Hydrogeochemical Characteristics And Water-Rock Interactions Of The Ambient-Temperature Springs And Hot Springs In The Dabie Mountain Area Of Anhui Province

In the process of groundwater circulation,water-rock interactions occur with surrounding rocks in different degrees,and its hydrochemical compositions are often controlled by the compositions of the surrounding rocks.Studies of the hydrochemical characteristics and formation mechanisms of springs are of important significance for the sustainable development,utilization,and protection of groundwater resources.The main purpose of this paper is to reveal the hydrochemical characteristics and formation mechanisms of the 5 ambient-temperature springs and 5 hot springs in the Dabie Mountains of Anhui Province.Field investigation and sampling and detection of the springs were conducted.The ambient-temperature springs include the Chanyuan Village Spring(AH1),Tianzhushan Town Spring(AH3),Millennium Ancient Well(AH4),Xiangchang Town Spring(AH5),and Shuifan Village Spring(AH8),and the hot springs include the Tangwan Hot Spring(AH2),Hot-Spring Town Hot Spring(AH6),Xifei Hot Spring(AH7),East-Tang-Chi Hot Spring(AH11),and West-Tang-Chi Hot Spring(AH12).A rainwater sample(AHYS1)was also collected.Based on the analyses of the basic characteristics of the hydrochemical compositions of the springs in the study area,Gibbs diagram,rock weathering diagram,silicate stability field diagram,main ion proportional coefficient diagram,etc.are used to understand the hydrochemical formation mechanisms of the springs.Reverse hydrogeochemical simulation is carried out with the PHREEQC software,and the actual contribution of dissolution and precipitation of main minerals to groundwater through hydrochemical evolution is further quantitatively studied.The results show that(1)the temperature of the five ambient-temperature springs(mineral spring water)in the Dabie Mountains ranges from 19.2 to 24.6?;the p H values range from 5.9to 6.8,showing weak acidity;and TDS vary from 90 mg/L to 218 mg/L,all of which are freshwater springs(<1 g/L).The temperature of the five hot springs ranges from 46.0 to 64.0?,showing hot water of low to medium temperature.The p H values of the hot springs range from7.6 to 9.1,showing weak alkalinity,and TDS of the hot water ranges from 253 to 1518 mg/L.(2)The ambient-temperature springs in the study area are mainly of HCO₃-Ca·Na and HCO₃-Ca·Mg type,the hot spring water samples are mainly of SO₄-Na and SO₄·HCO₃-Na type,and the rainwater water sample is of HCO₃-Ca type.The contents of Sr and H₂SiO₃in ambient-temperature springs and the hot springs in the study area exceed the limits of drinking natural mineral water in China(Sr content>0.2 mg/L,H₂SiO₃content?25 mg/L).(3)The?²H and?¹⁸O values of the springs shows that all the spring water samples in the Dabie Mountains are of meteoric origin and have a slight ¹⁸O shift.According to the elevation effect of hydrogen and oxygen stable isotopes,it is estimated that the elevation,average temperature,average temperature and average temperature of the hot spring supply area are 100-400 m,11-12?,900-1100 m and 8-9?,respectively.The temperature of the geothermal reservoirs of the hot springs in the study area is estimated to be 80-120?,and the hot water circulation depth is estimated as 1400-1800 m.(4)The chemical compositions of the springs in the study area are mainly controlled by rock weathering.Ca²⁺in the spring water mainly comes from the dissolution of carbonate rocks and gypsum,and a small amount comes from leaching of silicate rocks.Na⁺in the groundwater mainly comes from the widely distributed silicate rocks(such as albite and sodium montmorillonite,etc.)in the study area.The main source of Cl^-is the dissolution of rock salts,the content of SO₄^2-is mainly affected by the dissolution of gypsum,and the content of HCO₃^-is mainly affected by the dissolution of silicate and carbonate minerals.(5)The hot springs in the Dabie Mountains of Anhui Provinc are formed after groundwater receives recharge from infiltration of precipitation in the mountain areas,is heated by heat flow from below during deep circulation,and then interacts with silicate minerals,rock salt,sulfate,and a small number of carbonate minerals in the surrounding rocks,rises along the fault zones or fracture zones,and emerges in the lower parts of valleys and river valleys.Compared to the hot springs,the formation of the ambient-temperature springs undergoes a shallow circulation of groundwater.