Multiple isotopic constraints on multistage antimony-mercury mineralization events in the Jiangnan orogenic belt, South China

The Sandu–Danzhai metallogenic belt (SDMB), which has abundant low-temperature gold (Au), antimony (Sb), and mercury (Hg) deposits, is a critical component of the South China low-temperature metallogenic domain (LTMD). The ages and metal sources of these deposits remain ambiguous, hindering our understanding of their metallogenic background. In this work, mineralogical analysis, in situ U-Pb geochronology coupled with trace element analysis of calcite, in situ Pb-isotope analysis, and sulfide Hg-isotope analysis were conducted on three deposits (Miaolong, Paiting, and Wangjiazhai) in the SDMB. Based on textural observations and crosscutting relationships, the mineralization in the SDMB is characterized by four distinct assemblages: Au (pyrite + arsenopyrite + quartz), Au-Sb (pyrite + arsenopyrite + stibnite + quartz), Sb (stibnite + barite + dolomite + quartz), and Hg (cinnabar + calcite). The calcite from the Miaolong deposit is rich in middle rare earth elements and has a U-Pb age of 420.8 ± 9.1 Ma. The calcite from the Wangjiazhai Hg deposit is rich in light rare earth elements, with a U-Pb age of 385 ± 11 Ma. The Δ199Hg values (−0.22‰ to 0‰; n = 19) of pyrite, stibnite, and cinnabar from the three deposits indicate ore-forming metals derived from Precambrian basement rocks, which the in situ Pb isotopic ratios confirmed. Combined with evidence of contemporaneous tectonothermal events, the findings of this study confirm a close genetic link between Sb-Hg mineralization in the SDMB and Paleozoic orogenic processes. These intracontinental tectonothermal activities facilitated the large-scale reactivation of basement materials and the formation of hydrothermal fluids containing abundant basement metals. Furthermore, this study highlights the combined use of multiple isotopes as a robust tool for providing critical constraints on the mechanisms of regional metallogenesis.