Mineralogical and Geochemical Studies on the Daum Vent Field, Central Indian Ridge

Abstract

The Daum Vent Field (DVF) was newly discovered in the Central Indian Ridge during the hydrothermal expedition by the Korea Institute of Ocean Science & Technology (KIOST) in 2021. In this paper, we describe the detailed mineralogy and geochemistry of hydrothermal chimney and mound to understand the nature of hydrothermal mineralization in the DVF. The mineral assemblages (pyrite±sphalerite±chalcopyrite) of dominant sulfides, FeS contents (mostly <20 mole %) of sphalerite, and (Cu+Zn)/Fe values (0.001–0.22) of bulk compositions indicate that the DVF has an strong affinity with basaltic-hosted seafloor massive sulfide (SMS) deposit along the oceanic ridge. Combined with the predominance of colloform and/or dendritic-textured pyrite and relatively Fe-poor sphalerite in chimneys, the fluid-temperature dependency of trace element systematics (Co, Mn, and Tl) between chimney and mound indicates that the formation of mound was controlled by relatively reducing and high-temperature fluids compared to chimney. The δ34S values (+8.31 to +10.52‰) of pyrite reflect that sulfur and metals were mainly leached from the associated basement rocks (50.6–61.3%) with a contribution from reduced seawater sulfur (38.7–49.4%). This suggests that the fluid-rock interaction, with little effect of magmatic volatile influx, is an important metal source for the sulfide mineralization in the DVF.