288 



UNITED STATES MINERAL RESOURCES 



SPECULATIVE RESOURCES 



Helium, although now supplied as a byproduct of 

 natural-gas fuel, originates from different source 

 materials and therefore is not necessarily limited to 

 oil and gas areas. Because of the extensive explora- 

 tion for natural gas for fuel and because helium 

 needs are being satisfied from known gas fields, a 

 separate search for helium has not been necessary. 

 When the few large gas fields that now supply most 

 of the country's helium needs are exhausted, helium 

 may cease to be a byproduct of natural gas and may 

 become a target for direct exploration. If this hap- 

 pens, then some of the gas deposits in Paleozoic 

 rocks in the Rocky Mountain region that have such 

 high content of nitrogen or carbon dioxide as to 

 be unsatisfactory for fuel may become economically 

 valuable for their helium content. The extent of 

 these gas deposits is not known because most de- 

 velopers do not explore beyond the original dis- 

 covery well. Three such deposits, the Woodside and 

 Harley Domes of Utah and the Model Dome of 

 Colorado, have been set aside as helium reserves. A 

 fourth deposit of this type, the Tip Top field occurs 

 in western Wyoming. Only the Pinta Dome field in 

 Arizona is producing gas solely for its helium con- 

 tent. The remaining gas in the field is mostly 

 nitrogen. 



Regions within which deposits of nonfuel gases 

 are known cover at least 20,000 square miles. Lipper 

 (1970, p. 83) reported that about 8 percent of the 

 known domestic helium reserves (in gases contain- 

 ing more than 0.3 percent helium) is in gases that 

 are noncombustible or that have such low heating 

 value that they are not salable as fuel. The extent 

 of these nonfuel gases is unexplored in large areas. 



Sedimentary rocks derived from the erosion of 

 igneous rocks may be sources of helium because of 

 the uranium and thorium content of the sediments. 

 (See chapter on "Nuclear fuels.") Helium atoms, 

 because of their very small size and light weight, 

 are able to migrate through very small pore spaces 

 and fractures to reach traps where other natural 

 gases accumulate. 



The minute amounts of uranium and thorium 

 present in rocks and the long time required for their 

 radioactive decay indicate that time is an important 

 factor in the accumulation of helium deposits. Hy- 

 drocarbon gases form comparatively quickly, and 

 the greatest volumes have been found in Tertiary 

 and Cretaceous rocks. Helium concentrations, on the 

 other hand, are largest in the Paleozoic rocks. Some 

 of the gas fields of the United States and Canada 

 which contain comparatively high percentages of 

 helium are listed in table 56. 



The information in table 56 suggests the follow- 

 ing potential source rocks and localities, both within 

 and outside oil and gas areas, in which future ex- 

 ploration for helium may hold promise. 



1. Black shales and other dark-colored sedimentary 



rocks having comparatively high radioactivity 

 and of large extent and volume could generate 

 helium that would be trapped in overlying 

 rocks, particularly in rocks of Paleozoic age. 

 Examples of such possible source rocks are 

 the Pennsylvanian Heebner Shale Member of 

 the Oread Limestone in shales of the Pennsyl- 

 vanian Cherokee Group in Kansas and equiva- 

 lents in Oklahoma and the Devonian and Mis- 

 sissippian Chattanooga Shale and equivalents 

 of the midcontinent region. Gamma-ray logs 

 of these rocks reveal high radioactivity. 



2. Granitic rocks of basement highs and "granite 



wash" derived from these highs are the prob- 

 able sources of helium in the Panhandle and 

 Otis-Albert gas fields (table 56). Little natural 

 gas has been found north and northeast of the 

 Central Kansas uplift, but study of the base- 

 ment rock map of the United States (Bayley 

 and Muehlberger, 1968) suggests that this 

 would be a good area in which to look for gas 

 with appreciable helium content. Although gas 

 deposits in this area apparently would not be 

 large and the gases from them might have 

 little or no value as fuel, they would be found 

 at comparatively shallow depths. 



3. Igneous rocks apparently are the source of 



helium in the gas fields of New Mexico and 

 Arizona listed in table 56. This apparent 

 source suggests that other areas of igneous 

 activity, which were very extensive in the 

 Western United States, may also have helium 

 resources both in natural gas deposits and in 

 geothermal areas. In many areas, exploration 

 and development of geothermal sources of 

 energy are receiving much attention, and in 

 some of the areas the fluids and gases may be 

 abnormally high in helium. 

 Most of the gas fields listed in table 56 are on or 

 near the highest parts of uplifts. The largest accu- 

 mulations of helium in the United States are in 

 structurally high areas around the southern, west- 

 ern, and northern margins of the Anadarko basin 

 of Oklahoma. Natural-gas fields occur also in struc- 

 turally lower parts of the basin, but these do not 

 contain large amounts of helium. Contours of the 

 basement surface on the basement rock map of the 

 United States (Bayley and Muehlberger, 1968) de- 



