64 • Marine Minerals: Exploring Our New Ocean Frontier 



Photo credit: National Science Foundation 



Black "smoker" at a seafloor spreading center. Mineral- 

 laden hot water shoots upward in geyser-like plumes 

 from vents on the seafloor. These mineral-laden 

 plumes, first discovered In 1978, are called smokers. 

 Most plumes are black with rich mineral content. 

 Chimneys develop around the vents as the minerals 

 precipitate in the cold ocean water forming sulfide 

 deposits containing zinc, copper, iron, 

 lead, cadmium, and silver. 



dance of seabed nodules was a basic premise on 

 which the Third United Nations Conference on the 

 Law of the Sea was founded. Economic change and 

 subsequent research indicate both a more Umited 

 mineable resource base and much lower projected 

 rates of return from nodule mining. However, as 

 often happens, positions that become established 

 on the basis of one set of assumptions are difficult 

 to amend when the assumptions change. 



Creating expectations on the basis of highly 

 speculative estimates of recoverable tonnages and 

 values for hypothetical metal deposits serves little 



Pttoto credit: U.S. Geological Survey 



Hand sample of sulfide minerals recovered from 

 Juan de Fuca Ridge. 



purpose. Avoiding the present temptation to ex- 

 trapolate into enormous dollar values could avoid 

 what may, upon further research, prove to be less 

 than a spectacular economic resource in terms of 

 recovery. This is not to say that the resource may 

 not be found, but simply that it is premature to de- 

 fine its extent and estimate its economic value. 



What then can be said about expectations for the 

 U.S. EEZ? The Gorda Ridge is a relatively slow 

 spreading active ridge crest. Until recently, most 

 sulfide deposits were found on the intermediate- to 

 fast-spreading centers (greater than 2 inches per 

 year). This trend led some investigators to consider 

 the potential for sulfide mineralization at slow- 

 spreading centers to be lower than at faster spread- 

 ing centers. On the other hand, the convective heat 

 transfer by hydrothermal circulation is on the same 

 order of magnitude for both types of ridges. This 



