100 



UNITED STATES MINERAL RESOURCES 



of the world's resources of bitumen-bearing rocks. 

 The in situ bitumen in all U.S. deposits that have 

 been studied is here estimated to total a maximum 

 of approximately 29 billion barrels (table 19). Nu- 

 merous U.S. deposits need additional study. It should 

 be noted, however, that any future estimate of 

 energy in all bitumen-bearing rocks of the United 

 States will probably be small compared to estimates 

 for the remainder of the world. The estimate of 

 world resources in major tar-sand deposits (those 

 containing more than 15 million barrels of bitumen 

 in situ) is 915.2 billion barrels (Phizackerley and 

 Scott, 1967, p. 551). 



Although substantial tonnages of tar sand in the 

 United States are available for producing crude oil, 

 there seems to be little incentive to develop the de- 

 posits in the near future. The National Petroleum 

 Council, in its assessment of future energy supplies 

 and demands, has predicted that Canadian deposits 

 will be the primary and probably the only North 

 American source of tar-sand oil through the year 

 1985 (Burk, 1971, p. 171). 



EXPLOITATION 



In many States, bituminous sandstone and bitu- 

 minous limestone have long been mined commer- 

 cially for use as road material, but currently there 

 is activity at only a few places. The demand for 

 asphalt, although it has increased greatly in recent 

 years, is being supplied mostly by refinery asphalt. 

 In 1968, bituminous limestone was produced in Ala- 

 bama and Texas, and bituminous sandstone was 

 produced in Kentucky and Missouri. During 1948- 

 68, production of native asphalt and bitumens 

 (bituminous sandstone, bituminous limestone, and 

 gilsonite) increased from 1,136,126 to 1,786,840 

 short tons, and during the same period, there was 

 approximately a threefold increase in production 

 of refinery asphalt and road oil (Redfield and 

 Spencer, 1950; Kirby and Moore, 1969). 



Two basic production methods are used to recover 

 the bitumen: (1) strip mining followed by extrac- 

 tion treatment and (2) in situ extraction. The first 

 method recovers about 90 percent of the bitumen, 

 and the second method 35-50 percent (Burk, 1971, 

 p. 178). Mining and hot-water extraction method is 

 being used in commercial development of the Atha- 

 baskan tar-sand deposits. The depths to which strip 

 mining is feasible are limited, however, and deeper 

 deposits will require in situ recovery methods. Ex- 

 perimentation with in situ recovery has had only 

 limited success. Some nonfluid bitumen deposits con- 

 tain appreciable amounts of sulfur and certain 



metals that may, with proper treatment, be recov- 

 ered profitably. 



Environmental problems that may be associated 

 with a large-scale tar-sand development have not 

 been studied extensively but in handling huge ton- 

 nages of material in a strip-mining operation some 

 problems can be predicted, for example, water pol- 

 lution, silting of streams, and unstable fill. In situ 

 recovery has the advantage of not disturbing the 

 surface, but the disadvantage of a lower bitumen 

 recovery rate. 



GEOLOGIC ENVIRONMENT 



Nonfluid bitumen deposits occur most abundantly 

 in sandstone and limestone, in lesser amounts in 

 other types of sedimentary rocks, and rarely in 

 igneous and metamorphic rocks (commonly adja- 

 cent to petroliferous sedimentary source rocks). 

 Primary pore spaces in clastic rocks are host to 

 more than 95 percent of the bitumen in deposits 

 studied in detail. In secondary openings produced by 

 weathering, solution, and structural movement, 

 hydrocarbon deposits of gilsonite, ozocerite, and 

 grahamite have been found. Gilsonite deposits 

 in vertical veins in eastern Utah and western 

 Colorado are the only sizable accumulations of 

 solid hydrocarbons in the United States. 



Sedimentary rocks containing bitumen represent 

 a variety of environments of deposition, including 

 marine, nearshore, and fluvial. Most of the large 

 bitumen-bearing sandstone deposits occur in estua- 

 rine or fresh-water rocks (Phizackerley and Scott, 

 1967, p. 566), along basin margins where petroleum- 

 bearing beds have been tilted and brought to or 

 near the surface. Some bitumen-bearing rocks occur 

 adjacent to faults, joints, unconformities, brecciated 

 zones, and other geologic features which allow 

 gases and light oil fractions to escape from accumu- 

 lations of liquid petroleum. 



The source and evolution of nonliquid bitumen 

 evidently are not the same in all deposits. Studies 

 of various deposits yield evidence to support all the 

 following statements about the bitumen : (1) formed 

 in situ, (2) migrated to present location, (3) a 

 precursor of liquid petroleum, (4) a residue of 

 liquid petroleum, (5) was deposited with the sedi- 

 ment, and (6) accumulated after deposition of 

 sediments. 



RESOURCES 



Bitumen deposits in the United States are nu- 

 merous and some individual deposits are extensive, 

 but the fragmental information available does not 



