Geochemical characteristics of Triassic granites in the Songpan-Ganzi orogenic belt and its implication for lithium mineralization

Mesozoic granite and granite-pegmatitic lithium deposits are found in the Songpan-Ganzi orogenic belt, on the northeastern margin of the Tibetan Plateau. This paper systematically collected the geochemical data of both Li-bearing and barren granites formed contemporaneously in this belt, from which the magmatic source conditions associated with lithium ore mineralization are revealed. The results indicate that both Li-bearing and barren granites were formed in the Late Triassic within a similar spatial distribution. However, Li-bearing granites are characterized by high silica content ( averaged value = 71. 57% ), elevated lithium content ( > 100 × 10-6 ), and weakly peraluminous properties ( A/CNK = 1. 04 ∼ 1. 63 ); they also exhibit relatively lower values for Ba, Sr, Zr/Hf, and higher Rb and Rb/Sr ratios than barren granite. These Li-bearing granites are classified as highly differentiated S-type peraluminous granites formed under relatively water-poor conditions. Additionally, they show low δ7Li ( - 3‰ ∼ 1‰) and ϵNd (t) (-10 ∼ -8) values, indicating significant contributions from sedimentary components and ancient materials. The barren granites, in contrast, display variable SiO2 content, with an average aluminum saturation index of 1. 04 and relatively high values for Ba, Sr, Zr/ Hf, and Nb/Ta. They are categorized as metaluminous to peraluminous I-type granites formed under water-rich conditions. These granites have high δ7Li ( - 1 ‰ ∼ 5‰) and ϵ Nd(t) (- 7 ∼ 0) values, suggesting contributions from juvenile materials. A comprehensive analysis of the geochemical characteristics of the two types of granites reveals that the Li-bearing ones were derived from ancient crustal materials (ϵ Hr(t) 0. 6), and exhibit a high degree of magmatic differentiation (Zr/Hf © 2024 Science Press. All rights reserved.