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Using Technology to Explore Potential Resources

Dr. Bramley J. Murton,
Principal Scientist,
Marine Geoscience Group, National Oceanography Centre

Natural resources of energy and minerals are vital for modern human civilization. Yet as the global demand grows, their supply continues to diminish. This is especially the case for strategic metals, whose commodity prices have risen manyfold in the last decade. There is now a risk of supply shortage for some elements critical to modern industrial economies. Pressure is growing for science and technology to provide solutions to secure future supply.

With nearly 75 percent of the Earth’s solid surface lying underwater, interest in seafloor mineral deposits is growing rapidly. This previously occurred during the 1970s, and within the last decade, mining the deep seafloor for massive sulfide deposits and polymetallic nodules has re-emerged to become a likely reality in the next decade. The European Commission (EC) estimates that, by 2020, 5 percent of the world’s minerals, including cobalt, copper and zinc, could come from the deep ocean floor. This could rise to 10 percent by 2030, with global annual turnover of marine mineral mining growing to €10 billion.

There are two major reasons why seafloor mineral deposits are becoming more attractive: Compared with their terrestrial counterparts, the base-metal grades of these deposits are high, and seafloor mineral deposits are not buried under hundreds of meters of rock. This makes seafloor mineral deposits relatively accessible and economically viable, despite being at water depths of 2,000 to 6,000 meters.

Seafloor mineral deposits’ resource viability depends on underwater technology to locate, assess, extract and process the ore. The U.K.’s National Oceanography Centre (NOC) has recently joined a research consortium receiving €10 million in funding from the EC to develop an exploration and assessment strategy for extinct seafloor massive sulfide deposits (eSMS) on the midocean ridge crest.

We will deploy AUVs equipped with geophysical sensors, e.g., electrical self-potential, three-component magnetics, sub-bottom geoacoustic profilers, multifrequency side scan sonars, multibeam sonars, and Eh chemical sensors to locate eSMS deposits on and under the seafloor on the Mid-Atlantic Ridge. The work will occupy an area about 500 square kilometers, with missions up to 75 hours down to 4,000 meters depth.

We also aim to develop an integrated geological and geophysical model for the subsurface structure using near-bottom, deep-towed, multichannel seismic reflection profiling. Additionally, ocean bottom seismometers will be deployed using Hydro-Lek Ltd.’s (Finchampstead, England) HyBIS in a tight grid around several well-known 200-to-500-meter-diameter eSMS deposits to determine their subseafloor velocity and density structure. The subsurface metal and sulfide content of the eSMS deposits will be determined via active electromagnetic tomographic data. Our active electromagnetic instruments comprise deep-towed, near-bottom source and receiver arrays, as well as stationary seafloor instruments and sources placed on the seafloor in a tight array.

The geophysical data must be calibrated against samples for synthesis and development of a geophysical response model. For this, we will deploy a seafloor drilling rig, the 6-tonne RD2, operated by the British Geological Survey, down to 4,000 meters depth. This coring system can drill 50-meter-deep holes and deploy downhole logging tools. NOC will analyze the core for geophysical properties, e.g., electrical resistivity, seismic velocity, shear strength, magnetic intensity and susceptibility. We will also analyze its mineralogical and geochemical properties to assess the process operating deep within the eSMS deposit after the high-temperature, ore-forming fluids have ceased to flow. We aim to determine to what extent hydrothermally extinct SMS deposits decompose and lose their valuable metal content once exposed to oxygen-rich seawater.

This research will improve our estimates of the resource potential of seafloor mineral deposits. Our mission is to develop the knowledge base to better understand the formation and preservation of these deposits for the public good.

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