Gray, metal-bearing molten sulfur was collected from the central volcanic cone of an active off-axis caldera (MTJ-1) in the northeastern Lau Basin, southwestern Pacific Ocean, during an expedition for hydrothermal vents undertaken by the Korea Deep Ocean Study (KODOS) program in 2006. The molten sulfur enveloped the frame and chain bag of the dredge at a depth of ∼1700 m. Microscopically, the sulfur matrix contains numerous covellite (CuS) inclusions of various sizes and irregular shapes, indicating their formation via volcanic sublimation. The molten sulfur is enriched in elements commonly associated with magmatic input, including Cu, As, Au, Bi, Te, and Sb. The low sulfur isotope composition of the sulfur (δ34S = –7.5‰ to –8.2‰) indicates an origin via the magmatic degassing of SO2 and disproportionation. The present results represent field-scale evidence for metal transport via sulfur-rich volcanic degassing in submarine massive sulfide deposits. The molten sulfur deposit plays an important role in enhancing the efficiency of the transfer of magmatic fluid to the hydrothermal system.

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