Abstract:Texture, geochemistry, and in-situ Pb isotope of galena were investigated to probe the origin of anomalous Ag enrichment in the Dayingezhuang Au(-Ag) deposit. Silver enrichment postdates the main Au mineralization and occurs in the south of the Dayingezhuang deposit. It is primarily associated with galena and the exsolution of Ag-rich sulfosalts (e.g., matildite) in distal vein-ores related to steeply dipping brittle fractures. Silver-rich galena is characterized by the least radiogenic Pb isotope signature (²⁰⁶Pb/²⁰⁴Pb 17.195–17.258 and ²⁰⁸Pb/²⁰⁴Pb 37.706–37.793), possibly indicating a metasomatized lithospheric mantle or modified lower crustal source for Pb and Ag. Both of these mafic and ultramafic source regions have been previously suggested as Au reservoirs for other Jiaodong Au deposits, implying that the metal reservoir has only a weak control on the uneven Ag-enrichment. Since the Ag-enrichment areas are located in the footwalls of both the Dayingezhuang and Zhaoping faults, the enrichment was most likely dominated by local rotational stress during coeval movements of the two faults in a NE–SW compression and NW-SE extension regime. This work highlights the shallow-crust structural deformation responsible for controlling the flow of late ore-forming fluid resulting in local anomalous metal enrichment.

Key words: galena; lead isotope; silver; Dayingezhuang deposit; Jiaodong Peninsula