Chinese research vessel Dayang Yihao returned to its home port in Qingdao on Thursday afternoon after a voyage covering 31,000 nautical miles and lasting 216 days.
On China's 39th oceanic expedition mission, the vessel traveled to the Indian Ocean to conduct oceanic surveys into polymetallic sulphide and sea floor rare earth, as well as to take sea water and geological samples.
China and the International Seabed Authority signed a contract in 2011 granting China exclusive rights to search for polymetallic sulphide in a 10,000-square-km area in the southwest Indian Ocean for 15 years.
Li Huaiming, chief scientist of the expedition team, said breakthroughs made during the mission included obtaining sulphide core samples from hydrothermal zones for the first time.
