Sea Technology

AUG 2012

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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The Role of AUV Technology in Seafloor Massive Sulfide Exploration Proof-of-Concept Trial in Tongan Waters Tests AUV Technique For Seafloor Mapping in Sulfide Exploration By Dr. Ian Stevenson Chief Geophysicist and Sean Plunkett Senior Geophysicist Nautilus Minerals Inc. Brisbane, Australia eafloor massive sulfides (SMS) deposits are typically located in water deeper than 1,000 meters and in close proximity to tectonic plate boundaries and submarine volcanic activity. Commercial exploration of SMS deposits requires mapping the seafloor at various scales, from regional mapping (greater than 10,000 square kilometers) to detailed prospect delineation (1 to 10 square kilometers). Vessel-based multibeam echosounder (MBES) surveys are commonly used at the regional scale of mapping. Follow-up detailed high-resolution mapping has been done with either ROVs or deep-towed geosurvey plat- forms. With the SMS exploration and production industry still in its early stages, significant opportunities exist to reapply existing technologies to this new industry. One technology with signif- icant market benefit and growth potential is AUVs. Nautilus Minerals (Brisbane, Australia), which holds almost 600,000 square kilometers of exploration tenements granted or under application, thinks AUV technology can deliver a faster and improved assessment exploration technique to decrease the cost and delivery time of prospective seafloor sampling and drill targets. The company is developing a copper-gold produc- tion operation at Solwara 1, located in the territorial waters of Papua New Guinea, and building an exploration pipeline in the western Pacific. S SMS Exploration Techniques During the early stages of exploration, vessel-based MBES systems are used to map large areas of the seafloor, typically at 25-meter cell size. This enables identification of broad-scale volcanic and tectonic features associated with SMS mineral- ization. While this technique is rapid and efficient for surveying large areas, it does not provide the resolution needed to con- fidently discriminate the mound features and chimney struc- tures associated with SMS formation. In addition to vessel-based MBES operations, CTD sensor tow-yo operations are undertaken to map plume signatures in 10 st / AUGUST 2012 the water column from active (venting) hydrothermal systems. This technique involves the deployment of a deep-tow sled be- hind the survey vessel, which is repeatedly winched in and out as the vessel steams along a predefined course, so that the sled acquires a continuous vertical profile of data within the water column, using CTD, Eh and light-scattering sensors. Once regional targets have been identified, in order to pro- ceed to prospect delineation, high-resolution surveys must be The Abyss AUV operations loaded in the launch and recovery system.

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