Geochronology, geochemistry, and geological implications of the Hanjiaoshan composite granite, southern Jiangxi

Highly fractionated granites of the Yanshanian Period are widely distributed in the southern Jiangxi (Gannan) region, and are closely associated with large-scale W-Sn mineralization. However, there are relatively few reports on highly fractionated granitic plutons related to the mineralization of rare metals such as Nb, Ta, and Li. The Hanjiaoshan composite pluton is one of the few granitic bodies in the southern Jiangxi associated with rare metal mineralization. This study focuses on the Hanjiaoshan composite pluton. Based on detailed field investigations, petrological, petrochemical, and isotopic geochronological studies were conducted on the granites. The Hanjiaoshan composite pluton can be divided into three intrusive phases (from early to late): coarse-grained biotite monzogranite, inequigranular biotite monzogranite, and fine-grained biotite monzogranite. LA-ICP-MS monazite U-Pb isotopic ages for these phases are 143.7±1.0 Ma, 144.5±1.8 Ma, and 143.4±1.5 Ma, respectively. These ages are consistent within error, all belonging to the Early Cretaceous. The rocks exhibit high SiO2 (76.58%~76.9%) and total alkali (6.97%~9.03%) contents, low Al2O3 (12.35%~14.41%) and P2O5 (0.007%~0.011%) contents, high TFeO/MgO (5.85~169.02), A/CNK (0.99~1.57) ratios, and differentiation DI (92.5~96.8). These characteristics classify them as highly fractionated granites. They show relatively high total rare earth element (ΣREE) contents (197.2×10-6~510.6×10-6), moderate fractionation between light and heavy REEs (LREEs and HREEs), significant negative Eu anomalies (δEu = 0.011~0.032), LREE enrichment, and an indistinct tetrad effect (TE1, 3 = 0.88~1.13). The rocks are relatively enriched in Rb, K, and Pb, but depleted in Sr, Ba, Nb, and P. Li contents range from 17.3×10-6 to 370×10-6, and F contents range from 2 682×10-6 to 6 265×10-6. The coarse-grained biotite monzogranite, inequigranular biotite monzogranite, and fine-grained biotite monzogranite of the Hanjiaoshan pluton all exhibit characteristics of S-type granites. It is inferred that the magmas were primarily derived from crustal pelitic sources and their formation was related to an intraplate extensional setting during the Early Cretaceous. The complex lithofacies and highly fractionated characteristics of the Hanjiaoshan composite pluton indicate potential for rare metal mineralization. This suggests that highly fractionated granites related to rare metal mineralization continued to develop in the Gannan region after the large-scale Late Yanshanian W-Sn mineralization event.