Ch. 5— Mining and At-Sea Processing Technologies • 193 



Offshore Titaniferous Sands 

 Mining Scenario 



Location. — Concentrations of titciniferous sands 

 are known to occur on the seabed adjacent to the 

 coast of Georgia (figure 5-17). These sands consti- 

 tute a resource of titanium oxide minerals (primar- 

 ily ilmenite, but also lesser amounts of rutile and 

 leucoxene, (figure 5-18)) and associated light heavy 

 minerals. However, little detailed exploration has 

 been done in the area, so the extent and grade of 

 the resource is not precisely known. 



Two mineral companies that mine onshore titan- 

 iferous sands in nearby northeastern Florida have 

 expressed interest in the area. In fact, in 1986, the 

 Minerals Management Service issued geological 

 and geophysical exploration permits to Associated 

 Minerals U.S.A., Ltd., and E.I. du Pont de Nemours 

 & Co. The companies have undertaken shallow cor- 

 ing, sub-bottom profiling, and radiometric surveys 

 in the area. The area of interest extends from Ty- 

 bee Island in the north to Jekyll Island in the south, 

 a distance of about 85 nautical miles, and from State 

 waters to about 30 nautical miles offshore. The 

 proximity of onshore titanium mineral processing 

 facilities in northeastern Florida is a particular rea- 

 son this scenario site was selected over other po- 

 tential sites on the Atlantic Ocean continental shelf. 



Operational and Geological Characteristics.— 



Within this area, a typical mine site was selected 

 approximately 30 nautical miles offshore. Water 

 depths at this site average 100 feet. Northeasterly 

 winds tend to prevail from October to March. The 

 site is in the path of occasional "northeasters" and 

 hurricanes, but wind, wave, tide, and current con- 

 ditions are otherwise moderate. Wave heights of 

 6 feet are common during winter months, but 

 waves of 1 to 4 feet are more typical the rest of the 

 year. Infrequent severe storms may produce waves 

 in excess of 20 feet, typically from the southeast or 

 northeast. It is assumed that operations can be con- 

 ducted 300 days per year. 



The geological features of the site were identi- 

 fied primarily by sub-bottom profiling and include 

 buried stream channels and submerged shorelines. 

 A similar ancient shoreline target onshore in north- 

 eastern Florida would be 12 miles long, 1 mile wide, 

 and 20 feet thick. Little is known about any over- 



burden at this time, so it is assumed that the de- 

 posit, like similar deposits onshore at Trail Ridge, 

 Florida, consists of unconsolidated heavy mineral 

 sands without significant overlying sediments. 



The average concentration of total heavy min- 

 erals in the ore is assumed to be between 5 and 1 5 

 percent by weight, about half of which are economic 

 heavy minerals. This range includes the average 

 grade of the heavy mineral concentrations detected 

 in the few samples from the site that have been ana- 

 lyzed to date. 



Mining Technology. — The most appropriate 

 technology for mining titaniferous minerals at the 

 selected site is considered to be a trailing suction 

 hopper dredge. This dredge is capable of operat- 

 ing in the open ocean at the mining site and of 

 shuttling to and from its shore base during the nor- 

 mal seas expected in this region. Trailing suction 

 hopper dredges have been widely used for sand and 

 gravel mining and for removing unconsolidated 

 material from harbors and channels. It is assumed 

 that the titaniferous sand is at most only mildly 

 compacted. The unconsolidated mineral sands are 

 sucked up the drag arms, which can adjust to ves- 

 sel heave and pitch to maintain the suction head 

 on the seabed. A booster pump is installed in the 

 suction line, enabling the dredge to reach minerals 

 at the assumed bottom of the mineralized zone, 

 about 120 feet below sea level. If cutting force is 

 needed to loosen the compacted sand and clay, 

 high-pressure water jets and cutting teeth can be 

 added to the suction head. A dredge with a hop- 

 per capacity of 5,000 cubic yards is used. The 

 dredge is assumed to be of U.S. registry, built and 

 operated according to Coast Guard regulations, and 

 more expensive than a similar dredge built abroad. 

 All equipment is assumed to be purchased new at 

 1987 market prices. 



At-Sea Processing. — The dredge is outfitted 

 with a wet primary concentration plant capable of 

 producing 450,000 tons per year of heavy mineral 

 concentrate for delivery to a dry mUI on shore. The 

 efficiency of economic heavy mineral recovery is 

 assumed to be 70 percent for the wet plant and 87.5 

 percent for the dry plant. The final product con- 

 centrate supplies the raw material for a pigment 

 plant. It is assumed that no major technical prob- 

 lems are encountered in designing the primary con- 



