Coupled Fe-S isotope composition of sulfide chimneys dominated by temperature heterogeneity in seafloor hydrothermal systems.

Seafloor hydrothermal chimneys are significant metal resources and have fundamental effects on marine chemistry balance. Previous studies on growth of the chimneys focused on mineral composition and elemental distribution in chimney walls, but the isotopic composition of different elements and their correlations remain poorly understood. Here, we report lateral Fe and S isotopes from sulfides across a chimney wall in detail from the Deyin-1 hydrothermal field (DHF) on the South Mid-Atlantic Ridge. Pyrite was characterized by increases in both δS and δFe from the exterior to the interior within the chimney wall, which is likely related to enhanced S and Fe isotope fractionation between pyrite and fluids derived from the temperature gradient. Furthermore, δFe displayed a well-defined, linear, positive correlation with δS in pyrite from the DHF as well as in pyrite from other areas. A model of hydrothermal pyrite formation suggests that, under conditions with uniform hydrothermal fluid, different temperatures and similar pyrite-fluid exchange degrees could result in the observed linear relationships between δS and δFe. The regular and coupled Fe-S isotope variations within the chimney wall efficiently constrain the process of hydrothermal sulfide formation.