Ch. 5— Mining and At-Sea Processing Teciinologies » 175 



Figure 5-6.— Cutter Head Suction Dredge 



Suction- 

 line 



Direction 

 of dredging 



-Cutter head 



Dredges such as this have been used at inland mine sites to mine heavy minerals such as ilmenite, rutile, and zircon. 



SOURCE: Dredge Technology Corp. 



United States (Florida), Australia (Queensland), 

 and South Africa (Richards Bay). Ore disaggre- 

 gated by the cutter is pumped through a flexible 

 pipeline to a wet concentrating plant floating sev- 

 eral hundred feet behind the dredge. This config- 

 uration, while common on protected dredge ponds 

 inland, may not be suitable for mining in the open 

 water of the marine environment because of wave, 

 current, and wind conditions. 



Large self-propelled cutter head suction dredges 

 have been built that are capable of steaming in 

 rough water with the cutter suction ladder raised. 

 While not able to operate in heavy seas, this type 

 of dredge can disengage from the bottom and "ride 

 out" storms. Adaptation of a sea-going cutter head 

 dredge to mining may require a motion compen- 

 sated ladder and installation of onboard process- 

 ing facilities and would require addition of a hop- 

 per or the use of auxiliary barges. 



The capital costs of cutter head suction dredges 

 vary widely with size and configuration. For sea- 

 going, self-powered dredges the capital costs would 

 be similar to those of hopper dredges, i.e., up to 

 $50 million. The capacities of cutter head dredges 

 vary with the size of the dredge pumps, which range 

 in diameter between 6 and 48 inches. This range 

 of diameters corresponds to mining volumes of 

 solids between 100 and 4,000 cubic yards per hour. 



Like suction hopper dredges, the operating 

 depths of available cutter head dredge designs are 

 limited by dredge pump technology to between 35 

 and 260 feet, although greater mining depths could 

 be achieved with incremental technical improve- 

 ments. The cutter head suction dredge is not con- 

 sidered suitable for cleaning bedrock to recover gold 

 or other very dense minerals in placer deposits, due 

 to inefficiency in recovering the heavier minerals. 



