Abstract <p>Helium is an indispensable and scarce strategic resource. Both research and exploration targeting geothermal-associated helium resources in geothermal fields on both sides of the Cangdong Fault, China remain entirely lacking. To investigate the helium origin, source rocks, phase partitioning, as well as identify helium accumulations, the research team collected geothermal gases and water samples from 25 sampling sites across different geothermal reservoirs in the study area. The collected samples were subjected to comprehensive geochemical analyses including: helium isotope composition, major gas composition, CH₄ and CO₂ carbon isotope, and hydrochemical parameters. The test results show that the helium in the study area is mainly of crustal origin; the average proportion of mantle-derived helium of sandstone geothermal reservoirs, bedrock geothermal reservoirs, and mixed geothermal reservoirs are: 2.78, 4.63, and 5.89%, respectively; N₂ accounts for the largest proportion of geothermal gases composition; CH₄ is coal-type or oil-type. Quantitative calculations revealed that granite and bauxite constitute the predominant helium source rocks, with free gas phase helium being hosted within geothermal reservoirs. The detection of helium-bearing horizons within bedrock geothermal reservoirs and adjacent regions surrounding sampling site D81 constitutes a critical factor for successful helium exploration.</p>