462 



UNITED STATES MINERAL RESOURCES 



pyrochlore-bearing alkalic rocks at Araxa, Brazil, 

 and in Ontario, Canada (Rowe, 1958) ; sodalite foy- 

 aite and nepheline syenite near Julianehaab, Green- 

 land (Bondam and Sorensen, 1958) ; riebeckite 

 granite in Nigeria ; and alaskitic rock near Rossing, 

 South West Africa. 



URANIFEROUS PHOSPHATIC ROCKS 



Most phosphatic rocks are uraniferous and their 

 uranium content generally increases with the phos- 

 phate content. Marine phosphorite is the dominant 

 source of phosphate and constitutes a very large 

 resource of uranium. In such rocks, geosynclinal 

 facies tend to be more uraniferous than platform 

 facies. Uraniferous marine phosphorite deposits, 

 commonly 5-10 feet thick, underlie hundreds of 

 square miles, and their uranium content generally 

 ranges from 0.007 to 0.07 percent UsOs. Phosphorite 

 beds in the Phosphoria Formation of Permian age 

 underlie 135,000 square miles of Idaho, Montana, 

 Utah, and Wyoming (McKelvey and Carswell, 1956). 

 Their uranium content ranges from 0.001 to 0.075 

 percent UaOs, but beds more than 3 feet thick and 

 with more than 31 percent PoO,-, generally average 

 0.012-0.024 percent UaOs. Prosphorite in the Bone 

 Valley Formation of Pliocene age in the land-pebble 

 phosphate field in Florida ranges in thickness from 

 6 to 7 feet over several hundred square miles and 

 averages 0.012-0.024 percent U3O5 and 20-30 per- 

 cent P2O5 (Altschuler and others, 1956). Uranium 

 in marine phosphorite deposits was probably de- 

 posited from sea water during sedimentation, or in 

 some places possibly later by dovinaward percolating 

 ground water. 



Large portions of extensive deposits of marine 

 phosphorite in countries along the Mediterranean 

 Sea from Morocco to Israel contain at least 0.01 per- 

 cent UaOs (Davidson and Atkin, 1953). Near Recife, 

 Brazil, deposits of phosphorite somewhat like those 

 in Florida yield phosphate products that contain 0.02 

 percent UsOs. Phosphorite that fills large depressions 

 formed by solution of dolomite in Central African 

 Republic are also uncommonly rich in uranium 

 (Mabile, 1968). Deposits of aluminum phosphate in 

 Senegal and Nigeria are also uraniferous. Marine 

 phosphorite of Cambrian age in the Kara-Tau Moun- 

 tains, Kazakhstan, U.S.S.R., resemble the Phos- 

 phoria Formation and are probably uraniferous. 



URANIFEROUS MARINE BLACK SHALES 



Many marine black shales rich in organic matter 

 contain minor amounts of uranium that was de- 

 posited under anaerobic conditions with the organic 

 fraction of the shale during sedimentation in shal- 



low epicontinental seas. Most of the identified domes- 

 tic black shale resources are in the upper member of 

 the Chattanooga Shale of Late Devonian and Early 

 Mississippian age in central Tennessee and adjacent 

 Kentucky and Alabama (Swanson, 1961). This mem- 

 ber is 12-18 feet thick over an area of about 4,000 

 square miles, and averages about 0.007 percent UaOs. 

 Moreover, the Chattanooga and its correlatives 

 underlie about 800,000 square miles extending from 

 eastern Tennessee to Texas and Montana ; its urani- 

 um-bearing strata average about 40 feet in thickness 

 and about 0.0035 percent UnOg in grade. In Sweden, 

 black shale of Late Cambrian and Ordovician age, 

 which is 9-18 feet thick, is unusually rich in ura- 

 nium and averages about 0.03 percent UgOg (Svenke, 

 1956). Radioactive shale of the same age in the 

 U.S.S.R. near the Baltic Sea may not be as rich as 

 that in Sweden, but no modern determinations of its 

 uranium content have been announced. 



RESOURCES 



IDENTIFIED AND HYPOTHETICAL RESOURCES 



Both identified and hypothetical uranium re- 

 sources can be divided into three subclasses: (1) 

 recoverable resources, those that can be extracted 

 profitably under 1972 economic conditions, (2) para- 

 marginal resources, here defined as those that might 

 be extracted profitably with a 50-percent to 5-fold 

 increase in the price of UaOs, and (3) submarginal 

 resources, those that require more than a 5-fold price 

 increase. Nearly all of the domestic recoverable re- 

 sources can be produced as a sole or principal prod- 

 uct of mining operations, but they represent only a 

 small fraction of the total identified resources. Most 

 of the much larger paramarginal and submarginal 

 resources are not likely to become major sources of 

 uranium in the near future — either because the tech- 

 nology of extraction is costly or unsolved, because 

 limits on land use might restrict mining large vol- 

 umes of material, or because the most nearly eco- 

 nomically recoverable uranium can be obtained only 

 as a byproduct. 



RECOVERABLE RESOURCES 



The identified recoverable resources in the United 

 States totaled 273,000 tons of U^Os, as of December 

 31, 1971 (table 93) and are in rock averaging about 

 0.22 percent UaOg (4 lb. UaOs per ton) . Of this total, 

 more than 99 percent — 270,800 tons — is in penecon- 

 cordant deposits in sandstone and related rocks, and 

 the remaining 2,200 tons is in veins and other types 

 of deposits. About 50 percent of these resources is in 

 northwestern New Mexico, about 35 percent in Wy- 

 oming, about 5 percent in Texas, about 3 percent 



