12 • Marine Minerals: Exploring Our New Ocean Frontier 



To be competitive, marine minerals 

 probably must either prove to exist in 

 large, high-quality deposits, and/or to 

 be cheaper to mine and process than 

 their onshore counterparts. 



and must be sampled by taking cores through many 

 feet of sediment and sometimes down to bedrock. 

 Sampling polymetallic svilfides is considerably more 

 difficult than the other EEZ minerals. The thick- 

 ness of polymetallic sulfide deposits is expected to 

 be much greater, sometimes extending into the 

 basement rocks of the seabed. Polymetallic sulfides 

 are generally found in deeper water, and prohibi- 

 tively expensive hard-rock coring techniques are 

 required to adequately sample them. Resource assess- 

 ments of cobalt-manganese crust deposits and man- 

 ganese nodules are on somewhat firmer footing than 

 placers or polymetallic sulfides. Nodule and crust 

 distribution can be observed and visually mapped, 

 while grab samples and shallow coring devices can 

 assess the thickness of these deposits and obtain 

 samples for chemical analysis. 



More is known about sand and gravel than other 

 hard mineral resources in the U.S. EEZ as a re- 

 sult of extensive sampling by the U.S. Army Corps 

 of Engineers. Although onshore sand and gravel 

 resources in most areas of the United States are am- 

 ple to meet mainland needs for the near future, off- 

 shore deposits of high-quality sand may be locally 

 important in the future, especially in New York and 

 Massachusetts. Geologists have identified several 

 offshore areas that have potential for hosting heavy 

 mineral placer deposits, although data are still too 

 sparse for compiling resource assessments. Occur- 

 rences of shallow-water mineral placer deposits have 

 been identified in both State waters and the Fed- 

 eral EEZ. 



One of the most promising areas for titanium 

 sands and associated minerals in the U.S. EEZ is 

 located between New Jersey and Florida. On the 

 west coast, the best prospects for chromite placers. 



Only a miniscule portion of the U.S. 

 EEZ has been explored for minerals. 



other associated minerals, and perhaps precious me- 

 tals are offshore southern Oregon. In Alaska, gold 

 is being investigated off the Seward Peninsula near 

 Nome where some test mining has occurred, and 

 platinum has been recovered onshore near Good- 

 news Bay on the Bering Sea, providing some evi- 

 dence that precious metal placers may also lie off- 

 shore; in the Gulf of Alaska, lower Cook Inlet may 

 be a promising area to prospect for gold. 



Phosphorite beds located onshore in North Caro- 

 lina and South Carolina extend seaward in the con- 

 tinental shelf. Extensive phosphorite deposits are 

 found near the surface of the seabed in the Blake 

 Plateau of the southeastern Atlantic coast, as well 

 as off southern California. 



Cobalt-rich ferromanganese crusts on the seabed 

 adjacent to the Pacific Islands have piqued the in- 

 terest of an international mining consortium. Data 

 on the manganese crusts are insufficient to deter- 

 mine the resource potential, to identify a potential 

 mining site, or to design a mining system. Ferro- 

 manganese nodules are located in the Blake Pla- 

 teau and have been recovered in experimental 

 quantities while testing deep seabed mining systems 

 that were intended for use in the Pacific Ocean. 

 The Blake Plateau nodules are in shallower water 

 than those in the Pacific and thus may be more eas- 

 ily mined, but they have lower mineral content. 



Polymetallic sulfide deposits located in the vol- 

 canically active Gorda Ridge in the U.S. EEZ and 

 also located in the Juan de Fuca Ridge, that strad- 

 dles the U.S. -Canadian EEZs off the Northwestern 

 United States, have attracted considerable scien- 

 tific curiosity. Although these deposits are known 

 to contain large quantities of copper, lead, zinc, 

 and other metals, uncertainties about the quality, 

 composition, and extent of the deposits makes their 

 resource potential difficult to determine. 



