Geochronology and tectonic setting of the giant Guobaoshan Rb deposit, Central Tianshan, NW China

Abstract

Triassic magmatism and associated rare metal deposits are increasingly being identified within the Central Tianshan Massif in NW China. A lack of geochronological studies on these mineralized plutons, however, has limited our understanding of their origins and tectonic setting. The Guobaoshan pluton, situated in the eastern segment of Central Tianshan Massif, contains ca. 281,000 tons of Rb2O resource and may be the largest Rb deposit in the world. The pluton exhibits a gradual lithological zonation from muscovite granite to amazonite(-bearing) muscovite granite from west to east; pegmatite veins of amazonite occur within the pluton and around its periphery. In this contribution, LA–ICP–MS U–Pb age dating and trace-element analysis have been conducted on zircon, monazite, cassiterite, and columbite to address the timing of magmatism and Rb mineralization, and the processes that generated the mineralization. Internal textures and trace-element contents suggest that these minerals crystallized during the magmatic–hydrothermal transition stage over a period of ca. 10 million yeas from the Early to Middle Triassic (240–249 Ma). Combined with available data, it is suggested that the Triassic was an important period for granitic magmatism and rare metal metallogeny in the Central Tianshan Massif, which may be a response to this region being dominated by an intra-continental extensional setting during this time period.