Tracing Sources of Geochemical Anomalies in a Deeply Buried Volcanic-Related Hydrothermal Uranium Deposit: the Daguanchang Deposit, Northern Hebei Province, North China Craton

Abstract

Radon (Rn) and helium (He) gases from uranium decay form distinct anomalies related to buried uranium deposits. In order to trace the geochemical anomalous sources from the volcanic-related uranium deposits in deeply buried areas, systematical Rn contents and He isotope ratios were analyzed from the Daguanchang uranium deposit. The soil gas Rn concentrations above the deep uranium are ten times higher than those in barren areas, indicating that instantaneous Rn content measurements can be used to detect deeply buried uranium. The helium isotope ratios (³He/⁴He) of the unmineralized samples from the mineralized drill hole (ZK1) are relatively lower and uniform compared to those of the samples from no-mineral drill hole (ZK2). However, the Th and U contents of the drill core samples from ZK1 are slightly lower than those of the samples from ZK2, indicating that the lower ³He/⁴He ratios in ZK1 are most likely due to the addition of ⁴He from underlying uranium intervals. The differences in the instantaneous Rn contents are consistent with the variations in the He isotope ratios of the drill core samples. These results demonstrate that soil gas Rn and ³He/⁴He ratios are useful tracers and can indicate the existence of deeply buried volcanic-related hydrothermal uranium ores.