Hydrothermal state and mechanical property variability in seafloor massive sulfides from the Arctic Mid-Ocean Ridge

Engineering characterization of seafloor massive sulfides (SMS) remains limited, particularly for Arctic Mid-Ocean Ridge (AMOR) deposits, where mineral assemblages include barite, anhydrite, carbonate, talc, and Fe-oxyhydroxide phases and where hydrothermal systems occur in active, transitional, inactive, and extinct states. This study presents an exploratory laboratory dataset from five SMS cores collected by ROV from the Mohns and Knipovich ridges, together with one volcanic host-rock control, to evaluate whether hydrothermal state may serve as a first-order classifier of SMS geomechanical behavior. The workflow combined X-ray computed tomography, helium pycnometry, fluid permeability measurement, and Brazilian tensile strength (BTS) testing under a standardized protocol. Inactive and extinct samples (n = 2) exhibited higher tensile strength than samples from active settings (n = 3), with mean BTS values of 6.0 MPa (range 5.34–6.61 MPa) and 2.2 MPa (range 1.28–3.08 MPa), respectively. Porosity overlapped substantially between groups and does not by itself explain the mechanical contrast. Grain density followed the same trend as tensile strength, with inactive/extinct samples averaging 5.39 g/cm3 against 3.30 g/cm3 for active samples, indicating that mineralogical composition and bulk density also contribute. Permeability showed no clear relationship with hydrothermal state. Given the limited sample population, the results are preliminary and hypothesis-generating.