In-situ apatite U-Pb dating and geochemistry reveal two stages of mineralization in the Linjiasandaogou gold deposit of Liaoning Province, North China Craton

The Qingchengzi gold-dominated polymetallic district, situated in the North China Craton, has a mining history of over 400 years, with estimated reserves of 300 t Au and 4000 t Ag. Despite extensive studies, the genesis of gold deposits in this orefield remains controversial. Existing models invoke either Paleoproterozoic deposition and metamorphism overprinted by later hydrothermal activity or Mesozoic hydrothermal mineralization. The Linjiasandaogou deposit, a representative Au deposit of the orefield, hosts three ore types: schist-hosted stratiform, lamprophyre-hosted disseminated, and granite porphyry-hosted disseminated ores. A comprehensive petrographic, geochronological, and geochemical investigation shows that apatite occurs in all ore types, namely, Ap-1 in schist-hosted stratiform ore, Ap-2 in lamprophyre-hosted disseminated ore, and Ap-3 (Ap-3 m and Ap-3 h) in granite porphyry-hosted disseminated ore. Integrated petrographic and geochemical analyses distinguish three apatite origins. Metamorphic-hydrothermal Ap-1 has low rare earth elements (REE) contents, minimal fractionation between light rare earth elements (LREE) and heavy rare earth elements (HREE), pronounced negative Eu anomalies, and low Sr/Y ratios. Magmatic Ap-2 and Ap-3 m show REE-enriched patterns, strong LREE-HREE fractionation, and melt-like Sr/Y ratios. Hydrothermal Ap-3 h is marked by REE depletion, weak LREE-HREE fractionation, a pronounced positive Eu anomaly, and relatively low Sr/Y ratios. In-situ LA-ICP-MS U-Pb dating of these apatites yielded lower intercept ages of ∼ 1830 Ma (Ap-1), ∼214 Ma (Ap-2), ∼220 Ma (Ap-3 m), and ∼ 190 Ma (Ap-3 h). These results confirm the following key geological events in the Linjiasandaogou region: Mesozoic magmatic activity at ∼ 220–214 Ma, and two episodes of gold mineralization (Paleoproterozoic ∼ 1.83 Ga and Mesozoic ∼ 190 Ma). Collectively, the apatite petrography, geochemistry, U-Pb geochronology, and regional geochronological constraints indicate that the Linjiasandaogou deposit records a Paleoproterozoic lode gold system (ca. 1.83 Ga) overprinted by Mesozoic gold mineralization (ca. 190 Ma). This study provides new evidence for the existence of Precambrian lode gold mineralization in the North China Craton and recommends the utility of in-situ U-Pb dating of hydrothermal accessory minerals (e.g., apatite) in polished thin sections as a robust method for recognizing multiple mineralization events.