The Patania II nodule collector became uncoupled from a 5-km umbilical cable during trials underway in the Pacific Ocean's Clarion Clipperton Zone (CCZ), and drifted to the sea bed, said GSR.

However, following a survey by a different remotely operated underwater vehicle, a recovery mission was undertaken and Patania II  was re-connected on April 29.

"Today we were able to reconnect Patania II and we look forward to completing the mission, including further deployments," said Kris Van Nijen, managing director of GSR.

"We are taking a cautious, step-by-step approach to project development. We conduct these trials to better understand the challenges involved so we can continuously refine our technology."

Launched on April 6, the trial is a joint initiative with European research project MiningImpact. Set to last four weeks, it will include input from scientists from 29 European institutes along with the German exploration contract holder, BGR (Institute of Geosciences and Natural Resources).

GSR reported on April that its underwater robot has collected its first polymetallic nodules, stating that these contain  nickel, cobalt, manganese and copper .