Native Hg liq in the metalliferous sediments of the East Pacific Rise (21°S)

Abstract

Native Hg droplets, documented here for the first time in mid-ocean ridge metalliferous sediments, were found in the surface sediment of a magmatically robust and ultra-fast spreading mid-ocean ridge, the East Pacific Rise. The surface sediment and Fe–Mn micronodules in it are enriched in Hg. Two different processes can produce Hg 0 liq in this environment: hydrothermal and biogenic. Bio-transfer of ionic Hg dissolved in the hydrothermal fluids into Hg 0 in the sediment can account for the eventual native Hg occurrences in the close vicinity of the hydrothermal vents. The Hg 0 liq occurrences in the distal metalliferous sediments most probably have originated directly from the hydrothermal fluids and been transported by hydrothermal plumes away from the vents. Condensation of Hg 0 liq from Hg 0 vap in the vent fluids subjected to near critical phase separation seems the most plausible mode of origin of the native Hg occurrences. The high-temperature vents at the global spreading ridge chain introduce an assessed amount of 1.62–4.86 × 10 3 t/yr Hg 0 liq into the ocean. With time, the deposited Hg 0 liq will likely be dissolved in the overlaying seawater and will not survive in the geologic record.