Lithium-rich albite–topaz–lepidolite granite from Central Vietnam: a mineralogical and geochemical characterization

Abstract

A potential lithium deposit has been discovered in the La Vi mining district, located in Quang Ngai Province, Central Vietnam. The Li-rich rocks (average contents: 1.3 ± 0.9 wt.% Li 2 O) are highly fractionated peraluminous granites, which are characterized by high contents of Al 2 O 3 , Na 2 O, and K 2 O, as well as F (up to 2.19 wt.%) and P 2 O 5 (up to 0.65 wt.%), but very low concentrations of CaO, MgO, MnO, and Fe 2 O 3 . Among the trace elements, Rb, Cs, Sb, Nb, and Ta occur in relatively high concentrations. The granites exhibit a light pink colour and contain mainly albite, quartz, muscovite, lithian muscovite, and lepidolite, with minor amounts of amblygonite–montebrasite, herderite, fluorapatite, topaz, and cassiterite, as well as accessory beryl and goyazite. Electron microprobe analyses of amblygonite revealed high Na 2 O concentrations, but these are due to the presence of micrometre-sized lacroixite inclusions. Under the optical microscope, the granite samples are characterized by a range of grain sizes and microfabrics, which indicate that the original granites were hydrothermally altered. We conclude that this late-stage alteration was associated with albitization, greisenization and Li enrichment, so that the unique features of the rare albite–topaz–lepidolite granites are probably of secondary rather than primary origin.