192 • Marine Minerals: Exploring Our New Ocean Frontier 



ing of these minerals is likely to require crushing 

 or grinding to reduce particle size, followed by 

 chemical separation methods. In some cases (i.e., 

 for gold veins) fine grinding may liberate minerals 

 which then may be recovered using gravity sepa- 

 ration alone. However, in most cases some flota- 

 tion and/or other chemical processing is likely to be 

 required. The Bureau of Mines has experimented 

 with column flotation techniques for separation of 

 cobalt-rich manganese crust from substrate. Crust 



separated in this manner, however, cannot simply 

 be concentrated by inexpensive mineral process- 

 ing techniques. Most of these processes have not 

 been adapted for use at sea. Crushing and grind- 

 ing circuits could be mounted on floating platforms 

 or on the seafloor, but unless the economic incen- 

 tive to mine this type of seafloor deposit improves, 

 these techniques will not likely be used offshore in 

 the near future. The same comment applies to flo- 

 tation and other chemical processing technologies. 



OFFSHORE MINING SCENARIOS 



To illustrate the feasibility of offshore mining, 

 OTA constructed five scenarios, each depicting a 

 prospective mining operation in an area where ele- 

 vated concentrations of potentially valuable min- 

 erals are known to occur. The scenarios illustrate 

 factors affecting the feasibility of offshore mining, 

 including the physical and environmental condi- 

 tions that may be encountered offshore, the capa- 

 bilities of the avaOable mining and processing tech- 

 nologies, and estimated costs to mine and process 

 offshore minerals. The scenarios selected include 

 mining of: 



• titanium-rich sands off the Georgia coast, 



• chromite sands off the Oregon coast, 



• gold off the Alaska coast near Nome, 



• phosphorite off the Georgia coast near Tybee 

 Island, and 



• phosphorite in Onslow Bay off the North 

 Carolina coast. 



These shallow-water mineral deposits were selected 

 because they are judged to be potentially mineable 

 in the near term, unlike, for example, deposits of 

 cobalt-rich ferromanganese crusts or massive sul- 

 fides, both of which would require considerable 

 engineering research and development. 



For each scenario, the ocean environments are 

 considered to be acceptable for dredging operations, 

 dredging technologies are judged to be available 

 with little modification, and existing processing 

 technologies are considered adaptable for shipboard 

 use, although some development will be needed. 

 The greatest uncertainties arise from lack of data 

 on the nature of the placer deposits (except for 

 Nome, reserves have not been proven by drilling) 



and from the lack of operating experience under 

 conditions encountered in the U.S. EEZ (i.e., 

 waves and long-period swells). 



OTA did not attempt detaUed engineering and 

 cost analyses. Too little information is currently 

 available to accurately assess the profitability of off- 

 shore mining. For example, the grade of ore may 

 vary considerably throughout a deposit, but little 

 information about grade variability has been com- 

 piled yet at any site. Estimates of mining and proc- 

 essing costs can vary considerably depending on 

 the amount of information on which they are based. 

 Given that estimates cannot now be based on de- 

 tailed information, OTA has attempted simply to 

 estimate the range within which costs are most likely 

 to fall. Rough estimates do not satisfy the need for 

 detailed feasibility studies based on comprehensive 

 data; however, they do provide criteria with which 

 to judge if recovery of large quantities of high grade, 

 valuable minerals on the seabed is likely to be 

 profitable or at least competitive with land-based 

 sources of minerals. 



Similar scenarios for titanium, chromite, and 

 gold placers also have been developed recently by 

 the U.S. Bureau of Mines." The scenarios are not 

 directly comparable, but, after allowing for differ- 

 ent assumptions and uncertainty, the general con- 

 clusions reached are roughly the same. Tables 5- 

 9, 5-10, and 5-11 at the end of the chapter com- 

 pare OTA and Bureau of Mines scenarios. 



"A/1 Economic Reconnaissance of Selected Heavy Mineral Placer 

 Deposits in 'the U.S. Exclusive Economic Zone, Open File Report 

 4-87 (Washington, D.C.: U.S. Bureau of Mines, January 1987). 



