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[Display omitted] • Garnets from Bailongshan deposit are magmatic in origin. • The composition of garnets from Bailongshan deposit mainly depends on the competing effects of coexisting minerals. • Garnet is a potential exploration indicator for rare-metal mineralization in Bailongshan deposit. The Bailongshan deposit is a newly-discovered super-large lithium polymetallic pegmatite deposit. Garnets occur widely in muscovite granites and pegmatites at Bailongshan, but comprehensive study is yet to be done on the geochemical evolution of garnet from the magmatic to the hydrothermal stages. Here, we present a systematic study of in-situ major and trace elemental variations of garnet from Bailongshan, and discuss the geochemical behaviors during magmatic to hydrothermal stage and the mineral indicator of large-scale mineralization of rare metal. Three types of garnet have been identified at Bailongshan, including disseminated garnet in muscovite granite (Grt I), medium-coarse-grained garnet in barren pegmatites (Grt II), and medium-grained euhedral-subhedral garnet in ore-bearing pegmatites (Grt III). EPMA and LA-ICP-MS geochemical analyses reveal that the garnet belong to almandine-spessartine solid-solution series. The garnets have varied REE contents (∑REE = 3.64～382 ppm), and HREE-enrichment, negative Eu anomalies, and LREE below or close to their detection limits. Grt III has higher Mn and Zn, but lower Fe, Y and HREE than those of Grt I and Grt II. The contents of Li, Zr, Hf, Nb and Ta increase from Grt I to Grt II, but decrease abruptly to Grt III. During the evolution of granitic magma, the increasing magma fractionation and fluid-phase accumulation and the crystallization of zircon lead to the continuous decrease of Y and HREE contents from Grt I to Grt III, and the gradual decrease of Y and HREE contents from core to rim of garnet crystals. In the quartz-albite-spodumene pegmatites, the crystallization of spodumene and columbite-group minerals removes Li, Nb and Ta from the melt, which significantly reduces the contents of these elements in garnet. The crystallization of spessartine-rich garnet is a reflection of a high degree of melt evolution at low pressure which facilitates the formation of LCT type pegmatite deposit. The Zr/Hf and Y/Ho ratios also indicate that magma fractionation degree and fluid activity increase from muscovite granites to barren-pegmatites and ore-bearing pegmatites, The combination of some major (e.g., Fe and Mn) and trace elements (e.g., Li, Ta, Nb, Sc and HREE) signatures, as well as the Zr/Hf, Y/Ho ratios in garnets can indicate the magma fractionation degree and the crystallization of some ore minerals (e.g., spodumene and columbite-group minerals), and may be a potential exploration indicator for rare-metal mineralization. [ABSTRACT FROM AUTHOR]

• Akesayi magnetite was occurred mainly during the retrograde skarn and oxide stages. • Akesayi comprises of banded (BO), disseminated (DO), primary (MO-1) and secondary massive (MO-2) magnetite. • Variable magnetite compositions controlled by multiple factors. • Magnetite compositions in skarn deposits are more variable than previously thought. The Akesayi skarn iron (Fe) deposit is hosted by the Huangyangling Group within the Tianshuihai Terrane of the Western Kunlun orogenic belt, Xinjiang, China, and consists of several orebodies that formed along contacts between Miocene syenogranite, diorite porphyry dykes and late Paleozoic carbonate rocks. Manganese-bearing skarn minerals are common within the deposit. The ore-forming process can be divided into five stages: Prograde skarn stage (I), retrograde skarn stage (II), oxide stage (III), quartz-sulfide stage (IV), and carbonate stage (V), with this evolution being typical of Fe skarns. Magnetite, which formed mainly during the retrograde skarn and oxide stages, includes banded (BO), disseminated (DO), and massive (MO) magnetite. Backscattered-electron images indicate that magnetite within the massive ores can be further classified as primary (MO-1) and secondary (MO-2) magnetite. Magnetite within all ore types exhibits a strongly negative correlation between Si and Fe3+ contents, indicating that Si was incorporated into intra-crystalline sites of magnetite by substitution of Si4+ for Fe3+. Positive correlation among Al, Mn, Mg, and Si contents indicate that these elements behaved similarly during magnetite formation. The δ18O V-SMOW values of MO-1 magnetite range from 4.3‰ to 4.7‰, higher than magmatic magnetite (1‰–4‰), while the BO and DO magnetite have lower δ18O V-SMOW values of 1.7‰ to 2.4‰ and 1.8‰ to 2.5‰ respectively. Its anomalous oxygen isotopic composition indicates that most magnetite in the Akesayi Fe deposit precipitated from evolved ore-forming fluids formed by reaction between country rocks and primary magmatic fluids during the early stages of mineralization, with input from meteoric water during the later stages of mineralization. Trace-element patterns indicate that the different types of magnetite share a common source, with variations in the magnetite geochemistry amongst the different ore types of the Akesayi Fe deposit reflecting variations in the extent of fluid-rock interaction, dissolution-reprecipitation, mineral precipitation, temperature, and oxygen fugacity (ƒO 2). The different types of magnetite of the Akesayi skarn Fe deposit form distinguishable populations in (Ca + Al + Mn)-(Ti + V) and (Ni/(Cr + Mn))-(Ti + V) discrimination diagrams, with the range of compositions possibly indicating more variable magnetite compositions in skarn deposits than previously thought. [ABSTRACT FROM AUTHOR]