Trace element and sulfur isotope constraints on the Genesis of Sb-(Au) deposits in Southern China: Insights from the Longkou deposit

The Xiangzhong Metallogenic Province (XZMP) in southern China hosts the region's most extensive Sb-polymetallic mineralization system, comprising two principal deposit types: Sb-only and Sb–Au–(W). To investigate their genetic distinctions, we conducted in-situ LA-ICP-MS and sulfur isotope analyses on stibnite from the Longkou SbAu deposit in the Shaoyang Basin, and integrated these results with published data from the Xikuangshan, Daocaowan, Woxi, and Banxi deposits. Multivariate statistical analyses (PCA and PLS-DA) of stibnite trace elements reveal systematic geochemical differences between the two deposit types. SbAu deposits (e.g., Longkou, Woxi, Banxi) are enriched in Cu and Pb, whereas Sb-only deposits (e.g., Xikuangshan, Daocaowan) show elevated Hg and lower CuPb concentrations. These patterns suggest that, while Sb in both deposit types was likely derived from Proterozoic basement rocks, metals such as Au, Cu, and Pb in SbAu deposits originated from deep magmatic-hydrothermal fluids. In contrast, ore-forming fluids in Sb-only systems were dominated by shallow-crustal or metamorphic sources, with limited magmatic input. The δ³⁴S values of stibnite are relatively uniform across most deposits, further supporting a shared sulfur source linked to basement lithologies. Trace element and sulfur isotope data point to two distinct mineralization mechanisms: in SbAu systems, magmatic-hydrothermal fluids transported metals from depth and leached Sb and S from basement rocks, while in Sb-only systems, magmatic activity primarily acted as a heat source, promoting the circulation of meteoric and metamorphic fluids that leached Sb and S from the basement. These findings provide a geochemical framework for distinguishing Sb deposit types and offer new insights into the metallogenic processes of Sb–(Au) systems in South China.