Mineralogy and geochemistry of hydrothermal sulphide from a submarine volcanic high at 18°36.4′S Central Lau Spreading Center, Southwest Pacific

We report the mineralogy and geochemistry of hydrothermal sulphide from the crater of a volcanic high near 18°36.4′S of the Central Lau Spreading Center. During 1990s, that volcanic structure was reported active and sulphide samples were collected by MIR submersible. A section of a chimney-like structure from the crater-floor was studied here. The Fe-depleted sphalerites, and Co-depleted pyrites in that chimney were similar to those commonly found in low to moderate temperature (<300°C) sulphides from sediment-starved hydrothermal systems. Bulk analyses of three parts of that chimney section showed substantial enrichment of Zn (18%–20%) and Fe (14%-27%) but depletion of Cu (0.8%–1.3%). In chondrite-normalized rare earth element-patterns, the significant negative Ce-anomalies (Ce/Ce*=0.27–0.39) and weakly positive Eu-anomalies (Eu/Eu*=1.60–1.68) suggested sulphide mineralisation took place from reduced low-temperature fluid. The depleted concentration of lithophiles in this sulphide indicates restricted contribution of sub-ducting plate in genesis of source fluid as compared to those from other parts of Lau Spreading Centre. Uniform mineralogy and bulk composition of subsamples across the chimney section suggests barely any alteration of fluid composition and/or mode of mineralisation occurred during its growth.