Ocean Drilling Program (ODP) Leg 193 investigated two sites of hydrothermal activity along the crest of the Pual Ridge in the eastern Manus Basin. A site of low-temperature diffuse venting, Snowcap (Site 1188), and a high-temperature black smoker site, Roman Ruins (Site 1189), were drilled to depths of 386 and 206 m below seafloor (mbsf), respectively. Although the two sites are <1000 m apart, the 87Sr/86Sr and δ34S signatures of anhydrite recovered at both sites are very different. The data suggest a complex interplay among hydrothermal fluid, magmatic fluid, and seawater during alteration and mineralization of the PACMANUS (Papua New Guinea–Australia–Canada–Manus) system. These new results significantly expand the subsurface data on seafloor hydrothermal systems and may begin to explain the earliest processes of multistage mineralization and alteration history that typify ancient massive sulfide systems.

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