206 • Marine Minerals: Exploring Our New Ocean Frontier 



Mining and At-Sea Processing Cycle. — Min- 

 ing is assumed to take place 80 percent of the avail- 

 able time — 292 days or about 7,000 hours per year. 

 The beneficiated ore is loaded continually on 5,500- 

 ton capacity barges for transport to the onshore 

 processing plant. Barge transport is deemed nec- 

 essary for both economic and pollution control rea- 

 sons. A tug picks up one barge at a time, taking 

 it to a mooring point just outside the channel at 

 the Savannah River entrance. A push boat then 

 takes a four-barge group about 20 miles upstream 

 to the processing facility. After the ore is discharged, 

 the barges are reloaded with tailings sand and 

 returned to the mooring point. The tug then returns 

 the barge to the mining area, initially to discharge 

 tailings and then to be taken to the dredge and left 

 to be filled with feed. 



Capital and Operating Costs. — Capital and 

 operating cost estimates for the Zellars-Williams 

 scenario (table 5-7) have been updated to reflect 

 changes in plant, equipment, wages, and other cost 

 factors. The revised figures are expressed in 1986 

 dollars. Capital and operating costs include costs 

 for dredging and primary concentration, transpor- 

 tation of beneficiated ore to port, onshore process- 

 ing to 66 percent BPL, calcining to 68 percent BPL, 

 contingency, and working capital. 



The Zellars-Williams scenario and associated 

 costs are regarded as a "best-case" situation.'^ In 



1986 dollars, the operating costs to mine and wash 

 the ore and to transport the primary concentrate 

 to an onshore processing plant amount to about 

 $4.60 per short ton. Onshore processing would cost 

 about $10 per short ton, and a depreciation expense 

 of almost $10 per ton must be added to this figure. 

 Hence, a "breakeven" price for calcined concen- 

 trate would be close to $25 per short ton. Calcined 

 concentrate, however, is currently selling for only 

 $19 to $25 per short ton, depending on grade and 

 whether the product is sold domestically or ex- 

 ported. Furthermore, given uncertainties such as 

 costs for mitigating environmental impacts, the 

 acceptability of at-sea disposal of flocculated clays, 

 and the uncertain effectiveness of both dredging and 

 processing technology in the offshore environment, 

 investors would probably require a discounted cash 

 flow return larger than the 16.5 percent return in- 

 dicated in the Zellars-Williams study. The break- 

 even price does not include additional requirements 

 for profit and risk. 



The largest component of total capital cost and 

 of total operating cost is for onshore processing of 

 the primary concentrate to 66 percent BPL, and 

 the second largest cost component is for calcining 

 to 68 percent BPL. Savings might be possible if an 

 existing onshore processing plant could be used for 

 flotation and/or calcining or if flotation at sea be- 



"More information about the Zellars-Williams and other phos- 



phorite studies may be found in the OTA contractor report "Offshore 

 Phosphorite Deposits: Processing and Related Considerations," by 

 William Harvey. November 1986. 



Table 5-7.— Offshore Phosphorite Mining, Tybee Island, Georgia: 

 Capital and Operating Cost Estimates 



Millions of dollars 



Capital costs: 



Dredging and primary concentration $17 



Transport to port 26 



Processing to 66 percent BPL 80 



Calcining to 68 percent BPL 33 



Contingency 15 



Working capital 14 



Total $185 



(million $/year) ($/ton product) 



Operating costs: 



Dredging and primary concentration $9 $ 2.50 



Transport to port 7 2.10 



Processing to 66 percent BPL 22 6.20 



Calcining to 68 percent BPL 12 3.50 



Contingency 2 0.70 



Total $52" $15.00 



SOURCE: Zellars-Williams, Inc., "Outer Continental Shelf Hard Minerals Leasing: Phospfiates Offshore Georgia and South Caro- 

 lina," report prepared for U.S. Geological Survey, May, 1979. Figures updated by OTA contractor, William Harvey. 



