Characteristics of ore-forming fluids of Li-Be deposits and its application to mineral exploration in Middle Altun Region, Xinjiang

Abstract

The Middle Altun region, located at the northern edge of the Tibetan Plateau, constitutes one of China’s vital polymetallic metallogenic belts. Recent discoveries of large to medium-sized pegmatite-type Li-Be deposits, including the Tugeman, South Washixia, Shaliangxi, and Huanglongling sites, have revealed a prolific ∼ 400 km long Li-Be rare metal metallogenic belt. Current research primarily concentrates on the mineralization processes of individual deposits. This study integrates systematic sampling of ore-bearing pegmatite veins from various deposits, utilizing microthermometric analysis of fluid inclusions, laser Raman spectroscopy, and in-situ LA-ICP-MS compositional analysis of quartz in the pegmatites. The aim is to elucidate the temperature–pressure conditions, elemental enrichment characteristics, fluid evolution processes, and mechanisms of metallogenic element precipitation. The results indicate that the ore-forming fluids consist of a medium-temperature, low-salinity H₂O-NaCl-CO₂ system that contains sulfate, carbonate, and chrysotile minerals. LA-ICP-MS in-situ analysis of quartz suggests that the pegmatites in the Tugeman area likely originated from metamorphic-anatectic processes, while those in the West Shaliangxi region are more closely linked to highly fractionated granitic magmatism. The concentrations of elements such as Al, Li, Ti, and Ge in quartz serve as potential indicators for assessing the mineralization potential of pegmatites. Combined analyses of Ti-in-quartz thermometry and other geological evidence suggest that Li-Be mineralization in the Middle Altun region may be structurally influenced by magmatic domes. The southern Tugeman area, located at the dome’s apex, has undergone significant erosion, exposing high-temperature vein systems from the lower orebody. Conversely, the main Tugeman area exhibits limited mineralization, somewhat distal from the dome summit. In contrast, the Shaliangxi and South Washixia regions, which are situated farther from the magmatic domes, show lower degrees of erosion and well-preserved ore bodies, making them promising targets for mineral exploration.