Paleo-Pacific Plate Subduction and Basement Mobilization Triggered Large-Scale Formation of Mesozoic Gold Deposits in the Northern Margin of the North China Craton

The northern margin of the North China Craton (NNCC) hosts Mesozoic gold deposits of significant economic importance. The metal sources of these gold systems have long been debated with mainly magmatic-hydrothermal versus metamorphic fluid models. Mercury (Hg) isotopes, which undergo unique mass-independent fractionation, can provide important insights into the source of metals in gold deposits due to the close association between Hg and Au in such systems. Here, we investigated the Hg isotopic composition of six gold deposits of the Middle Jurassic to Early Cretaceous age and potential source rocks in the NNCC. Variable Delta Hg-199 values were observed in bulk ore and pyrite samples (-0.28 parts per thousand to 0.34 parts per thousand, n = 51) and coeval granites (-0.21 parts per thousand to 0.13 parts per thousand; n = 25). The negative Delta Hg-199 values of bulk ore and pyrite samples mostly agree with that observed for metamorphic basement rocks (-0.37 parts per thousand to 0.11 parts per thousand; n = 32). The positive Delta Hg-199 values of bulk ore and pyrite samples agree with those reported in marine sediments (0 parts per thousand-0.3 parts per thousand). So the data suggest binary mixing of ocean-recycled Hg originated from the subducted oceanic slab, and terrestrial-recycled Hg from the Precambrian basement in Mesozoic gold deposits. The contribution of Hg (and Au, by analogy) from both reservoirs varies depending on active continental arc versus intracontinental setting and is ultimately controlled by translithospheric heat flow driven by paleo-Pacific plate subduction. Plain Language Summary Photoreduction of Hg(II) on Earth's surface system leads to mass-independent fractionation of Hg isotopes, resulting in positive and negative Delta Hg-199 values in marine and terrestrial systems, respectively. Here, we observe negative to positive Delta Hg-199 values in the Mesozoic gold deposits in the northern margin of the North China Craton. These results suggest binary mixing of ocean-recycled Hg from the fluids released by subducting oceanic slab or the mantle metasomatized by these fluids, and terrestrial-recycled Hg from the Precambrian basement in Mesozoic gold deposits. Paleo-Pacific plate subduction and translithospheric heat flow may have played a key role in the metallogenic metal enrichment of the Mesozoic gold deposits in the northern margin of the North China Craton.