Abstract:

Hydrochemical and genetic investigations of hot springs are of great significance for the exploitation of geothermal resources. The Chaluo hot springs are located along a river valley in the Batang County of Sichuan Province. The occurrence of the springs is controlled by the Chaluo-Songduo fault. Triassic limestone, conglomerate and granite of the Yanshan Period occur near the hot spring. There are about twenty spring vents on both sides of the river, some are boiling vents and at least two are geysers. Hot water samples were taken from 10 vents. Due to different rock conditions and cold water mixing status, the temperatures of the two vents in the northeastern region ranged from 45 to 51 ℃, while in the central and western areas the vent temperatures ranged from 77 to 89 ℃. The discharge of the vents ranged from 0.01 to 1.8 L/s. The main chemical characteristics of the hot spring water are: pH=6.1-8.1, TDS=0.39-1.06 g/L, [F^-]=15-22 mg/L, and [H₂SiO₃]= 69-356 mg/L. The major cations in the hot springs are Na⁺, K⁺ and Ca²⁺, and the major anions are {\mathrm{CO}}_3^{2-}, {\mathrm{HCO}}_3^{-}, Cl^- and {\mathrm{SO}}_4^{2-}. Most of the hot water samples are of HCO₃-Na type. The δ²H and δ ¹⁸O of the hot spring water samples indicate that the hot water is meteoric in origin. The recharge altitude was estimated to be 4400-4800 m, and the average temperature of the recharge area is about -10 ℃. The estimated temperature of the geothermal reservoir is 150-200 ℃, and the calculated depth of the thermal ground water is 2810-3480 m. The geothermal waters of the Chaluo hot springs receive recharge from precipitation infiltration. Heated by heat flow during the deep circulation process, the hot waters emerge along the fault zones in the river valley. Thick limestones near the springs are dissolved by groundwater to form cavities, inside which the shallow cold and deep hot waters are mixed and heated to boiling temperature forming geysers.

Key words: hot spring, geyser, hydrochemistry, genesis, Sichuan