Deciphering origin and fertility of the Zhaojinci granitic rocks in the southern Hunan district (South China): using zircon U-Pb dating and geochemistry

South China is a globally recognized domain for Mesozoic magmatic-metallogenic systems. At the confluence of the Qin-Hang Metallogenic Belt and the Nanling Range lies its Southern Hunan district, a key area renowned for prolific Jurassic magmatism and related skarn W–Sn/Cu deposits. The Zhaojinci district, located within the Pingbao orefield of southern Hunan, hosts extensive intrusions of granodiorite porphyry, granite porphyry, and other granitic varieties. However, the formation age, magmatic source, and ore-bearing potential of these intrusions remain poorly understood. This study investigates twelve granitic stocks at Zhaojinci using zircon U–Pb dating and in situ trace element analysis, and Hf isotope analysis. These methods are employed to determine their formation ages, explore the magmatic sources, and assess the fertility of the rocks. Zircon U–Pb geochronology reveals that the Zhaojinci granitic rocks were emplaced at 168–159 Ma, which coincides with a major regional magmatic event (165–155 Ma) in southern Hunan. This period also corresponds to magmatism genetically associated with Cu mineralization (168–159 Ma) in southern Hunan. The zircon ε Hf(t) values (– 28.4 to – 5.0) and T DM2 ages (3,004–1,526 Ma) suggest that the Zhaojinci granitoids predominantly originate from a mixed crust-mantle source, incorporating Mesoarchean to Paleoproterozoic crustal components. Additionally, zircon from these rocks exhibits an average of Ce 4+ /Ce 3+ ratios of 99, temperatures averaging 784 °C, and Dy/Yb ratios ranging from 0.11 to 0.58 (avg. 0.21; predominantly below 0.3). These geochemical signatures align closely with those of regional magmatic rocks genetically linked to skarn Cu mineralization, but notably differ from magmatic rocks associated with skarn W–Sn mineralization. These findings suggest a high potential for Cu skarn mineralization of the Zhaojinci granitic rocks. This study provides new insights into regional mineralization potential in the Pingbao orefield, even in the South China.