Iron isotopes constrain sub-seafloor hydrothermal processes at the Trans-Atlantic Geotraverse (TAG) active sulfide mound

Abstract Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to the formation of seafloor massive sulfide deposits and oceanic iron cycling, yet nature their relationship is poorly understood. Here we apply isotope analysis minerals from Trans-Atlantic Geotraverse (TAG) mound underlying stockwork, 26°N Mid-Atlantic Ridge, trace inside an actively-forming deposit in a sediment-free mid-ocean ridge setting. We show that data for recently formed chalcopyrite imply fluid–mound interactions cause small negative shifts (<−0.1‰) δ 56 Fe signature dissolved released TAG into North Atlantic Ocean. Texturally distinct types pyrite, turn, preserve range −1.27 +0.56‰ reflects contrasting precipitation mechanisms (hydrothermal fluid–seawater mixing vs. conductive cooling) variable degrees progressive maturation during >20 kyr evolution complex. The identified may explain variations found fossil onshore deposits.