Spatial Distribution and Enrichment Mechanisms of Major Trace Elements in Budonquan Salt Lake from Hoh Xil Basin, Northern Tibetan Plateau

Salt lakes on the Tibetan Plateau (TP) are vital repositories of China’s strategic mineral resources, including boron and lithium. The Budongquan Salt Lake (BDQSL) in eastern Hoh Xil Basin (HXB) represents a hypersaline system with combined geothermal recharge and intense evaporation, yet its hydrochemical characteristics and B-Li enrichment mechanisms remain poorly understood. Through systematic hydrochemical and isotopic analysis (δD, δ18O, d-excess) of 69 surface samples, 14 depth-stratified profiles, and 131 regional water samples, we reveal that: (1) BDQSL exhibits extremely saline Na-Cl brines (TDS: 192,700–220,700 mg/L) significantly enriched in B and Li (45–54 mg/L), with overall spatial homogeneity and complete vertical mixing; (2) B and Li demonstrate strong correlation (R2 = 0.95), controlled by coupled hydrothermal input, water–rock interaction, and evaporative concentration, with hydrothermal delivery as the predominant source; (3) depleted isotopic signatures (δ18O = −1.4‰, d-excess = −5‰) confirm intense evaporation, while upstream cascade connectivity and climate warming drive lake expansion and brine dilution, indicating transition toward lower salinity; (4) a distinctive hydrothermal–evaporative composite mineralization model differentiates BDQSL from regional mono-evaporative systems. This study elucidates B-Li enrichment mechanisms in hydrothermally active plateau salt lakes, providing geochemical constraints for resource assessment and predictive frameworks for evaluating mineral evolution under climate change.