

Why have the abundant mineral deposits or the so called manganese nodules of the deep oceans not been developed to provide mankind with an abundance of metals such as copper and nickel?

Manganese nodules are red-brown to black coloured polymetallic concretions composed predominantly of oxides of manganese (Mn) and iron (Fe), clay minerals and water. They can also contain traces of over 70 additional elements, the most abundant and commercially important of which are copper (Cu), nickel (Ni) and cobalt (Co) (Earney, 1990). Ranging in size from one to twenty centimetres, manganese nodules come in a variety of shapes from spherical and ellipsoidal to botryoidal and irregular (Barton, 1970; Kent, 1980; Earney, 1990; Hsü and Thiede, 1991; Thurman and Trujillo, 2004; Glasby, 2006). Although they have been known from freshwater deposits for hundreds of years, they were first recovered in the Kara Sea, Siberia in 1868, and more extensively on the voyage of the HMS Challenger in 1872, 160 miles southwest of the island of Ferro in the Canary Islands Group (Anon, 1979; Cronan, 1980; Earney, 1990; Thurman and Trujillo, 2004). They have since been discovered on the floor of all the Earth's major oceans at depths of 3000 to 6000 metres (Barton, 1970; Earney, 1990), forming a carpet of varying density on top of the abyssal clays.

Manganese is an important element in the steel industry for making alloys; copper has a variety of uses including electrical wiring, pipes and making brass and bronze; nickel is used to make stainless steel; and cobalt is used as an alloy with iron to make strong magnets, steel tools, and jet engine parts (Barkenbus, 1979; Thurman and Trujillo, 2004). The co-existence of these three metals in one ore makes manganese nodules an exciting reliable economic resource; but this potential was not recognised until the late 1950s (Barton, 1970). As global mineral shortages were predicted, the publication of Mero's over-optimistic study into the economics of manganese nodule mining in 1965 prompted widespread interest in exploration for and research into manganese nodules throughout the 1960s and 70s (Glasby, 2000). However, despite substantial investment and decades of research and innovation, the dreams of deep-ocean mining vessels tapping into this abundant source of Ni, Cu and Co has not materialised. What follows is a brief history of manganese nodule research and exploration, and the reasons for the failure to mine them.

Finally, concerns about the environmental impact of deep-sea mining came to the forefront and were relatively unknown. Initial studies suggested little environmental problems associated with discharge of sediment and disturbance of the sea floor (Amos, et al., 1977; Mero, 1977), but more research is needed, especially taking into account processing as well as mining (Hsü and Thiede, 1991).

In conclusion, the high costs of and risks involved in developing and operating the deep-sea mining systems, together with the low metal prices, complicated political and legal situation regarding mineral exploitation in the deep oceans, environmental concerns, advances in terrestrial mining technology, and new finds of terrestrial mineral deposits have prevented the commercialisation of manganese nodule mining. Although limited research continues, manganese nodules are unlikely to be a source of Ni, Cu and Co in the near future. There is, however, interest in deep-sea mining of sulphide deposits and shallower-water Co-rich manganese crusts (Glasby, 2000, 2002), which may at least learn from the past failures and successes of the nodule mining research.

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