A Study Of The Hydrochemistry And Genesis Of Hot Springs In The Mangshi-ruili Area Of Yunnan

The total number of hot springs in Yunnan Province exceeds 1000,and there are many hot springs in the study area from Mangshi to Ruili in the western Yunnan,some of which are high-temperature hot springs.Studies by the hydrochemical characteristics and causes of hot springs is of great significance for enriching the understanding of the subsurface groundwater cycle,and can also provide an important basis for the development and utilization of local geothermal resources.In the western Yunnan,the structure is complex,and the famous Longling-Ruili deep fault runs north-east through the Ruili Basin.The faults formed from the Caledonian period to the present,and they all exhibit multi-stage superposition activities,controlling the Paleozoic and Mesozoic deposition.It is also the main controlling fault for the formation and evolution of the basin.At the end of the Yanshan Movement and the Himalayan period,the inheritance of the fault was obvious,and beaded basins such as Mangshi,Zhefang,and Ruili Basins were formed along the fault.In this paper,15 hot springs in the Mangshi-Ruili area in Yunnan were investigated along the Longling-Ruili fault,20 water samples were collected,and their hydrochemical and isotopic compositions were detected and analyzed.The strata or rocks exposed near the hot springs are the boundary zone of the Quaternary sediments in the basins or the strata at the edge of the basins.The YR19,which the water temperature reaches103?is a high temperature hot spring,and the temperature of other water samples ranges from 37.5 to 72.8?,which is low-medium temperature and medium temperature geothermal water.The hydrochemical types of the hot springs in the study area are mainly of HCO₃-Ca and HCO₃-Na types,and a few are SO₄-Na type.The TDS of the water samples ranges from 228 to 1812 mg/L,which is fresh water or brackish water.pH of the hot springs is 6-8.4;Eh of YR3,YR8 and YR17 to YR19 is less than 0 mV,and Eh of the remaining water samples is 14-138 mV.The study of the major ions,minor ions,etc.found that the thermal water in the study area was mainly leached during underground circulation,as well as water-rock interactions such as cation alternation;Trace components such as Li and Sr and characteristic components such as H₂SiO₃and F in the water sample reached 0.663-2099?g/L,31.8-862?g/L,18.8-159 mg/L,and 0.095-18.5 mg/L,respectively.The?²H-?¹⁸O data indicate that the thermal groundwater is originates from atmospheric precipitation and the elevation of the recharge area is estimated as about 685-1374 m,and the temperature of the recharge area is about 7-14?;²²⁶Ra-²²²Rn radioisotope is used to estimate the age of the hot water as about 2-13 years based on the decay principle.SiO₂ geothermometers and multi-mineral equilibrium graphic method are used to estimate the temperature of the reservious in the study area as about 43-168?.The silicon enthalpy equation method was used to calculate that the average cold water samples exceeded 50%and the depth of the hot water circulation is estimated to be about 465-3262 m.The formation of hot springs in the study area is summarized as:atmospheric precipitation infiltrates the groundwater in the mountain areas and groundwater flow to the basins.Groundwater undergoes deep circulation and obtains heat by heat flow heating from belows,rises when it encounters fissures generated by fault zones and intrusions,and approaches the land surface after mixed with shallow cold water,and finally emerges on the surface or exposed with a geothermal well,and some hot springs occur on the land surface in the Quaternary sediments,which is a fracture-deep cycle geothermal system.