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Sulphur isotopes can be used as a powerful tool to trace fluid evolution and explore the formation of chimneys. To clarify the in situ S isotopic variations of sulphides at the micro-scale, we analyzed a sulphide chimney collected from the hydrothermal field in the East Pacific Rise 1–2° S using a sensitive high-mass-resolution ion micro-probe for stable isotopes (SHRIMP SI). Three mineral zones can be identified in the chimney: an external outer wall of porous anhydrite and colloform pyrite, an internal middle zone of sub-euhedral pyrite and massive chalcopyrite, and an inner zone of massive pyrite. The δ34SV-CDT values of the sulphides fall within the range 1.83–7.51 ‰ (avg. 4.05 ‰, n = 16), and S isotopic values increase from the core (3.09 ‰, n = 3) to the middle (3.78 ‰, n = 11) to the edge (6.99 ‰, n = 2). These results illustrate mineral crystallization processes and the mixing between seawater-derived S and magmatic–hydrothermal fluids during the growth of the chimney. The zones from the edge to the core are characterized by crystal morphologies of colloform/anhedral pyrite to massive pyrite with decreasing δ34S values, revealing multi-stage mineral deposition and sulphur isotopic fractionation. In contrast to the increase in δ34S values from the core to the edge in one profile (profile A), anomalously low δ34S values in fine-grained pyrite relative to chalcopyrite in another profile (profile B) in the middle zone result from S isotopic exchange between seawater SO42− and fluid H2S due to different fluid–seawater mixing, possibly caused by variations in permeability and porosity across the chimney. [ABSTRACT FROM AUTHOR]

• To characterize the petrographic features of pyrite across the chimney. • To investigate the trace elements in varying types of pyrite and the enrichment factors. • To illustrate the sources of S and evolution of the fluids across the chimney. • To reveal the history of chimney growth. 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. [ABSTRACT FROM AUTHOR]

The Okinawa Trough is a sediment-covered intra-continental back-arc basin with active hydrothermal activities. The sulfur isotopic systematics of the hydrothermal systems in the Okinawa Trough remain unclear owing to the complex sulfur reservoirs. To address these uncertainties, we conducted in situ S isotopic combined with whole-rock geochemical, Pb isotopic, and barite Sr isotopic analyses of typical hydrothermal precipitates from three hydrothermal fields with varying sediments thickness (Iheya North Knoll (INK) < Yonaguni Knoll IV (YK) < Noho) in the Okinawa Trough. The δ34S values of barite from INK (+16.4‰ to +19.6‰, median + 18.5‰) and YK (+16.2‰ to +22.2‰, median + 19.5‰) mostly indicate lower values than those obtained for seawater (~ +21‰), combined with the observation of high S and O fugacity (fO 2 –fS 2) mineral assemblages (e.g., low-Fe sphalerite ± enargite ± tennantite ± chalcopyrite), and high Cu and Au contents of hydrothermal precipitates, consistent with the addition of magmatic volatile to these two fields. In contrast, the in situ δ34S values of sulfide minerals from INK (+5.6‰ to +10.4‰, median + 9.0‰) and YK (+3.5‰ to +5.5‰, median + 4.7‰) fields were all positive, inconsistent with the S isotopic characteristics of H 2 S formed from SO 2 disproportionation. We conclude that a large proportion of thermochemical SO 4 2− reduction-derived heavy sulfur likely obscure the characteristics of H 2 S sourced from disproportionation. This was likely resulting from (1) sediment controlled long-scale lateral hydrothermal circulation, (2) the existence of early precipitated anhydrite, and (3) high concentrations of H 2 in the high-temperature reaction zone. The Noho field have low δ34S values (−0.2‰ to +5.3‰, median + 0.9‰) of sulfide minerals, combined with high sediment contributions reflected by high Pb isotopic ratios and low-fS 2 –fO 2 mineral assemblages (e.g., high-Fe sphalerite ± pyrrhotite ± isocubanite), which indicates that the low δ34S value sulfur was derived from leaching of biogenic pyrite in thick sedimentary strata by hydrothermal fluid. Near surface, the high-temperature discharging hydrothermal fluids interacted with different thicknesses of sedimentary strata and leached different proportions of biogenetic pyrite, resulting in a negative correlation of sedimentary strata thickness and sulfide δ34S values of the Okinawa Trough hydrothermal fields. • Mineralogy, and S–Pb–Sr isotopes were studied for three hydrothermal fields in OT. • Barite subseawater δ34S and high-fO 2 –fS 2 indicate addition of magmatic volatiles. • Magmatic volatiles-derived light S was obscured by TSR-derived heavy sulfur. • Leached biogenetic S from sedimentary strata is the main source of light S. [ABSTRACT FROM AUTHOR]

