Tungsten enriched in submarine hydrothermal fluids

Abstract

Here we report the first data for W in hydrothermal vent fluids in the deep oceans. Vented hydrothermal fluids were collected from the Kairei Field, a mid ocean ridge hydrothermal field at the Rodriguez Triple Junction, Central Indian Ridge, and from arc–backarc hydrothermal systems at the Suiyo Seamount in the Izu–Bonin Arc, North Pacific Ocean and at the Hatoma and Yonaguni Knolls in the Okinawa Trough, East China Sea. While the dissolved W concentration in hydrothermal fluids linearly increased with a decrease in the Mg concentration for each system, the W concentration in endmember fluids was very different. It was 0.21 nmol/kg at the Kairei Field, 15 nmol/kg at the Suiyo Seamount, and 123 nmol/kg at the Hatoma Knoll, which was 4 orders of magnitude above the ambient level in seawater. The W concentration was not a simple function of Cl, alkalinity, B, and NH 4. The hydrothermal fields are efficiently enriched with W through reaction with fractionated calc-alkaline dacite and with terrigenous sediments. Although Mo is a chemical analogue of W in oxic seawater, the Mo concentration decreased in the hydrothermal fluids to 2–7 nmol/kg probably due to precipitation of Mo sulfide.