An Analysis Of Hydrochemical And Isotopic Characteristics And Geneses Of Some Of The Hot Springs In The Lushui Area Of Yunnan

The Lushui area is located in the northwestern part of Yunnan Province and lies in the Yunnan-Tibet geothermal belt.A lot of hot springs occur in the area where geothermal resources are abundant.The structural deformation is complex in the area and the Nujiang Deep Fault controls the overall structural pattern of the Lushui area.The study area is underlain by the stratigraphic lithology from Proterozoic to Mesozoic and Cenozoic,in addition to the missing Cretaceous and Tertiary of the Mesozoic rocks.The main strata and rocks exposed in the hot springs in the study area are metamorphic rocks of the Gaoligongshan Group,limestone of the Carboniferous,limestone of the Triassic and basalt of the Carboniferous.Some hot springs in Lushui area are investigated,including the Mankouhe hot spring?YLS1-1,YLS1-2,YLS1-3?,the Zhonglongtan hot spring?YLS2?,the Denggeng hot spring?YLS3-1,YLS3-2,YLS3-3,YLS3-4,YLS3-5?,the Mabu hot spring?YLS4-1,YLS4-2?,the Zaotang hot spring?YLS5?and the Laowo hot spring?YLS6?.Studies of the characteristics of the hydrochemistry and isotopes and genetic analyses of the hot springs in the study area,are of great significance for promoting the development and utilization of the local geothermal resources.The temperature of hot springs ranges from 21.5 to 69.6?,TDS from 0.163 to1.505 g/L,pH from 6.0 to 7.7 and Eh from-22 to 126 mV.The main cations in the hot water are Na⁺,Ca²⁺,K⁺and Mg²⁺,and the main anions are HCO₃^-,SO₄^2-and Cl^-.Li,Sr,Rb and Cs are relatively abundant in the hot water.The hydrochemical types of hot water are of HCO₃-Na·Ca,HCO₃-Ca·Mg and HCO₃-Ca·Na types.The F^-concentrations of the hot springs range from 0.134 to 4.5 mg/L,and YLS1-1,YLS1-2,and YLS1-3 of the Mankouhe hot spring and YLS4-2 of the Mabu hot spring can be named as silicic acid water.The H₂SiO₃ concentrations,from 15.8 to 149.0 mg/L,and the content of H₂SiO₃ in YLS1-1,YLS1-2 and YLS1-3 of the Mankouhe hot spring and YLS4-1 and YLS4-2 of the Mabu hot spring has reached the standard of natural mineral water for silicic acid water treatment.The values of?²H and?¹⁸O of the spring samples water indicate that the hot springs in the study area are meteoric in origin.The elevation of the hot spring,s recharge areas is estimated as 1292 to 1863 m,and the temperature of the recharge area,from 3.8 to 9.1?.The geothermal reservoir temperatures are calculated as 49-132?.The formation of the hot spring can be summarized as:thermal groundwater rises up to the land surface after groundwater receives recharge from infiltration of precipitation in the recharge areas,undergoes deep circulation and obtains heat from heat flow.The hot springs are of the deep infiltration-cycle type and are of low to moderate temperature.The hot water mixes with the shallow cold water when it rises to the land surface.The proportion of mixing cold water is about 40-98%,and circulation depth of the hot water ranges from 715 to 3466 m.The contents of Ca²⁺and HCO₃^-in hot water are rich,and the percentages of milliequivalent concentrations of HCO₃^-and Ca²⁺are high.Alcite and aragonite in the hot water are in the saturated state,the contents of CO₂ in water are high and the pCO₂ in the hot water are much higher than atmospheric pCO₂.The hydrochemical and hydrodynamic conditions are favorable to CaCO₃ deposition.Travertines are precipitating near YLS1-1 and YLS1-3 of the Mankouhe hot spring and YLS3-1,YLS3-3 and YLS3-5 of the Denggeng hot spring and YLS4-1 of the Mabu hot spring.