HYDROTHERMAL MINERALIZATION OF PB-ZN CHIMNEY IN THE WESTERN TA25 CALDERA, TONGA ARC

Abstract

Korea Institute of Ocean Science and Technology has conducted research and development programs for exploitation of seafloor massive sulphide deposits on the exclusive economic zone of the Kingdom of Tonga since 2008. The seafloor hydrothermal sulphide vents and mounds have been found on the western TA25 subsea volcano caldera in the Tonga arc. The hydrothermal vents and mounds are densely populated within SW-trending radial fractures. The short chimney and simple sulphide assemblage reflects these hydrothermal vents are immature in incipient stage. These active chimneys are emitting the transparent fluids of which temperatures range from 150°C to 242°C (average=203°C). The hydrothermal ores recovered by remotely-operated vehicle (ROV) mainly comprise sulphides such as sphalerite, pyrite, marcasite, galena, chalcopyrite, covellite, tennantite, enargite and sulfates such as barite, gypsum/anhydrite. Sphalerite is predominant sulphides in chimneys and mounds, indicating Zn-rich hydrothermal mineralization is dominant. The hydrothermal ores also have minor enargite, implying that mineralization occurred in high sulphidation environment.The FeS content of sphalerite and its proportion increase from outside to inside of the hydrothermal chimney, respectively. Sphalerite from the chimney, in particular, shows a great silver content (up to ~10 wt.%). Chalcopyrite is examined in both mound and chimney but it is more mal sulphide vents and mounds have been found on the western TA25 subsea volcano caldera in the Tonga arc. The hydrothermal vents and mounds are densely populated within SW-trending radial fractures. The short chimney and simple sulphide assemblage reflects these hydrothermal vents are immature in incipient stage. These active chimneys are emitting the transparent fluids of which temperatures range from 150°C to 242°C (average=203°C). The hydrothermal ores recovered by remotely-operated vehicle (ROV) mainly comprise sulphides such as sphalerite, pyrite, marcasite, galena, chalcopyrite, covellite, tennantite, enargite and sulfates such as barite, gypsum/anhydrite. Sphalerite is predominant sulphides in chimneys and mounds, indicating Zn-rich hydrothermal mineralization is dominant. The hydrothermal ores also have minor enargite, implying that mineralization occurred in high sulphidation environment.The FeS content of sphalerite and its proportion increase from outside to inside of the hydrothermal chimney, respectively. Sphalerite from the chimney, in particular, shows a great silver content (up to ~10 wt.%). Chalcopyrite is examined in both mound and chimney but it is more