B, Mg, Li, and Sr isotopes in acid-sulfate fluids and volcanic rocks from the Manus Basin, Papua New Guinea

The data is used to understand the controls of their compositional variability. In particular, the formation of acid-sulfate and hybrid smoker fluids is still poorly understood, and their high Mg concentrations are explained either by dissolution of Mg-bearing minerals in the basement or by mixing between unmodified seawater and magmatic fluids.

Mg isotope ratios of the acid-sulfate fluids from Manus Basin are seawater-like, which supports the idea that acid-sulfate fluids in this study area predominantly form by mixing between unmodified seawater and a Mg-free magmatic fluid. Changes in the B, Li, and Sr isotope ratios relative to seawater indicate water-rock interaction in all acid-sulfate fluids. Further, the combination of δ7Li with B concentrations of the same fluids links changes in δ7Li to changes in (1) basement alteration, (2) water-to-rock ratios during water-rock interaction and/or (3) the reaction temperature.