Abstract: Thorium--Other Natural Source of Nuclear Fuel
Mortimer H. Staatz
Reactors using thorium, although having several advantages over the common light-water reactor, have been slow to develop, and in 1976 only the high-temperature-gas reactor was beyond the experimental stage.
Thorium is widespread in the earth's crust and about five times more abundant than uranium. Although much of it is disseminated in small amounts, thorium is present in seven types of economic or subeconomic deposits. These types are in (1) beach placers, (2) stream placers, (3) unconsolidated sedimentary rocks, (4) consolidated sedimentary rocks, (5) silicic igneous rocks, (6) carbonatites, and (7) veins. Beach placers, which include older deposits of Pleistocene age as well as those along modern beaches, are the only type of deposit from which thorium now is being recovered in the United States. Stream placers in the Carolinas were the first commercial source of thorium in the United States, but most of these placers are too small to work under present conditions. Unconsolidated sedi entary rocks are similar to beach placers but generally have more overburden. Consolidated sedimentary rocks are classified separately because they are considerably more expensive to mine because of the extra cost of grinding. Large tonnages of low-grade thorium are present in plutons of alkalic igneous rocks, but the thorium in these rocks is relatively costly to recover. Carbonatites commonly contain minor amounts of thorium which could be recovered as a byproduct of some other mineral. The largest known resource of high-grade thorium in the United States is in veins, principally in the minerals thorite, monazite, and brockite.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC