Investigation of marine mineral resources

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, which form the primary focus of marine resource exploration activities at the BGR. Deep-sea minerals can generally be grouped into three categories that are likely to be mined in the near future: (1) polymetallic (manganese) nodules, (2) cobalt-rich ferromanganese crusts, and (3) massive sulphides. Such resources, which in part are found in international waters, offer countries which are poor in metallic raw deposits, such as Germany, the opportunity to acquire exploration licenses from the International Seabed Authority (ISA) of the United Nations. These could pass into exploitation licenses at a later stage. On behalf of the German Federal government, the BGR holds one exploration license for manganese nodules in the Equatorial North-eastern Pacific (since July 2006) and one license for massive sulphides in the western Indian Ocean (since May 2015).

Locations of important marine mineral deposits. Red dots: sulphide deposits. Pink areas: manganese nodule deposits. Yellow crosses: phosphorite deposits. Blue areas: manganese crust deposits Source: BGR

Polymetallic nodules

Seafloor with a dense coverage of manganese nodules in the German exploration license area (NE Pacific). Water depth: 4100 m Source: BGR

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 centimetres. 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 millimetres per million years. The largest and economically most important deposits are found in the North-eastern 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 which are, for example, required for electro- and steel industries, amongst others.

Cobalt-rich ferromanganese crusts

Cobalt-rich crust on a hyaloclastic substrate from the flank of a seamount in the Central Pacific; thickness of crust ca. 8 cm Source: Prof. Halbach, FU Berlin

Ferromanganese crusts are Mn-Fe-oxides 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 two-thirds of all known deposits are found in the Pacific (especially in the western Central Pacific), about one quarter 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 (massive) sulphides

Black smokers with anemones and orange-brown fragments of massive sulphides in the German exploration license area (Indian Ocean) Source: BGR

Hydrothermal polymetallic sulphides are 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 waters up to 3000 meters depth. As hot, metal-rich hydrothermal fluids mix with the surrounding sea water at such sites, sulphide minerals precipitate out of the water column and 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.