212 • Marine Minerals: Exploring Our New Ocean Frontier 



Table 5-12.— Scenario Comparisons: Onslow Bay and Tybee Island Phosphorite 



Zellars-Williams (Tybee Island) (updated 1986) OTA (Onslow Bay) 



Deposit kind Pebbles and sand Sands 



Grade 11.1 percent P2O5 11.2 percent PiOs 



Size 150 million short tons Not specified 



Distance to shore unloading 



point 30 miles 80 miles 



Maximum dredging depth .... 100 feet 98 feet 



Anriual mining capacity- 

 tonnage dredged 2.5-3.5 million short tons 6.9 million short tons 



Mining system Ocean-going cutter suction dredge with Trailing suction hopper dredge; onboard 



onboard screening and cycloning screening, sizing, and flotation 



Mining system operating 



days 292 days 300 days 



Shore processing plant Washing and sizing, flotation, calcining Calcining only 



Capital costs (million $) 

 Dredge & offshore 



processing $17 $ 41 



Transportation to shore .... 26 16 



Onshore processing 113 — 



Other.... 29 14 



Total $185 $ 71 



Cash operating costs $U.S. 



per short ton $ 25 $ 28 



Comments (OTA'S) • Cash operating cost is break-even; Does • Cash operating cost is break-even; Does 



not include profit and risk. not include profit and risk. 



• Estimate considered "best • Does not include capital costs of existinc 

 case." onshore calcining plant. 



• Estimate may be off by • Estimate may be off by factor of two 

 factor of two or more. or more 



SOURCE: Office of Tecfinology Assessment, 1987. 



