Thematic Articles

Deep-sea mining presents complex regulatory challenges due to its multi-faceted political, economic, technological, scientific, environmental, social, industrial and legal aspects. These must all be sensitively addressed to achieve a commercially viable and socially responsible industry. Furthermore, these aspects are either governed by, or must take into account, the burgeoning regulatory regime promulgated by the International Seabed Authority. This paper addresses the regulatory challenges associated with the three types of deep-ocean mineral deposits of greatest interest to the deep-sea mining industry: polymetallic nodules, ferromanganese crusts, and polymetallic sulfides. We review current resource interest, the international regulatory context, selected regulatory challenges, and the International Seabed Authority’s innovative responses to selected issues.

A key question for the future management of the oceans is whether the mineral deposits that exist on the seafloor of the deep ocean can be extracted without significant adverse effects to the environment. The potential impacts of mining are wide-ranging and will vary depending on the type of metal-rich mineral deposit being mined. There is, currently, a significant lack of information about deep-ocean ecosystems and about potential mining technologies: thus, there could be many unforeseen impacts. Here, we discuss the potential ecological impacts of deep-ocean mining and identify the key knowledge gaps to be addressed. Baseline studies must be undertaken, as well as regular monitoring of a mine area, before, during, and after mineral extraction.

The future extraction of deep-ocean mineral deposits depends on being able to recover the metals in an economic and environmentally sensitive way. Metal production is one of the most energy intensive industrial sectors. The characteristics of some deep-ocean mineral deposits permit them to be readily dissolved and to release their contained metals into solution. Current innovations in hydrometallurgy, including metal leaching with ionic liquids and solvent extraction in non-dispersive phase contactors, demonstrate how metals could potentially be extracted from Fe–Mn deposits with increased energy efficiency and a reduced environmental footprint compared with traditional processing techniques. The importance of biological processes in the formation of deep-ocean Fe–Mn deposits is poorly understood. However, understanding how microorganisms select and deposit metal ions could further enhance targeted extraction of ‘critical’ metals.

Marine ferromanganese oxide crusts (Fe–Mn crusts) are potentially important metal resources formed on the seafloor by precipitation of dissolved and colloidal components from ambient seawater onto rocky surfaces. The unique properties and slow growth rates of the crusts promote adsorption of numerous elements from seawater: some, such as Te and Co, reach concentrations rarely encountered elsewhere in nature. Consequently, Fe–Mn crusts are potential sources of metals used in technologies considered essential for the transition to a low-carbon economy. However, the precise distributions and metal concentrations of Fe–Mn crusts at regional and local scales are poorly constrained because of the diversity of geological, oceanographic and chemical processes involved in their formation.

Seafloor massive sulfides are deposits of metal-bearing minerals that form on and below the seabed as a result of heated seawater interacting with oceanic crust. These occurrences are more variable than previously thought, and this variability is not necessarily reflected in the analogous volcanogenic massive sulfide deposits that are preserved in the ancient rock record. The geological differences affect both the geochemistry and the size of seafloor massive sulfide deposits. Current knowledge of the distribution, tonnage, and grade of seafloor massive sulfides is inadequate to rigorously assess their global resource potential due to the limitations in exploration and assessment technologies and to our current understanding of their 3-D characteristics.