Evolution of gold in basic magmas in the giant Jiaodong Gold Province

Abstract The Jiaodong gold province, with proven resources of more than 5,700 tonnes, is the largest gold-producing region in China. Owing to the close spatial and temporal relationships between mantle-derived intrusions and gold deposits, the role of mantle magmatism in Jiaodong gold mineralization has long been debated. Integration of field observations, petrography, and major and trace element geochemistry of mantle-derived lamprophyres, monzodiorites, and mafic microgranular enclaves is required to address this issue. The Jiaodong lamprophyres, monzodiorites, and mafic microgranular enclaves were derived from a common metasomatized mantle lithosphere source but followed distinct evolutionary pathways. Lamprophyres represent relatively primitive mantle-derived magmas that mainly experienced fractional crystallization, whereas the monzodiorites and MMEs represent more evolved magmas that underwent variable degrees of crustal contamination and magma mixing. Chalcophile element geochemistry indicates that sulfide segregation during lamprophyre magma evolution was limited. Consequently, the Au concentrations of the lamprophyres closely reflect the primary Au contents of their parent magmas (0.24–2.34 ng/g). In contrast, the evolved monzodiorites and MMEs experienced significant sulfide segregation and contain lower Au concentrations (0.05–0.60 ng/g). Overall, the Jiaodong mantle-derived magmas did not possess an unusually large magmatic Au budget compared to global magmas genetically associated with magmatic-hydrothermal Au systems (1.30–5.50 ng/g). Mineral–melt thermobarometry, together with previous estimates of regional exhumation, indicate that these mantle-derived magmas were emplaced at depths that precluded extensive H2O–CO2 fluid exsolution. Increasing X(Cl/F) and X(OH/F) ratios from lamprophyres to monzodiorites and mafic microgranular enclaves further demonstrate that little fluid exsolved during the late stages of magma crystallization. Combined with the limited volume of mantle-derived intrusions, these factors suggest that mantle-derived magmas were unlikely to have directly generated the ore-forming fluids responsible for the giant Jiaodong gold deposits.