In Situ Fe and S isotope analyses in pyrite from the 3.2 Ga Mendon Formation (Barberton Greenstone Belt, South Africa): Evidence for early microbial iron reduction.

摘要: On the basis of phylogenetic studies and laboratory cultures, it has been proposed that ability microbes to metabolize iron emerged prior Archaea/ Bacteria split. However, no unambiguous geochemical data supporting this claim have put forward in rocks older than 2.7-2.5 giga years (Gyr). In present work, we report situ Fe S isotope composition pyrite from 3.28-to 3.26-Gyr-old cherts upper Mendon Formation, South Africa. We identified three populations microscopic pyrites showing a wide range compositions, which cluster around two δ 56 values −1.8‰ +1‰. These groups can also be distinguished based on crystallinity mass-independent signatures. One group displays poorly crystallized minerals with positive Δ 33 > +3‰, while other display more variable closer 0‰ recrystallized rims. It is worth note all core similar trace element compositions.