Abstract:

Gaobei felsic dikes are exposed in the middle of the Yushan metallogenic belt, south Jiangxi Province, intruding into the Precambrian metamorphic strata, and their rock type is mainly granite porphyry. In order to reveal the emplacement age, petrogenesis and relationship with mineralization in the Gaopi ore deposit in south Jiangxi Province, petrography, geochemistry, zircon U-Pb dating and Hf isotopic analyses were carried out on the Gaopi granite porphyry. The results show that the Gaobei granite porphyry is characterized by high silicon (74.53% on average), high potassium (4.34% on average) and aluminum-rich (15.36% on average), and belongs to the high-k calc-alkaline series or k-basalt series granite; It has a low Nb/Ta, Zr/Hf ratio, and the REE fractionation is not obvious with strong Eu negative anomaly, proving to be highly differentiated granites. Zircon LA-ICP-MS U-Pb data has yielded concordant age of (135.73±0.46) Ma (MSWD=1.7), and a mean age of (135.62±0.92) Ma (MSWD=0.27), indicating that the Gaobei granite porphyry was emplaced in Early Cretaceous. Zircon Hf isotope analysis results show that the 176Hf/177Hf=0.282322-0.282450, εHf（t）=-13.3--8.5, and the two-stage model age TDM2 varies from 2.03 Ga to 1.73 Ga, inferring that the Gaobei granite porphyry may be mainly derived from the melting of the Proterozoic crustal materials. The field investigations found that the surrounding rocks around the Gaobei ore deposit have undergone intense hydrothermal alterations such as argillization, beresitization, and silicification, and are distributed in a planar pattern. Meanwhile, the borehole has revealed net-vein molybdenum mineralization, inferring that the deep area has the potential for porphyry molybdenum deposits.

Key words: geochemistry, zircon U-Pb age, Hf isotope, granite porphyry, mineralization, porphyry molybdenum deposit, south Jiangxi Province