20 • Marine Minerals: Exploring Our New Ocean Frontier 



nature and extent of the deposits to allow the de- 

 velopment of prototype mining systems at this time. 



Mineral processing technology has evolved 

 through centuries of experience with onshore 

 minerals, although such techniques have not been 

 widely applied at sea. No major technological 

 breakthroughs are considered to be needed to adapt 

 onshore processing technologies to shipboard use, 

 but considerable uncertainty remains about the 

 costs and efficiency of operating a minerals proc- 

 essing plant at sea. 



Shore-based v. at-sea minerals processing will be 

 a trade-off that a seabed mining enterprise must 

 consider. If shipboard processing is installed, it may 

 be cheaper to transport smaller amounts of high- 

 grade processed ore (beneficiated) than to haul large 

 volumes of unprocessed ore containing as much as 

 85 to over 90 percent waste material to an onshore 

 processing plant. Economic conditions that would 

 influence such a decision could vary for each case. 



ENVIRONMENTAL CONSIDERATIONS 



Little direct experience exists with com- 

 mercial offshore mining with which to 

 estimate the potential for environmental 

 harm. 



Little direct experience exists with commercial 

 offshore mining with which to estimate the poten- 

 tial for environmental harm. Even channel and har- 

 bor dredging operations or recovery of sand for 

 beach nourishment, which have been studied in 

 some detail, are sporadic operations and do not re- 

 flect the impacts that could result from long-term 

 placer dredge mining operations that would move 

 considerably more material from a larger area of 

 the seafloor. Less is known about impacts to deep 

 water environments than shallow water envi- 

 ronments. 



Physical disturbance from dredge mining oper- 

 ations will consist of removing a layer of the 

 seafloor, conveying it to the surface, and reinject- 

 ing the unwanted material onto the seabed. The 

 mining operation will generate a transient "plume" 

 of sediment that will affect the surface, the water 

 column, and adjacent areas of the oceanfloor for 

 an uncertain period of time. 



Experience with sand and gravel mining in Eur- 

 ope and with the dredging operations of the U.S. 

 Army Corps of Engineers suggests that as long as 

 sensitive areas (e.g., fiish spawning and nursery 



grounds) are avoided, surface and mid-water ef- 

 fects from either shallow or deep water mining 

 should be minimal and transient. Benthic commu- 

 nities assuredly will be destroyed if mined, and 

 some nearby areas may be adversely affected by 

 sediment returning to the seafloor. However, min- 

 ing equipment can be designed to minimize such 

 damage, and, except where rare animals occur, en- 

 tire benthic populations are eliminated, or the sub- 

 strate is permanently altered, the seafloor should 

 recolonize. Recolonization is expected to take place 

 quickly in high-energy, shallow water communi- 

 ties, but very slowly in deep-sea areas. If any at- 

 sea processing of the mined material occurs — with 

 subsequent discharge of chemicals — negative im- 

 pacts would possibly be more severe. 



It is not scientifically or economically feasible to 

 research ecological baseline information on all of 

 the marine environments that may be affected by 

 seabed mining. Furthermore, the consequences of 

 the range of possible mining scenarios are unknown. 

 Anticipating and avoiding high-risk, sensitive areas 

 and mitigating damage through improved equip- 

 ment design and operating procedures can reduce 

 the impacts from offshore mining. Environmental 

 monitoring during the mining process will provide 

 an additional margin of safety and add to the knowl- 

 edge of what effects seabed mining might have on 

 the marine environment as well. Concurrent ob- 

 servations in undisturbed control areas similar to 

 those being mined could also provide an under- 

 standing 6f the processes at work. 



