Trace-elements and sulfur isotopic compositions for pyrite across the mineralization zones of a sulfide chimney from the East Pacific Rise (1-2°S)

Abstract Active black smokers represent important products of seafloor hydrothermal systems and can reveal the fluid evolution and ore genesis in sulfide deposits. The key for understanding the details of fluid circulation and mineralization within sulfide zonation of chimneys lies in the understanding of variation in micro-scale trace elements and sulfur isotopes in sulfide deposits. An active pyrite-dominated chimney collected from the East Pacific Rise 1-2°S hydrothermal field supplies a unique opportunity to exhibit on-going ore-forming processes, especially the detailed fluid processes among the sulfide zonation of chimney, as well as to constrain the mineralization environment that is crucial for metal transport and deposition across the chimney. Pyrites, as the ubiquitous sulfide, present crystal morphologies varying from anhedral though euhedral to massive textures at different mineralization stages. The characterization of trace elements in different types of pyrite, from rim to core, evolves from Zn, Pb, Cd, Tl, Ag, Mn and Ba to Cu, Se, Sn, Bi, Co and Ni in response to increasing mineralization temperature. The dominant control on Co and Ni contents in pyrite from the exterior and interior of the chimney changes from temperature to sulfur fugacity as the hydrothermal circulation becomes active and subsequently wanes. In addition to the physicochemical environment, the chemical variations like As, Sb and Mo in pyrite from different mineral zonation are mostly like related to the temporal evolution of fluid compositions. Seawater-fluid mixing not only influences seawater-derived species of trace elements like V and Mg, and the spatial distributions of temperature-sensitive elements like Co, Cu, Se and Sn, but also increases the S isotope values of pyrite in the mineral sequence of the chimney. However, the incorporation of approximately 8 ∼ 24% bacteria-derived S leads to anhedral pyrite with abnormally light S isotopes in the outer mineral zonation.