Granite–pegmatite connection and mineralization age of the giant Renli Ta[sbnd]Nb deposit in South China: Constraints from U–Th–Pb geochronology of coltan, monazite, and zircon

Abstract

The recently discovered Renli TaNb deposit in northeastern Hunan Province is the largest known pegmatite TaNb deposit in South China. Previous research has shown that biotite monzogranite is locally spatially associated with the pegmatites and could be the parental granite of the NbTa mineralization. In this study, we determine that muscovite monzogranite also has a close spatial relationship with the NbTa pegmatites. We present new U–Th–Pb ages for coltan, monazite, and zircon that constrain the timing of NbTa mineralization and related magmatism. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) UPb dating of coltan from the NbTa pegmatite yielded a weighted mean 206Pb/238U age of 140.2 ± 2.3 Ma. Zircon grains from the biotite monzogranite and muscovite monzogranite yielded weighted mean 206Pb/238U ages of 154.1 ± 2.5 Ma and 141.0 ± 2.4 Ma, respectively, and monazite grains from the muscovite monzogranite yielded a weighted mean ThPb age of 140.7 ± 2.2 Ma. Rare-earth-element contents of the coltan suggest that the NbTa mineralization is related to highly evolved granite. The muscovite monzogranite shows highly evolved features, with higher contents of SiO2 and Al2O3 and lower contents of Fe2O3T, K2O, TiO2, CaO, MgO, and P2O5 than the biotite monzogranite. The obtained ages and the close spatial relationship between the pegmatite-type mineralization and the muscovite monzogranite, together with the major- and trace-element compositions, indicate that the NbTa mineralization is genetically related to the Early Cretaceous muscovite monzogranite rather than the Late Jurassic biotite monzogranite. Muscovite monzogranite that formed during the Early Cretaceous should be considered a target for NbTa exploration in South China.