NUCLEAR FUELS 



473 



ered as a byproduct of rare-earth mining at Moun- 

 tain Pass, Calif. ; of niobium mining at Araxa, Brazil ; 

 or of copper mining at Palabora, South Africa. 



Most granite contains an average of 0.0025 per- 

 cent thorium, but granite with a greater content of 

 thorium could be a potential low-grade resource. The 

 Conway Granite underlies a large area in New Hamp- 

 shire and, in addition to uranium, contains more than 

 twice as much thorium as the average value already 

 cited (Adams and others, 1962, p. 1903). The gran- 

 ites of the Tokovskii complex in the U.S.S.R. con- 

 tain four times the average thorium content of 

 granite (Filippov and Komlev, 1959, p. 541). 



RESOURCES 



IDENTIFIED RESOURCES 



The resources of thorium are not well known, ow- 

 ing in part to the small demand in relation to avail- 

 able supply. The increased use of thorium for gen- 

 erating electricity, however, has stimulated interest 

 in resources. Because the amount of byproduct Th02 

 recovered throughout the world in 1972 was more 

 than sufficient to meet current needs, deposits in 

 which thorium is the principal element cannot be 

 mined at a profit. 



The present known resources of ThOa in the 

 United States as given in table 94 include resources 

 recoverable as byproducts as well as both high- and 

 low-grade nonbyproduct resources. The only min- 

 able reserves at present are some of the Atlantic 

 Coast beach placers, where monazite is produced as 

 a rather minor byproduct of titanium mining. Re- 

 sources of beach placers along the Atlantic coast in- 

 clude 15,600 tons of ThOa estimated to be in mon- 

 azite in the sands in Florida, on Hilton Head 

 Island, S.C, and in some of the ancient beach 

 placers near Folkston, Ga. 



The United States has large resources (table 94) 

 of thorium in relatively high-grade veins — those 

 containing more than 0.1 percent ThOa. The Wyom- 

 ing and Michigan resources, which occur in detrital 

 monazite in conglomerates, are too low-grade for 

 recovery to be feasible until higher grade and easier- 

 to-handle ores such as placers and veins have been 

 depleted. These conglomerates are nonuraniferous, 

 and thorium cannot be recovered from them as a 

 byproduct as it can in the uranif erous conglomerates 

 at Elliot Lake, Canada. A large potential source of 

 thorium is in the low-grade deposit of granite near 

 Conway, N.H. This granite, the Triassic or Jurassic 

 Conway Granite which has an average grade of 

 0.0064 percent ThOa, underlies an area of about 307 

 square miles (Adams and others, 1962, p. 1903), and 

 could be mined at a cost of about $50-$100 per pound 



of ThOa (Brown and others, 1963, p. 6-11). More 

 than half of the world's identified resources of thori- 

 um are in beach placers, principally in India (table 

 94). The total resources of thorium in beach placers 

 are undoubtedly larger, inasmuch as in some coun- 

 tries, such as Brazil, Australia, and Malaysia, only 

 part of the beach placers has been evaluated. Fur- 

 thermore, present-day beach placers are being 

 formed continually, and in some areas new placers 

 may form several years after the old one has been 

 worked out. 



Carbonatites are also an important resource of 

 thorium, containing more than one-sixth of the 

 evaluated thorium resources potentially recoverable 

 as a byproduct (table 94) . Thorium can be recovered 

 as a byproduct of copper and uranium mining at 

 Palabora, South Africa, and of niobium and rare 

 earths at Araxa, Brazil. About 40 percent of the 

 known resources of thorium potentially recoverable 

 primarily as a byproduct is in the uranium deposits 

 in the Elliot Lake district in Canada. As these de- 

 posits are being actively mined for uranium, only a 

 separate circuit need be added to the mill waste after 

 the precipitation of the uranium in order to recover 

 a thorium-rich concentrate. 



The largest known resources are in Greenland, 

 where several square miles of lujavrite, a variety of 

 nepheline syenite, contains 200 ppm to several tenths 

 percent thorium and a half to a quarter as much 

 uranium. The cost of recovery of either element, 

 however, would be high. 



Although the identified resources of thorium are 

 small compared to those of many other metals, they 

 are large compared to the amounts of thorium used 

 in the past. Known resources are about 10,000 times 

 greater than the amount used in 1968. The general 

 use of thorium in reactors would, however, greatly 

 enlarge the demand for this element, hence the ap- 

 praisal of potential resources becomes important. 



HYPOTHETICAL AND SPECULATIVE RESOURCES 



Beach placers have been and will continue to be 

 major sources of thorium. Resources in some places 

 will probably be increased as additional areas of 

 known monazite-bearing sand are evaluated. Thus, a 

 favorable area for finding new placers is below the 

 water level, off present beaches, where seaward ex- 

 tensions of known placers could be mined under 

 somewhat more difficult conditions. McKelvey (1968, 

 p. 40) estimated the monazite content in undiscov- 

 ered marginal offshore deposits on the U.S. conti- 

 nental shelf to be about 4 million tons. Even larger 

 off-shore deposits probably occur in Australia, 

 Brazil, and India. 



