Metasomatized mantle source and far-field effect of flat-slab subduction at the Huangtuliang gold deposit, northern margin of the North China Craton

The metasomatized lithospheric mantle has been proposed as the primary source for gold mineralization at cratonic margins, yet without much direct evidence. To substantiate this theory with geochemistry, we study ore-hosting alkaline syenite and mineralization-related lamprophyre dikes from the Huangtuliang gold deposit at the northern margin of the North China Craton. We provide new zircon U-Pb geochronology and Hf isotope data, as well as whole-rock major and trace element analyses. The alkaline syenite was emplaced during the Early Devonian (397 ± 1 Ma), while the lamprophyre magmatism and associated gold mineralization occurred in the Late Jurassic (152 ± 1 Ma). The alkaline syenite is characterized by high K2O (10.4–10.9 wt%; loss-on-ignition–free) contents and K2O/Na2O (4.0–4.3) ratios, as well as negative zircon εHf(t) values (−22.5 to −18.2). Its formation is interpreted to have involved (1) low-degree partial melting of a phlogopite-rich lithospheric mantle potentially metasomatized by subduction-derived fluids and carbonatitic melts and (2) fractional crystallization during magma ascent. The lamprophyre dikes exhibit high K2O (2.19–4.17 wt%) and TiO2 (2.98–3.22 wt%) contents and positive zircon εHf(t) values (+3.1 to +8.2), suggesting their parent magma likely originated from a metasomatized, garnet-bearing asthenospheric mantle source and evolved through fractional crystallization. Our results imply that the lithospheric mantle beneath the northern margin of the North China Craton likely underwent prolonged subduction and metasomatism since at least the Devonian. This process has been key to enriching volatiles and metals, as well as weakening the lithosphere. The emplacement of the lamprophyre dikes and the associated gold mineralization at Huangtuliang are proposed to be linked to far-field effects of the Late Jurassic flat-slab subduction of the Paleo-Pacific Plate, which triggered asthenospheric upwelling, localized lithospheric thinning and melting, and generated hydrous, volatile-rich, Au-bearing magmas.