CONTENTS 



Page 



Introduction ^"' 



Dredging Unconsolidated Materials 169 



Bucketline or Bucket Ladder Dredging. . .169 



Suction Dredging 172 



Grab Dredges 177 



New Directions and Trends in Dredging 



Technology 1'" 



Mining Consolidated Materials Offshore ... 180 



Massive Polymetallic Sulfides 181 



Cobalt-Rich Ferromanganese Crusts 182 



Solution/Borehole Mining 183 



Offshore Mining Technologies 185 



At-Sea Processing ■ 185 



Processing Unconsolidated Deposits of 



Chemically Inert Minerals 186 



Processing Unconsolidated or Semi- 

 Consolidated Deposits of Chemically 



Active Minerals 1"^ 



Processing Consolidated and Complex 



Mineral Ores 1"! 



Offshore Mining Scenarios 192 



Offshore Titaniferous Sands Mining 



Scenario l"'^ 



Offshore Chromite Sands Mining 



Scenario 196 



Offshore Placer Gold Mining Scenario ... 199 

 Offshore Phosphorite Mining Scenarios: 

 Tybee Island, Georgia and Onslow 

 Bay, North Carolina 204 



Box 



Box 



5-A. Sand and Gravel Mining 



Page 

 .199 



Figures 



Figure No. -Page 



5-1. Bucket Ladder Mining Dredge 170 



5-2. Capital and Operating Costs for 



Bucket Ladder Mining Dredges 171 



5-3. Motion Compensation of Bucket 



Ladder on Offshore Mining Dredge . . 172 

 5-4. Components of a Suction Dredge .... 172 



5-5. Trailing Suction Hopper Dredge 174 



5-6. Cutter Head Suction Dredge 175 



5-7. Bucket Wheel Suction Dredge 176 



5-8. Airlift Suction Dredge Configuration . 177 



5-9. Grab Dredges 178 



5-10. Cutter Head Suction Dredge on Self- 

 Elevating Walking Platform 179 



5-11. Conceptual Design for Suction Dredge 

 Mounted on Semi-Submersible 

 Platform 180 



Figure No. ^^ge j 



5-12. Conceptual System for Mining 



Polymetalhc Sulfides 182 



5-13. Schematic of Solution Mining 



Technology (Frasch Process) 184 



5-14. Technologies for Processing Placer 



Minerjil Ores 187 



5-15. Operating Principles of Three Placer 



Mineral Separation Techniques 189 



5-16. Technologies for Processing Offshore 



Mineral Ores 191 



5-17. Offshore Titaniferous Mineral 



Province, Southeast United States .... 194 

 5-18. Values of Ti02 Content of Common 

 Titanium Mineral Concentrates 



and Intermediates 195 



5-19. Offshore Chromite Sands, Oregon 



Continental Shelf -197 



5-20. Nome, Alaska Placer Gold District . . .201 

 5-21. Offshore Phosphate District, 

 Southeastern North Carolina 

 Continental Shelf 208 



Tables 



Table No. ^^ge 



5-1. Offshore Mineral Mining Worldwide 



Commercial Operations 168 



5-2. Currendy Available Offshore 



Dredging Technology 170 



Ratio of Valuable Mineral to Ore 190 



Offshore Titaniferous Sands Mining 

 Scenario: Capital and Operating Cost 



Estimates 196 



5-5. Offshore Chromite Sands Mining 



Scenario: Capital and Operating Cost 



Estimates 198 



5-6. Offshore Placer Gold Mining 



Scenario: Capital and Operating Cost 



Estimates 203 



5-7. Offshore Phosphorite Mining, Tybee 

 Island, Georgia: Capital and 



Operating Cost Estimates 206 



5-8. Offshore Phosphorite Mining, Onslow 

 Bay, North Carolina: Capital and 



Operating Cost Estimates 209 



5-9. Scenario Comparisons: East Coast 



Placer 210 



5-10. Scenario Comparisons: West Coast 



Placer 211 



5-11. Scenario Comparisons: Nome, Alaska 



Gold Placer 211 



5-12. Scenario Comparisons: Onslow Bay 



and Tybee Island Phosphorite 212 



5-3. 

 5-4. 



