Li–B isotope and major-trace element data of zoned elbaite from the Bailongshan Li pegmatite deposit, western Kunlun, China

Table S1 – Elbaite major and trace element data: Major element compositions were determined by electron probe microanalysis (EPMA) using a JEOL JXA-iSP100 microprobe (15 kV, 50 nA, 10 μm beam diameter). Trace element contents were measured by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) using a NWR 193 nm ArF Excimer laser system coupled to an iCAP RQ ICPMS (35 μm spot size, 6 Hz repetition rate, 3.5 J/cm² fluence). Data include SiO₂, TiO₂, Al₂O₃, FeO, MnO, MgO, CaO, Na₂O, K₂O, F, Cl, Li₂O(cal), H₂O(cal), and trace elements (Li, Be, Mg, K, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Nb, Sn, Cs, Ba, Hf, Ta, Pb, Th, U, etc.) for three elbaite zones: Elb-1 (core, magmatic origin), Elb-2 (mantle, late magmatic origin), and Elb-3 (rim, magmatic-hydrothermal transition origin). Table S2 – Boron isotope data: In situ boron isotope analyses of elbaite were conducted by LA-MC-ICP-MS using a Neptune Plus MC-ICP-MS coupled with a NWR 193 nm ArF Excimer laser-ablation system (25–30 μm spot size, 6 Hz, ~3.5 J/cm²). δ¹¹B values are reported relative to NIST SRM 951. Matrix-matched standard TYTurE was used for instrumental drift correction, and Elbaite#98144 and IAEA-B4 (GIGT) were used as monitoring standards. External reproducibility is ≤ ±0.3 ‰ (2SD). The table also includes Rayleigh fractional crystallization modeling parameters and results for B isotope fractionation during tourmaline crystallization and fluid exsolution. Table S3 – Lithium isotope data: In situ lithium isotope analyses were performed by fs-LA-MC-ICP-MS using a Neptune Plus MC-ICP-MS combined with a femtosecond ablation system (65 μm spot size, 20 Hz). δ⁷Li values are reported in per mil (‰). Matrix-matched Elbaite#98144 was used as the bracketing standard, and Schorl#112566 and IAEA B-4 served as monitoring standards. Long-term external reproducibility is ±0.46 ‰ (2SD). All samples were collected from the same mineralized dike swarm of zone VI at the Bailongshan deposit (sample numbers: 23BLS03-4-1, 23BLS-07-1-J to 23BLS-07-5-J, 23BLS-TS-3, and 23BLS-N7-3). Each elbaite crystal preserves a complete core-mantle-rim (Elb-1/Elb-2/Elb-3) zoning sequence recording the transition from magmatic crystallization to hydrothermal fluid activity. These data support the interpretation that early-exsolved hydrothermal fluids were re-injected into residual pegmatitic magmas during the magmatic-hydrothermal transition, promoting rare metal (Li, Be, Nb, Ta) mineralization.