Lithium isotope behavior during magmatic differentiation and fluid exsolution in the Jiajika granite–pegmatite deposit, Sichuan, China

•The Jiajika granitic pegmatites are the final products of extreme fractional crystallization of two-mica granitic magmas.•The Li-poor pegmatites derived from early differentiation of the two-mica granitic magmas before they evolved into Li-rich pegmatites.•Fluid exsolution and kinetic diffusive fractionation account for the Li isotopic variations in the Li-rich and Li-poor pegmatites.•Extreme crystal fractionation, fluid exsolution and Li-rich surrounding strata resulted in the formation of the Jiajika large Li deposit.