286 



UNITED STATES MINERAL RESOURCES 



The United States, because of its early develop- 

 ment of natural-gas resources for fuel, was the first 

 country to find large resources of helium, which is 

 present in natural gas in trace to small amounts, 

 along with other nonflammable gases such as nitro- 

 gen, carbon dioxide, and argon. When the natural 

 gas is liquefied, the helium remains a gas and is 

 recovered as crude helium for further refinement. 

 Much of the growth in the use of helium in the 

 United States was due to its availability at reason- 

 able prices from the huge natural-gas fields of the 

 Texas and Oklahoma Panhandles and southwestern 

 Kansas. 



From 1950 to 1968, annual use of helium in the 

 United States increased more than tenfold, from 81 

 to 842 million cubic feet (fig. 32) (Lipper, 1965, p. 



Figure 32.— Helium sales in the United States, 1920-70. 

 Adapted from Seibel (1968, fig. 8). 



437; 1970, p. 84). In 1968, in addition to the 842 

 million cubic feet of helium sold in the United States, 

 about 25 million cubic feet was exported, and 3,988 

 million cubic feet was pumped into underground 

 storage as part of the government's long-range con- 

 servation program (Lipper, 1970, p. 84). Helium not 

 separated from natural gas when the gas is with- 

 drawn for fuel is lost to the atmosphere. Helium 

 pumped underground and stored will assure a future 

 supply, possibly for several decades after the natural 

 gas has been exhausted. 



In 1968, use of helium outside the United States 

 was probably not more than 100-150 million cubic 

 feet. Canada supplied about 3 percent of the free- 

 world supply from one recovery plant in Saskatche- 

 wan (Lipper, 1970, p. 79). In 1969, France began 

 recovering helium from natural gas supplied by the 

 Netherlands, and the U.S.S.R. produced 70 million 

 cubic feet of helium. 



The United States has the largest known reserves 

 of helium, which, at the present level and rate of 



use, are expected to supply the Nation's needs until 

 at least the end of this century. Intensive explora- 

 tion for and development of natural-gas resources, 

 which have begun outside the United States only 

 within the last decade or two, doubtless will lead 

 to discovery of new helium resources as well. 



GEOLOGIC ENVIRONMENT 



Although helium is of great cosmic abundance, 

 second only to hydrogen, it is one of the rarer ele- 

 ments of the earth. Uranium and thorium are radio- 

 active elements that are present in trace amounts 

 in all rocks, but they are most abundant in the 

 accessory and iron-rich varietal minerals of gra- 

 nitic igneous rocks and in dark shaly marine sedi- 

 mentary rocks (Clark, 1966, p. 522-540). During 

 the radioactive decay sequences in which these 

 elements are transformed to lead, each alpha par- 

 ticle given off becomes a stable helium atom (Ruth- 

 erford and Royds, 1909) : 



U^38 8He*-|-Pb="'' 



U"» 7He^+Pb=" 



Th232 6He^+Pb2»8 



Almost all the helium atoms in natural gas are 

 of the heavier He* isotope (atomic weight, 4) ; the 

 lighter He^ isotope (atomic weight, 3) occurs only 

 in trace amounts and is thought to originate from 

 tritium, the radioactive isotope of hydrogen (Aid- 

 rich and Nier, 1948). He^ is about 10 times more 

 abundant in helium in the atmosphere than in 

 helium in natural gas and is produced by various 

 actions of cosmic rays and by auroral precipitation 

 of solar wind plasma (Johnson and Axford, 1969, 

 p. 2436) . Helium atoms, because of their low atomic 

 weights, are able to escape from the earth's atmos- 

 phere to outer space, and as a result their average 

 concentration in the atmosphere is only 4 or 5 

 parts per million. 



Studies of the amounts of radiogenic helium in 

 minerals, natural gas, and the atmosphere suggest 

 that less than half the helium formed in rocks is 

 retained in the mineral structures; the remainder 

 is either dissolved in interstitial fluids, entrapped 

 with other natural gases as a gaseous phase in rocks, 

 or lost to the atmosphere (Hurley, 1954 ; Damon and 

 Kulp, 1958). 



The helium that is distributed in sedimentary 

 rocks probably migrates through porous aquifers 

 either as a gas or in the connate waters, or it travels 

 along fractures. Some of it may have leaked into 

 sedimentary rocks from deep crystalline rocks that 

 underlie the sedimentary strata. Much of it is prob- 

 ably first dissolved as a trace constituent in connate 

 waters from which it was expelled as the water 



