Tectonic transition from a compressional to extensional metallogenic environment at -120 Ma revealed in the Hushan gold deposit, Jiaodong, North China Craton

摘要

The world-class giant gold province ( 4000 t) in the Jiaodong Peninsula has attracted global attention and extensive studies for decades. However, most of the works have been focused on the western Zhaoyuan-Laizhou and eastern Muping-Rushan gold metallogenic belt, leaving the middle Penglai-Qixia belt largely unexplored. The Hushan gold deposit in the Penglai-Qixia belt shows a unique two-stage gold mineralization, i.e., an earlystage pyrite-sericite-quartz altered-rock type mineralization and a late-stage pyrite-pyrrhotite vein type mineralization. Hydrothermal monazite coexisting with Au-bearing pyrite is observed in the early-stage mineralization. The widespread "circular zoned" metasomatic relict structures indicate that monazite was formed by the strong interaction between (Ca, P, REE)-rich fluids and feldspars (plagioclase and K-feldspar). Therefore obtained in-situ U-Pb age of 120.0 +/- 3.1 Ma for the "pure" monazite without mineral inclusions (such as feldspars) can represent the timing of the early-stage gold mineralization. The in-situ monazite epsilon(Nd) (t) (t = 120 Ma) values vary from -20.6 to -18.4, well corresponding to Nd isotopes of the late Jurassic Linglong granite. It is inferred that the REE-rich components in the ore-forming fluids were extracted during the process of primary mineralizing fluids passing through the lower Linglong granite body, and that the Nd isotopic compositions were altered due to the strong fluid-rock interaction. In this regard, Linglong granite contributes some ore-forming materials to the mineralizing fluids during fluid-rock interaction.