Geochemical Constraints on the Origin and Evolution of Spring Waters in the Changdu‐Lanping‐Simao Basin,Southwestern China

Chemical and isotopic data were measured for 51 leached brine springs in the Changdu‐Lanping‐Simao Basin (CD‐LP‐SM), China. The predominance of Cl and Na, saturation indices of carbonate minerals, and Na/Cl and Ca/SO₄ ratios of ～1 suggest that halite, sulphate, and carbonate are the solute sources. Integration of geochemical, δ¹⁸O, and δD values suggests that springs are mainly derived from meteoric water, ice‐snow melt, and water‐rock interactions. B concentrations range from 0.18 to 11.9 mg/L, with δ¹¹B values of –4.37‰ to +32.39‰, indicating a terrestrial source. The δ¹¹B‐B relationships suggest B sources of crustal origin (marine carbonates with minor crust‐derived volcanics); we did not identify a marine or deep mantle origin. The δ¹¹B values of saline springs (+4.61‰ to +32.39‰) exceed those of hot (–4.37‰ to +4.53‰) and cold (–3.47‰ to +14.84‰) springs; this has contributed to strong water‐rock interactions and strong saturation of dissolved carbonates. Conversely, the global geothermal δ¹¹B‐Cl/B relationship suggests mixing of marine and non‐marine sources. The δ¹¹B‐Cl/B relationships of the CD‐LP‐SM are similar to those of the Tibet geothermal belt and the Nangqen Basin, indicating the same B origin. These differ from thermal waters controlled by magmatic fluids and seawater, suggesting that B in CD‐LP‐SM springs has a crustal origin.