Lithological and Structural Interpretation of Airborne Gamma-Ray Uranium Anomalies for Exploration: A Case Study from the Longshoushan Metallogenic Belt, China

Abstract

To improve the geological constraints on regional screening for alkali-metasomatic uranium deposits, we analysed high-resolution airborne gamma-ray spectrometric data from the Xinshuijing–Yushigou area of the Longshoushan metallogenic belt, integrating ground gamma-ray spectrometry, geological zoning, fault structures, and drill-hole geological sections from the Xinshuijing and Jiling deposits. We assessed the lithological dependence of K, equivalent uranium (eU), equivalent thorium (eTh), and total count (TC), and developed a multi-parameter interpretation framework comprising the expected uranium background (Gu), relative uranium deviation (Hu), U–K relative enhancement index (F), and normalized relative uranium deviation (B). The regional radioelement distribution is primarily controlled by granitic intrusions and parts of the pre-Sinian metamorphic basement. However, the spatial extent of several local anomalies does not fully coincide with lithological boundaries, indicating variations in radioelement proportions superimposed on the lithological background. Drill-hole sections from Xinshuijing and Jiling show that known ore bodies and mineralized zones occur within granitic–dioritic rock associations and structurally controlled alteration zones. Their surface-projection neighbourhoods are characterized by a combination of high radioactive backgrounds, locally negative Hu values, enhanced F values, and adjacent positive relative uranium deviations. This correspondence improves the geological interpretability of the multi-parameter anomalies, although it represents retrospective validation using known deposits. Yushigou exhibits a similar parameter assemblage near the contact between a granitic intrusion and a NW-trending fault and is therefore identified as a candidate exploration target requiring independent field verification. These results demonstrate that decomposing absolute radiometric responses into lithological background, relative uranium deviation, and K–U–Th ratio variations helps identify local radioelement decoupling within regionally elevated radioactive backgrounds, providing complementary near-surface evidence for regional screening of concealed uranium mineralization in complex bedrock terrains.