Ch. 4— Technologies for Exploring the Exclusive Economic Zone • 161 



Although improvements in drilling rates and core 

 recovery are needed, the techniques demonstrated 

 during Leg 106 open up new possibilities for drilling 

 into massive sulfides. 



In 1989, iheJOIDES Resolution is tentatively 

 scheduled to visit the Juan de Fuca Ridge, thus pro- 

 viding an opportunity to obtain a few cores from 

 massive sulfide deposits. However, the JOIDES 

 Resolution is a large, specially designed drill ship. 

 Its size is governed, in part, by requirements for 

 handling and storing drilling pipe. Because oper- 

 ating the JOIDES Resolution is expensive, it is not 

 economically advantageous for inexpensive explo- 

 ration sampling of massive sulfides in extensive 

 areas. 



An alternative and relatively less expensive ap- 

 proach to using a large and expensive drill ship for 

 hard-rock sampling is to use a remotely operated 

 submersible drill which is lowered by cable from 

 a surface vessel to the seafloor.^^ In addition to 

 lower cost, the advantages to using this type of drill 

 are the isolation of the coring operation from sea- 

 state-induced ship motions and reduced station- 

 keeping requirements. Maintaining contact with 

 a remotely operated drill while it is drilling remains 

 difficult; if the umbilical is jerked during the drilling 

 operation, the drill can easily jam. Several remotely 

 operated drills have been conceived and/or built, 

 as described below. 



The drill developed by the Bedford Institution 

 of Oceanography in Canada has probably had the 

 most experience coring sulfides, although the per- 

 formance of the drill to date has not met its design 

 specifications. The Bedford drUl is electrically pow- 

 ered from the surface and is designed to operate 

 in over 3,500 meters of water. The drill can be de- 

 ployed in winds of 25 to 30 knots and in currents 

 up to 3 knots. It is designed to cut a core 6 meters 

 long (extendable another 2.5 meters) with a di- 

 ameter of 2.5 centimeters. A commercial version 

 of this drill, made by NORDCO of St. John's, 

 Newfoundland, is now available and has been sold 

 to Australia, India, and Norway.^'' 



Nine cores drilled through basalt were obtained 

 with the Bedford drill in 1983 on the Juan de Fuca 

 Ridge, but the total core length retrieved was only 

 0.7 meter. ^' Obtaining long cores has been diffi- 

 cult. Drillers have found that competent, unfrac- 

 tured rocks, such as metamorphic or intrusive 

 types, yielded the longest cores, while young, 

 glassy, highly fractured basalts were difficult to sam- 

 ple. ^^ The massive sulfides themselves are easier 

 to drill than fractured basalts. 



Since 1983, the performance of the Bedford drill 

 has improved. Recently, two cores, each about 1 

 meter long, were retrieved in gabbro. Drilling took 

 place at the Kane Fracture Zone. Several foot-long 

 cores containing sulfides also were taken from the 

 Endeavor Segment of the Juan de Fuca Ridge. Me- 

 chanically, the drill has not been changed much, 

 but electronics and control systems are better. The 

 experience gained thus far suggests that it is essen- 

 tial to do preliminary reconnaissance work before 

 emplacing the drill. During emplacement, a video 

 camera attached to the drill frame also has proved 

 helpful, as it lets drillers locate a stable position for 

 the drill. 



Several other remotely controlled drills have been 

 designed and/or built. In the early 1970s, Woods 

 Hole Oceanographic Institution built a rock drill 

 designed to recover a 1 meter long, 2 centimeter 

 diameter rock core from water depths as much as 

 4,000 meters. The drill was originally designed to 

 be deployed from the research submersible Alvin 

 but was later reconfigured to be deployed from a 

 surface ship. It has not been used extensively.'"" 

 A Japanese firm, Koken Boring & Machine Co., 

 has built a remote battery-powered drill and used 

 it successfully in 500 meters of water. NORDCO 

 has recendy developed a sampling system, that, de- 

 pending on its configuration, can be used to sam- 

 ple either sediment or rock. This system was used 

 in October 1985 to recover eight cores in 800 meters 

 of water off Baffin Island."" Finally, design of a 



^^R. Fetters and M. Williainson, "Design for a Deep-Ocean Rock 

 Core Drill," Marine Mining, vol. 5, No. 3, 1986, p. 322. 



"P.J.C. Ryall, "Remote Drilling Technology," Journay of Ma- 

 rine Mining, in press, 1986. 



"Hale, Offshore Minerals Section, Energy, Mines, and Resources 

 Canada, OTA Workshop on Site-Specific Technologies for Explor- 

 ing the Exclusive Economic Zone, July 1986. 



"Ryall, "Remote Drilling Technology." 



'»°R.E. Davis, D.L. WUliams, and R.P. Von Herzen, "ARPA 

 Rock Drill Report," Woods Hole Oceanographic Institution, Tech- 

 nical Report 75-28, June 1975. 



'"'Ryall, "Remote Drilling Technology." 



