760 • Marine Minerals: Exploring Our New Ocean Frontier 



Photo credit: Analytical Services, Inc., Cardiff, CA 



Prototype crust sampler about to be deployed from 

 stern of ship. 



to collect as many as 30 short cores during each 

 deployment. The speed at which samples can be 

 taken and the cost per sample are important de- 

 sign features — especially for corers that are used 

 in proving a mine site — and this coring operation 

 is designed to be both relatively quick and inex- 

 pensive. Sampling is initiated by a bottom-sensing 

 trigger that starts a firing sequence. To fire the 

 "gun," an electric spark ignites the powder. As 

 many as four samples may be taken at any one site, 

 after which the system can be lifted from the seabed, 

 moved to another spot, and lowered again. Cores 

 are expected to be 10 to 12 centimeters long (long 

 enough to sample crust and some substrate in most 

 cases) and 2 centimeters (1 inch) in diameter. The 

 system is designed to operate in water depths of 

 5000 meters. Eventually, a video system, scanning 

 sonar, and thruster will be incorporated into the 

 system, enabling the sampler to be steered. A 

 second- generation prototype sampler has been built 

 and was tested in 1987. 



Large, bulk samples are required for processing 

 and tonnage/grade studies. To meet these needs, 

 the Bureau of Mines is developing a dredge capa- 

 ble of cutting into crust that may be similar in prin- 

 ciple to a commercial mining dredge of the future.'^ 

 Current dredges are not designed to cut into crust 

 and substrate. The experimental dredge would the- 

 oretically collect 500 pounds of in situ material in 

 each pass. Problems were encountered in initial 



testing of the dredge in rough terrain, but the 

 dredge may be redesigned to better cope with rough 

 seafloor features. The continuous bucket line 

 dredge, used in sampling manganese nodules, is 

 also proposed to be adapted for bulk sampling of 

 crusts. 



Polymetallic Sulfides 



Massive sulfides have a third dimension that 

 must be considered in sampling. At the moment, 

 very little is known about the vertical extent of sul- 

 fide deposits, as drilling them has not been very 

 successful. The problem lies in the absence of suit- 

 able drills. ^^ Without a sediment overburden of 100 

 meters (328 feet) or so it is difficult to confine the 

 drill bit at the start of drilling. The state-of-the-art 

 of massive sulfide sampling is demonstrated by the 

 fact that one of the largest samples collected to date 

 was obtained by ramming a research submersible 

 into a sulfide chimney, knocking the chimney over, 

 and picking up the pieces with the submersible's 

 manipulator arm.^* Clearly, current bulk and core 

 sampling methods leave something to be desired. 



Recent advances have been made in bare-rock 

 drilling. For example, one of the main purposes of 

 Leg 106 of the Ocean Drilling Program (ODP) in 

 December 1985 was to test and evaluate new bare- 

 rock drilling techniques. Drilling from the ODP's 

 143 meter (470 foot) drill ship JOIDES Resolution 

 took place in the Mid-Atlantic Ridge Rift Valley 

 some 2,200 kilometers (1,200 nautical miles) south- 

 east of Bermuda. The scientists and engineers of 

 Leg 106 were partly successful in drilling several 

 holes using such innovative techniques as a hard- 

 rock guide base to confine the drill bit during ini- 

 tial "spud-in," a low-light television camera for 

 imaging the seafloor and for monitoring drilling 

 operations, and new downhole drilling and coring 

 motors. The first hole took 25 days to penetrate 33.3 

 meters (110 feet) of rock below the seafloor, while 

 recovering about 23 percent of the core material. '^ 



"R. Willard, Bureau of Mines, OTA Workshop on Site-Specific 

 Technologies for Exploring the Exclusive Economic Zone, Washing- 

 ton, DC, July 16, 1986. 



"J.M. Edmond, P.P. Agterberg, et al., "Report of the Working 

 Group on Marine Sulfides, ' ' Marine Minerals: Advances in Research 

 and Resource Assessment, P.G. Teleki, et al. (eds.) (Dordrecht, Hol- 

 land: D. Reidel Publishing Co., 1987), NATO ASI Series, p. 36. 



'■•P. "Hale, Offshore Minerals Section, Energy, Mines, and Re- 

 sources Canada, OTA Workshop on Site-Specific Technologies for 

 Exploring the Exclusive Economic Zone, Washington, DC, July 16, 

 1986. 



"R.S. Detrick, "Mid-Atlantic Bare-Rock Drilling and Hydrother- 

 mal Vents," Nature, vol. 321, May 1986, pp. 14-15. 



