A Study Of The Characteristics And Genesis Of The Hot Springs And Salty Springs In The Xichang Area Of Sichuan

Spring is a natural outcrop of groundwater,which can usually reveal the hydrogeochemical and geothermal processes of groundwater.In this paper,the hydrochemical characteristics and genesis of hot springs and salt springs in the Xichang area of Sichuan province are studied by the hydrogeochemical method and comprehensive analysis method,which is not only of profound significance to understand the material migration in groundwater circulation and the development and utilization of geothermal resources,but also provide a information on prospecting for the exploration of potash resources in China.The Xichang area is located in the north of the Kangdian axis,with complex landform,high mountains,high northwest and low southeast terrain,frequent crustal activities,crisscross fault zones,and numerous springs,and is situated at the tropical edge of Yunnan-Tibet terrestrial tropics.The strata in the study area are range in age from Sinian to quaternary,and is mainly composed of clastic rock,carbonate rock,dolomite,and a large number of granite.The water samples in the study area were divided into Yanyuan county salty spring?Xiaoyanjing salty spring S1,Yanshuiwan salty spring S2,Zhonghecun spring S3,Yanjingzhen brine S4,Baiwuzhen salty spring S5,Heiyantang salty spring S6,Heiyantang spring S7?and other hot springs,including Gonggashentang S8,Caoke spring S9,Jinhe spring S10,Hexi spring S11,Libinhuayuan spring?S12,S13?,Chuanxing spring S14,Zhuhe spring?S15,S16?,Qinglin spring S17 and Xide spring?S18,S19,S20?.The characteristics of hydrochemistry and isotopes are analyzed,and the formation mechanisms are summarized.The stable hydrogen and oxygen isotope of the water samples indicate that the springs are of meteoric origin,the temperature in the recharge areas ranges from-4to 5?,and the elevation of the recharge areas from 2207 to 3069 m.The groundwater age calculated by ²²⁶Ra-²²²Rn method is from 5 to 1153 years,the calculation result is too large,which may be caused by measurement errors.Nine samples of springs and brine water?S1?S7,BJ,W02?in Yanyuan county can be divided into the brine samples with TDS of 311.69 g/L and Cl-Na type,salty springs with TDS of 55.77?89.43 g/L and Cl-Na type,brackish springs with TDS of 1.17 g/L and Cl-Na type and fresh springs with TDS of 0.26?0.56 g/L and mainly HCO₃-Ca and HCO₃·SO₄-Ca·Mg type.The characteristic ion ratios show that they are of lixiviation type and have no indications of potash prospecting.The salinity of the springs is mainly derived from the incongruent dissolution of minerals such as halite,gypsum,calcite and dolomite.The formation mechanisms of salty springs are summarized as follows:after receiving infiltration of precipitation in the mountain areas,groundwater undergoes shallow and deep circulations,obtains increasing TDS as a result of the incongruent dissolution of salt-bearing strata or salt mines,and gather in lower topography to emerge to the land surface in the form of springs.The temperature of hot spring?S8?S20?ranges from 24.1 to 62.4?,TDS from153 to 7070 mg/L,and pH value from 6.4 to 9.6.The hot springs are mainly of HCO₃·SO₄-Ca·Na type,HCO₃-Na type and SO₄-Na type.According to temperature and TDS,hot spring can be divided into medium and low temperature brackish springs?S12,S14,S17,S19,S12?,medium and low temperature fresh water springs?S8,S9,S10,S11,S13,S15,S16,S20?and normal temperature fresh water springs?S18?.The circulation depth of the hot spring is estimated from 816 to 3233 m,the geothermal storage temperatures of the hot springs range from 42 to 119?,and the mixture ratio of cold water is from 79%to 92%.The formation mechanisms of the hot spring can be summarized as follows:after receiving infiltration of precipitation in the mountain areas,the groundwater undergoes deep circulation and the geothermal heating,collects in the fault zones due to the resistance of the faults,and it eventually emerge to the lower ground surface to form a spring,or a spring out of the ground surface along a channel formed by a fault.