Abstract:

The Gaojiadian pluton, located in the eastern Hebei Province on the northern margin of the North China craton, is a composite batholith that intruded during the early Yanshan period. It primary rock types include diorite, syenite, granite, with transitional varieties present. The pluton hosts hydrothermal vein-type gold deposits, primarily found in granite and diorite.To accurately determine the invasion period of the Gaojiadian pluton, four rock samples were analyzed by zircon chronology and trace element characteristics using LA-ICP-MS zircon U-Pb dating. The results indicate crystallization age of (197.4±1.9) Ma for quartz syenite, (176.7±1.2) Ma for fleshy-red biotite monzonitic granite, (175.8±1.7) Ma for gray-white biotite monzonitic granite, and (175.3±1.9) Ma for diorite-porphyrite, suggesting an intrusion age from the Early to Middle Jurassic. Dark diorite enclaves within the granite imply a mixed crust-mantle origin formed in an extensional tectonic setting. Zircon trace elements of all samples exhibit a left-leaning rare earth partitioning pattern with strong Ce positive anomalies and varying degrees of Eu negative anomalies. The zircon saturation temperature ranges from 682 to 824 ℃, representing the initial magma formation temperature. The magma exhibited a gradual cooling trend over evolutionary time and shares a similar partitioning pattern and crystallization temperature range with regional magmatic zircons. The high Ce4+/Ce3+ values of zircon represent relatively high oxygen fugacity, revealing the stronger mineralization potential of the Gaojiadian pluton, especially in the biotite monzonitic granite.

Key words: Gaojiadian gold deposits, hydrothermal vein type, zircon U-Pb age dating, zircon trace elements, oxygen fugacity, geochemistry, Gaojiadian pluton, eastern Hebei Province