The New Frontier of Seafloor Polymetallic Exploration

18 Sep 2012

Since 2010, RPS' Subsea team has been working with Canadian-based Nautilus Minerals Inc (Nautilus) on their deepwater mineral exploration project. Over the past 15 years, developments in undersea survey techniques have identified vast resources offshore.

Nautilus is the first company to commercially explore the seabed for high-grade copper, zinc, gold and silver ores and has identified high-grade polymetallic Seafloor Massive Sulphide (SMS) deposits on the seabed of the Bismarck Sea offshore Papua New Guinea.

RPS has been involved in the resource estimation and exploration surveys and has recently been working with Nautilus to identify an ideal seabed positioning system for the planned mining tools. As required the MetOcean and WA Environment teams have been involved in different project stages.

SMS deposits occur around deep marine hydrothermal vents associated with volcanic rifts in back arc basins. They represent marine analogies to the terrestrial volcanic-hosted massive sulphide deposits (VHMS), of which the Iberian Pyrite Belt, Kidd and Noranda Camp in Canada and the Kuroko in Japan form notable examples. The deposits form where superheated water enriched with minerals mix with cold seawater, precipitating metal-rich elements.

Solwara 1 will be the first deposit to be mined and lies at a mean water depth of 1,600 m, some 50 km off Rabaul (New England Province, Papua New Guinea). The planned development, which is at the forefront of undersea technologies, comprises a combination of three Seafloor Production Tools: a Cutting Machine, an Auxiliary Cutter and a Bulk Cutter, which will rip and excavate the SMS deposits from the seabed. The Auxiliary and Bulk Cutter will discharge their cuttings via Stockpile Hoses to a Stockpile Diffuser Hood, acting as a central stockpile heap on the seafloor.

The Collecting Machine will then suck up the cut ore from the marine stockpile and pump it as slurry to the Production Support Vessel, through the Subsea Slurry Lift System, via the rigid Riser Transfer Pipe. The slurry will then be dewatered on the vessel prior to being transferred to cargo barges and transported to the Port of Rabaul for stockpiling. The site will be continually monitored by two Remotely Operated Underwater Vehicles (ROVs). The mineralised ore will then be shipped for concentrating and then smelting. An expected 1.2 to 1.8 million tonnes will be mined annually.

Solwara 1 lies within Mining Lease Application 154, granted by the PNG Mineral Resources Authority in January 2011. It covers an area of 59.11 square kilometres. The currently outlined mineralised zone is about 1.3 km long and up to 200 m wide and has been test-drilled to depths of up to 19 m below the seafloor. The seabed deposits show a high 7.3% average grade of copper with some peaks of over 30%. The ore also contains average inferred resources of 7.2g/t gold and 37g/t silver. The mining lease has been granted for an initial 20 year term. Nautilus also hold over 600,000 km2 of offshore exploration licenses in PNG, Fiji, Tonga, Vanuatu, the Solomon Islands, New Zealand and the Eastern Pacific.

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