GUANGZHOU -- Chinese marine research vessel Haiyang 6 (Ocean 6) has completed its deep-sea exploration mission in the Western Pacific ocean after 122 days and 35,000 km at sea.

The vessel, which is under the Guangzhou Marine Geological Survey, Ministry of Natural Resources, returned to Guangzhou on Wednesday.

According to the GMGS, the mission has carried out a comprehensive geological and geophysical survey in some areas of the Northwest Pacific Ocean and obtained sediment samples rich in rare earth elements, laying a foundation for the scientific research on deep-sea ecosystems and evaluation of new resources.

Meanwhile, the expedition team also carried out the annual investigation in the contract area of cobalt-rich crusts.

China signed a cobalt-rich crust mining contract with the International Seabed Authority in April 2014. The crust is located in the seamount area of the Northwest Pacific Ocean, covering some 3,000 square km.

China is entitled to survey the area and conduct experiments in mining and smelting for 15 years, is obliged to hand over two-thirds of the area within 10 years and provide training to technicians from other developing nations.

He Gaowen, a GMGS engineer, said that during the mission, the researchers optimized the performance of the acoustic sensor system of in-situ thickness measurement, which enables precise detection of the cobalt-rich crusts and improves the stability and efficiency of deep sea shallow drilling.

The Haiyang 6 is the first modern comprehensive geophysical survey ship designed and built independently in China, whose basic design inspired many marine scientific survey vessels in China.

Since 2009, the vessel has carried out 55 missions to the South China Sea, the Pacific Ocean and the Antarctic waters.