Fluid–substrate coupled controls on mineral‑phase selection in the Kunlun hydrothermal system

Mineral precipitation at submarine hydrothermal vents transfers redox‑sensitive elements from the lithosphere to the ocean. However, conventional plume and sediment‑trap sampling poorly preserves particle‑scale signatures generated at reactive interfaces, hindering robust interpretation of near‑vent mineralization. Here, we deployed open‑cell Fe, Ni, Cu, and Fe–Ni foams within diffuse low‑temperature alkaline fluids of the serpentinization‑driven Kunlun hydrothermal field. The results reveal that the hydrothermal system mainly favoured goethite‑dominated Fe‑oxyhydroxide coatings, while ambient seawater promoted lepidocrocite precipitation. Substrate chemistry further modulated mineral‑phase selection: NiO precipitated on Ni‑bearing substrates, hematite occurred exclusively on Fe–Ni foam, and maghemite formed on Cu foam. The Fe foam yielded the thickest Fe‑rich deposits, fed both by hydrothermal Fe supply and anodic dissolution of the metallic substrate. For serpentinization‑related hydrothermal systems, naturally occurring reactive mineral surfaces—Fe–Ni alloys such as awaruite—behave as geochemically active interfaces that steer mineralization, rather than as passive particle collectors. Such interfacial effects can improve reconstructions of mineral assemblages and improve reconstructions of lithosphere‑to‑ocean element fluxes in serpentinization‑driven systems.