Understanding the relationship between sulfide chimney maturity and fluid evolution in submarine hydrothermal systems is essential for deciphering mineralogical changes, sulfur dynamics, and fluid flux over time. We investigate this link through sulfur isotopic analysis of sulfides from three maturity stages of sulfide chimneys at the Niaochao hydrothermal field (East Pacific Rise, 1–2°S), integrated with δ34S values from diverse global hydrothermal fields. Based on mineral associations and sulfur isotopes, the sulfide chimneys are classified into Zn-Fe-rich, Fe-Cu-rich, and Fe-Cu-Zn-rich chimneys, representing the increasing maturity. A systematic increase in δ34S values (from 1.54‰ to 7.22‰) from chimney cores to rims indicates the progressive reduction of seawater sulfate during fluid-seawater mixing in open systems. Fluctuations in δ34S values within chimney zones are attributed to the interaction between hydrothermal fluids and pre-existing minerals. As chimneys grow, rapid sulfur isotopic exchanges occur between seawater sulfate and fluid H 2 S in localized semi-closed systems, leading to a significant drop in δ34S values of pyrites, decreasing by up to 4.82‰. A new chimney evolutionary model has been developed utilizing mineralogical and sulfur isotopic data of sulfide chimneys from global hydrothermal vents. This model encompasses birth, growth, and waning stages, accompanied by an elevation of mean δ34S values from 2.1‰ (n = 66) to 3.2‰ (n = 435) and 3.8‰ (n = 61) due to ongoing seawater sulfate reduction. Conversely, the infusion of magmatic sulfur during chimney growth contributes to a decrease in δ34S values of sulfides. This study underscores the significance of sulfur isotopes as indicators of sulfide chimney maturity, which enhances our understanding of the evolution and formation processes of hydrothermal systems. • Three maturity stages of sulfide chimneys at the Niaochao vent field have been classified. • The evolutionary degree of sulfate reduction in fluids from open to semi-closed systems within the chimney has been deciphered. • A new chimney evolutionary model by variations in δ34S values is established. • The study reveals the link between mineralogy, δ34S values, and maturity of zoned chimneys in submarine hydrothermal systems. [ABSTRACT FROM AUTHOR]

The petrographic and geochemical features of the modern hydrothermal sulfides can reveal the growth processes of chimney and the evolution of hydrothermal fluids. To clarify the geochemical variations and ore-forming fluids evolutions during the chimney growth, we performed laser ablation ICP-MS and Nano-SIMS (Nanometer-second ion mass spectrometry) to characterize the variations of trace elements and S isotopes of pyrite across a pyrite-dominated chimney collected from the hydrothermal field on East Pacific Rise. Three types of pyrite were distinguished from exterior to interior of the chimney, which varies from anhedral through euhedral to massive textures. Trace elements of pyrite evolves from high-temperature (Cu, Se, Sn, Bi, Co and Ni) to low-temperature characteristics (Zn, Pb, Cd, Tl, Ag, Mn, Ba, Mg and V) with the decreasing degrees of crystal morphologies from core to rim in response to the changes in temperature and fluid chemistry caused by seawater-fluid mixing. The massive pyrite in core features lower Se/Tl ratios but higher Co/Ni ratios relative to euhedral pyrite, possibly attributed by the decreasing T or ƒS2 of fluids with the waning hydrothermal circulation. The δ34SV-CDT values of pyrite range from -0.51 to 6.43‰ (avg. 3.56‰, n=39). The decreasing S isotopic values in the mineral sequence of chimney result from the decreasing seawater derived-S, whereas the incorporation of approximately 8%–24% of bacteria derived-S lead to partial anhedral pyrite with negative δ34SV-CDT values (down to -0.51‰).The systematic variations in the S isotopic compositions and morphology of the pyrite across the chimney wall reflect multiple stages of mineralization and fluid evolution. Based on in situ sulfur isotope and micro-scale trace elements compositions of pyrite, we propose a chimney growth model that focuses on different degrees of fluid-seawater mixing and variations of the permeability across the chimney. [ABSTRACT FROM AUTHOR]

[Display omitted] • A model was established to better understand the metal mobilization and sulfur cycles in the shallow seawater-hydrothermal circulation system. • The variations in δ34S values of pyrites are due to the variable sulfur contribution of shallow-origin reduced sulfur from seawater sulfate and reduction of anhydrite. • Pyrite mineralization clarifies the subseafloor mineralization related to shallow seawater-hydrothermal circulation. • PCA results reveal that the control on fluid compositions changes from the early shallow seawater-hydrothermal circulation to later intense hydrothermal activity. The shallow seawater-hydrothermal circulation system plays a crucial role in the subseafloor mineralization of the hydrothermal field. However, its key fluid processes and impacts on the metal mobilization and sulfur cycles in the stockwork mineralization are still poorly understood. We first present the systemic variations in micro-scale trace element and sulfur isotope compositions of pyrite varieties in a stockwork-like sulfide assemblage from the Longqi hydrothermal field to constrain the transport and deposition of metals and the origins and cycles of sulfur in the shallow seawater-hydrothermal circulation system. Pyrites considered as the dominant sulfides can be clarified into disseminated fine-grained (Py-I), euhedral (Py-II), and subhedral-euhedral (Py-III) varieties based on the textures. The wall-rock-derived elements Ti, Cu, and Ni and seawater-derived elements V, U, Mo, Mg, and Mn are concentrated in Py-I in the breccias, which is related to the fluid-rock interaction and fluid-seawater mixing in the shallow seawater-hydrothermal circulation system. Short-lived shallow seawater-hydrothermal circulation results in fluid fluctuation and oscillatory-zoned Py-II with depletion of Co, Ni, Cu, As, and Se in the mantles relative to those in the rims and cores. As the later hydrothermal activity was active, Py-III was overgrown from Py-II rich in hydrothermally inherited metals Se, Te, and Co, possibly implying the hydrothermal field is coming into the main mineralization. The sulfur isotope compositions of pyrites range from 4.30 to 9.98‰ (n = 37), with distinct δ34S variations in the individual Py-I crystals (>1.5 ‰ within a 20 × 20 µm2 region). This variation is attributed to changes in the relative proportion of sulfur sourced from (i) the shallow-origin reduced seawater via reduction by ferrous iron released from basalt, and (ii) the reduction of pre-existing anhydrite by later hydrothermal overprinting in the shallow subseafloor. These findings provide evidence for a model to better understand the effect of the shallow seawater-hydrothermal circulation system on the subseafloor stockwork mineralization of hydrothermal fields. [ABSTRACT FROM AUTHOR]