Robust monazite U-Pb and molybdenite Re-Os ages reveal the magmatic and metallogenic history of a highly evolved granitic system in the Xianghualing deposit, South China

Abstract

Tin, tungsten, and rare metals are key strategic metals and are regarded as having potentially relationship with highly evolved granites. However, excessive U accumulation with magmatic evolution, complex melt-fluid interaction, and late hydrothermal alteration make it difficult to obtain accurate age information from the highly evolved granitic system. The Xianghualing deposit, located in southern Hunan Province, China, is a giant Sn-Nb-Ta-polymetallic deposit with various types of mineralization spatially associated with the Laiziling and Jianfengling highly evolved granite plutons, and is an ideal target to investigate the magmatic-hydrothermal process of highly evolved magmas and related Sn-Nb-Ta-polymetallic mineralization. Previous studies have reported a relatively wide range of intrusion ages and multi-stage mineralization ranging from Triassic to Cretaceous. However, the timing and genetic link between magma emplacement and Sn-Nb-Ta-polymetallic mineralization remain controversial. Here we employ multiple dating methods, including SHRIMP zircon U-Pb analysis, LA-ICP-MS zircon and monazite U-Pb analysis, and molybdenite Re-Os dating analysis with a view to obtain a precise geochronological framework of the Xianghualing deposit. The SHRIMP zircon U-Pb data from the Laiziling protolithonite granite yielded a weighted 206Pb/238U age of 156.4 ± 1.5 Ma, whereas the LA-ICP-MS monazite U-Pb age for the Laiziling albite granite and the greisenized granite show 207Pb-corrected lower intercept 206Pb/238U ages of 155.5 ± 0.7 and 155.3 ± 0.5 Ma, respectively, which represent the emplacement ages of the Laiziling granite stock. Compared with the scattered SHRIMP and LA-ICP-MS zircon U-Pb age, monazite from the albite granite and greisenized granite yields more precise age information. Our study shows that monazite can be used as a robust tool for dating highly evolved granites. Molybdenite from the Laiziling pegmatite yields a Re-Os isochron age of 157.8 ± 4.2 Ma, which is consistent with the emplacement age of the Laiziling pluton. This result, integrated with previously reported metallogenic age, suggests a temporal and genetic link between the Laiziling granite and Sn-Nb-Ta polymetallic mineralization. Although multi-stage Sn-W metallogenic events have been identified in Nanling Region, it is suggested that the Xianghualing Sn-Nb-Ta mineralization formed during the Late Jurassic within a short duration coeval with the regional large-scale W-Sn mineralization at 160–150 Ma.