Formation of large mound-shaped sulfide deposit on axial volcanic ridge - A case from the Wocan-1 hydrothermal field, Carlsberg Ridge

The hydrothermally active Wocan-1 mound is a nearly circular mound, similar to 260 m wide and similar to 50 m high, located on the northwestern slope of an axial volcanic ridge in Carlsberg Ridge. Seafloor observations and sampling indicate a large variability of venting styles as a result of local permeability control. High temperature black smokers are widely distributed over the summit area with significant metal flux indicating limited subseafloor seawater mixing. Clear vent fluids as well as diffuse fluid venting is common in the central and northern areas suggesting subseafloor metal precipitation. Copper-rich sulfides are most abundant in the summit region and along its eastern slope with chalcopyrite and atacamite being major minerals, whereas pyrite and anhydrite are the major minerals in the northern margin area. Sulfur isotope ratios reveal a larger contribution of entrained seawater in the central and the northern areas, when compared to southern area. The increase of delta S-34 is related to recrystallization of primary sulfides in the presence of fluids with abundant sulfate-derived sulfur. The active Wocan-1 mound is larger than the well-known TAG active mound on the Mid-Atlantic Ridge indicating that axial volcanic ridges also have the potential to host large sulfide deposit.