The newly discovered Li-Rb-Cs mineralization at the Bu Me Sn-W greisen deposit within the Truong Son orogenic belt in Vietnam

Abstract

The Truong Son Orogenic Belt (TSOB) is one of the most significant orogenic belts within the Indochina block. The Bu Me deposit is located within this belt and has historically been significant for the mining of Sn-W metals. Recently, newly discovered metal assemblages at the Bu Me Sn-W deposit has also shown significant lithium–rubidium–cesium (Li-Rb-Cs) mineralization. To constrain the timing and petrogenesis of the magma and Sn-W-Li-Cs-Rb mineralized, a systematic study involving U–Pb ages dating, as well as whole-rock and minerals chemical analyses, was conducted for the Bu Me deposit. U-Pb zircon geochronology of biotite granite, leucogranite, and granite porphyry indicates that these rocks were emplaced at 29.3 ± 0.2 Ma, 29.2 ± 0.4 Ma, and 28.6 ± 0.3 Ma, respectively. The granites exhibit moderate to high SiO₂ content (71.91––74.08 wt%), high total alkali, and a peraluminous signature, classifying them as A2-type granites. Leucogranites and granite porphyries are notably enriched in lithium, with concentrations reaching up to 1400 ppm. Based on detailed observations and characterization of textures and mineral assemblages, three principal mineralization stages have been identified: (1) Early Li-Rb-Ca ± Nb quartz-topaz-mica stage, (2) Sn-W ± sulfides quartz-topaz greisen stage, and (3) Quartz vein stage. Detailed EPMA analyses of minerals from these stages suggest that Li-Rb-Cs-Sn-W mineralization is primarily hosted in minerals such as siderophyllite, protolithionite, cassiterite, and wolframite. These findings demonstrate the significant economic potential of rare metal (Li-Rb-Cs-Sn-W) mineralization in the Truong Son Orogenic Belt.