At a depth of 2,700 metres beneath the Southwest Indian Ocean, a scalding “black smoker” vents thick plumes, and the unusual seabed environment nurtures distinctive mineral deposits and life. This is the Southwest Indian Ocean sulphide area.
Recently, the Dayang Hao (Ocean) research vessel slowly berthed at the Shekou Cruise Center in Shenzhen, marking the formal return of China’s Dayang Cruise 95. After China first discovered a sulphide zone on the Southwest Indian Ridge in 2007, it signed with the International Seabed Authority in 2011 the world’s first exploration contract for an international seabed sulphide mine area, and the Second Institute of Oceanography of the Ministry of Natural Resources has carried out exploration work in the contract area continuously ever since.
Just before this year’s Spring Festival, expedition members from 18 institutions set out together. After a long voyage of 23 days, they reached the work area in the Southwest Indian Ocean in mid-March. “There is no mobile signal here, and you almost never see another ship,” one young team member said. Their operating window was only a little over a month, and the task list was long: recovering core samples from the seabed, giving the orebody structure the equivalent of a CT scan, and recording ecological and environmental information.
The mine area covers 2,500 km2, so how do you prospect it precisely? The secret is a fixed-point electromagnetic-acoustic detection system called Tongjing (Bronze Mirror). Cruise chief scientist Tao Chunhui, a researcher at the Second Institute of Oceanography, told reporters that the sulphide mine area is rich in copper, zinc and other metals, so as soon as the electromagnetic system comes near, the resistivity readings show anomalies, like a mirror that quickly makes the orebody reveal itself. This was the first use in a Dayang expedition of the Tongjing system, developed independently by the National Key Laboratory of Submarine Science and Delimitation, and its detection reaches to a thickness of up to 100 metres.
After locking onto the orebody, the expedition team used equipment including drill rigs and grabs to drill and sample the seabed rock. At the same time, they used two wave gliders to conduct underway observations of the marine geomagnetic field and ocean background noise, drawing a magnetic field map of the seabed while recording the ocean’s acoustic environment, over a cumulative track of nearly 1,000 kilometres, obtaining valuable first-hand data.
The cruise produced rich results. The expedition team discovered several new ore occurrences and also obtained a batch of environmental baseline samples. Tao Chunhui said these important discoveries will help scientists understand metallogenic patterns, resource distribution and geological characteristics, providing a basis for decisions on future peaceful development and use.
Tao Chunhui has worked in deep-sea resource surveys for more than 30 years and has spent more than 2,000 days and nights at sea. As chief scientist he has led teams that discovered a large number of sulphide zones, and he serves as chief geologist for this mine area.
Turn the clock back to Spring Festival 2007. At that time, the Chinese expedition team had already been searching the vast ocean for two years in the hunt for deep-sea sulphide zones. The international academic community then generally believed that ultraslow-spreading mid-ocean ridges could not host much hydrothermal activity, let alone form large deposits. On that day, they finally locked onto a patch of sea in the Southwest Indian Ocean showing temperature and turbidity anomalies. Suddenly, the towed camera sled banged into seabed rock, and in the returned images a cloud of glittering golden “smoke” rose up. “Found it!” The ship’s cabin erupted in an instant.
