Mineral resources from the marine realm include near-coastal occurrences of phosphorites, sand, gravel and heavy mineral enrichments, many of which are already being actively mined today, and the resources of the deep sea. Deep-sea minerals can generally be grouped into three categories:
Polymetallic nodules, also called manganese nodules due to their high manganese content, are blackish-brown, irregularly to roundly formed concretions with diameters of about 1 to 6 cm. They occur in deep sea areas where sedimentation rates are low, and form due to the precipitation of Mn- and Fe-oxides as well as numerous other major and trace metals from sea water and the pore waters of the sediment. Growth rates are extremely low, with values varying between about 2 and 100 mm/Ma. The largest and most important deposits are found in the NE Pacific (in the so-called manganese nodule belt between the Clarion and Clipperton fracture zones), where commonly about 50% of the sediment surface is covered by manganese nodules. Economically relevant metals contained in the nodules are copper, nickel and cobalt, which together form up to 3 weight percent of the nodules and are, for example, required by the electro- and steel industry, amongst others.
Cobalt-rich ferromanganese crusts
Ferromanganese crusts are Mn-Fe-oxide layers which form on rocky surfaces on the flanks and summits of underwater seamounts (submarine mountains) and ridges, and are typically only several centimetres thick. A detailed analysis of global and regional deposits of ferromanganese crusts and their metal contents has shown that the thickest and economically most interesting deposits occur in water depths between 800 and 2500 m. About 66% of all known deposits are found in the Pacific (especially in the western Central Pacific), about 23% in the Atlantic and only 11% in the Indian Ocean. Approximately 40 billion tons of dry ore are estimated to occur on the ocean floor, of which about half are considered to be potentially minable. In addition to cobalt, crusts are an important potential source of nickel, manganese, titanium, copper and cerium, and of trace metals such as platinum, molybdenum, tellurium and tungsten.
Hydrothermal polymetallic sulphides
Hydrothermal polymetallic sulphides are always associated with marine volcanic structures such as mid-oceanic ridges, back-arc spreading zones or island arcs. Spectacular “black smokers” characterise hydrothermally active zones in water depths up to 3000 m. As heated hydrothermal fluids discharged from the black smokers mix with the surrounding sea water, metal sulphides are precipitated onto so-called chimneys and the nearby seabed, where they can generate local ore deposits with a diameter of several hundreds of meters. High concentrations of base metals (copper, lead and zinc) and precious metals (gold, silver) as well as high-technology metals such as indium, germanium, bismuth and selenium make these deposits economically attractive.
All three deep-sea mineral types form raw material deposits which could be minable in the near future. Their distribution in part in international waters gives Germany, as a country which is poor in metallic raw material deposits, the opportunity to obtain mineral exploration licenses from the International Seabed Authority (ISA) of the United Nations. These could pass into exploitation licenses at a later stage. The BGR carries out exploration research for manganese nodules in the equatorial NE Pacific, after signing a 15 years exploration contract with the ISA in July 2006 (Manganese nodule exploration in the German license area). Furthermore, a preparatory project for the application for an exploration contract for polymetallic sulphides is currently underway.