Mineralogy and trace element geochemistry of hydrothermal sulfides from the Ari vent field, Central Indian Ridge

Abstract The Ari vent field (AVF) is an ultramafic-hosted seafloor massive sulfide (SMS) deposit in the middle part of Central Indian Ridge. In this paper, we describe detailed mineralogy and geochemistry hydrothermal samples from AVF, which can be classified into Fe–Cu- Cu-rich types based on major minerals. Sulfide mineralisation former type comprises: (1) stage I, early deposition magnetite, pyrrhotite, isocubanite, chalcopyrite, subhedral–euhedral pyrite under high-temperature fluid conditions (> 335 °C); (2) II, colloform pyrite, sphalerite, galena, electrum low-temperature fluids (< 200 °C) during later stage; (3) III, seawater alteration that caused precipitation uraninite chalcocite. This indicates AVF had decreasing temperature ƒS 2 increasing ƒO as proceeded. have mineral assemblages a paragenesis similar to those Fe–Cu-rich samples, but higher proportion isocubanite indicative relatively high-temperatures reducing mineralisation. Bulk chemical compositions sulfides are characterised by high U contents (up 51.9 ppm) distinct Sn distribution (2.1–86.4 between two different differ other deposits. content controlled mainly discrete grains 1 μm size) altered surfaces hematite. oxidative Fe-bearing minerals fixation seawater-derived U. Laser ablation–inductively coupled plasma–mass spectrometry analysis showed most trace elements occur solid solution minerals, physicochemical (e.g. temperature, , ). particular, comparative mid-ocean ridge systems shows sphalerite more enriched compared with hosted basaltic rocks. However, Sn-poor 10.2 ppm), because substantially depleted (mostly < regardless effect situ element especially for Sn, provide insights basaltic- systems, cannot necessarily inferred bulk analysis. Our comparison also suggests SMS deposits would possible source volcanogenic (UM-VMS) deposit. δ 34 S values (+ 6.2 + 8.5‰) record thermochemical sulfate reduction seawater, sulfur metals were predominantly leached associated host rocks contribution (29–40%) reduced sulfur. conclusion, rock-dominated system contains