A view of a seafloor deposit containing large amounts of solid sulfides. Photo: CCTV News

Chinese researchers have discovered a large high-temperature active hydrothermal field in the western Pacific, with preliminary findings showing that the potential polymetallic sulfide resources in the area could reach the level of world-class seafloor deposits. Some ore samples were also found to contain much higher levels of gold and silver than deposits on land, according to CCTV News. 

The research team, formed by Tsinghua University, the Qingdao Institute of marine geology under the China Geological Survey, Shanghai Jiao Tong University and other institutions, carried out the expedition aboard the Chinese oceanographic research ship Xiangyanghong 10. 

The scientific expedition team set sail from Shenzhen on August 10 aboard the research vessel Xiangyanghong 10 for an 18-day voyage, during which researchers conducted seven dives with submersibles.

The newly discovered mineral deposit is located in a back-arc basin in the western Pacific within China's exclusive economic zone.

A picture of Chinese oceanographic research ship Xiangyanghong 10 in the ocean carrying out a scientific research operation Photo: CCTV News

The team had already carried out more than 10 previous surveys in the area and identified dozens of high-temperature hydrothermal vents at depths of about 700 to 1,500 meters. Temperatures of hydrothermal fluids at the vents reached more than 315 C.

Building on previous surveys, the latest expedition used detailed exploration and in-situ sampling to precisely identify a new and massive seafloor hydrothermal field in the basin. The associated hydrothermal sulfide deposit consists of three large cone-shaped mineral structures.

Preliminary analysis by the shipboard laboratory showed that the ore bodies are mainly composed of important economic minerals including chalcopyrite, pyrite and sphalerite.

Some samples contained as much as 15.4 parts per million (ppm), equivalent to 15.4g of gold per ton of ore, while silver content reached as high as 1,271 ppm, or 1,271g per ton. Their average concentrations were also significantly higher than those in land-based deposits.

Preliminary estimates suggest that the potential polymetallic sulfide resources in the area could reach the level of a world-class seafloor deposit, CCTV reported.

The back-arc basin where the deposit was found lies near the boundary between the Eurasian Plate and the Philippine Sea Plate, where tectonic activity is intense.

Seawater moving down through cracks in the seafloor is heated by magma below and undergoes a series of physical and chemical reactions. The resulting high-temperature hydrothermal fluids extract and concentrate materials from deep within the crust. When the hot fluids rise and enter cold seawater, dissolved metals react with reduced sulfur in the seawater to form solid sulfides, which gradually accumulate into seafloor mineral deposits.

The research team also discovered and photographed thriving communities of life in the hydrothermal field, including shrimp, crabs, shellfish and extremophile.

A thriving community of crabs and other marine life around deep-sea hydrothermal vents, where organisms obtain energy from chemical reactions in hydrothermal fluids. Photo: CCTV News

Song Shiji, deputy dean of the Institute for Ocean Engineering at Tsinghua University, said the biological communities living in such extreme deep-sea environments are also of important scientific value for studying life processes under extreme conditions.

Despite the deposit's high concentrations of gold, silver, copper, zinc and other resources, active hydrothermal deposits of this kind are currently not ready for mining because of factors including high pressure in the deep sea and complex geological conditions, according to CCTV News. 

Global Times