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The Chakabeishan (CKBS) deposit is the first pegmatite-type Li-Be deposit discovered in the eastern North Qaidam Tectonic Belt (NQTB) of Tibetan Plateau. The correct understanding of its petrogenesis and the precise determination of its formation age are of great significance for further regional prospecting and the discovery of new economically valuable rare-metal deposits. Therefore, a systematic study of texture, major-element composition, and U-Pb dating of columbite-tantalite group minerals (CGMs) in the spodumene pegmatite dyke from the CKBS deposit was undertaken. Three types of CGMs were identified, including concentric oscillatory ferrocolumbite (CGMs-1), homogeneous ferrocolumbite (CGMs-2), and irregular ferrotantalite (minor manganocolumbite) with abundant early ferrocolumbite replacement remnants (CGMs-3). The zoning patterns and chemical compositions in the CGMs record the complex evolutionary history of their host pegmatite from the magmatic stage (CGMs-1, disequilibrium crystallization) to the magmatic-hydrothermal transition stage (CGMs-2, equilibrium crystallization) and then to the late metasomatic stage (CGMs-3, replacement/re-equilibrium). CGMs U-Pb dating results suggest that the spodumene pegmatite dyke (No.15) emplaced at 230.1 ± 2.6 Ma. Subsequently, it experienced fluid metasomatism at 221 ± 5.3 Ma. Based on the new age data and published geochronological data, it can be concluded that the spodumene pegmatite dykes in the CKBS deposit formed in an oceanic subduction-related setting, representing a new metallogenic event in western China. Except for the CKBS deposit, a large number of rare-metal pegmatite dykes have also been discovered in the eastern NQTB, indicating that the eastern NQTB may be an important potential rare-metal metallogenic belt that should be explored in detail and arouse painstaking attention. [ABSTRACT FROM AUTHOR]

[Display omitted] • Elemental and B isotopic compositions in tourmalines suggest that fluids were unsaturated during the evolution of the CKBS barren pegmatites. • The ratios of Mn/Zn, Mn/Li, Sc/Li and Nb/Sc of tourmalines are useful geochemical criteria for distinguishing the CKBS fertile from the CKBS barren pegmatites. • (Zn + Li) - (V + Sr), Li-Zr/Sr, Sn/10Nb-Li-100Nb and Zn/Sn-Li/10Sc-5Sc are potential elemental groups for discriminating tourmalines of granite-derived pegmatite-type Li-Be deposits from those of other geological environments. To assess the potential of tourmaline as an indicator for pegmatite evolution and exploration, we measured and compared the geochemical compositions in tourmalines of the barren, Be-rich and Li-rich pegmatites from the Chakabeishan (CKBS) deposit, eastern North Qaidam Tectonic Belt, northeastern Tibetan Plateau. Two types of tourmalines from the barren pegmatites are identified: optically homogeneous fine-grain tourmalines (H-Tur) and optically zoned coarse-grain tourmalines (OZ-Tur). Both H-Tur and OZ-Tur are of magmatic origin, showing high Na/(Na + Ca) (0.961–0.990), Y Al (0.389–0.757 apfu) and low Mg/(Fe + Mg) (0.085–0.230). The core-to-rim δ 11B increase within H-Tur and OZ-Tur, together with the enrichment of 11B from H-Tur (crystallized earlier) to OZ-Tur, indicates that fluids were unsaturated in the evolution of barren pegmatites. Compared to H-Tur and OZ-Tur, tourmalines from the Be- and Li-rich pegmatites show higher Nb/Sc (>3:4) and lower Mn/Zn (<1:1), Mn/Li (<3:1), and Sc/Li (<1:500), which are useful indirect criteria of distinction between the fertile and the barren pegmatites. The reliable tourmaline geochemical criteria for further distinguishing the Li-rich from the Be-rich pegmatites are Pb/Sr < 0.11, Nb/Sr < 0.15, and Pb/Co < 4. A compilation suggests that diagrams of (V + Sr)-(Li + Zn), Li-Zn/Sr, Sn/10Nb-Li-100Nb, and Zn/Sn-Li/10Sc-5Sc could discriminate tourmalines of granite-related pegmatite-type Li deposits from those of other deposits and rocks, showing implications for determining prospective areas for further Li-rich pegmatite exploration by using tourmalines recovered from surface sediments. [ABSTRACT FROM AUTHOR]