The most important cobalt crust area is the Prime Crust Zone (PCZ) in the western Pacific. Each of these resources has its own especially abundant regions.
2.19 > Cobalt crusts occur in different ocean regions than manganese nod-ules. Furthermore, in the southern area of the PCZ, comparatively high contents of rare earth elements are found in the crusts. However, the quantities of manganese in the PCZ are still almost 3 times greater than the economically minable amounts on land today. In absolute terms the crusts of the Prime Crust Zone do not contain as much manganese as the manganese nodules of the Clarion-Clipperton Zone. Tellurium is necessary particularly for the production of highly efficient thin-film photovoltaic cells. Tellurium is also comparatively abundant in cobalt crusts. The crusts are often more precisely referred to as “cobalt-rich ferromanganese crusts”. The largest share of metals in the cobalt crusts, however, consists of manganese and iron. As the name suggests, the crusts contain a relatively large amount of cobalt compared to deposits on land and to manganese nodules. Like manganese nodules, cobalt crusts also represent a very large metal resource in the sea. In the manganese nodules nickel and copper predominate, while in cobalt crusts cobalt, nickel and rare earth elements are more significant. For the other elements making up lower weight per cents of the deposits, however, there are great differences to occurrences on land. Because iron is plentiful in land deposits, it is not a key factor in marine mining. 2.18 > Manganese nodules and cobalt crusts contain primarily manganese and iron. The amount of crust in the PCZ is estimated to total 7.5 billion tonnes. This area, around 3000 kilometres southwest of Japan, is called the Prime Crust Zone (PCZ). Accordingly, many metallic compounds were deposited here over a long period of time to form comparatively thick crusts. The world’s oldest seamounts were formed here during the Jurassic period around 150 million years ago. The western Pacific is of particular interest. The Pacific is thus the most important cobalt crust region in the world. Around 57 per cent are located in the Pacific. It has been estimated that there are over 33,000 seamounts worldwide. They will have to be laboriously separated and removed from the underlying rocks. Because the cobalt crusts are firmly attached to the rocky substrate, they cannot simply be picked up from the bottom like manganese nodules. On some seamounts they are only 2 centimetres thick, while in the richest areas thicknesses can be up to 26 centimetres. Depending upon the concentration of metal compounds in the sea water, crusts with different thicknesses have formed in different ocean regions. Crusts grow 1 to 5 millimetres per million years, which is even slower than nodules.
Similar to manganese nodules, these crusts form over millions of years as metal compounds in the water are precipitated.Īs with manganese nodules, deposition occurs very slowly. A coating on the rocksĬobalt crusts are rock-hard, metallic layers that form on the flanks of submarine volcanoes, called seamounts. Smaller seamounts are also called knolls. They are found in all of the oceans and reach heights of 1000 to 4000 metres.
Seamounts grow through volcanic activity to great heights on the sea floor over millions of years.
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