Formation of hydrothermal sulfides precipitates in the Edmond field, central Indian ridge: Lead and sulfur isotope constraints

The Edmond field, a basalt-hosted hydrothermal system located in the Central Indian Ridge (CIR) 23°52'S, was first discovered in 2000. Lead and sulfur isotope data are reported in this paper for nine hydrothermal sulfides samples in the Edmond field. The sulfides exhibit a narrow range of Pb isotope ratios (206Pb/204Pb=17.879-17.970, 207Pb/204Pb=15.433-15.550, 208Pb/204Pb=37.743-38.130). Reported in Pb-Pb diagrams, Edmond sulfide data nearly define a small domain compared with the large field of upper oceanic crust (CIR MORB), indicating that the main lead sources for the Edmond mineralization are the components of the upper oceanic crust with little sources from the the components of seawater. The sulfides have a δ34S of 5.7‰-7.2‰, which is obviously higher than MORB (δ34S≈0‰), and also higher than sulfides (δ34S=1‰-5‰) from other hydrothermal fields in East Pacific Rise and Mid-Atlantic Ridge. A two end-member mixing model at about 70/30 between basalt-derived sulfur and sulfur from reduction of seawater sulfate is suggested for the sulfur source. A shallow hydrothermal circulation system under the sulfide mound maybe the main mechanism for the heavy sulfur isotope signature in the Edmond field.