Environmental Problems, Their Causes, and Sustainability 1

First, carefully investigate its potential ecological,health, and societal risks. Second, develop guidelinesand regulations for controlling and guiding its spreaduntil we have better answers to many of the “What happensnext?” questions about this technology.Can We Get More Minerals from Seawaterand by Mining the Ocean Floor? SomeProblemsMost minerals in seawater cost too much toextract, and mineral resources found on the deepocean floor are not being removed because of highcosts and squabbles over who owns them.Ocean mineral resources are found in seawater, sedimentsand deposits on the shallow continental shelf,hydrothermal ore deposits (Figure 16-17), and manganese-richnodules on the deep-ocean floor.Most of the chemical elements found in seawateroccur in such low concentrations that recovering themtakes more energy and money than they are worth.Only magnesium, bromine, and sodium chloride areabundant enough to be extractedprofitably at current prices withexisting technology.Deposits of minerals (mostlysediments) along the continentalshelf and near shorelines are significantsources of sand, gravel,phosphates, sulfur, tin, copper,iron, tungsten, silver, titanium,platinum, and diamonds.Rich hydrothermal depositsof gold, silver, zinc, and copperare found as sulfide deposits inthe deep-ocean floor and aroundblack smokers (Figure 16-17).Currently, it costs too much to extractthese minerals even thoughsome of these deposits contain large concentrations ofimportant metals.Manganese-rich nodules found on the deep-oceanfloor at various sites may be a future source of manganeseand other key metals. They might be sucked upfrom the ocean floor by giant vacuum pipes orscooped up by buckets on a continuous cable operatedby a mining ship.So far these nodules and resource-rich mineralbeds in international waters have not been developedbecause of high costs and squabbles over who ownsthem and how any profits from extracting themshould be distributed among the world’s nations.Some environmentalists believe seabed miningprobably would cause less environmental harm thanmining on land. But they are concerned that removingseabed mineral deposits and dumping back unwantedmaterial will stir up ocean sediments, destroy seafloororganisms, and have potentially harmful effects onpoorly understood ocean food webs and marine biodiversity.They call for more research to help evaluatesuch possible effects.Black smokerSulfide depositsWhite smokerMagmaFigure 16-17 Natural capital:hydrothermal ore deposits form whenmineral-rich superheated watershoots out of vents in solidifiedmagma on the ocean floor. After mixingwith cold seawater, black particlesof metal ore precipitate out andbuild up as chimneylike ore depositsaround the vents. A variety of organisms,supported by bacteria that producefood by chemosynthesis, existin the dark ocean around these blacksmokers.WhitecrabWhite clamTubeworms348 CHAPTER 16 Geology and Nonrenewable Mineral Resources