MINERALOGY AND URANIUM GEOCHEMISTRY OF SELECTED VOLCANICLASTIC SEDIMENTS IN THE WESTERN UNITED STATES - AN EXPLORATION MODEL.
Abstract
This work describes uranium geochemistry of diagenetically altered volcaniclastic sediments from parts of the western United States. Geochemical criteria based on analysis of selected volcaniclastic samples are found to be useful in recognizing functional uranium source rocks and act as a frame work and guide for future exploration for uranium in new areas.
Comparison of the chemical composition of samples from different localities studied show that Ca, Fe and Mg are enriched relative to silicic igneous rocks. Lack of uranium enrichment in the zeolite facies samples in this study contrasts with the results of others that zeolites adsorb U. It is important to note that the efficiency of adsorption is a function of pH. High pH associated with zeolite formation favors U desorption.
The association of uranium with opalite is illustrated by moderate positive correlation of U with Si. The association of U with silica is explained by the fact that both U and Si are released during diagenesis and by the fact that opal coprecipitates with U. High correlation of U with organic carbon in the Anderson Mine and Reese River samples indicate the ability of carbonaceous matter to adsorb and/or precipitate U. High Th/U ratio (more than 7) represent highly leached systems which have released a significant quantity of U to the ground water system. Low Th/U ratios (less than 2) are found in mineralized units, while Th/U ratios between 2 and 7 represent systems closed to U and Th.
In systems that have not lost U the samples plot very close or on the trend found in unaltered igneous rocks on a log U-log Th graph. The scatter and relative position of the points relative to the igneous trend indicate whether the system has lost or gained uranium.
In geologic systems that have not lost or gained uranium such as unaltered igneous rocks, the triangular variation diagram of Th-U-K shows a tight group that is closer to and projects to the Th corner. In systems that have lost or been enriched in U, the data points are scattered in the triangle. In systems in which there is uranium mineralization, the samples plot in a trend that projects to the U corner.
The best indicator elements for U mineralization in volcaniclastic sediments are organic carbon, V, Mo, As, and Cu. Uranium has moderate positive correlation with Cs and Th in systems closed to uranium.
Subject Area
Geochemistry
Recommended Citation
ORAJAKA, IFEANACHO PAUL, "MINERALOGY AND URANIUM GEOCHEMISTRY OF SELECTED VOLCANICLASTIC SEDIMENTS IN THE WESTERN UNITED STATES - AN EXPLORATION MODEL." (1981). ETD Collection for University of Texas, El Paso. AAI8211064.
https://scholarworks.utep.edu/dissertations/AAI8211064