Seabed mineral deposits represent the most important yet least explored resource of CRM and base metals on the planet. These polymetallic deposits include: nodules rich in manganese, copper and nickel; crusts rich in cobalt, tellurium, rare earth elements and platinum group elements; phosphorites rich in phosphorous, yttrium and rare earth elements; seafloor massive sulphides rich in copper, zinc and gold. In addition, economically important marine placer deposits accumulate elements like tin, titanium, thorium and gold. 

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It is this combination of traditional (base) metals and the extreme enrichment in critical elements that makes the varied types of seafloor mineral deposits particularly interesting to both science and society. For example, a recent estimate of the global resource, based on the sparse data available, infers a dry mass of ferromanganese crusts on the seafloor of 35 x 10^9 tonnes (Halbach et al. 2017). In a rapidly changing global economic landscape, recovering deep-sea minerals has gone from a distant possibility to a likely reality within just a decade.

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