Deep-sea mining to realise its promise?

On paper, metal resources lying on the deep ocean floor look like an economic panacea. Large areas are covered with either a crust or scattered, potato-sized nodules rich in manganese, copper, cobalt, nickel and several other metals. In some ocean basins, one scoop might provide ore grades for all of them, as in the best onshore multi-metal deposits. ‘Black smokers’ and the metal-rich pillars and muds that develop from them seem just as promising for lead, zinc, copper and even gold: such submarine hydrothermal exhalations probably formed many of the rich massive sulphide deposits sought on land. The 1960s and early 70s seemed likely to foster a fundamental shift in metal extraction, but despite rises in metal prices after the 1973 Yom Kippur war and Iranian revolution of 1978, the excitement faded to insignificance.  There were a few ironies too. A ship was designed and almost completed by one of Howard Hughes’ many companies, Global Marine, supposedly to harvest ocean-floor manganese nodules. In fact, the venture was to be secretly directed at salvaging a sunken Soviet nuclear submarine, and the code books that it carried, from the floor of the Pacific Ocean. It now seems that ocean-floor mining might be resurrected – assuming that all does not descend into further wrangling over the Law of the Sea and who should benefit from profits (Thwaites, T. 2005.  Treasure Ocean. New Scientist, 17 December 2005, p. 40-53). An Australian company called Seacore is soon to drill around New Guinea and New Zealand to evaluate the potential of exhalative deposits.  They claim that if thicknesses greater than 15 m, at decent grades for gold, copper, zinc, silver and lead, are found dredging up the ores would be commercially possible.  Essentially it would be literally a smash and grab job, unlike the massive logistics of on-shore open-pit and subsurface mining, albeit tempered by problems connected with depths of several kilometres. Understandably, there are environmental concerns about exposing highly anomalous concentrations of metals and associated sulfide minerals, probably in a fine-grained soft state. Ocean ecosystems are fundamentally based on clear water, and mud plumes could wreak havoc far afield.  The deposits would have to be sucked to the surface using the air-lift dredge technique pioneered by marine archaeologists, but on a much larger scale.  Yet this appears to be more than a means of attracting and siphoning off venture capital, for the groundwork of identifying targets has already been done by Placer Dome, a well-heeled Canadian mining company.  Also, the thorny issue of the legality of harvesting the global oceanic ‘commons’ in international waters is being avoided by drilling within national offshore limits, as has long happened with offshore oil development.

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