Nautilus Minerals plans to begin testing of sea-mining robots in the first half of 2016 that will ultimately be used to dig for copper and gold from the ocean floor off Papua New Guinea.
The company has commissioned a Bulk Cutter, Collecting Machine and Auxiliary Cutter and now awaits completion of a production support vessel that will act as operational base for the mining of the Solwara 1 site, expected to begin in 2018.
Nautilus has developed a production system using technologies adapted from the offshore oil and gas, dredging and mining industries to enable extraction of minerals at the site off New Guinea. The company says the site contains copper and gold of significantly higher grades than those typically found on land. Rock will be dug up on the seafloor by two large robotic machines that excavate material by a continuous-cutting process, not unlike those used for coal or other bulk continuous-mining operations on land.
The Auxiliary Cutter (AC) is a preparatory machine that deals with rough terrain and creates benches for the other machines to work. It will operate on tracks and has a boom-mounted cutting head for flexibility. The second machine, the Bulk Cutter, has higher cutting capacity but will be limited to working on flatter areas and benches created by the AC. Both machines leave cut material in temporary positions on the seafloor for collection by the third machine, the Collecting Machine (CM).
The CM, also a large robotic vehicle, will collect the cut material by drawing it in as seawater slurry with internal pumps and pushing it through a flexible pipe to the Riser and Lifting System (RALS). The RALS comprises a large pump and rigid riser pipe supported from the vessel that delivers the slurry to the surface. The pump is supported on a solid vertical (riser) pipe suspended beneath the support vessel. On the deck of the Production Support Vessel (PSV), the slurry is dewatered.
The dewatered solid material is stored temporarily in the PSV’s hull and then discharged to a transportation vessel moored alongside. Filtered seawater is pumped back to the seafloor through the riser pipes and provides hydraulic power to operate the RALS pump. Discharge of the return water at the seafloor eliminates mixing of the water column and is designed to minimize the operation’s environmental impact.
According to Nautilus, the Solwara 1 deposit, which sits on the seafloor at a depth of 1,600 meters, boasts a copper grade of approximately 7%. That compares with land-based copper mines, where the copper grade averages 0.6%. Gold grades of over 20 g/metric ton have been recorded in some intercepts at Solwara 1, which compare with an average grade on land of approximately 6 g/ton.
The PSV is under construction in China. When completed, it will measure 227 meters in length and 40 meters in width, generate approximately 31 megawatts of power and be able to accommodate up to 180 people. All the below-deck mining equipment will be installed in the PSV during the build process to minimize the work required following its delivery.