Geochronology of the Guilaizhuang gold deposit, Luxi Block, eastern North China Craton: constraints from zircon U-Pb and fluorite-calcite Sm-Nd dating

Abstract

The Guilaizhuang deposit is the largest gold producer in the southwestern Shandong Province with a unique Au–Te mineralization feature different from the other gold deposits in the adjacent Jiaodong Peninsula. The Tongshi alkaline intrusive complex, which is composed of syenites and monzonites with a crystallization age of ~ 180 Ma, is the main magmatic unit in this area, and considered to represent post-collisional magmatism. The syenite intruded into the sedimentary carbonate sequence in the Guilaizhuang district, cryptoexploded and was altered by fluorine-rich fluid. The intensely mineralized cryptoexplosive breccias along the EW-trending fault are extensively cemented by fluorite and calcite minerals. The intrusive age of the syenite should mark the lower limit of the gold mineralization age, whereas the formation age of the fluorite and calcite would represent the upper limit. In this study, we analyzed zircons from the altered syenite in the open-pit, and the results show U–Pb ages of 179–180 Ma consistent with those of the Tongshi intrusive complex. We also present a Sm–Nd isochron age from the fluorite–calcite mineral pair that shows 181 Ma. Based on those results, we infer the timing of gold mineralization to be approximately 180 Ma, coeval with the intrusion of the Tongshi complex. A correlation with the regional tectonic milieu shows that the Guilaizhuang gold deposit was located in a post-collision setting at this time, following the amalgamation between the North China Craton and the Yangtze Craton. Thus, the Guilaizhuang deposit should mark an important alkaline rock-related gold-forming event within the eastern margin of the North China Craton in a post-collisional setting associated with the collision of the North China Craton and Yangtze Craton during late Triassic to Early Jurassic, and is obviously different from the Early Cretaceous intensive gold mineralization in the adjacent Jiaodong Peninsula.