NUCLEAR FUELS 



475 



high-grade metamorphic rocks inland and Tertiary 

 or Cretaceous clastic rocks along the coastline. 



Additional resources of thorium will also be found 

 in vein deposits in areas that have not been thor- 

 oughly prospected because of lack of demand for 

 thorium. Undiscovered resources exist both in known 

 districts at untested depths (hypothetical resources) , 

 and in areas where no thorium deposits have yet 

 been found (speculative resources). Districts con- 

 taining vein deposits, such as Lemhi Pass, Idaho- 

 Montana, Hall Mountain, Idaho, and the Wet Moun- 

 tains, Colo., have had little subsurface exploration 

 and parts of the areas are covered by thin Quater- 

 nary deposits. Exploration in these areas will un- 

 doubtedly discover many new deposits, and addition- 

 al exploration at depth may well increase resources 

 several times over those now known in veins. The 

 origin of many thorium vein deposits is related to the 

 formation of alkalic stocks and their associated car- 

 bonatites. Hence, prospecting within a radius of 

 about 20 miles from known alkalic stocks well may 

 locate new thorium vein districts. 



PROSPECTING TECHNIQUES 



Methods of prospecting for thorium vary accord- 

 ing to type of deposit and other factors. The most 

 useful methods rely on the radioactivity of thorium. 

 Geiger and scintillation counters have been widely 

 used in detection and appraisal of thorium deposits. 

 Abnormal radioactivity can also be detected with a 

 gamma-ray spectrometer, and the content of thori- 

 um, potassium, and uranium daughter products can 

 be measured in a few minutes with this instrument. 



Except for the radioactivity methods, thorium 

 prospecting is carried out by traditional techniques 

 of examination and sampling of favorable terrane. 

 Panning for heavy minerals is particularly useful in 

 areas where placer concentrations occur. Methods of 

 exploration by panning and churn drilling of placer 

 deposits in Idaho, North and South Carolina, and 

 other States have been described by Kline (1952). 

 Water sampling has not been used for thorium de- 

 posits because of the low solubility of thorium in 

 ground water, lakes, and rivers. Sampling of stream 

 sediments has been tested by Staatz, Bunker, and 

 Bush (1971) in the Lemhi Pass district where its 

 usefulness is quite limited. 



Because of the limited market for thorium, very 

 few deposits have been explored at depth by drilling 

 or underground excavations. Radioactivity methods 

 penetrate only a very thin surface layer, hence in 

 most areas the extent and grade of deposits at depth 

 are conjectural. 



RESEARCH NEEDED ON DOMESTIC 

 THORIUM RESOURCES 



The United States will probably continue to obtain 

 the greater part of its thorium needs, at least for 

 the next few years, from foreign sources. Embar- 

 goes by several principal producing countries tend 

 to diminish this supply greatly. These embargoes, 

 coupled with the very likely large growth in demand, 

 would shift some of the interest from foreign to do- 

 mestic sources. The most easily available resources 

 of thorium in the United States are beach placers in 

 Florida and Georgia mined for their titanium con- 

 tent, but the monazite recoverable is limited not only 

 by the size and grade of the deposits but by the de- 

 mand for titanium. 



A larger and still untapped U.S. resource is the 

 thorium veins of the West. Complete reserve esti- 

 mates are needed on the veins in each district 

 (length, thickness, depth, and average grade). Infor- 

 mation is needed on the relation of these veins to 

 regional faulting and to alkalic intrusives and on 

 their ages, mineralogy, total rare earth content, and 

 on the relative distribution of the various rare 

 earths to one another in the veins. 



Small amounts of thorium also occur in carbona- 

 tites in the United States. Additional study of the 

 mineralogy and chemistry of these deposits would 

 help to determine the amount and recoverability of 

 thorium, possibly as a byproduct of rare earths or 

 niobium. 



Definition of thorium-rich metallogenic provinces, 

 by the grouping of deposits or districts and the thor- 

 ium content of various rocks, should aid in outlining 

 target areas for future prospecting. 



REFERENCES CITED 



Adams, J. A. S., Kline, M .C, Richardson, K. A., and Rogers, 

 J. J. W., 1962, The Conway Granite of New Hampshire 

 as a major low-grade thorium resource: Natl. Acad. 

 Sci. Proc., V. 48, p. 1898-1905. 



Bhola, K. L., Dar, K. K., Rama Rao, Y. N., Suri, S. C, and 

 Mehta, N. R., 1965, A review of uranium and thorium 

 deposits in India, in International Conference on Peace- 

 ful Uses of Atomic Energy, 3d, Geneva, 1964, Proc., v. 

 12, Nuclear fuels — [Pt.] 3, Raw materials: New York, 

 United Nations, p. 86-93. 



Borrowman, S. R., and Rosenbaum, J. B., 1962, Recovery 

 of thorium from a Wyoming ore: U.S. Bur. Mines Rept. 

 Inv. 5917, 8 p. 



Bowie, S. H. U., 1959, The uranium and thorium resources 

 of the Commonwealth: Royal Soc. Arts Jour., v. 107, 

 p. 704-715. 



Brown, K. P., Hurst, F. J., Crouse, D. J., and Arnold, W. D., 

 1963, Review of thorium reserves in granitic rock and 

 processing of thorium ores: U.S. Atomic Energy Comm., 

 Oak Ridge Natl. Lab., ORNL-3495, OC-26, 25 p. 



Christman, R. A., Brock, M. R., Pearson, R. C, and Singe- 



