29 



TABLE V.-OCEAN MINING TECHNOLOGY TIME TABLE 



Depth of water 



50 feet 



300 feet 



600 feet 



1000 feet 



Mining using air lift device _ 1960 



Mobile miner (ocean floor) 1970 



Barge dredge lift,... _ 1900 



Stationary mining platform. 1960 



Buoyant submersible system -. - 



Underwater open pit hardrock mining 1975 



Underwater "aerial" photographic reconnaisance 1960 



Exploration submarine (corer) 



Underwater site development station 1970 



Solution mining (sulfur, potash)... 1961 



Hardfock mining (below shelO 1900 



Mining shaft... 1970 



Conventional dredging is done by four main types of dredges : 



1. Bucket-ladder dredge, limited to 150 feet. 



2. Surface pump hydraulic dredge, limited to 200 feet. 



3. Wire line dredges (grab bucket, clamshell, orange peel, etc.), 

 limited to 500 feet. 



4. Air lift dredge, limited to 1,000 feet. 



Although these dredge types have functioned successfully at much 

 greater depths, the depth limits given above are those for 'practical 

 operations. 



For deep-sea areas, the deep-sea drag dredge and the deep-sea 

 hydraulic dredge have been envisioned, which might prove practical 

 for mining phosphorite and manganese nodules. The cost of mining a 

 ton of nodules by deep-sea drag dredge was estimated by Mero ^* to 

 range from about $12 at a depth of 1,000 feet to more than $40 at 10,- 

 000, provided the nodule concentration is one pound per square foot. 

 The use of deep-sea hydraulic dredging, on the other hand, lowers 

 these figures to an acceptable range of $2.29 per ton at 1,000 feet and 

 roughly $5 at 20,000 feet. 



The most recent breakthrough in sea floor dredging is an elaborate 

 system of air-lift dredge successfully tested in July 1970 on the Blake 

 Plateau, approximately lYO miles off the cost of Georgia and Florida. 

 From depths between 2,400 and 3,000 feet, the dredge succeeded in 

 extracting a continuous flow of nodules from the ocean floor. The sys- 

 tem on board the Deepsea Miner was operated by Deepsea Ventures, 

 Inc., a subsidiary of Tenneco, Inc. It represents approximately a decade 

 of research and an investment of nearly $18 million. The objective 

 following this initial success is the capability to operate at greater 

 depths between 18,000 and 20,000 feet, probably in the Pacific ocean 

 where nodules are plentiful. With a processing plant planned for the 

 mid-seventies, the operators hope to attract an investment of $150 t:o 

 $200 million to finance full-scale production before the end of this 

 decade. The Japanese ship No. 2 Chiyoda Maru has succeeded in re- 

 covering nodules from comparable depths in the vicinity of Tahiti by 

 using a continuous bucket trawling system. 



While this manuscript was being readied for the press, a break- 

 through was achieved in processing manganese nodules. After investi- 



^^Mero, op. cit., page 257. 



