Growth and Composition
Nodule growth is one of the slowest of all geological phenomena, on the order of a centimeter over several million years. Several processes are involved in the formation of nodules, including the precipitation of metals from seawater (hydrogenous), the remobilization of manganese in the water column (diagenetic), the derivation of metals from hot springs associated with volcanic activity (hydrothermal), the decomposition of basaltic debris by seawater (halmyrolitic) and the precipitation of metal hydroxides through the activity of microorganisms (biogenic). Several of these processes may operate concurrently or they may follow one another during the formation of a nodule.
The chemical composition of nodules varies according to the kind of manganese minerals and the size and characteristics of the core. Those of greatest economic interest contain manganese (27-30%), nickel (1.25-1.5 %), copper (1-1.4 %) and cobalt (0.2-0.25 %). Other constituents include iron (6%), silicon (5%) and aluminium (3%), with lesser amounts of calcium, sodium, magnesium, potassium, titanium and barium, along with hydrogen and oxygen.
Read more about this topic: Manganese Nodule
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