Ch. 2— Resource Assessments and Expectations • 53 



Una. Five beds containing high phosphate values 

 have been cored in two areas of Onslow Bay. The 

 northern area harboring three phosphate beds con- 

 tains an estimated resource of 860 million short tons 

 of phosphate concentrate with average phosphorus 

 pentoxide (P2O5) values of 29.7 to 31 percent. The 

 P2O5 content of the total sediment in these beds 

 ranges from 3 to 6 percent. The Frying Pan area 

 to the south contains two richer beds estimated to 

 contain 4.13 billion tons of phosphate concentrate 

 with an average content of 29.2 percent PzOs.'^ The 

 P2O5 content of the total sediment in these beds 

 ranges from 3 to 21 percent. Of the two areas, the 

 Frying Pan district is given a better potential for 

 economic development. The deposits are in shal- 

 low water relatively close to shore. 



Further to the south, from North Carolina to 

 Georgia, phosphates occur on the shelf in relict 

 sands. Phosphate grain concentrations of 14 to 40 

 percent have been reported in water depths of 100 

 to 130 feet. On the Georgia shelf off, the mouth 

 of the Savanna River, a deposit of phosphate sands 

 over 23 feet thick has been drilled. Other deposits 

 near Tyber Island, off the coast of Georgia, include 

 a 90-foot-thick bed of phosphate in sandy clay aver- 

 aging 32 percent phosphate overlying a 250-foot 

 thick bed of phosphatic limestone averaging 23 per- 

 cent phosphate. Concerns over saltwater intrusion 

 into an underlying aquifer may constrain poten- 

 tial development in this area. 



Further offshore, the Blake Plateau is an area of 

 large surficial deposits of manganese oxides and 

 phosphorites (figure 2-6). The Plateau is swept by 

 the Gulf Stream and water depth ranges from 2,000 

 feet on the northern end to nearly 4,000 feet on the 

 southeastern end. Phosphorite occurs in the shal- 

 lower western and northern portions as sands, 

 pellets, and concretions. The northern portion of 

 the Blake Plateau is estimated to contain 2.2 bil- 

 lion tons of phosphorite. ^° 



Off the Florida coast near Jacksonville, deep and 

 extensive sequences of phosphate-rich sediments ex- 



"S.R. Riggs, S.W.P. Snyder, A.C. Hine, et a]., "Geologic Frame- 

 work of Phosphate Resources in Onslow Bay, North Carolina Con- 

 tinental Shelf," Economic Geology, vol. 80, 1985, pp. 716-738. 



'"F.T. Manheim, "Potential Hard Mineral and Associated Re- 

 sources on the Adantic and Gulf Continental Margins," Program Fea- 

 sibility Document — OCS Hard Minerals Leasing, app. 12, U.S. De- 

 partment of Interior, 1979, p. 42. 



tend eastward onto the shelf. One bed, 20 feet thick 

 beneath 260 feet of overburden, containing 70 to 

 80 percent phosphate grains, was slurry test-mined 

 in this area. A core hole 30 miles east of Jackson- 

 ville contained a 115-foot section of cyclic phos- 

 phate-rich beds with the thickest unit up to 16 feet 

 thick. The phosphate facies ran between 30 and 70 

 percent phosphate grains. 



Deep drill data in the Osceola Basin have shown 

 two phosphate zones extending eastward onto the 

 continental shelf. The lower grade upper zone is 

 1,000 feet thick with 140 feet of overburden and 

 phosphate grain concentratrations of 10 to 50 per- 

 cent of the total sediment. The higher grade deeper 

 zone is 82 feet thick with 250 feet of overburden 

 and phosphate grain concentrations ranging from 

 25 to 75 percent of total sediment. 



The Miami and Pourtales Terraces off the south- 

 east coast of Florida are also known to have phos- 

 phate occurrences. On the Pourtales Terrace, 

 phosphorite occurs as conglomerates, phosphatic 

 limestone, and phosphatized marine mammal bones. 

 This deposit is thought to be related to the phos- 

 phatic Bone Valley Formation onshore. 



Manganese Nodules and Pavements 



Ferromanganese nodules are concretions of iron 

 and manganese oxides containing nickel, copper, 

 cobalt, and other metals that are found in deep 

 ocean basins and in some shallower areas such as 

 the Blake Plateau off the Southeastern United 

 States. On the Blake Plateau, nodule concretions 

 are found at depths of 2,000 to 3,300 feet; and their 

 centers commonly are phosphoritic. Ferroman- 

 ganese crusts and pavements are more common at 

 shallower depths of around 1,600 feet. The fer- 

 romanganese concretions of the Blake Plateau are 

 well below the metal values found in the prime nod- 

 ule sites in the Pacific Ocean, but the Blake Pla- 

 teau offers the advantages of much shallower depths 

 and proximity to the U.S. continent. Potential fer- 

 romanganese nodule resources on the Blake Pla- 

 teau are estimated to be on the order of 250 billion 

 tons averaging 0.1 percent copper, 0.4 percent 

 nickel, 0.3 percent cobalt, and 15 percent man- 

 ganese.^' 



•Ibid. 



15. 



