A Study Of The Hydrochemical Cahracteristics And Geneses Of The Hot Springs In The Midu-Xiangyun Area Of Yunnan Province

The Midu-Xiangyun area of Yunnan Province is located at the boundary line between the two major first-class structural units of the Yangtz-Zhundi Platform and the Tanggula-Ludu-Lanping-Sioma fold system.It is located near the Chenghai and Honghe faults.Hot springs with different temperatures and pH exist in this area.The research on the hydrochemistry and genesis of the hot springs can help to enrich the understanding of groundwater circulation and have a certain guiding reference in the development of local geothermal resources.This research examines 11 hot springs,and a total of 17 water samples are studied.They are the Jiashidong south hot spring?YMD1-1?,the Jiashidong north hot spring?YMD2-1?,the Baizongqi hot spring?YMD3-1?,the Gaoqin hot spring?YMD4-1?and the Shizui Hot Spring?YMD5-1?which were investigated in 2015.In2017,we collected the water samples from Jiashidong south hot spring?YMD1-2?,Jiashidong north hot spring?YMD2-2?,Baizongqi hot spring?YMD3-2?,Gaoqin hot spring?YMD4-2?,Shizui hot spring?YMD5-2?,Jianba hot spring?YMD6?,Reshuitang hot spring?YMD7?,Zulai hot spring?YMD8?,Tangzi hot Spring?YMD9?,Wangjiareshuijing hot spring?YMD10-1?,Julong hot spring?YMD10-2?and Mafang hot spring?YXY2?.The temperature of the hot spring in the study area ranges from 32.1 to 66.9°C,the pH,from 6.6 to 10.8,and the Eh,from-60 to 115 mV,indicating that some of the geothermal waters are in a reducing environment and others are in an oxidizing environment.The F^-enrichment of the hot springs in the study area may be related to pH and is generally negatively correlated to pH.The TDS ranges from 314 to 2826mg/L.YMD1-2,YMD2-2,YMD3-3,YMD4-2,YMD5-2 and YMD7 are fresh water,and YMD6,YMD8,YMD9,YMD10-1,YMD10-2 and YXY2 are brackish water.The hot springs in the study area is of meteoric origin.The temperature in the recharge area is about-2-4.22°C,and the recharge altitude is about 1910-2807 m.The age of thermal groundwater is estimated to be about 81-794 a with the²²⁶Ra-²²²Rn method.The hot springs belong to the deep-circulation springs and the circulation depth of the geothermal systems ranges from 2014 to 3174m.Through the muti-mineral dissolution equilibrium curve,silica geothermometers,cationic geothermometer method,the temperatures of the geothermal reservoirs are calculated as about 64-93?,which belongs to the medium-low temperature geothermal systems.The main hydrochemical types of the hot springs in the study area are of HCO₃-Na and SO₄-Ca type.The alkalinity of the Wangjiazhuang hot spring may be affected by₂,and the smaller₂,the stronger the basicity.The genetic models of the hot springs in the study area show the recharge of precipitation in the surrounding mountainous areas.The groundwater of different water hydrochemical types are formed after long-term circulation and dissolution in different rock layers.During the deep circulation,groundwater obtains heat from heat flow,rises along the fault zones or the fractured zones rises and emerges in the form of hot springs of different temperatures.