Ch. 2 — Resource Assessments and Expectations • 69 



the coast south of the Salmon River and in sedi- 

 ments in Chagvan Bay.^* The possibiHty exists that 

 platinum placers may be found on the shelf if gla- 

 cially transported material has been concentrated 

 by marine processes. Source rocks are thought to 

 be dunites in the coastal Kuskokwim Mountains, 

 but lode deposits have not been found. Gold placers 

 are also found along the coast of the Bering Sea 

 and are especially important to the north near 

 Nome. Lode gold and alluvial placers are common 

 along the southern side of the Seward Peninsula, 

 and tin placers have also been worked in the area. 

 Gold has been found offshore in gravel on sub- 

 merged beach ridges and dispersed in marine sands 

 and muds. Economic deposits may be found in the 

 submerged beach ridges or in buried channels off- 

 shore. The region around Nome has yielded about 

 5 million ounces of gold, mainly from beach de- 

 posits, and it is suggested that even larger amounts 

 may lie offshore.'' How much of this, if any, may 

 be discovered in economically accessible deposits 

 is uncertain, but the prospects are probably pretty 

 good in the Nome area. 



*'R.M. Owen, "Geochemistry of Platinum-Enriched Sediments: 

 Apphcations to Mineral Exploration," Marine Mining, vol. 1, No. 

 4, 1978, pp. 259-282. 



'^Beauchamp and Cruickshank, "Placer Minerals on the U.S. Con- 

 tinental Shelves — Opportunity for Development," p. 700. 



Other Heavy Minerals 



The eastern Gulf of Alaska is strongly influenced 

 by the modern glaciers in the area. Fresh, glacially 

 derived sediments, including large amounts of fine- 

 grained material, are entering the area and being 

 sorted by marine processes. Heavy mineral suites 

 are likely to be fairly immature and burial is rapid. 

 In general, the prospects for locating economically 

 interesting heavy mineral placers offshore in this 

 area would not be great. 



About 2,000 tons of tin have been produced from 

 placers on the western part of the Seward Penin- 

 sula. Tin in association with gold and other heavy 

 minerals may occur in a prominent shoal which ex- 

 tends over 22 miles north-northeast from Cape 

 Prince of Wales along the northwest portion of the 

 Seward Peninsula. While seafloor deposits off the 

 Seward Peninsula might be expected to contain 

 gold, cassiterite, and possibly tungsten minerals, 

 data are lacking to evaluate the resource potential. 



In general, the Chukchi and Beaufort seas may 

 not contain many economic placers. Source rocks 

 are distant, and ice gouging tends to keep bottom 

 sediments mixed. 



HAWAII REGION AND U.S. TRUST TERRITORIES 



Hawaii is a tectonically active, mid-ocean vol- 

 canic chain with typically narrow and limited shelf 

 areas. Sand and gravel resources are in short sup- 

 ply. The narrow shelf areas in general do not pro- 

 mote large accumulations of sand and gravel off- 

 shore. One area of interest is the Penguin Bank, 

 which is a drowned shore terrace about 30 miles 

 southeast of Honolulu (figure 2-10). The bank's re- 

 source potential is conservatively estimated at over 

 350 million cubic yards of calcareous sands in about 

 180 to 2,000 feet of water. '^ This resource could 

 supply Hawaii's long-term needs for beach resto- 

 ration and, to a lesser extent for construction. How- 

 ever, high winds and strong currents are common 



"W.B. Murdaugh, "Preliminary Feasibility Assessment: Offshore 

 Sand Mining, Penguin Bank, Hawaii," Program Feasibility 

 Document — OCS Hard Minerals Leasing, app. 19, U.S. Department 

 of the Interior, 1979, p. 14. 



on the Penguin Bank. Total sand and gravel re- 

 source estimates for Hawaii may be as high as 25 

 billion cubic yards (table 2-4). 



No metalliferous deposits are mined onshore in 

 Hawaii. Thus the prospects are somewhat poor for 

 locating economically attractive placer deposits on 

 the Hawaiian outer continental shelf. Minor phos- 

 phorite deposits have been found in the Hawaii 

 area, although phosphorite is found on seamounts 

 elsewhere in the Pacific. 



The geology of the U.S. Trust Territories is gen- 

 erally similar to Hawaii with the islands being of 

 volcanic origin, often supporting reefs or limestone 

 deposits. Clastic debris of the same material is 

 present and concentrated locally, but very little in- 

 formation is available as to the nature and extent 

 of any sand or gravel deposits. Other areas are rela- 



