56 • Marine Minerals: Exploring Our New Ocean Frontier 



Table 2-4.— Estimates of Sand and Gravel Resources 

 Within the U.S. Exclusive Economic Zone 



Volumes 

 Province (cubic meters) 



Atlantic: 



Maine— Long Island 340 billion 



New Jersey — South Carolina 190 billion 



South Carolina— Florida 220 billion 



Gulf of Mexico 269 billion 



Caribbean: 



Virgin Islands > 46 million 



Puerto Rico 170 million 



Pacific: 



Southern California 30 billion 



Northern California— Washington . . . insufficient data 



Alaska > 160 billion 



Hawaii 19 billion 



SOURCE; Modified after S.J. Williams, "Sand and Gravel Deposits Wittiin the 

 United States Exclusive Economic Zone: Resource Assessment and 

 Uses," 18tti Annual Offshore Technology Conference, Houston, TX, 

 1986, pp. 377-386. 



Placer Deposits 



Although reconnaissance surveys have not been 

 conducted over much of the region, concentrations 

 of heavy minerals have been found in a number 

 of locations in the Gulf of Mexico. Several offshore 

 sand bars or shoals are found off Dog Island, Saint 

 George Island, and Cape San Bias in northwestern 

 Florida that may contain concentrations of heavy 

 minerals.^' Some of these shoals are believed to be 

 drowned barrier islands. 



One recent survey of the shelf off northwest 

 Florida found heavy mineral concentrations asso- 

 ciated with shoal areas offshore of Saint George and 

 Santa Rosa Islands. ^^ The heavy minerals of eco- 



"W.F. Tanner, A. Mullins, andJ.D. Bates, "Possible Masked 

 Heavy Mineral Deposit: Florida Panhandle," Economic Geology, vol. 

 56, 1961, pp. 1079-1087. 



"J.D. Arthur, S. Melkote, J. Applegate, et al., "Heavy Mineral 

 Reconnaissance Off the Coast of the Apalachicola River Delta, North- 

 west Florida," Florida Bureau of Geology in Cooperation with U.S. 

 Minerals Management Service, Contract No. 14-12-001-30115, Aug. 

 16, 1985 (unpublished). 



nomic interest totaled about 39 percent of the heavy 

 mineral fraction averaged over the study area. 

 However, the percentages of heavy minerals and 

 the composition of the heavy mineral sites reported 

 are lower and of less economic interest, respectively, 

 than those on the Atlantic shelf. Sediments derived 

 from the Mississippi River off Louisiana contain 

 heavy mineral fractions in which ilmenite and zir- 

 con are concentrated. In the western part of the 

 Gulf, less economically interesting heavy minerals 

 of the amphibole and pyroxene groups are domi- 

 nant. ^^ 



An aggregate heavy-mineral sand resource esti- 

 mate was not attempted for the gulf coast as part 

 of the Department of the Interior's Program Fea- 

 sibility Study for Outer Continental Shelf hard 

 minerals leasing done in 1979. Too little data are 

 available and aggregate numbers are not very 

 meaningful in terms of potentially recoverable re- 

 sources. 



Phosphorite Deposits 



Recent seismic studies indicate that the phos- 

 phate-bearing Bone Valley Formation extends at 

 a relatively shallow depth at least 25 miles into the 

 Gulf of Mexico and the west Florida continental 

 shelf. An extensive Miocene sequence also extends 

 across the shelf, and Miocene phosphorite has been 

 dredged from outcrops on the mid-slope. This sit- 

 uation would suggest that the west Florida shelf may 

 have considerable potential for future phosphate ex- 

 ploration.^^ Core data would be needed to assess 

 this region more fully. 



^'R.G. Beauchamp and M.J. Cruickshank, "Placer Minerals on 

 the U.S. Continental Shelves — Opportunity for Development," 

 Proceedings OCEANS '83, vol. II, 1983, pp. 698-702. 



^'W.C. Burnett, "Phosphorites in the U.S. Exclusive Economic 

 Zone," Proceedings, the Exclusive Economic Zone Symposium Ex- 

 ploring the New Ocean Frontier, held at Smithsonian Institution, 

 Washington, DC, October 1985 (Washington, DC: U.S. Department 

 of Commerce, May 1986), pp. 135-140. 



PACIFIC REGION 



The continental margin along the Pacific coast 

 and Alaska has several subregions. Southern Cali- 

 fornia, from Mexico northward to Point Concep- 

 tion, is termed a "borderland," a geomorphic ex- 



tensional complex of basins, islands, banks, ridges, 

 and submarine canyons. Tectonically, this region 

 is undergoing lateral or transform movement along 

 the San Andreas fault system. The offshore base- 



