136 



UNITED STATES MINERAL RESOURCES 



been intensified, particularly in the Eastern 

 States, and the use of lower-sulfur coal has 

 been increased. A few older coal-burning util- 

 ity plants in the Midwest have converted from 

 high-sulfur local coal to low-sulfur Rocky 

 Mountain coal. This substitution has required 

 payment of transportation costs of $3-$5 per 

 ton, and acceptance of the lower heat content 

 of Rocky Mountain coal. Such high transpor- 

 tation costs obviously will intensify research 

 efforts mentioned in item 1. 



3. Much research is in progress on methods to 



produce a high-Btu, sulfur-free gas from coal. 

 This is also a technical possibihty soon to be 

 realized. It has the multiple advantages of 

 lowering the costs of long-distance transpor- 

 tation of energy, of eliminating the sulfur 

 problem, of augmenting declining resources 

 of natural gas, of reducing dependence on 

 foreign sources of oil and gas, and ultimately 

 permitting use of high-sulfur eastern coal. 



4. Research on improved methods of producing 



electric power by nuclear fission and fusion 



is continuing. 

 These varied avenues of approach suggest that 

 the amount of sulfur. released to the atmosphere by 

 the burning of coal will soon be greatly reduced. 



MINOR ELEMENTS IN COAL 

 Coal contains small quantities of virtually all 

 metallic and nonmetallic elements, that were intro- 

 duced into the coal bed in one or all of four differ- 

 ent ways: 



1. As inert material washed into the coal swamp 



at the time of plant accumulation. 



2. As a biochemical precipitate from the swamp 



water. 



3. As a minor constituent of the original plant 



cells. 



4. As a later addition, introduced after coal forma- 



tion, primarily by ground water moving down- 

 ward and laterally. 

 When coal is burned, most of these elements are 

 concentrated in the coal ash, but a few of the more 

 volatile elements are emitted into the atmosphere. 

 Coal ash is composed largely of the oxides of Si, Al, 

 Fe, Ca, Mg, K, Na, and S, which typically make up 

 93-98 percent of the total weight of the ash (Aber- 

 nethy and others, 1969a). The remaining few per- 

 cent of coal ash is made up of small individual 

 amounts of many other elements, which differ in 

 variety and quantity in different areas and beds. 

 These elements are generally measured in parts per 

 million or billion, and for this reason are termed 



minor elements, although they may not be minor 

 elements in other contexts. 



The minor elements in coal are of considerable 

 interest because some may become of future re- 

 source importance, and others may be pollutants. 

 Most of the minor elements occur in coal in about 

 the same concentration as their estimated concen- 

 tration in the earth's crust, but 25-30 elements occur 

 locally in greater concentration and these have re- 

 ceived the most study. A few elements, notably U, 

 Ge, As, B, and Be, occur locally in vastly greater 

 concentrations than their estimated concentration 

 in the earth's crust; others, including Ba, Bi, Co, 

 Cu, Ga, La, Pb, L, Hg, Mo, Ni, Sc, Se, Ag, Sr, Sn, 

 V, Y, Zn, and Zr, occur locally in appreciably greater 

 concentrations. Other elements of interest that gen- 

 erally occur in lower concentrations than those 

 listed above include Cr, Mn, P, Te, Tl, Ti, and W. 

 It should be noted that the concentration of an 

 element in excess of the estimated concentration in 

 the earth's crust, although of great interest and 

 geologic significance, does not necessarily imply an 

 economic or paramarginal concentration, because 

 that is determined by the concentration in typical 

 commercial sources of the respective element. 



Reports by Abernethy and Gibson (1963) ; Aber- 

 nethy, Peterson, and Gibson (1969a, b) ; Zubovic 

 (1966a, b) ; Zubovic, Sheffey, and Stadnichenko 

 (1967) ; Zubovic, Stadnichenko, and Sheffey (1960a, 

 b, c; 1961a, b; 1964; and 1966); and by Sun, 

 Vasquez-Rosas, and Augenstein (1971) summarize 

 available information concerning minor elements in 

 coal. A selected bibliography on trace elements in 

 coal, applicable primarily to U.S. coals, has been 

 compiled by Averitt, Breger, Gluskoter, Swanson, 

 and Zubovic (1972). 



UNITED STATES COAL RESOURCES 



The remaining coal resources of the United States 

 as of January 1, 1972, are estimated to total 3,224 

 billion tons. Of this large total, 1,581 biUion tons, 

 or 49 percent, has been identified on the basis of 

 mapping and exploration, and the remainder of 

 1,643 billion tons, or 51 percent, is classed as hypo- 

 thetical because it has been determined by extrapo- 

 lation of the data on identified resources into un- 

 mapped and unexplored areas. The distribution of 

 this tonnage by State is given in table 27. 



The figures in table 27, and in subsequent tables 

 and figures, express resources in the ground. The 

 recoverability in coal mining ranges from 40 to 90 

 percent, depending largely on the method of mining, 

 but it is influenced by many other diverse factors 

 such as the nature of the roof rock, joints, faults, 



