TORONTO (miningweekly.com) – Prospective seafloor miner Nautilus Minerals has awarded a contract for the detailed design of the Solwara 1 dewatering plant to be used on the company’s production support vessel to the Brisbane office of global consulting engineering firm DRA Group.

The scope of work awarded to DRA involved the detailed design of the vessel-mounted material processing facilities. With a design capacity of 400 t/h, the plant would include screening the seafloor massive sulphides into a number of size fractions, followed by dewatering using centrifuges and filter presses, eventually filtering to eight microns.

The combined dewatered product would then be temporarily stored in the vessel’s hold, before transhipment by Handimax vessels to Nautilus’s processing partner in China. The remaining filtered water would then be returned through the enclosed riser system to drive the subsea lift pump and discharged within 50 m of the seafloor from where it originally came.

The detailed design phase was expected to be complete by the fourth quarter, following which the vessel-mounted modules would be fabricated and precommissioned onshore before integration onto the completed vessel.

Construction of the process plant was expected to start early next year, with first production from the Solwara 1 project, offshore Papua New Guinea (PNG), being scheduled for 2018.

DRA had accumulated significant specialised experience from its offshore diamond recovery projects off the coast of south-west Africa. DRA regional director Donald Holley explained that this experience included overcoming the challenges in designing and operating process plants mounted on ships, resulting particularly from the impact of the dynamic environment from wave movement, and the need for modular construction.

The company was in the process of pioneering the concept of mining the ocean bed for copper, gold, zinc and silver.

Using a trio of submersible robots, Nautilus was intent on recovering high-grade polymetallic seafloor massive sulphide (SMS) deposits at 1 600 m below the surface of the Bismarck Sea, within the Western Pacific Ocean’s Rim of Fire.

The operation aimed to produce ore at a rate of more than 1.3-million tons a year, with the capacity to ultimately ramp up to 1.8-million tons a year of dewatered ore, which would be delivered to the PNG Port of Rabaul.

The Solwara 1 project team in 2007 reported the world's first SMS resource statement after it drilled a National Instrument 43-101-compliant resource using newly developed, remotely operated drills.

As of November 25, 2011, the Solwara 1 project had an indicated mineral resource of one-million tons, grading 7.2% of copper, 5 g/t of gold, 23 g/t of silver and 0.4% of zinc. Its inferred resource comprised 1.54-million tons, grading 8.1% of copper, 6.4 g/t of gold, 34 g/t of silver and 0.9% of zinc.