TIME-BOUND CHARACTER OF URANIUM DEPOSITS

Uranium concentrations exist in many environments throughout the world. This wide distribution of concentrations of one of the more uncommon crustal elements is a reflection of the lithophile and mobile character of uranium. About 90 percent of uranium ore deposits, as presently known, occur in environments in which the uranium appears to have been deposited from either surficial or ground waters. Analysis of the distribution of these water-transported deposits in terms of the geological section shows that most of them are time bound. Typical quartz-pebble conglomerate ores are not present in rocks younger than about 2,200 m.y. Paleosurface-controlled veinlike deposits appear to have formed preferentially in time between 2,000 and 1,500 m.y. ago. Preserved sandstone deposits are generally confined to Mesozoic and younger rocks. The time-bound character exhibited by most uranium ore deposits is considered to be controlled by the physical and chemical environments prevalent, both worldwide and locally, at the geologic time involved. An understanding of the geologic conditions and processes relevant to uranium concentration furnishes useful guidelines within which to search for more ore. © 1978 Society of Economic Geologists, Inc.