Magma evolution and Indications for Li migration at the 509 Daobanxi Li-bearing pegmatite deposit at Dahongliutan in the West Kunlun Orogen

The extensive presence of monzogranite at the major “509 Daobanxi Li deposit” is interpreted as closely related to the formation of pegmatite veins and anomalous enrichment in lithium (Li). The recent identification of abundant pegmatite veins hosted by large-scale granodiorite bodies offers a new perspective for exploring the genetic and evolutionary relationships of phases within the Dahongliutan pluton. A systematic comparison of granodiorite, monzogranite, and pegmatite provides a more comprehensive understanding of the petrogenetic evolution between composite granites and pegmatites in the region, as well as the behaviour of Li during various magmatic stages. Representative granodiorite and pegmatite samples were systematically sampled based on detailed geological field investigations. Zircon U-Pb geochronology constrains the age of both the composite granite and pegmatite to ca. 220–207 Ma, indicating temporal continuity between the two. Tracing the Sr-Nd isotopic ratios and Li isotope Rayleigh fractionation modelling indicate that Triassic turbiditic sedimentary rocks in the Bayankalashan Group probably provided a common source for both the composite granite and associated pegmatites. Integrated analysis of whole-rock geochemistry and electron microprobe data from feldspar and mica reveals that the granitic magma originated from the dehydration melting of a muscovite-rich source, whereas the pegmatitic melt was generated through fractional crystallisation of the granitic magma. Trace element variations in feldspars, along with Rayleigh fractionation modelling of Li, Rb, and Sr, suggest that the pegmatitic melt represent represented 70–80% of the fractional crystallisation, primarily driven by the differentiation of mica, plagioclase, and K-feldspar. Overall, the petrogenesis of the Dahongliutan pegmatite is subdivided into the stages of partial melting, ascent of granitic magma, and fractional crystallisation. The Li migration process also discussed in terms of source region characteristics and the evolution of the pegmatitic melt.