Genetic implications of Th/U, Th/K, and U/K ratios for U mineralizations: A case study from El-Missikat and El-Erediya shear zones, Eastern Desert, Egypt

Abstract

The current work is an attempt to reveal the possible utilization of the radiometric measurements to build-up a complete genetic scenario for magmatic, hydrothermal, and supergene uranium mineralization. For this purpose, ground gamma-ray survey was performed through the exploratory tunnels dug perpendicular to El-Missikat and El-Erediya shear zones, the Central Eastern Desert of Egypt. Contents of U, Th, and K were measured for the host pink granite (e.g., avg.15.94 U ppm, 35.62 Th ppm, and 6.63% K), alteration zones (brecciation, silicification, greisenization, kaolinization and hematitization) (e.g., avg. 124.01 U ppm, 63.67 Th ppm, and 3.13% K), and mineralized silica veins (e.g., avg. 312.65 U ppm, 92.22 Th ppm, and 2.62% K). All of these data were graphically represented as correlation plots of Th vs. U, Th/U vs. U, Th vs. K, and U/K vs. Th/K. The overall results indicate magmatic, hydrothermal, and supergene sources of El-Missikat and El-Erediya U mineralization. The magma-derived U contents are enclosed mainly in the pink granite that is mostly characterized by normal Th/U (2.5–5) and Th/K ratios (3–5*10^–4). The hydrothermal processes through the alteration zones and mineralized silica veins are reflected by the weak correlation of Th with U (e.g. r = 0.13 and − 0.39), the strong negative correlation of Th/U ratio with U (e.g. r = − 0.82), 2.5˃Th/U˃0.1, Th/K˃5*10^–4, Th/K < 3*10^–4, and the strong positive correlation of U/K with Th/K (e.g. r = 0.91) as well as the occurrence of thorite, columbite, xenotime and hydrothermal zircon (0.5 > Th/U ≤ 0.1). Afterwards, the hydrothermal mineralization underwent some degrees of chemical weathering that resulted in supergene U mineralization whose fingerprints can be traced by the occurrence of secondary U minerals (e.g. kasolite and uranophane), Th/U ratios ≤ 0.1, and the weak correlation between Th/K and U/K (e.g. r = 0.39 and − 0.11).