Chemistry of Borehole Fluids Collected at PACMANUS, Papua New Guinea, OPD Leg 193

Abstract

Four samples of borehole fluid collected with the Water Sampling Temperature Probe at the PACMANUS hydrothermal during Leg 193 were all significantly diluted by entrained seawater, and one also contained residual deionized water from the tool. The least contaminated sample (88% seawater) was collected 130 meters below seafloor in Hole 1189B, at a temperature of 55°C. Its trace element and strontium isotope constitution indicate the presence of a hydrothermal component similar to high-temperature fluids vented from seafloor sulfide chimneys at PACMANUS, plus excess CaSO4 dissolved from wallrock anhydrite. A fluid collected at 6°C close to the seafloor in Hole 1188B has ~2% of a less well defined hydrothermal component mixed with CaSO4 dissolved from wallrock anhydrite deeper in the hole. It has anomalously high Mn, Zn, and Mo contents. Unlike the Hole 1189B sample and two more highly diluted samples from Hole 1188F, its Mn/Fe ratio lies well outside the constrained range measured previously at PACMANUS for chimney vent fluids, plume particulates, and diffusely vented fluids collected above the seafloor by funnel. Uncertainties associated with these results demonstrate that improved technology is desirable for sampling high-temperature fluids during future drilling at oceanic hydrothermal sites.