Cobalt-rich, manganese- oxide crusts, forming a thin layer of mineralization which covers some areas of the ocean floor in shallow water off the west coast of the U.S., have subplanted manganese nodules as the most likely subsea mineral deposit to be mined in the near future.
In a 106-page report on sea-floor resources, prepared by the U.S. Geological Survey, author Vincent McKelvey says the crusts are more valuable than nodules at current metals prices. “Add to that the fact that extensive deposits lie within the U.S. 200-mile Exclusive Economic Zone proclaimed by President Ronald Reagan in 1983, and the legal uncertainty about their availability for mining may be much reduced and perhaps eliminated,” he says. The complex Law of the Sea Treaty, drafted by the United Nations in 1982, which would regulate mining outside of various exclusive economic zones, has never been put into force because an insufficient number of countries have ratified it.
“In some areas of the Pacific Ocean, such as the Hawaiian Archipelago and the Johnston-Palmayra islands region, the crusts are so weakly bonded to sea- floor bedrock that they can be scraped off easily; and because they occur in much shallower water (than do nodules), they may pose less difficult problems for mining.”
While there remain technical problems for recovering the crusts from the sea floor, an operation on the Gorda Ridge could potentially produce a total of 30 million tons of ore over 20 years at a value of $348 a ton, the report says.
Copies are available from the Book and Open-File Reports Section of the U.S. Geological Survey, Federal Center, Box 25425, Denver, Colo. 80225.
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