Ch. 5— Mining and At-Sea Processing Technologies • 199 



wmf^. 



Box 5-A. — Sand and Gravel Mining 



Mining offshore sand and gravel is likely to be profitable at selected sites well before mining of most 

 other offshore minerads. Sand and gravel occurs in enormous quantities on the U.S. continental shelf How- 

 ever, due to onshore sources of supply in many parts of the country, the low unit value of the resource, and 

 significant costs to transport sand and gravel long distances, profitable offshore sand and gravel mining is 

 likely to be restricted to areas near major metropolitan centers that have depleted nearby onshore sources 

 and/or have encountered conflicting land use problems. 



Sand and gravel are currently being dredged in State waters in the Ambrose Channel between New York 

 and New Jersey. This operation, begun 2 years ago, is the only offshore sand and gravel mining currently 

 tciking place in U.S. waters. The Great Lakes Dredge & Dock Co., the dredge operator, mines approximately 

 1.5 million cubic yards per year of high-quality fine aggregate from the channel. This aggregate is sold to 

 the concrete ready-mix industry in the New York/New Jersey area at an average delivered price of $11.50 

 per cubic yard. The Federal Government benefits from this operation because it enables the Ambrose Chan- 

 nel, which is a major navigation channel into New York Harbor, to be maintained at significant savings to 

 the government. In addition, both New York and New Jersey receive royalties of 25 cents per cubic yard 

 of aggregate mined. 



Great Lakes Dredge & Dock uses one trailing suction hopper dredge in its operation. The dredge is au- 

 thorized to mine to a depth of 53 feet below the mean low water mark. When full, the dredge proceeds to 

 a mooring point about one-half mile offshore South Amboy, New Jersey. The aggregate is then pumped to 

 shore via a pipeline. The company estimates that there is enough sand and gravel in the channel to operate 

 for 10 to 15 more years (longer if the chamnel is widened and/or deepened). 



Sand and gravel mining has not yet occurred in the U.S. Exclusive Economic Zone, but the Bureau of 

 Mines has tentatively identified two metropolitan areas, New York and Boston, where significant potential 

 exists for the near-term development of offshore sand and gravel deposits.* Local onshore supplies are fast 

 becoming depleted in these areas. The Bureau estimates that, for both areas, dredge and plant capital costs 

 would range from a low of about $21 million for a 1 .3-million cubic-yard-per-year operation 10 nautical miles 

 from an onshore plant to a high of $145 million for a 6.7-million cubic-yard-per-year operation 80 nautical 

 miles from shore. Operating costs for a product that has been screened (i.e., sorted) are estimated to range 

 from about $3.30 per cubic yard for the smaller nearshore operation to $4.00 for the larger, more distant 

 operation. Estimates are based on 250 operating days per year for the dredge and 323 for the plant. Other 

 cities where offshore sand and gravel eventually could be competitive include Los Angeles, San Juan, and 

 Honolulu. 



•An Economic Reconnaissance of Selected Sand and Gravel Deposits in the U.S. Kxclusive Economic Zone, Open File Report 3-87 (Washington, 

 DC: U.S. Bureau of Mines, January 1987). 



There are no active facilities for processing chro- 

 mite in the Pacific Northwest. Ferrochromium 

 plants and chromium chemicals and refractories 

 producers are concentrated in the eastern half of 

 the country. However, one company, Sherwood 

 Pacific Ltd., was recently formed for the purpose 

 of constructing and operating a chromium smelter 

 in Coos Bay, Oregon. Coos Bay has a deep draft 

 ship channel, rail access, land, and a work force. 

 Initial raw material for the smelter is expected to 

 come from onshore deposits in southern Oregon 

 and northern California. 



The costs per ton of concentrate projected in this 

 scenario allow only small margins to make and dis- 



tribute a finished product, currently worth about 

 $40 per ton. Hence, it is clear that chromite alone 

 would not be worth recovering. Unless the price 

 of chromite were to increase or byproducts such as 

 gold or zircon could be economically recovered, the 

 costs projected in this scenario do not justify eco- 

 nomic chromite mining in the near future. 



Offshore Placer Gold Mining Scenario 



Location. — Gold-bearing beach sands were dis- 

 covered and mined at Nome, Alaska, in 1906. Min- 

 ing gradually extended inland from the current 

 shoreline to old shorelines now above sea level. By 



P 



