796 • Marine Minerals: Exploring Our New Ocean Frontier 



4. steams to the shore base, and 



5. it discharges the preconcentrate from the 

 hopper. 



Each of these cycles takes 4 days: 3 days for dredg- 

 ing and processing and 1 day for transit and offload- 

 ing. Seventy-five such cycles per year can be made 

 using a trailing suction hopper dredge with a 5,000- 

 cubic-yard hopper capacity. This allows 60 days 

 per year for drydocking, maintenance, and down- 

 time due to weather or other contingencies. The 

 average distance from offshore deposits to the shore- 

 side discharge point is estimated to be 100 miles. 



The requirement to stop dredging and return to 

 port could be eliminated by loading shuttle barges 

 instead of filling the dredge hoppers. Other alter- 

 natives to the scenario probably would be evalu- 

 ated by prospective miners who, for example, might 

 process to a higher concentrate grade offshore. 



Capital and Operating Costs. — Total capital 

 requirements are estimated to range from $55 mil- 

 lion to $86 million, depending on average ore grade 

 (ranging from 15 to 5 percent respectively). Capi- 

 tal costs include costs of the dredge, onboard wet 

 mill, onshore unloading installation, dry mill, and 

 working capital (table 5-4). Capital costs for both 

 the dredge and onboard wet mill decrease as the 

 ore grade increases because less mining (pumping) 

 capacity is required. Total operating costs are 

 higher for lower grade ore because more ore must 

 be mined by a larger dredge to produce the same 

 amount of concentrate. Annual costs to operate the 

 dredge, wet mill, and dry mill, and for general and 



Table 5-4.— Offshore Titaniferous Sands Mining 

 Scenario: Capital and Operating Cost Estimates 



Ore grade 

 5% 10% 15% 



Capital costs (million $): 



Dredge $40 $36 $32 



Offshore processing 34 18 14 



Onshore processing 4 4 4 



Working capital 8 6 5 



Total capital costs $86 $64 $55 



Annual operating costs (million $): 



Dredge and offshore processing ....$17 $14 $12 



Onshore processing 2 2 2 



General and administrative 2 1 1 



Depreciation expense 16 11 10 



Total operating costs $37 $28 $25 



SOURCE: Office of Tecfinology Assessment, 1987. 



administrative expenses and depreciation are esti- 

 mated to be from $25 million to $37 million, de- 

 pending on the heavy mineral content (15 to 5 per- 

 cent). Given these estimates for capital and 

 operating costs, breakeven revenue requirements 

 have been calculated to range from $170 to $250 

 per ton of marketable product. 



Given the risks inherent in developing an offshore 

 deposit, the developers would expect higher returns 

 than for a conventional land-based mineral sands 

 operation and require a more rapid payback on in- 

 vestment. For example, under the 1986 tax law, 

 a 3-year payback would require revenues of be- 

 tween $420 and $280 per ton of product for ore 

 grades ranging from 5 to 15 percent. Since the cur- 

 rent U.S. east coast price of ilmenite concentrate 

 is $45 to $50 per short ton, it is clear that the de- 

 posit would require appreciable concentrations of 

 other valuable minerals (e.g., rutUe, zircon, and/or 

 monazite with values ranging from $180 to $500 

 per ton) to be profitable. 



Offshore Chromite Sands 

 Mining Scenario 



Location. — Concentrations of heavy mineral 

 sands containing primarily chromite, lesser amounts 

 of ilmenite, rutile, and zircon, and traces of gold 

 and other minerals occur in surface and near-sur- 

 face deposits on the continental shelf off southern 

 Oregon (figure 5-19). Many reconnaissance sur- 

 veys conducted by academic researchers have been 

 completed in the area, but no detailed mineral ex- 

 ploration has taken place. The largest heavy 

 mineral sand area appears to extend westward from 

 the mouth of the Rogue River and northward 

 toward Cape Blanco. A second area of chromite- 

 rich black sands is located seaward of the mouth 

 of the Sixes River. Additional small deposits oc- 

 cur on the continental shelf and on uplifted ma- 

 rine terraces between Coos Bay and Bandon. The 

 Rogue River deposits are approximately 75 miles 

 south of Coos Bay, the nearest deep-water indus- 

 trial port, and 100 miles north of the port of Eu- 

 reka, California. 



No State or Federal exploration permits have 

 been issued in the area to the private sector. How- 

 ever, one company, Oregon Coastal Services, has 

 expressed interest in obtaining a permit to explore 

 for minerals in State waters. 



