Marine Mineral Resource Potential

Earth provides natural resources including minerals and metals that are vital for human life. At present almost all of these resources are mined on land with large high-grade deposits becoming more and more difficult to find, driving industry to lower-grade sites where mining has greater environmental impacts or to greater depth. At the same time, the global demand for metals is suspected to rise further due to steady population growth, expected to reach 9.7 billion by the year 2050 (United Nations, 2015), and economic growth of countries such as China, Brasil, and India. The population growth may cause increasing land use conflicts between the mining industry and the need to feed and house the growing population. In addition to the rising demand for metals, geopolitical issues can also limit the availability of metal resources. This was evident over the past years with China blocking export of “rare earth elements” from global markets awakening the media and policy. There is therefore a foreseeable risk of increasing resource supply shortages for metals that are important to the economy. Hence, a number of countries are looking for ways to ensure secure supplies of these critical metals beyond recycling and usage of less raw material. In this rapidly changing global economic landscape, mining in the submerged parts of the continental shelf or in the deep sea is one of the areas of interest not only for commercial entities but also for governments as they have to balance metal supply needs and environmental impacts (Hannington et al., 2017; Beaulieu et al., 2017; Petersen et al., 2016).  

 

Seafloor Massive Sulfides

Seafloor massive sulfides (SMS), also known as black smoker deposits, are occurrences of metal-bearing minerals that form on and below the seabed as a consequence of the interaction of seawater with a heat source (magma) in the sub-seafloor region of volcanically active oceanic spreading centers and along volcanic arcs (Figure 1). These occurrences are commonly associated with “oasis of life” harboring chemosynthetic faunal communities. By far the majority of SMS occurrences presently known are small, 3-dimensional bodies that can contain metals such as copper, zinc, gold, and silver. Other trace elements that are important for a variety of industry uses can be enriched at certain sites and are commonly considered as possible important by-products. Known SMS deposits at the seafloor rarely exceed a few million tonnes of metal with the exception of the metalliferous muds in the Atlantis II Deep of the Red Sea. The amount of sulfide close to the current spreading centres has been estimated to be 600 million tons globally, but more sulfides might be present in inactive deposits away from the spreading centres. New technologies to explore for such inactive sites are currently being developed in order to investigate the full ocean potential for sulfides. As a result, there is considerable interest in exploration both within the EEZ of coastal states and international waters. The International Seabed Authority, responsible for seabed activities in areas beyond national jurisdiction has approved 7 contracts for exploration, 3 in the Atlantic and 4 in the Indian Ocean.

The technology for mining these deposits is currently being built, and first deep-sea tests were performed by the Japanese in their coastal waters. The Canadian company Nautilus Minerals is constructing deep-sea SMS collectors for its Solwara 1 deposit in the territorial waters of Papua New Guinea. This site could become the first deepsea mine site for SMS, as a mining license was issued by the PNG government in 2011. Current planning foresees the start of mining operations in 2018.

Figure 1: Worldmap of known submarine hydrothermal fields (GEOMAR 2017). The location of Exclusive Economic Zones (EEZ) is also indicated.

 

 

Manganese Nodules

Manganese nodules occur widely on the vast, sediment-covered abyssal plains at depths of about 4,000–6,500 m (Figure 2). They are mineral concretions made up largely of manganese and iron that form around a hard nucleus and incorporate metals from the sediment and seawater. As manganese nodules form directly on the seafloor, these deposits can be regarded as a 2-dimensional resource. The greatest concentrations of metal-rich nodules occur in the Clarion-Clipperton Zone (CCZ), which extends from Hawaii to Mexico. A conservative calculation for the CCZ suggests that there are about 21,100 million dry metric tons of nodules in this region alone. Nodules are also concentrated in the Peru Basin, near the Cook Islands, and at abyssal depths in the Indian and Atlantic Oceans. Manganese and iron are the principal metals in polymetallic nodules, but the metals of greatest economic interest are nickel, copper, and cobalt that combined can reach between 2.5 and 3 wt%. In addition, there are enrichments of other valuable metals, such as molybdenum, vanadium, titanium, the rare earth elements (REE), and lithium, that have industrial importance in many high-tech and greentech applications and can possibly be recovered as by-products once appropriate processing techniques are developed. Mining technology is currently being developed in many countries and by commercial companies.

The International Seabed Authority has approved 17 contracts for exploration, mainly in the CCZ.

Figure 2: Worldmap with permissive areas for manganese nodules (after Hein et al., 2013). The location of EEZs is also indicated.

 

 

Cobalt-rich ferromanganese crusts

Cobalt-rich ferromanganese crusts form on nearly all rock surfaces in the ocean that are free of sediment and are composed of manganese oxides and iron oxyhydroxides that precipitate directly from seawater (Figure 3). Their thickness varies from less than 1 mm to about 20 cm. They form at water depths of 600–7,000 m on the flanks of volcanic seamounts, ridges, and plateaus with the thickest and most metal-rich crusts forming in depths between 800 and 2,500 m. Due to their slow growth rate of only 1–5 mm/million years, economic occurrences are limited to old volcanic edifices. Many of these volcanic seamounts are located within the EEZs of Pacific Island states with fewer seamounts, and hence crusts, in the Atlantic and Indian Ocean. Ferromanganese crusts have, in general, lower copper and nickel concentrations than manganese nodules, and therefore, cobalt is the metal of greatest economic interest commonly exceeding values of 0.5 wt% cobalt. Other potential by-products are the rare earth elements (REE), platinum group elements, and tellurium. One estimate of the quantity of crusts in the central Pacific region has been given at 7,533 million dry tons, containing about four times more cobalt, three and a half times more yttrium, and nine times more tellurium than the entire land-based reserves of these metals. Mining of crusts seems technologically more difficult as crusts are attached to a substrate rock, and dilution of the crusts by the substrate needs to be minimized. On the other hand, dispersion of sediments may not be a major issue of crust mining due to the lack of sediments. Technology for crust mining is still in a conceptual state.

The International Seabed Authority has approved 5 contracts for exploration, 4 in the western Pacific and one in the southern Atlantic.

Figure 3: Worldmap with permissive areas for Co-rich ferromanganese crusts (after Hein et al., 2013). The location of EEZs is also indicated.


References

Beaulieu, S.E., Graedel, T.E., Hannington, M.D., 2017. Should we mine the deep seafloor? Earths Future 5, 655–658. doi:10.1002/2017EF000605

Hannington, M., Petersen, S., Krätschell, A., 2017. Subsea mining moves closerto shore. Nature Geoscience 10, 158–159. doi:10.1038/ngeo2897

Hein, J.R., Mizell, K., Koschinsky, A., Conrad, T.A., 2013. Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: Comparison with land-based resources. Ore Geology Reviews 51, 1–14. doi:10.1016/j.oregeorev.2012.12.001

Petersen, S., Krätschell, A., Augustin, N., Jamieson, J., Hein, J.R., Hannington, M.D., 2016. News from the seabed – Geological characteristics and resource potential of deep-sea mineral resources. Marine Policy 70, 175–187. doi:10.1016/j.marpol.2016.03.012