SHRIMP 4-S isotope systematics of two pyrite generations in the 3.49 Ga Dresser Formation

The 3.49 Ga Dresser Formation has been considered to host evidence of the earliest microbes metabolising sulfur species on Earth. However, previous bulk analyses and in situ measurements conclude disparate metabolisms based opposite ΔS. This study first established generations pyrite growth, then measured multiple isotopes using Sensitive High Resolution Ion MicroProbe-Stable Isotope analyses. Two main were revealed core-rim textures isotopic compositions: ΔS-positive Generation One (G1) δS- ΔS-negative (G2). In chert-barite unit, diluted photochemical products mainly sequestered G1 barite, respectively. G2 formed via sulfide pathway with derived from sulfate reduction magmatic HS. δS-ΔS-ΔS systematics suggests an abiological origin for G1, thermochemical possible (minor) microbial G2.