New insights on the formation of the Heizhushan Pb-Zn-Ag-barite deposit (China, East Kunlun Orogenic Belt) from the mineral chemistry and sulfur isotope

• The Heizhushan deposit represents a low to moderate temperature hydrothermal system. • BSR of Late Devonian seawater sulfate played a significant role in Pb-Zn mineralization. • The Heizhushan deposit is a vent-proximal SEDEX deposit. The study of metallogenic processes in sedimentary exhalative (SEDEX) deposits has long been a central focus in the scientific community. However, the scarcity of well-preserved vent-proximal SEDEX deposits and their widespread overprinting by post-mineralization metamorphism and deformation present significant obstacles to in-depth investigation. The Heizhushan Pb-Zn-Ag-barite deposit in the Qimantag metallogenic belt is a well-preserved Late Devonian SEDEX deposit, and contains proven reserves of 4.48 million tonnes with average grades of 57.93 % BaSO 4 , 1.94 % Pb, 1.70 % Zn, and 43.67 g/t Ag. As the first systematic study of this deposit, we integrate field geology with LA-ICP-MS trace element analysis and sulfur isotopes of minerals to constrain its genetic type and mineralization processes. The deposit is hosted by slates of the Late Devonian Heishangou Formation. The deposit contains disseminated, laminated, and brecciated ores mainly composed of sphalerite, galena, pyrite and barite. Four mineralization stages are identified: (I) precipitation of fine-grained sulfides on the seafloor; (II) coarse-grained sulfides precipitation formed through subseafloor replacement; (III) veinlet sulfides mineralization via acid-driven replacement of calcite and barite; and (IV) breccia-filling sphalerite-barite mineralization. Trace element data show that galena from the stockwork zone contains higher Ag-Bi contents and pyrite exhibits greater Co/Ni ratios compared to the laminated zone, reflecting a temperature decrease from stockwork to laminated zones. Trace element correlations indicate Cd mainly substitutes for Fe/Mn in sphalerite lattices, while Ag incorporates into galena via (Sb, Bi) 3+ + (Ag, Tl) + ↔ 2Pb 2+ substitution. Sulfur isotopes show δ 34 S values of −5.5 ‰ to + 28.4 ‰ in sulfides (progressive enrichment of δ 34 S values in later-formed sulfides from main ore-forming stages), indicating bacterial sulfate reduction of Late Devonian seawater sulfate in a restricted basin. The combined evidence from host rocks, mineralization styles, mineral trace elements, and sulfur isotopes confirms the Heizhushan Pb-Zn-Ag-barite deposit as a vent-proximal SEDEX deposit.