Ch. 5— Mining and At-Sea Processing Technologies • 181 



offshore polymetallic sulfide deposits occur in deep 

 water, beyond the range of technologies used for 

 conventional placer mining. 



Much of the technology needed to mine massive 

 polymetallic sulfide and cobalt crust deposits is yet 

 to be developed. EEZ hard-rock deposits and mas- 

 sive polymetallic sulfide deposits are, therefore, 

 probably of more scientific than commercial interest 

 at this time. Research on the genesis, distribution, 

 extent, composition, and other geological aspects 

 of these deposits has been underway for only a few 

 years, and more knowledge will likely be required 

 before the private sector is likely to consider spend- 

 ing large sums of money to develop needed min- 

 ing technology. A more immediate need is to re- 

 fine the technology for sampling these hard-rock 

 deposits (see ch. 4). Before mining equipment can 

 be designed, more technical and engineering data 

 on the deposits will be required.^ 



In the deep ocean, technology must be designed 

 to cope with elevated hydrostatic pressure, the cor- 

 rosive saltwater environment, the barrier imposed 

 by the seawater column, and rugged terrain. Even 

 onshore, mining equipment requires constant re- 

 pair and maintenance. Given deep ocean condi- 

 tions, it will be particularly important that mining 

 equipment be as simple as possible, reliable, and 

 sturdy.^ 



Massive Polymetallic Sulfides 



Although technology for mining massive sulfides 

 has not been developed, the steps likely to be re- 

 quired are straightforward. To start, any overbur- 

 den covering the massive sulfides would have to be 

 removed, although it is likely that initial mining 

 targets would be selected without overburden. 

 Then, the resource would then have to be frag- 

 mented, collected, possibly reduced in size, trans- 

 ported to a surface vessel, optionally beneficiated 

 on the vessel, and finally transported to shore. 



'R. Kaufman, "Conceptual Approaches for Mining Marine Poly- 

 metallic Sulfide Deposits," Marine Technology Society Journal , vol. 

 19, No. 4, 1985, p. 56. 



'D.K. Denton, Jr., "Review of Existing, Developing, and Required 

 Technology for Exploration, Delineation, and Mining of Seabed Mas- 

 sive Sulfide Deposits," U.S. Bureau of Mines, Minerals Availability 

 Program, Technical Assistance Series, October 1985, p. 13. 



A number of conceptual approaches have been 

 suggested to fragment and/or extract massive sul- 

 fides. These include use of cutter head dredges; 

 drilling and blasting; high-pressure water jets; 

 dozers, rippers, or scrapers; high-intensity shock 

 waves; and in situ leaching.* All proposed extrac- 

 tion methods have some drawbacks, and none have 

 been tested in the ocean environment. Crushing 

 or grinding, where required, is not technically dif- 

 ficult on land but has not yet been done in com- 

 mercial operations on the seafloor. Transport of 

 crushed ore to the surface would most likely be 

 accomplished by hydraulic pumping (using either 

 airlift or submerged centrifugal pumps). This tech- 

 nology has been studied for mining seabed manga- 

 nese nodule deposits, so it is perhaps the most 

 advanced submerged part of many proposed hard- 

 rock mining systems. 



No major technical innovations are expected to 

 be needed for surface ship operations, although the 

 cost of equipment such as dynamically positioned 

 semi-submersible platforms will be expensive. On- 

 board storage and transport of massive sulfide ore 

 would have similar requirements as storage and 

 transport of most other ores. Flotation technology 

 for beneficiating massive sulfides has not yet been 

 adapted for use at sea; however, the U.S. Bureau 

 of Mines has initiated research on the subject. 



One conceptual approach' for deposits on or just 

 below the seafloor envisions the use of a bottom- 

 mounted hydraulic dredge (figure 5-12). The dredge 

 would be equipped with a suction cutter-ripper head 

 capable of moving back and forth and also telescop- 

 ing as it cuts into the sulfide deposit and simultane- 

 ously fractures and picks up the material by suc- 

 tion. The dredged material would be first pumped 

 from the seabed to a crusher and screen system, 

 then into a storage and injection hopper on the sub- 

 merged dredge, and finally from the injection hop- 

 per to the surface. An airlift pump and segmented 

 steel riser would give vertical lift. The surface plat- 

 form would be a large, dynamically positioned, 

 semi-submersible platform. After dewatering, the 

 pumped material would be discharged into storage 

 holds on the platform. In concept, the ore would 

 be beneficiated on the platform, loaded on a barge, 



nbid., pp. 16-17. 



'Kaufman, "Conceptual Approaches for Mining," pp. 55-56. 



