干旱区生态环境知识资源中心

The application of various geophysical tools with different responses succeeded in fixing U-mineralization in Wadi Eishimbai area. The area was studied using detailed ground spectrometric, magnetic, and filtered very low-frequency electromagnetic (VLF-EM) surveys. The interpretation of the obtained spectrometric maps clearly reflects the sharp increase of equivalent uranium (eU) content. Meanwhile, K and Th contents show sharp decreases. The eU/equivalent thorium (eTh) ratio correlates positively with eU concentrations and negatively with eTh concentrations, indicating an increase in U potentiality than the surrounding granite. The N-S shear zone displays an eU content ranging from 20 to 140 ppm. The ENE-trending lamprophyre is characterized by elongated uranium anomalies trending in the E-W direction, with values > 90 ppm. Equivalent uranium content of the brecciated granite attains values up to 700 ppm. The ground magnetic and VLF-EM surveys played important roles in providing structural information which are proven useful in geological mapping and mineral exploration for the discovery of uranium mineralization in the study area. This study follows the expected subsurface extension of the Sela shear zone under Wadi sediments. The ground total magnetic intensity map shows a relatively narrow and an elongated shape for the lamprophyre anomaly extending for about 600 m in the Wadi toward the western direction. VLF-EM contour maps of the two used frequencies (17.1 and 28.5 kHz) show excellent agreement, indicating that the shear zone is distinguished with slightly strong conductivity westwards as an extension of the main shear zone. It is elongated in an ENE-WSW trend and extends in the western direction, referring to the existence of conductive materials. Most of the NW/SE-trending faults cause sudden changes in the magnetic and VLF-EM contour spacing over an appreciable distance, which suggests a discontinuity in depth due to their left-lateral strike-slip displacements. The interpreted faults, with an ENE-WSW trend representing the main trend of Sela shear zone through which hydrothermal solutions flowed, cause high alteration and uranium mineralization.