66 • Marine Minerals: Exploring Our New Ocean Frontier 



Figure 2-8.— Locations of IVIineral Deposits Relative to Physiographic Features (vertical scale exaggerated) 



Copper/gold j_ Base metals 

 Iron — V \ . Gold 



Placers I"' «'* ''' 

 I I 

 I li 



Sea level 



' Petroleum 



Spreading ridge crest 



Understanding the motion of the Earth's plates and 

 related processes helps geologists understand the 

 distribution of the Earth's resources. 



SOURCES: Office of Technology Assessment. 1987; Bonnie A. McGregor and f^illington Locl<wood. "Mapping and Researcfi in ttie Exclusive Economic Zone." Department 

 of tfie Interior, U.S. Geological Survey and Department of Commerce, National Oceanic and Atmosptieric Administration. 



sedimentary, metamorphic, volcanic, and intrusive 

 bodies. 



The Alaska Peninsula and Aleutian Islands con- 

 sist of intrusive and volcanic rocks related to the 

 subduction zone along the Pacific side. The shelf 

 narrows westward from a width of nearly 125 miles 

 to places where it is nearly nonexistent between the 

 Aleutian Islands. The Aleutians are primarily an- 

 desitic volcanics while granitic intrusives are found 

 on the peninsula. 



The Bering Sea shelf is very broad and gener- 

 ally featureless except for a few islands, banks, and 

 depressions. A variety of sedimentary, igneous, and 

 metamorphic rocks are found in the region. In the 

 south, of particular mineralogical interest, are the 

 Kuskokwim Mountains containing Precambrian 

 schist and gneiss, younger intrusive rocks, and 

 dunite. The Yukon River is the dominant drain- 

 age system entering the Bering shelf, although sev- 

 eral major rivers contribute sediments including 

 streams on the Asian side. The region also has been 



