Ch. 2— Resource Assessments and Expectations • 43 



Table 2-1.— Association of Potential Mineral 

 Resources With Types of Plate Boundaries 



Type of plate boundary/Potential mineral resources 



Divergent: 



• Oceanic ridges 



—Metalliferous sediments (copper, iron, manganese, 

 lead, zinc, barium, cobalt, silver, gold; e.g., Atlantis II 

 Deep of Red Sea) 



—Stratiform manganese and iron Ixodes and 

 hydroxides and iron silicates (e.g., sites on Mid- 

 Atlantic Ridge and Galapagos Spreading Center) 



— Polymetallic massive sulfides (copper, iron, zinc, 

 silver, gold, e.g., sites on East-Pacific Rise and 

 Galapagos Spreading Center) 



—Polymetallic stockw^ork sulfides (copper, iron, zinc, 

 silver, gold; e.g., sites on Mid-Atlantic Ridge, 

 Carlsberg Ridge, Costa Rica Rift) 



—Other polymetallic sulfides in disseminated or 

 segregated form (copper, nickel, platinum group 

 metals) 



—Asbestos 



— Chromite 



Convergent: 



• Offshore 



— Upthrust sections of oceanic crust containing types 

 of mineral resources formed at divergent plate 

 boundaries (see above) 



—Tin, uranium, porphyry copper and possible gold 

 mineralization in granitic rocks 



Convergent: 



• Onshore 



— Porphyry deposits (copper, iron, molybdenum, tin, 



zinc, silver, gold; e.g., deposits at sites in Andes 



mountains) 

 —Polymetallic massive sulfides (copper, iron, lead, 



zinc, silver, gold, barium; e.g., Kuroko deposits of 



Japan) 



Transform: 



• Offshore 



—Mineral resources similar to those formed at 

 divergent plate boundaries (oceanic ridges) may 

 occur at offshore transform plate boundaries; e.g., 

 sites on Mid-Atlantic Ridge and Carlsberg Ridge) 



SOURCE: Peter A. Bona, "Potential Mineral and Energy Resources at Submerged 

 Plate Boundaries," MTS Journal, vol. 19, No. 4, 1985, pp. 18-25. 



such as the Hawaiian Islands. These sites may adso 

 have significant potential for future recovery of 

 mineral deposits. 



The theory of plate tectonics has led to the rec- 

 ognition that many economically important types 

 of mineral deposits are associated with either pres- 

 ent or former plate boundaries. Each type of plate 

 boundary — divergent, convergent, or transform — 

 is not only characterized by a distinct kind of in- 

 teraction, but each is also associated with distinct 

 types of mineral resources (table 2-1). Knowledge 

 of the origin and evolution of a margin can serve 

 as a general guide to evaluating the potential for 

 locating certain types of mineral deposits. 



ATLANTIC REGION 



When the Atlantic Ocean began to form between 

 Africa and North America around 200 million years 

 ago, it was a narrow, shallow sea with much evap- 

 oration. The continental basement rock which 

 formed the edge of the rift zone was block-faulted 

 and the down-dropped blocks were covered with 

 layers of salt and, as the ocean basin widened, with 

 thick deposits of sediment. A number of sedimen- 

 tary basins were formed in the Atlantic region along 

 the U.S. east coast (figure 2-2). Very deep sedi- 



ments are reported to have accumulated in the Bal- 

 timore Canyon Trough. In addition, a great wedge 

 of sediment is found on the continental slope and 

 rise. In places, due to the weight of the overlying 

 sediment and density differential, salt has flowed 

 upward to form diapirs or salt domes and is avail- 

 able as a mineral resource. In addition, sulfur is 

 commonly associated with salt domes in the cap 

 rock on the top and flanks of the domes. Both salt 

 and sulfur are mined from salt domes (often by so- 



