Subseafloor mineralization related to the shallow seawater-hydrothermal circulation system in the Longqi hydrothermal field, Southwest Indian Ridge (49.6°E): Evidence from in situ trace element and sulfur isotope compositions of pyrite varieties

•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.