Subseafloor hydrothermal mineralization in a non-transform offset: Mineralogy and LA-ICP-MS study of sulfide from the Taiji-2 hydrothermal field, Southern Mid-Atlantic Ridge

In modern seafloor hydrothermal mineralization systems, subseafloor deposits are crucial alongside seafloor massive sulfides, consisting mainly of stockwork at the periphery and semi-massive sulfides at the central of subseafloor ore bodies. These two ore types exhibit contrasting mineralogical and elemental compositions, and the difference between their formation processes are unclear due to sampling challenges. The mafic-hosted Taiji-2 hydrothermal field, located on the Southern Mid-Atlantic Ridge, presents pyrite-enriched subseafloor sulfides on the seafloor, providing a good research opportunity. Our study included comprehensive analyses of mineralogy, pyrite chemistry, and in-situ sulfur isotopes through LA-MC-ICP-MS method on Taiji-2 subseafloor samples. Our findings suggest: (1) a hybrid source of ore-forming materials, (2) increased seawater involvement and decreased temperature and sulfur fugacity from the periphery to the central of subseafloor deposits, and (3) multistage of subseafloor ore-forming activities. Additionally, we characterized the seafloor alteration of Taiji-2 subseafloor sulfides. These results enhance our understanding of subseafloor mineralization in seafloor hydrothermal field.