Antimony sources and mobilization in environmental matrices surrounding the world's largest Sb mine: evidence from mineralogy and Sb isotope signatures.

China produces 48.2% of global antimony (Sb) annually, of which approximately 80% was produced in Southwest China in 2023. The distribution of high-Sb geological background areas in China overlaps with that of karst landforms. The external causes of the exploitation and utilization of Sb resources and the internal causes of the special high geochemical background have led to Sb pollution in the natural ecosystems in this area. This study selected the Xikuangshan (XKS) Sb mine in Hunan Province, a typical Sb deposit in the karst areas of China, as an example to quantitatively identify pollution sources and influencing factors of Sb in the environment around the Sb mining area. Based on the TESCAN integrated mineral analyzer analysis, the major mineralogical components of the representational soil sample were quartz (59.80%), kaolinite (9.93%), calcite (6.08%), albite (3.41%), chlorite-clinochlore (2.89%), clay (1.99%), dolomite (1.81%), and hematite (Fe₂O₃)/magnetite (Fe₃O₄) (1.67%). Antimony was found to be mainly rich in Fe₂O₃/Fe₃O₄, nepheline (NaAlSiO₄), and minerals consisting of O-Al-Si or O-S-Fe in the soil. Based on microscopic X-ray fluorescence analysis, Sb showed similar in situ distribution and enrichment characteristics to those of Al, Fe, S, and Si. The characteristics of the Sb isotope of the environmental samples from the XKS Sb mine were measured for the first time. A large variation in δ¹²³Sb values and chemical species fractions of Sb in soil samples suggests that Sb in soils from different geographical location may have different origins or migration behaviors. The Sb isotope composition of soil can be divided into four endmembers: atmospheric deposition, tailing leaching, river water surface runoff, and rock oxidative weathering. The differences in hydrochemical types and Sb isotopic signatures among river waters indicate multiple sources and factors influencing Sb migration in different locations. The Sb in river water may have been partly influenced by rock leaching. Sweet potato exhibited a similar Sb isotopic signature (δ¹²³Sb = 0.24‰) with surrounding soil (δ¹²³Sb = 0.22‰), which demonstrated that the sweet potato absorbed Sb through contaminated soil to the root. Soil erosion and tailings are the major sources of Sb in street dust. A conceptual model was established to elucidate the pollution sources and the main geochemical processes affecting the mobilization of Sb in environmental matrices in the XKS mining area. This study provides a scientific basis for environmental quality assessment of Sb mining areas and establishment of an effective early warning system for Sb pollution in soil.