Hydrochemical characteristics and genesis of thallium anomaly in groundwater of a lead-zinc mine in Hunan Province

【Objective】To identify the key geochemical processes controlling thallium anomalies in the groundwater of the Huangshaping Pb-Zn mining area.【Methods】This study employed multiple hydrochemical analysis methods, including correlation analysis, cluster analysis, factor analysis, Piper trilinear diagram, Gibbs diagram, chloro-alkaline index (CAI), and major ion ratios, to investigate the characteristics and formation mechanisms of thallium anomalies in the study area.【Results】The results show that the groundwater in the study area is low-mineralization, weakly alkaline water, with the dominant hydrochemical type being SO₄·HCO₃-Ca·Mg. Groundwater is primarily derived from atmospheric precipitation and is minimally affected by evaporation, with its hydrochemical characteristics mainly controlled by rock weathering. Thallium in the groundwater predominantly exists in the stable form of Tl⁺. Influenced by vertical variations in lithological characteristics and geological structural disturbances caused by mining activities, thallium exhibits a gradual enrichment trend from near-surface to intermediate and deep sections. The hydrochemical formation process of thallium in groundwater is primarily governed by the weathering and dissolution of silicate rocks (e.g., rhyolite porphyry), as well as the oxidative leaching of Tl-bearing sulfide minerals (e.g., pyrite) under mining disturbance. In addition, the positive cation exchange occurring in the groundwater of the study area also contributes to the enrichment of Tl⁺. Based on characteristic ion ratio analysis, the impact of agricultural and domestic pollution on groundwater in the study area is relatively limited, and the groundwater environment is primarily influenced by mining and smelting activities.【Conclusion】In summary, this study clarifies the sources and hydrochemical formation mechanisms of thallium in the groundwater of the study area, reveals the evolutionary pattern of thallium gradually enriching from shallow to deep sections, and provides a scientific basis for understanding the geochemical behavior of thallium in groundwater systems.