Mineralogy and sulfur isotope characteristics of metalliferous sediments from the Tangyin hydrothermal field in the southern Okinawa Trough

Abstract

We present and compare mineralogy and sulfur isotopic composition data of two surface metalliferous sediment samples, TVG11-2 and ROV11-R2, from the newly discovered Tangyin hydrothermal field in the southern Okinawa Trough (S-OT), and one surface metalliferous sediment sample 2-T4 from the Iheya North Knoll hydrothermal field in the middle Okinawa Trough (M–OT). The purpose of this study is to better understand the hydrothermal ore-forming environment and material source in the S-OT. Samples TVG11-2 and ROV11-R2 were derived from different types of chimneys. Sample TVG11-2 was derived from a black chimney which experienced formation process from high temperature to low temperature, with large gradients and fluctuations. ROV11-R2 was directly derived from a low-temperature white chimney or low-temperature diffuse flow. The sulfur isotopic compositions of sulfides and native sulfur in the S-OT are significantly lower than the sulfur isotopic compositions of pyrite and native sulfur in the M–OT, indicating there is another source with a lower sulfur isotopic composition. The low forming temperature and similar basement rocks of rhyolite in Iheya North Knoll, and dacite in Tangyin exclude phase separation and basement rock differences as the main reasons for low sulfur isotopic compositions in TVG11-2 and ROV11-R2. The occurrence of different bacterial communities between S-OT and M–OT may affect the sulfur isotopic compositions, but the influencing mechanism is still unclear. The addition of magmatic H2S may be the most possible reason for lower sulfur isotopic compositions in the Tangyin hydrothermal field.