Radon‐222 as an Effective Tracer to Distinguish Groundwater Circulation Patterns in the Deep Fault‐Controlled Geothermal System

Abstract Groundwater flow regulated by deep faults remains challenging to trace due to structural complexity. This study applies the noble gas tracer 222 Rn combined with hydrochemistry and stable isotopes (δ 2 H, δ 18 O) to distinguish circulation patterns of geothermal springs along a major fault in the Tibetan Plateau. 222 Rn activities in groundwater vary broadly (10 2 –10 5 Bq m −3 ) influenced by lithological heterogeneity, fault proximity, and circulation patterns. As a sensitive tracer of hydrological dynamics beyond conventional isotopic resolution, elevated 222 Rn accumulates in deep‐sourced or meteoric‐recharged groundwater, whereas depressed activities indicate degassing induced by water mixing. Integrated with mixing ratios and spring temperature, 222 Rn can effectively distinguish deep‐, mixing‐, and shallow‐dominated circulation regimes of geothermal groundwater. The efficiency of 222 Rn measurement provides a practical advantage in resolving intricate fault‐controlled flow paths. This framework presents a transferable tool for assessing geothermal resources in similar tectonic settings worldwide.