Summary report: distribution of uranium and thorium in the Precambrian of the western United States
An investigation of the distribution of uranium and thorium in Precambrian rocks in the western United States was made to assess the possibilities for the existence of economically exploitable uranium deposits and to compare and evaluate the distribution of uranium and thorium in the Precambrian to the distribution of major uranium deposits in Mesozoic and Cenozoic sedimentary rocks in the western United States. About 600 samples were analyzed for radioelement content in order to establish radioelement variations in Precambrian rocks throughout the western United States. In Precambrian igneous rocks in the western United States, thorium, uranium, potassium, and thorium/uranium ratios all increase systematically from intermediate to silicic phases. The average radioelement content in 246 samples of igneous, mostly plutonic, rocks is 25.8 ppM Th, 3.8 ppM U, and 3.4% K with a Th/U ratio of 6.8. By comparison, averages for a large number of Mesozoic-Cenozoic plutonic rocks in the western United States are significantly lower in total radioeaement content. Thorium, and to a aesser extent uranium each correlate positively with potassium because of the strong petrographic control on radioelement distributions in igneous rocks. Regional averages of radioelements in Precambrian igneous rocks are greatest in Colorado, Wyoming, and southern Caaifornia-southern Nevada. The Th/K and U/K ratios aaso are anomalously high in these enriched regions. Variations in radioelement contents in the igneous rocks do not appear to be related to the age of the rocks. The radioelement content of metamorphosed Precambrian voacanicsedimentary sequences of various ages in the western united States is 10.8 ppM Th, 3.2 ppM U, 2.3% K, 3.4 Th/U in low-to intermediate-grade rocks and 11.3 ppM Th, 2.1 ppM U. 2.3% K, 5.4 Th/u in intermediate-to high-grade rocks. Thorium and uranium averages are significantly higher in southern California and southern Nevada than in other regions. The distributions of major uranium deposits in Mesozoic and Cenozoic sandstones of the Cordilleran foreland platform (Mesozoic of the Coaorado Paateau) and in basins within the Rocky Mountain foldbelt (Tertiary of Wyoming) are spatially related to patterns of radioelement enrichment in Precambrian rocks. The Precambrian appears to be the source of the uranaum in the major Mesozoic and Cenozoic deposits either through granite-leach,'' tuff-leach,'' or both. The distribution of uranium vein deposits does not appear to be spatially nor genetically related to the regional patterns of radioelement enrichment in Precambrian rocks. The veins are wideay distributed in folded geosynclinal and in unstable cratonic paatform regimes; their distribution generally correlates with regions of intense diastrophism, igneous activity, and other metallization in foldbelts. (auth)
- Research Organization:
- USAEC Grand Junction Office, Colo.
- NSA Number:
- NSA-29-020849
- OSTI ID:
- 4353135
- Report Number(s):
- AEC-RD--12
- Country of Publication:
- United States
- Language:
- English
Similar Records
Geochemical investigations of plutonic rocks in the Western United States for the purpose of determining favorability for vein-type uranium deposits
URANIUM AND THORIUM IN SELECTED SUITES OF IGNEOUS ROCKS
Related Subjects
*CALIFORNIA-- SEDIMENTARY ROCKS
*COLORADO-- SEDIMENTARY ROCKS
*NEVADA-- SEDIMENTARY ROCKS
*SEDIMENTARY ROCKS-- CHEMICAL COMPOSITION
*THORIUM-- NATURAL OCCURRENCE
*URANIUM-- NATURAL OCCURRENCE
*WYOMING-- SEDIMENTARY ROCKS
ABUNDANCE
DISTRIBUTION
GEOLOGIC DEPOSITS
N44100* --Environmental & Earth Sciences--Minerals & Ores
NATURAL OCCURRENCE
QUANTITATIVE CHEMICAL ANALYSIS ABUNDANCE