Cobalt crustsCobalt crusts form at depths of 1000 to 3000 metres on the flanks of submarine volcanoes, and therefore usually occur in regions with high volcanic activity such as the territorial waters around the island states of the South Pacific. The crusts accumulate when manganese, iron and a wide array of trace metals dissolved in the water (cobalt, copper, nickel, and platinum) are deposited on the volcanic substrates. Their growth rates are comparable to those of manganese nodules. The cobalt crusts also contain relatively small amounts of the economically important resources. Literally tonnes of raw material have to be excavated in order to obtain significant amounts of the metals. However, the content of cobalt (up to 2 per cent) and platinum (up to 0.0001 per cent) is somewhat higher than in manganese nodules. Extracting cobalt from the ocean is of particular interest because it is found on land in only a few countries (Congo, Zaire, Russia, Australia and China), some of which are politically unstable. Alternative marine prospects could reduce our dependence on supplies from these countries.
- Technologically, the mining of cobalt crusts is much more complex than manganese nodules. For one, it is critical that only the crust is removed, and not the underlying volcanic rocks. In addition, the slopes of the volcanoes are very ragged and steep, which makes the use of excavation equipment more difficult. It is therefore not surprising that cobalt crust mining is only at the conceptual stage at present. Cobalt crust mining would also have a significant impact on the benthic organisms. It is therefore vital that prior environmental impact studies are carried out. In most cases monitoring by the International Seabed Authority (ISA) is not possible because many cobalt occurrences are located within the territo- rial waters of various countries.
- 7.5 > Massive sulphides form at black smokers – hot springs on the sea floor with temperatures approaching 400 degrees Celsius. These vents discharge minerals from the Earth’s interior, forming chimneys that rise to several metres above the seabed. Black smokers are also unique habitats.
Massive sulphidesThe third resource under discussion is a sulphur-rich ore that originates at “black smokers”. These occurrences of massive sulphides form at submarine plate boundaries, where an exchange of heat and elements occurs between rocks in the Earth’s crust and the ocean due to the interaction of volcanic activity with seawater. Cold seawater penetrates through cracks in the sea floor down to depths of several kilometres. Near heat sources such as magma chambers, the seawater is heated to temperatures exceeding 400 degrees Celsius. Upon warming, the water rises rapidly again and is extruded back into the sea. These hydrothermal solutions transport metals dissolved from the rocks and magma, which are then deposited on the sea floor and accumulate in layers. This is how the massive sulphides and the char- acteristic chimneys (“black smokers”) are produced. These were first discovered in 1978 at the East Pacific Rise. For a long time it was thought that massive sulphides with mining potential were only formed on mid-ocean ridges, because the volcanic activity and heat production here are especially intense. But since then more than 200 occurrences worldwide have been identified. Experts even estimate that 500 to 1000 large occurrences may exist on the sea floor. But there are also great differences in size. Most occurrences are only a few metres in diameter and the amount of material present is negligible. So far only a few massive sulphide occurrences which are of economic interest due to their size and composition are known. While the black smokers along the East Pacific Rise and in the central Atlantic produce sulphides comprising predominantly ironrich sulphur compounds – which are not worth considering for deep-sea mining – the occurrences in the southwest Pacific contain greater amounts of copper, zinc and gold. They are also located in comparatively shallow water (less than 2000 metres) and lie within the exclusive economic zones of nations near them (Chapter 10), which makes the possible mining more technologically and politically feasible. This is because a country can decide for itself with respect to the mining of marine resources within its own exclusive economic zone. The deep sea floor outside these sovereignty limits, however, is overseen by the International Seabed Authority (ISA; Chapter 10).
- Present mining scenarios primarily envision the exploitation of cooled, inactive massive sulphide occurrences that are only sparsely populated by living organisms. Active black smokers are rejected for the time being because most of them contain only comparatively minor amounts of resources. Furthermore, because of the nutrient rich waters rising from below, they provide an important habitat for numerous, and in part, endemic organisms. The largest known sulphide occurrence is located in the Red Sea, where tectonic forces are pulling Africa and the Arabian Peninsula apart. Here, the sulphides are not associated with black smokers, but appear in the form of ironrich ore muds with high contents of copper, zinc and gold. This occurrence, at a water depth of about 2000 metres, was discovered in the 1960s. Because of its muddy consistency, it appears that these deposits will not prove problematic to mine, and this was successfully tested in the 1980s.
- Of the three sea floor resources discussed here, massive sulphides are the least abundant in terms of total volume, but they are of particular interest because of their high resource content. Some mining companies have already obtained exploration licences in national waters, and are advancing the technology for prospecting and extraction. In May 2010 the ISA even has granted one exploration licence in the Indian Ocean to China. So far only permits for research have been granted for the deep sea. In the near future the mining of copper and gold from massive sulphides is likely to commence off the coasts of Papua New Guinea and New Zealand. Mining operations had been planned to start this year, but due to the present economic recession, major metal and mining companies have experienced a decline in turnover in spite of the relatively high prices of gold, and the projects were postponed at short notice. But a recovery of the metal market is expected for the future. The companies will therefore soon be able to proceed with their plans.
The future of marine miningOf the three resource types waiting to be extracted from the deep sea, the mining of massive sulphides in the exclusive economic zones (200 nautical miles) of west Pacific nations (Papua New Guinea) seems to be most feasible at present. Despite the latest economic crisis, production could start in the next few years. Because of their relatively high content of valuable metals, the mining of massive sulphides may be profitable for some companies. But the metal content of the global massive sulphides is lower than that of the ore deposits on land. It is therefore unlikely that the marine mining of massive sulphides will have a significant impact on the global resource supply.
- Manganese nodules and cobalt crusts present quite different prospects. The amounts of copper, cobalt and nickel they contain could without doubt rival the occurrences on land. In fact, the total cobalt is significantly more than in all the known deposits on land. About 70,000 tonnes of cobalt are presently mined on land each year and the worldwide supply is estimated at about 15 million tonnes. By comparison, a total of about 1000 million tonnes of cobalt is estimated to be contained in the marine manganese nodules and cobalt crusts. In spite of these immense resources, sea floor mining will only be able to compete with the substantial deposits presently available on land if there is sufficient demand and metal prices are correspondingly high. Furthermore, the excavation technology has yet to be developed. The serious technological difficulties in separating the crusts from the substrate, combined with the problems presented by the uneven sea floor surface, further reduce the economic potential of the cobalt crusts for the present. Therefore, it seems that marine mining of cobalt crusts should not be anticipated any time soon.