Limited gold endowment from the Paleo-Pacific plate: Direct evidence from lamprophyres in the Jinshan gold mine, Jiaodong Peninsula, North China Craton

The metasomatized subcontinental lithospheric mantle (SCLM) is widely recognized as a major source for the formation of giant gold deposits. However, it remains debated whether the Triassic subduction of the Yangtze plate or the Jurassic subduction of the Paleo-Pacific plate beneath the eastern North China Craton (NCC) contributed more significantly to the Au budget of the Jiaodong gold province. Lamprophyres, derived from low-degree partial melting of the SCLM, serve as sensitive probes of mantle source characteristics. This study presents petrological and geochronological (zircon and apatite U-Pb) data for the Jinshan lamprophyres, identifying Late Jurassic (ca. 155–152 Ma) vogesite and Early Cretaceous (ca. 139 Ma) odinite. Both types exhibit typical island-arc basalt (IAB)-like geochemical characteristics, including enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), and low abundances and fractionated patterns of platinum-group elements (PGEs), similar to those of regional Early Cretaceous IAB-type mafic rocks. Key geochemical evidence indicates a pyroxenite-rich, amphibole-bearing mantle as the source. The parental magmas of the Jinshan lamprophyres were derived from low-degree (~4%) partial melting of the mantle source within the spinel–garnet transition zone. However, they exhibit more enriched Sr-Nd-Pb isotopic signatures than the regional Early Cretaceous mafic rocks. Their isotopic similarity to coeval lamprophyres in eastern Liaodong and mafic rocks from the South China Block (SCB) suggests that the mantle source was significantly modified by Paleo-Pacific slab-derived metasomatism. In contrast, the isotopic signatures of the regional Early Cretaceous mafic rocks are more akin to those of the Sulu–Dabie orogen, implying a significant contribution from the Yangtze plate. The systematic depletion and fractionation of PGEs in the Jinshan lamprophyres indicate that these features were inherited from low-degree mantle melting and not produced by shallow crustal processes. The Au content of the Jinshan lamprophyres (~0.096 ppb) is higher than that of the ancient NCC SCLM (~0.085 ppb) but lower than that of the Sulu orogenic peridotites (~0.355 ppb) and that of the syn-mineralization Early Cretaceous mafic rocks (~1.35 ppb). Integrated with previous studies, the data presented here suggest that Yangtze-derived materials may have contributed more significantly to mantle Au fertility, whereas Paleo-Pacific metasomatism primarily enhanced the volatile–fluid conditions conducive to Au mobilization. Furthermore, the Early Cretaceous mafic rocks coeval with large-scale gold mineralization exhibit Au concentrations (~1.35 ppb) comparable to those of global metasomatized lithospheric mantle (~1–1.2 ppb). This implies that the extensive Early Cretaceous gold mineralization in the Jiaodong Peninsula did not require a pre-enriched mantle source but instead was controlled by favorable conditions for Au release and transport induced by Paleo-Pacific plate subduction.