First Ultramafic-Hosted Hydrothermal Sulfide Deposit Discovered on the Carlsberg Ridge, Northwest Indian Ocean

During R/V Zhukezhen Cruise DY33, Leg 1 (February 09 to March 29 2015, chief scientist: Dr. Xiqiu Han), we conducted comprehensive geophysical mapping, hydrothermal plume surveying, video sled observing and geological sampling along the slow-spreading Carlsberg Ridge. The most significant result of this leg is the discovery of a new ultramafic-hosted hydrothermal sulfide deposit which named Tianxiu Field at 63.82°E, 3.69°N in water depths of around 3450 m, on the southern rift-valley wall, ~5 km from the adjacent rift axis. The Tianxiu Field (700 m by 350 m) is currently active, with black smoker, massive sulfide talus, hydrothermal biota (shrimp, anemones, hairy gastropods, mussels, crabs, etc.) observed and significant hydrothermal anomalies (CH4, temperature, and turbidity). Cu-rich chimney with high concentration of copper (16.8 wt.%), massive sulfides, semi-sulfides, and serpentinized peridotites have been collected. Evidences from the oceanfloor observation and geological sampling imply that this area may contain rather promising economic sulfide ore deposit. The data and samples collected so far will serve to understand the tectonic, volcanic and hydrothermal processes of the ridge segment. More detailed and higher resolution survey work using the manned-submersible vehicle Jiaolong and AUV is needed in future to sampling the hydrothermal fluids and mapping the active site at the seafloor and to evaluate the ore resource potential of this field.