Anthropogenic Pb in recent hydrothermal sediments from the Tyrrhenian Sea: Implications for seawater Pb control on low-temperature hydrothermal systems

During a 1977 cruise of the R/V Bannock, a core was taken from an area of extensive hydrothermal mineralization located on the slope of Eolo Seamount, Aeolian Arc (Tyrrhenian Sea). The Eolo hydrothermal sediments exhibit unusual Pb isotopic compositions that cannot be solely derived from the plausible natural sources in the area. Mixing considerations indicate that a significant part of the Pb in these sediments is anthropogenic in origin. The anthropogenic Pb was most probably scavenged from the Mediterranean seawater by sinking hydrothermal plume particles. Apparently the hydrothermal products entering the seawater column did not carry significant amounts of Pb extracted from the underlying rocks, so their Pb isotopic compositions were swamped by the seawater Pb. This indicates that Pb in low-temperature hydrothermal products is controlled by the seawater Pb, not by hydrothermal leaching from underlying rocks.