Li-Nb-Ta mineralization in the Jurassic Yifeng granite-aplite intrusion within the Neoproterozoic Jiuling batholith, south China: A fluid-rich and quenching ore-forming process

摘要

The Neoproterozoic Jiuling batholith in northwestern Jiangxi Province, south China, is one of the largest batholiths in the Nanling Range, and it is intruded by Mesozoic granitic intrusions associated with mineralization. The Jurassic Yifeng granitic pluton intrudes to the southern part of the Jiuling batholith and comprises Li-rich muscovite (Li-Mus) granite, trilithionite (Tel) granite, and aplite dikes. The granitic rocks are enriched in rare metals (Li-Rb-Cs-Nb-Ta). We conducted whole-rock geochemical analyses, undertook columbite U-Pb dating, and examined the textures and chemistry of feldspars, micas and the accessory minerals montebrasite, columbite-group minerals (CGMs), microlite, cassiterite, and zircon. All three granitic rock types have high Li contents (up to similar to 6200 ppm), and the delta Li-7 values of the Li-Mus granite and aplite are - 3.55 +/- 0.14 parts per thousand and - 5.34 +/- 0.04 parts per thousand, respectively. The isolated grains of CGMs and cassiterite in the aplite are magmatic products, but intense fluid activity in the later stages and quenching resulted in unique mineral aggregates of cassiterite + CGMs + zircon. The Nb-Ta mineralization of the Li-Mus granite took place at 144 +/- 5 Ma according to columbite U-Pb dating, and this age is similar to that of the neighbouring Yichun granitic pluton to the south. Moreover, both the Yifeng and Yichun plutons contain P-rich rare-metal-bearing Li-F granitic rocks that contain P-rich feldspars, montebrasites (amblygonites), Cs-rich lepidolites, CGMs close to the Mn endmember, and Hf-rich zircons. It is inferred that a metallogenic district characterized by Li-Nb-Ta mineralization exists in northwestern Jiangxi Province, thus providing a reliable guide for further exploration.