -4 to +4‰, preserved in Precambrian sedimentary rocks opening a new avenue for in situ Fe isotope investigation.…”

“…After intra-and inter-grain homogeneity investigation, they concluded that Balmat-ORIGINAL was sufficiently homogenous to be used as a SIMS Fe isotope reference material, with a δ 56 Fe = -0.39 AE 0.18‰ (2s). Since that study, the following determination of pyrite δ 56 Fe values by SIMS has used the δ 56 Fe value of Balmat-ORIGINAL for correction of the IMF and/or accuracy calculation (e.g., Decraene et al 2021b, Marin-Carbonne et al 2011. It is worth noting that all these previous studies have tested the suitability of the Balmat reference material by using secondary pyrite reference materials, which have all given good agreement between SIMS measurements and MC-ICP-MS values.…”

Microbial biosignatures in ancient deep‐sea hydrothermal sulfides

“…3.5 Ga (Baumgartner, Caruso, et al, 2020;Philippot et al, 2007;Shen et al, 2001;Shen et al, 2009;Ueno et al, 2008; (Johnson et al, 2020). Substantial δ 56 Fe variation in natural Fe sulfide minerals (−4‰ to +4‰) may indicate intense redox cycling and potentially additional stable Fe isotope fractionation linked to pyrite precipitation (e.g., Decraene et al, 2021;Mansor & Fantle, 2019). Micro-organisms commonly control redox cycling in the environment and might also influence the degree of this fractionation.…”