Title: News from the seabed– Geological characteristics and resource potential of deep-sea mineral resources

Authors: Petersen et al.

Journal & Year: Marine Policy, 2016

BLUF: Deep-sea mineral resources offer a vast and geologically diverse potential supply of metals critical to global industry and green technologies. In Marine Policy (2016), Petersen et al. provide the first comprehensive geological review of these resources, emphasizing their formation environments, spatial distribution, and metal content. The study finds that manganese nodules and ferromanganese crusts hold especially high potential to impact global markets for nickel, cobalt, copper, and rare earth elements, given their large tonnage and metal concentrations. 

Most known seafloor massive sulfide (SMS) deposits are small, and mining them is therefore expected to have little impact on global metal supply, even though individual sites can be rich in gold, silver or zinc.

The authors highlight how exploration is advancing under the governance of the International Seabed Authority (ISA), and argue that new technologies and a phased approach can help unlock these resources while minimizing environmental risks.

For the deep-sea mining industry, the study affirms a resource base large enough to justify long-term investment and regulatory engagement, and encourages continued development of responsible exploration and extraction systems.

The deep ocean is home to mineral resources formed by natural geological processes over millions of years.

The three most promising deep-sea mineral commodities — manganese nodules, cobalt-rich ferromanganese crusts, and seafloor massive sulfides (SMS) — each occur in distinct environments, differ in composition, and offer complementary metals essential for renewable energy, battery production, and high-tech manufacturing. 

  • Manganese nodules, the most widely distributed, form on sedimented abyssal plains through a combination of chemical precipitation from seawater and sediment pore fluids. Found at depths of 3,000 - 6,000 meters, they contain economically valuable concentrations of nickel, copper, cobalt, and manganese. The most promising area, the Clarion-Clipperton Zone (CCZ), contains an estimated 21 billion tonnes of dry nodules, including more manganese than all known land reserves and significantly more nickel and cobalt than are currently available onshore.
  • Cobalt-rich ferromanganese crusts form on rocky slopes of underwater seamounts, primarily in the western Pacific's “Prime Crust Zone” (PCZ), at depths of 800 - 2,500 meters. These crusts grow slowly but adsorb high concentrations of cobalt, tellurium, and rare earth elements (REEs), making them a highly strategic resource. Although crusts occur widely, the most viable deposits are primarily within coastal states' Exclusive Economic Zones (EEZs), making this a geopolitically accessible target for national mining programs.
  • Seafloor massive sulfides are mineral deposits formed by hydrothermal activity at mid-ocean ridges, volcanic arcs, and back-arc basins. These deposits are rich in copper, zinc, gold, and silver, and often form towering chimneys and mounds. While most known SMS deposits are relatively small compared to land analogues, some sites — like Solwara 1 in Papua New Guinea — have been characterized in detail and are moving toward potential mining. The global estimated resource base is smaller than for nodules or crusts, but includes highly concentrated ores in accessible locations.

According to the table on page 11 (Table 6), the metal contents and estimated tonnages suggest that nodules and crusts could shift global metal supply if mining scales up. For example:

Characteristics of deep-sea mineral resources.
  • Manganese nodules in the CCZ: 2.4% combined Ni + Cu grade, 0.2% Co, and 28% Mn.
  • Ferromanganese crusts in the PCZ: 0.5% Cu+Ni, 0.7% Co, and 0.24% REE + Y.
  • Seafloor massive sulfides (median): 3% Cu, 9% Zn, 2 ppm Au, and 100 ppm Ag.

Grades are more consistent regionally for nodules and crusts, but SMS grades are highly variable and site-specific.

This variability poses challenges for resource estimation and mine planning, but also offers opportunity for high-value finds — especially in back-arc and arc settings where gold and silver concentrations can be elevated.

The map on page 10 (Fig. 4) shows that by 2016, the ISA had issued 27 exploration contracts covering 1.24 million km² in areas beyond national jurisdiction. These include:

  • 17 contracts for nodules (mostly in the CCZ),
  • 4 for cobalt crusts (in the Pacific and Atlantic),
  • 6 for SMS (in the Indian and Atlantic Oceans).

Additional licenses have been granted by coastal states within EEZs and commercial ventures are underway in Papua New Guinea and the Red Sea.

The study notes that while mining systems are not yet commercially operational, technological readiness is advancing. Japanese field tests for SMS mining have already begun, and prototype mining tools for nodules are in various stages of development.

A key takeaway from this paper is that not all seabed mining carries the same ecological footprint.

A single polymetallic nodule operation could affect up to 150 km² per year, whereas an SMS operation might disturb less than 0.2 km² annually. This vast difference is critical when evaluating trade-offs.

The authors suggest that ecosystems at active vent sites may naturally recover more quickly than those in stable abyssal plains, but also caution that more data are needed to validate long-term recovery patterns.

They also emphasize that the current pause before large-scale mining begins is an ideal time to implement forward-looking regulations and baseline monitoring — something the International Seabed Authority is actively pursuing.

Industry participants that support robust science and engage with precautionary governance are likely to benefit from public trust and regulatory stability over the long term.