38 



UNITED STATES MINERAL RESOURCES 



Most of the bauxite deposits in the United States 

 are composed chiefly of gibbsite; the principal im- 

 purity is kaoHnite, (OH)sSijAl.iOio. Jamaican 

 bauxite, the leading source of our imports, is 

 chiefly gibbsite but also contains some boehmite. 

 Most deposits in Europe and several in Asia are 

 composed chiefly of boehmite. Minor quantities of 

 diaspore are present in several bauxite deposits in 

 foreign countries and occur in refractory-clay de- 

 posits in Missouri and Pennsylvania. 



Bauxite minerals are formed mostly by weather- 

 ing of aluminous rocks. Various deposits of bauxite 

 in different parts of the world are known to have 

 formed from virtually every type of rock that con- 

 tains aluminum. Conditions favorable for the for- 

 mation of bauxite are (1) warm tropical climate, 

 (2) abundant rainfall, (3) aluminous parent rocks 

 having high permeability and good subsurface 

 drainage, and (4) long periods of tectonic stability 

 that permit deep weathering and preservation of 

 land surfaces. During weathering, the bauxite be- 

 comes enriched in aluminum by removal of most 

 of the other elements in the parent rocks mainly by 

 solution by subsurface water. Because of chemical 

 weathering and removal of essential plant nutrients, 

 soils developed on bauxite deposits commonly sup- 

 port a cover of undernourished, dwarfed vegetation. 



Useful guides in exploration for surflcial bauxite 

 are the recognition of old land surfaces and dwarfed 

 vegetation; such guides led to the discovery of the 

 bauxite deposits in Oregon and Hawaii, as well as 

 several very large deposits in other parts of the 

 world. 



Several types of bauxite deposits occur in the 

 United States. The major deposits in the Arkansas 

 region are of Eocene age, and they were formed by 

 weathering of nepheline syenite (Gordon and others, 

 1958). Some deposits in this region are residual on 

 the igneous rock; others have been transported and 

 are interlayered with marine shale that was depos- 

 ited in a sea that overlapped the syenite. The iron- 

 and titanium-bearing low-grade bauxites (table 7) 

 in Washington (Livingston, 1966), Oregon (Cor- 

 coran and Libbey, 1956), and Hawaii (Patterson, 

 1971) were formed from basalt lava flows. These 

 deposits are of the laterite type and have origins 

 similar to the very large deposits occurring in thick 

 residual soils in several tropical areas. The deposits 

 in Washington and Oregon occur on flows of prob- 

 able middle Miocene age, and the bauxite is thought 

 to have formed chiefly in late Miocene time. Those 

 in Hawaii formed mainly during the Pleistocene 

 Epoch. Some bauxite deposits in the Appalachian 

 region occur in areas of karst topography, and ap- 



parently they formed by leaching of fine-grained 

 aluminous materials that accumulated in sink holes. 

 These deposits are thought to be early Tertiary in 

 age. 



Table 7. — Chemical composition, in percent, of bauxite re- 

 sources in the United States 



AI2O3 



Arkansas 40-60 



Oregon! 35.0 



Washington ' 38.8 



Kauai, Hawaii ^ 25.9 



! Average of several analyses. 



3->6 



31.6 

 28 7 

 39.4 



15-35 

 20.2 

 21.7 

 20-23 



RESOURCES 



BAUXITE RESOURCES 



Compared with world resources of metallurgical- 

 grade bauxite, the United States reserves and po- 

 tential resources are very limited. The domestic 

 reserves, which are in beds 8 or more feet thick in 

 Arkansas, amount to approximately 40 million tons. 

 Potential resources of metallurgical bauxite in the 

 laterite deposits in Hawaii, Washington, and Ore- 

 gon, and thin, deeply buried deposits in Arkansas, 

 amount to 250 to 300 million tons. Some of the de- 

 posits in Washington and Oregon are as rich in 

 alumina as bauxite mined in some countries, but it 

 has not been established that alumina can be ex- 

 tracted profitably from this bauxite. With the de- 

 velopment of a process of profitable extraction, as 

 much as 100 million tons could be shifted from con- 

 ditional resources to the reserve category, thereby 

 increasing the reserves to 140 million tons. But even 

 with this larger figure, the United States would 

 have only about 1 percent of the world's bauxite 

 reserves. 



World bauxite reserves were estimated in 1965 

 by Patterson (1967) to be 5.8 billion tons and po- 

 tential resources to be 9.6 billion tons. Since this 

 estimate was made, very large deposits have been 

 discovered in several countries, and trihydrate 

 bauxite containing as little as 35 percent ALOa is 

 now mined in Australia and elsewhere. As the result 

 of the use of lower grade bauxite, much of that 

 considered to be potential resources in 1965 now 

 should be classified as reserves. The total world 

 bauxite reserves are now probably 12-15 billion 

 tons. Lack of reliable data precludes estimating 

 potential bauxite resources, but these resources are 

 undoubtedly much larger than the 1965 estimate. 



It is unlikely that new large deposits of metal- 

 lurgical-grade bauxite will be discovered in the 

 United States. Elsewhere, however, there are large 

 unexplored areas in South America, Africa, Asia, 



