Baseline radon concentrations in uranium-rich and faulted zones of the Eastern Cordillera, Central Andes, Peru

Radon is a naturally occurring radioactive gas that poses environmental and health concerns, particularly in regions characterized by uranium-rich geological formations and active fault systems that facilitate its migration from the subsurface into soil gas and near-surface environments. In the Eastern Cordillera of the Central Andes, southern Peru, uranium-bearing deposits intersected by geological faults create favorable conditions for elevated radon concentrations in the soil gas and near-surface environment, due to increased permeability that enhances upward transport. However, lack of systematic data on radon concentrations in these areas has limited development of a national radon framework and constrained regional assessments. This study establishes baseline concentrations of soil gas radon (Rn-222) in faulted and uranium-bearing zones of the Eastern Cordillera. Sixteen measurement sites were surveyed across key geological units, integrating lithogeochemical analyses of uranium in rock samples with in-situ radon measurements. Results reveal spatial variability, with soil gas radon concentrations reaching up to 567 kBq/m³, including high values in structurally controlled zones despite relatively low uranium content (23 ppm). These findings demonstrate that, while uranium-rich lithologies act as primary radon sources, fault-controlled permeability and fracture networks exert dominant control on radon migration. By integrating geological, geochemical, and radon data, this study provides a framework for radon mapping in Peru. Results highlight role of structural geology in radon distribution and support soil gas radon as indicator of uranium mineralization and fault-related permeability. These insights contribute to improved radon assessment strategies and provide scientific basis for future development of a national radon potential map.