Formation pathways of Precambrian sedimentary pyrite: Insights from in situ Fe isotopes

Iron isotope compositions (expressed as δ56Fe) in sedimentary pyrite have been widely used tracers of redox and chemical evolution the ocean through geological time. Previous studies mostly built on mechanical extraction sulfides from bulk rock samples, focused visible macroscopic pyrites, which may introduce a sampling bias. In situ analyses micropyrite grains can provide new insights into processes formation their time evolution. Here, we compile ca. 2000 iron Archean to Paleoproterozoic pyrite, previous literature well data. Contrasting with analyses, displays large constant range δ56Fe values, -4 +4‰, Micropyrite values are not significantly influenced by metamorphic grade. A bimodal distribution positive versus negative be attributed two different formation, Fe (oxyhydr)oxide sulfidation, kinetic possibly microbially mediated precipitation. These tightly related lithology thus conditions, existed since 3.8 Ga.