Volcanogenic massive sulphide (VMS) deposits are variably enriched in metals that are mobilised by two main processes: hydrothermal alteration of the oceanic crust’s lower sheeted dyke section and exsolution of metal-rich fluids into the hydrothermal system from differentiating magmas. The extent to which each process contributes to metal enrichment in VMS deposits varies, however, between different tectonic settings. Oceanic Drilling Program (ODP) Hole 786B recovers the volcanic section and the transitional zone of a supra-subduction zone oceanic crust including a 30 m wide mineralised zone at the base of the hole. Previous work has indicated that significant input of magmatic fluid into the hydrothermal system isresponsible for the formation of mineralisation. This study uses in-situ trace element and S-isotope analyses in sulphide minerals and whole rock data to characterise the metal endowment of the mineralised zone, the sources of the trapped metals and the signature of magmatic fluid inputs in the hydrothermal system. The mineralised zone shows strong enrichment in S, As, Se, Sb and Au, and probably Mo, Te and Bi, but little enrichment in base metals. It is subdivided in two main alteration domains: the upper alteration domain, characterised by mixing of high temperature hydrothermal fluids with sea water at relatively low temperature (150-200 °C), under reduced and near neutral pH conditions, and the central and lower alteration domain, characterised by extensive mixing of magmatic fluids with sea water at relatively high temperature (~250 °C), under oxidised and acidic conditions. Strong metal zonation occurs in the transitional zone with preferential enrichment of Zn, Cu, As, Au and Pb in the upper alteration domain and preferential enrichment of S, Se, Mo, Sb, Te and Bi in the central and lower alteration domain. This zonation is controlled by variations in fluid composition, temperature, redox, pH, and zone refining during sulphide paragenesis. The oceanic crust at Hole 786B has high As, Sb and Pb concentrations relative to mid oceanic ridge setting but similar Cu, Zn and Au, and low Se concentrations. The oceanic crust metal fertility suggests that the Cu, Zn, As, Sb and Pb enriched in the transitional zone could have been mobilised by rock buffered hydrothermal fluids but that the S, Se and Au must have been mobilised by magmatic fluids. Major and trace elements behaviour during magmatic differentiation of the oceanic crust at Hole 786B show evidences for a magnetite crisis event which is interpreted to trigger exsolution of metal-rich magmatic fluids into the hydrothermal system and which can account for the observed metal endowment in the transitional zone. The metal content in the oceanic crust at Hole 786B and the specific endowment of the mineralised zone suggests that significant fractionation between Au and base metals occur during fluid migration in supra-subduction oceanic crust and can promote the formation of Au-rich VMS deposits on the sea floor. Such process is as highlighted by the Au : base metal ratio close to unity in the mineralised zone.