Ch. 5— Mining and At-Sea Processing Technologies * 211 



Table 5-10.— Scenario Comparisons: West Coast Placer 



Bureau of Mines (January 1987) OTA 



Deposit l<lnd Chromite witin minor titanium, zircon, and Chromlte with insignificant amounts of 



gold ilmenite, rutile, and gold 



Grade >6% CraOs + .0048 oz. Au per short ton 6% Cr203 



Size 50 million short tons Not specified 



Distance to shore unloading 



point 40 nautical miles 75 nautical miles 



Maximum dredging depth . . . .150 feet 300 feet 



Annual mining capacity- 

 tonnage dredged 5,000,000 short tons 4,500,000 short tons 



Mining system Domestic built new hopper dredge Domestic built new hopper dredge 



Mining system operating 



days 250 300 



Shore processing plant New, to produce saleable mineral products New, to produce saleable mineral products 



Capital costs (million $): 



Dredge 41.4 40.0 



Plant and other 44.3 17.0 



Total 85.7 57.0 



Direct cash operating 

 costs $U.S. per short ton 

 dredged 5.42 4.00 



Comments (OTA'S) • Technically feasible but economically • Technically feasible but economically 



marginal for heavy mineral grades and marginal for heavy mineral grades and 



prices assumed prices assumed 



• No operating experience • No operating experience 



• No estimate of accuracy • No estimate of accuracy 



SOURCE: Office of Technology Assessment, 1987. 



Table 5-11.— Scenario Comparisons: Nome, Alaska Gold Placer 



Bureau of Mines (January 1987) OTA 



Deposit kind Gold Placer Gold Placer 



Grade 0.6 gram per yard^ 0.35 to 0.45 gram per yard^ 



Size 35,000,000 yard= 80,000,000 yard= 



Distance to shore unloading 



point 0.5 to 5 miles 0.5 to 10 miles 



Maximum dredging depth ... .80 feet 90 feet 



Annual mining capacity- 

 tonnage dredged 1,632,000 yd' 4,500,000 yd' 



Mining system Used seagoing bucket line dredge with full Used seagoing bucket line dredge with full 



gravity processing gravity processing 



Mining system operating 



days 150 150 



Shore processing plant Minimal for final cleaning of gold Minimal for final cleaning of gold 



concentrates concentrates 



Capital costs (million $) 



I Dredge 5 



Plant and other 10-15 



Total $9.1 15-20 



Direct cash operating costs 



$U.S. per yard' mined 2.00 1.55 



Comments (OTA'S) • Technically feasible and appears • Technically feasible and appears 

 economically profitable economically profitable 



SOURCE: Office of Tecfinology Assessment, 1987. 



