Petrogenesis of Mesozoic ore-related granites in the West 509-Daoban Li–Be rare metal deposit, West Kunlun orogenic belt, NW China: Implications for magmatic evolution and associated Li mineralization

Abstract

The West Kunlun orogenic belt (WKOB) is one of the largest economically rare metal metallogenic belts in NW China. The newly discovered West 509-Daoban Li–Be rare metal deposit is located in the eastern part of the WKOB. However, the genetic link between the petrogenesis of ore-related granites and associated Li mineralization has remained equivocal. We conducted a geochemical, isotopic, and geochronological study on the West 509-Daoban two-mica granites and metasedimentary rocks to determine their magma sources, petrogenesis, and tectonic setting and their implications for Li mineralization. Zircon and monazite U–Th–Pb dating revealed that the West 509-Daoban two-mica granites formed at 206–205 Ma. The 509-Daoban two-mica granites, characterized by high-K calc-alkaline to shoshonite series and strongly peraluminous affinity, are classified as S-type granites with initial ⁸⁷Sr/⁸⁶Sr (I_Sr) ratios of 0.71532 ∼ 0.71661, ε_Nd(t) values of −9.96 ∼ −9.52, ε_Hf(t) values of −9.73 ∼ −2.36, and δ⁷Li values of −0.7 ∼ +1.9 ‰, likely resulting from the partial melting of Triassic clay-rich pelitic metasedimentary rocks and subsequent extensive fractional crystallization. Given the regional geological setting, we propose that the 509-Daoban two-mica granites and corresponding Li mineralization formed in an extensional setting controlled by the consumption and closure of the Paleo-Tethys Ocean during the Late Triassic. A comprehensive discriminant analysis suggested that clay-rich pelitic metasediments, an external heat source, and a highly fractionated rare metal-enriched fertile granitic magma were favourable factors for Li mineralization in the WKOB.