THE CHANGING VISION OF MARINE MINERALS

Our vision and potential utilization of nonfuel marine minerals is expanding rapidly with advances in knowledge of the Earth and discoveries that link inorganic with organic processes. Ocean basins were regarded as passive containers of the ocean until the advent of plate tectonics in the 1960's. The former view accounts for deposits derived by mechanical and chemical erosion of continental rocks. These deposits comprise placer (sand and gravel, heavy metals, gemstones) and phosphorite deposits on continental margins, and manganese nodules in deep ocean basins (Mn, Cu, Fe, Ni, Co). Diamonds have developed into a major industry offshore southwest Africa. Sand and gravel for multiple uses (construction, beach restoration, and shore protection), and desalination of seawater are growing fastest as materials necessary for survival.

The theory of plate tectonics changed our view of ocean basins from passive sinks to active sources of mineralization. Magmatic heat related to the creation and destruction of the ocean crust at submerged plate boundaries drives subseafloor hydrothermal convection systems. These systems concentrate massive sulfide deposits (copper, iron, zinc, silver, gold) in ocean crust. The magmatic processes concentrate other metals (chromite, nickel, copper, and platinum group elements) in the upper mantle. Chemical erosion of continental rocks and seafloor hydrothermal systems together provide metals to manganese nodules on the abyssal plains and to cobalt-rich ferromanganese crusts on volcanic substrates of seamounts. The hydrothermal systems are also sources of chemical energy utilized by heat-loving microbes to manufacture their food at the base of a vent ecosystem hosted in ore-forming systems, thereby linking inorganic with organic processes. The microbes may interact in the process of mineral concentration; are sources of novel organic compounds with applications to industrial processes and pharmaceuticals; and certain microbes may relate to the base of the evolutionary tree of life.

Marine mining for both minerals and microbes is accelerating with potential for scientific and economic benefits and environmental impact. Considering the full spectrum of marine minerals, freshwater from seawater is the most critical because it is necessary for life and the terrestrial supply is being depleted faster than replenishment.