[HRE16-P07] Transformation of ore minerals and their geochemical signatures in submarine hydrothermal ore deposits in Izena Hole, Okinawa Trough
Keywords:Submarine hydrothermal ore deposits, Izena Hole, SIP, Replacement, Fe isotope, D/V Chikyu
Results of microscopic observations show that sphalerite and galena are comparatively dominant with minor occurrence of pyrrhotite and anglesite in the samples at shallow depths. In contrast, samples from middle and deep depths are more abundant on pyrite and chalcopyrite, and pyrite, respectively. The texture that pyrrhotite was dissolved and replaced by pyrite or marcasite was observed in the samples in the depth of 0.05 – 44.0 mbsf. The Fe content in sphalerite tends to decrease with increasing depth, and also change within single sphalerite grain. These results suggest that hydrothermal fluid geochemistry such as fugacity of S2 and O2, and temperature changes for the depth and time. The δ56Fe values (δ56Fe (‰) = 1000 * [(56Fe/54Fe) sample / (56Fe/54Fe) IRMM-014 -1]) of the bulk samples range from -0.62 to +0.11‰, which tends to increase toward the deeper part. This indicates that Fe sulfides at shallow depths was formed by non-equilibrium precipitation with a rapid cooling, which caused a kinetic isotope effect. In contrast, those at deeper depths were likely formed near the equilibrium conditions.