Petrogenesis of fine-grained muscovite granite in the Lianhuashan tungsten tin ore cluster area of northern Jiangxi province-Constraints from zircon U-Pb isotopes and elemental geochemistry

Lianhuashan tin-tungsten polymetallic ore concentration district in northern Jiangxi province is located on the southeast edge of the Yangtze plate.It is one of the important ore concentration districts of the Jiuling-Zhanggongshan tungsten-tin-copper-gold polymetallic metallogenic belt.It is determined as a class Ⅰ metallogenic prospect, with more than 10 tin-tungsten deposits(occurrences), including Maopengdian, Xujiajian, Bazinao, Mianhuawu, Shishan and so on, there are several non-metallic mining occurrences, such as Pancun fluorite deposit and Dazhou kaolin deposit, but most of them are small and medium-sized mineral deposits, and there has never been a significant breakthrough in mineral exploration.In addition, there is a lack of accurate chronological and geochemical testing data for granite during the mineralization period.The petrography, zircon U-Pb chronology and whole-rock geochemistry of the medium and fine-grained muscovite granite in Maopengdian tin-tungsten deposit are studied in this paper, which provide direct evidence for the study of regional mineralization patterns.The results show that the zircon LA-ICP-MS U-Pb age of the muscovite granite is 126.7 ± 1.2 Ma.The Yanshanian rock unit consists of medium-coarse-grained porphyritic biotite granite →medium-fine-grained porphyritic biotite granite →medium-fine-grained-coarse-grained porphyritic mica granite→medium-fine muscovite granite→ granite porphyry, which is the result of crystallization differentiation of homologous magma evolution.Geochemical studies show that the medium and fine-grained muscovite granite is a highly differentiated S-type granite, which is characterized by high silicon(SiO₂=75.08%~75.40%) and rich in alkali and peraluminous and high differentiation index DI.The fractionation of light and heavy rare earth elements is obvious, showing a deep V-type with high left and low right.Eu shows a strong negative anomaly and has four grouping effect of rare earth elements.The average values of Rb/Sr and Rb/Ba are 53.92 and 60.30 respectively, indicating that the magma experienced multi-stage fractional crystallization, and the highly differentiated granite is the main metallogenic geological bodies of W-Sn deposits in the area.