Résumé
At (ultra)slow-spreading ridges, the circulation of hot, acidic, reduced and metal-rich fluids triggers the formation of ultramafic-hosted seafloor massive sulphides deposits (UM-SMSs). These sites display a great variability from site to site, making it difficult to build a simple genetic model. They may notably be associated with Fe-Ca metasomatism, as observed in fossil mineralized systems, thus with possible genetic implications for the formation of mineralized systems. Similar Fe-Ca metasomatism is reported in mantle rocks drilled at the Mid-Atlantic Ridge Kane (MARK) area, offering access to the vertical dimension beneath an oceanic core complex to unravel the nature and geometry of deep magmato-hydrothermal processes. At MARK, mantle rocks record complex melt-rock and fluid-rock interactions. Magma channelling and interactions with peridotite enrich mantle silicates in Fe, Co and Zn. Subsequent hydrothermal alteration produces metamorphic mineral assemblages (e.g., amphibole, clinopyroxene, chlorite, talc, ilvaite, hydro-garnet, serpentine) and is responsible for Cu leaching. It occurs during early mantle exhumation and is followed by the serpentinization of the massif during progressive mantle denudation. Considering the lithological heterogeneity at (ultra)slow-spreading ridges, metal enrichment in mantle rocks through melt-rock interactions may be widespread, eventually accounting for metal endowment at UM-SMS