116 • Marine Minerals: Exploring Our New Ocean Frontier 



Table 4-1.— Closing Range to a Mineral Deposit 



Approximate 



range to deposit Method 



10 l<ilometers . . . .Long-range side-looking sonar 



Regional sediment and water sampling 

 1 kilometer Gravity techniques 



Magnetic techniques 



Bathymetry 



Midrange side-looking sonar 



Seismic techniques 

 100 meters Electrical techniques 



Nuclear techniques 



Short-range side-looking sonar 

 10 meters Near-bottom water sampling 



Bottom images 



meter Coring, drilling, dredging 



Submersible applications 



SOURCE: Adapted from P. A. Rona, "Exploration for Hydrothermal Mineral 

 Deposits at Seaftoor Spreading Centers," Marine Mining, vol. 4, No, 

 1, 1983, pp. 20-26. 



areas. Systematic exploration does not necessarily 

 mean comprehensive exploration of each acre of 

 the EEZ. 



Accurate information about seafloor topography 

 is a prerequisite for detaOed exploration. Side- 

 looking sonar imaging and bathymetric mapping 

 provide indispensable reconnaissance information. 

 Side-looking sonar provides an image of the seafloor 

 similar to that provided by aerial radar imagery. 

 Its use has already resulted in significant new dis- 

 coveries of subsea geological features within the 

 U.S. EEZ. By examining side-looking sonar im- 

 ages, scientists can decide where to focus more 

 detailed efforts and plan a more detailed explora- 

 tion strategy. 



Long-range side-looking sonar (e.g., GLORIA 

 or SeaMARC II, described below) may show pat- 

 terns indicating large seabed structures. At some- 

 what closer range, a number of other reconnais- 

 sance technologies (figure 4-1) may provide more 

 detailed textural and structural data about the 

 seabed that can be used to narrow further the fo- 

 cus of a search to a specific mineral target. 



Photo credit: U.S. Geological Survey 



USGS S.P. Lee 



