Lithium cycling in the source-to-sink system of a typical salt lake in the Western Kunlun: multi-isotopic constraints and end-member quantification

The Western Kunlun region of the Qinghai-Xizang Plateau is a premier lithium province characterized by the coexistence of super-large pegmatite and brine-type lithium deposits. This spatial association provides a unique laboratory to investigate the lithium cycle from the lithosphere to the hydrosphere. This study utilizes hydrochemistry and a multi-isotope (δ 7 Li、δ 11 B、 87 Sr/ 86 Sr) framework across 50 water samples from the Tianshuihai-Kushui Lake basin to quantify lithium sources and enrichment mechanisms. Results identify three End-members with distinct geochemical fingerprints: springs in the northwest of Kushui Lake (End‑member A), Tianshuihai water system (End‑member B), and Western Kunlun Mountain Rivers (End‑member C). The water–rock interaction during the upwelling of deep fluids is the key process for lithium enrichment in Kushui Lake. Sr isotope binary‑mixing modelling yields a fluid‑volume mixing fraction of 88.6 % for deep‑fluid‑dominated End‑member A; mass‑balance calculation further reveals End‑member A supplies 71.0 % of total dissolved Sr mass and 64.2 % of lithium mass to the system. Supergene lithium enrichment follows a three-stage evolution: evaporation-driven linear accumulation, an adsorption-buffering phase, and terminal-basin selective enrichment. Based on these findings, this study establishes a “mobilization-migration-enrichment” lithium cycle model. This model represents a transition from “endogenous enrichment” in the lithosphere to “exogenous ore formation” in the hydrosphere, this coupled genetic model is likely a common phenomenon in Li-rich salt lakes across the Kunlun orogenic belt on the Qinghai-Xizang Plateau. These insights offer a novel perspective for mineral exploration and enhance our understanding of lithium metallogeny in analogous geological settings worldwide.