Rare earth elements in hydrothermal fluids from Kueishantao, off northeastern Taiwan: Indicators of shallow-water, sub-seafloor hydrothermal processes

The rare earth element (REE) geochemistry of hydrothermal vent systems has been investigated intensively, but few studies have been carried out on marine shallow-water hydrothermal systems like that at Kueishantao. Here we present novel data sets of REE in hydrothermal fluids from Kueishantao, off northeastern Taiwan. The total REE (ΣREE) concentrations of yellowish fluids are similar to those of whitish fluids, 813–1212 ng/L, and are significantly higher than that of ambient seawater. The yellowish fluids have chondrite-normalized REE (REEN) distribution patterns with slight convex-downward curvatures at Eu; and the REE patterns of the whitish fluids are smooth at Eu, which is related to the lower temperature and more oxidizing conditions. The Kueishantao hydrothermal fluids are slightly enriched in light REE (La-Nd) relative to the heavy REE (Gd-Lu). The behaviors of REE in both yellowish and whitish fluids are affected by the short time of water-rock interaction. The REE distributions in the yellowish fluids are also affected by very low pH (2.81 and 2.29), boiling of the fluid and precipitation of native sulfur. In the whitish fluids, adsorption by small particles and formation of REE-chloride complexes has played a role in the distribution of REE.