Ch. 2— Resource Assessments and Expectations • 67 



significantly affected by glaciation and major sea 

 level changes. Glacial sediment was derived from 

 Siberia as well as Alaska. Barrier islands are found 

 along the northern side of the Seward Peninsula. 



The major physiographic feature of the north 

 coast of Alaska is the gently sloping arctic coastal 

 plain, which extends seaward to form a broad shelf 

 under the Chukchi and Beaufort Seas. This area 

 was not glaciated during the Pleistocene, and only 

 one major river, the Colville, drains most of the 

 region into the Beaufort Sea. The drainage area 

 includes the Paleozoic sedimentary rocks of the 

 Brooks Range and their associated local granitic 

 intrusives and metamorphosed rocks. 



Sand and Gravel 



Approximately 74 percent of the continental shelf 

 area of the United States is off the coast of Alaska. 

 Consequently, Alaskan offshore sand and gravel 

 resources are very large. However, since these ma- 

 terials are not generally located near centers of con- 

 sumption, mining may not always be economically 

 viable. 



While glaciation has deposited large amounts of 

 sand and gravel on Alaska's continental shelf, the 

 recovery of economic amounts for construction ag- 

 gregate is complicated by two factors: 



1. much of the glacial debris is not well sorted, 

 and 



2. it is often buried under finer silt and mud 

 washed out after deglaciation. 



Optimal areas for commercial sand and gravel de- 

 posits would include outwash plains or submerged 

 moraines that have not been covered with recent 

 sediment, or where waves and currents have win- 

 nowed out finer material. 



In general, much of the shelf of southeastern 

 Alaska has a medium or coarse sand cover and is 

 not presently receiving depositional cover of fine 

 material. The Gulf of Alaska is currently receiv- 

 ing glacial outwash of fine sediment in the eastern 

 part and, in addition, contains extensive relict de- 

 posits of sand and gravel. Economic deposits of sand 

 have been identified parallel to the shoreline west 

 of Yakutat and west of Kayak Island. An exten- 

 sive area of sand has been mapped in the lower 



Cook Inlet, and gravel deposits are also present 

 there (figure 2-9). Large quantities of sand and 

 gravel are also found on the shelf of Kodiak Island. 

 The Aleutian Islands are an unfavorable area for 

 extensive sand and gravel deposits. Relict glacial 

 sediments should be present on the narrow shelf, 

 but the area is currently receiving little sediment. 



Large amounts of fine sand lie in the southern 

 Bering Sea and off the Yukon River, but the north- 

 ern areas may offer the greatest resource potential 

 for construction aggregate. Extensive well-sorted 

 sands and gravels are found at Cape Prince of 

 Wales and northwest of the Seward Peninsula. 

 However, distances to Alaskan market areas are 

 considerable. Sand, silt, and mud are common on 

 the shelf in the Chukchi Sea and Beaufort Sea. 

 Small, thin patches of gravel are also present, but 

 available data are sparse. The best prospect of 

 gravel in the Beaufort Sea is a thick layer of Pleisto- 

 cene gravel buried beneath 10 to 30 feet of over- 

 burden east of the Colville River. 



Overall sand and gravel resource estimates of 

 greater than 200 billion cubic yards are projected 

 for Alaska (table 2-4). In many areas, environ- 

 mental concerns in addition to economic consider- 

 ations would significantly influence development. 



Precious Metals 



Source rocks for sediments in southeastern 

 Alaska are varied. Gold is found in the region and 

 has been mined from placer deposits. Platinum has 

 been mined from lode deposits on Prince of Wales 

 Island. Although few beach or marine placer de- 

 posits are found in the area, the potential exists 

 since favorable source rocks are present. However, 

 glaciation has redistributed much of the sediment, 

 and the shelf is receiving relatively little modern 

 sediment. 



Some gold has been recovered from beach placers 

 in the eastern Gulf of Alaska; but, in general, the 

 prospects for locating economic placers offshore 

 would not be great because of the large amount of 

 glacially derived fine-grained material entering the 

 area. In the western Gulf, the glaciation has re- 

 moved much of the sediment from the coastal area 

 and deposited it offshore where subsequent rework- 

 ing may have formed economically interesting 



