154 • Marine Minerals: Exploring Our New Ocean Frontier 



ASA equivalent speed film was used to take pic- 

 tures of the Titanic under more than 2 miles of 

 water. Higher film speed ratings, perhaps as high 

 as 2 million ASA equivalent, will enable pictures 

 to be taken with even less light. Improved lighting 

 will also help. The optimal separation between cam- 

 era and light in the ocean is about 40 meters, which 

 suggests that towed light sources could provide an 

 advantage. Use of polarization filters can also help 

 increase viewing potential. Gated light sources, 

 which emit short pulses of light, will be more ex- 

 pensive to develop. Development of a technique to 

 open the camera shutter at the precise time the 

 gated light illuminates the subject will help reduce 

 scattering of the reflected light. ^^ 



Direct Sampling by Coring, Drilling, 

 and Dredging 



Once a prospective site is located using geophysi- 

 cal and/or other reconnaissance methods, direct 

 sampling by coring, drilling, or dredging (as appro- 

 priate) is required to obtain detailed geological 

 information. Direct sampling provides "ground 

 truth" correlation with indirect exploration meth- 

 ods of the presence (and concentration) or absence 

 of a mineral deposit. The specific composition of 

 a deposit cannot be determined without taking sam- 

 ples and subjecting them to geochemical analyses. 

 Representative sampling provides potential miners 

 with information about the grade of deposit, which 

 is necessary to decide whether or not to proceed 

 with developing a mine site. 



Placer Deposits 



The state-of-the-art of sampling marine placers 

 and other unconsolidated marine sediments is more 

 advanced than that of sampling marine hard-rock 

 mineral deposits such as cobalt crusts and massive 

 sulfides. There are various methods for sampling 

 unconsolidated sediments in shallow water, whereas 

 technology for sampling crusts and sulfides in deep 

 water is only now beginning to be developed. Two 

 significant differences exist between sampling placer 

 deposits and marine hard-rock deposits. One is the 

 greater depth of water in which crusts and sulfides 



occur. The other is the relative ease of penetrating 

 placers. 



Grab samplers obtain samples in the upper few 

 centimeters of surfacial sediments. For obtaining 

 a sample over a thicker section of sediments and 

 preserving the sequence of sedimentary layers, 

 vibracore, gravity, piston, and other coring devices 

 are used. These corers are used to retrieve relatively 

 undisturbed samples that may indicate the concen- 

 tration of minerals by layer and the thickness of 

 the deposit. On the other hand, to determine the 

 average grade of ore at a particular site and for use 

 in processing studies, large bulk samples obtained 

 by dredging (including any waste material or over- 

 burden), rather than undisturbed cores, may be 

 sufficient. 



The characteristics of a sampling device appro- 

 priate for a scientific sampling program are not nec- 

 essarily appropriate for proving a mine site. In or- 

 der to establish tonnage and grade to prove a mine 

 site, thousands of samples may be required. It is 

 essential that the sampling device provide consist- 

 ently representative samples at a reasonable cost. 

 The ability to carry out commercial-scale sampling, 

 required to define an ore body, in water deeper than 

 about 60 feet is still very limited. Scientific sam- 

 pling can be done in deeper water, but as table 4-9 

 indicates, sampling costs rapidly escalate with water 

 depth. The costs of sampling in deeper water prob- 

 ably will have to be reduced significantly before 

 commercial development in these areas can take 

 place. 



Only a few areas within the U.S. Exclusive Eco- 

 nomic Zone have been systematically sampled in 

 three dimensions. Much of the data collected to date 

 have been from surface samples and hence are not 

 reliable for use in quantitative assessments.^' Ade- 

 quate knowledge of the mineral resource potential 

 of the EEZ will require extensive three-dimensional 

 sampling in the most promising areas. 



Several factors, as suggested above, are impor- 

 tant in evaluating the performance of a placer sam- 

 pling system^" (in general, these factors are equally 



"R. Ballard, Deep Submergence Laboratory, Woods Hole Oceano- 

 graphic Institution, OTA Workshop on Technologies for Surveying 

 and Exploring the Exclusive Economic Zone, June 10, 1986. 



"See, for example, Clifton and Luepke, "Heavy Mineral Placer 

 Deposits." 



""B. Dimock, "An Assessment of Alluvial Sampling Systems for 

 Offshore Placer Operations," Report, Ocean Mining Division, Re- 

 source Evaluation Branch, Energy, Mines, and Resources Canada, 

 January 1986. 



