Polymetallic Nodules 

The polymetallic nodules are formed by metals precipitation either from ambient seawater (hydrogenetic formation), from pore-waters in the sediments (diagenetic formation), from hydrothermal derived fluids (Bonatti and Nayudu, 1965; Bau et al., 2014; Kuhn et al., 2017) and the formation processes that represent a mix of these different end-member processes.

Figure 1
Figure 1

Underwater image showing polymetallic nodules field, Tropic Seamount (Canary Islands, Central East Atlantic Ocean). Photo: ROV ISIS 6000, NOC.

Figure 2
Figure 2

The photograph show a spherical small Fe-Mn nodule section. The nodule was recovered in the Guadalquivir Diapiric Ridge area (Gulf of Cádiz, NE Atlantic Ocean). Source: González et al. 2009 https://doi.org/10.1016/j.margeo.2008.11.005.

Figure 3
Figure 3

polymetallic nodules filed in the Gulf of Cadiz. Photo: IGME-IEO.

Figure 1
Figure 1

Underwater image showing polymetallic nodules field, Tropic Seamount (Canary Islands, Central East Atlantic Ocean). Photo: ROV ISIS 6000, NOC.

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Polymetallic nodules occur in abyssal plains (~4000 – 6000 mm water depth) of all major oceans as two-dimensional deposits, formed on or just below sediment-covered seafloor, rich in metals of economic interest such as manganese (Mn), nickel (Ni), copper (Cu), cobalt (Co), molybdenum (Mo), titanium (Ti), lithium (Li), and rare earth elements (REE). The nodules are generated in marine environments where the sedimentation rates are low, commonly less than 10 centimeters (cm) per thousand years.