GEOCHEMICAL GENESIS OF THE RUBU HOT SPRING IN DAOCHENG, THE WESTERN SICHUAN PLATEAU

A hydro geochemical analysis of hot springs (265 groups) in the western Sichuan Plateau shows that there are a class of low-Cl, low-TDS, medium-high temperature hot springs in the western Sichuan Plateau. In this study, we based on geologic survey and employed hydrochemical and isotopic data to analysis this kind of hot springs geochemical origin with Rubu hot spring take as an example. The results show that: (1)The temperature of the Rubu hot spring is as high as 68 °C, the flow rate is 81L/s, and it is exposed in the granite fissure, belong with the Ganzi-Litang deep fault. It is alkaline (pH is 9.4), the salinity is 156.4~237.7mg/l, and the Cl^-content is 2.13~5.32mg/l. The content of CO₃^2- and H₂SiO₃ in the hot spring is high, and the content of other trace components is low.(2)The isotopic value of Rubu hot spring is δD-160.3~-145.6‰, δ¹⁸O-21.98~-20.78‰, which falls near the atmospheric precipitation line of the Chinese southwest region, revealing that the recharge source of hot spring is atmospheric precipitation. The seasonal differences of δD and δ¹⁸O are obvious and in the summer the hot spring is relatively rich in light isotope, which is opposite to the seasonal effect of atmospheric precipitation isotope.(3)The temperature of geothermal reservoir of Rubu hot spring is 122.34~186.7 °C, revealing the high temperature heat source in the hot spring formation area. (4)Geochemical causes of the formation of the Rubu hot spring is that the development of heat storage is controlled by regional deep faults. The heat source is shallow and the temperature is high. The hot springs are formed in granite, and there is no halide in the geological environment. The hot spring formation process has a short circulation path, short residence time, fast heating, and small interaction between water and rock. The existence of such hot springs reveals a type of geothermal heat with deep fault heat control, high temperature heat storage, and strong underground runoff. This type of hot spring development area is a favorable area for the development of geothermal resources.

Key words：Hot springs; Hydro geochemistry; Isotope; Geothermal reservoir; Geothermal system