The Characteristics Of Isotopes And Hydrogeochemistry For Geothermal Water In The Piedmont Of Qinling Mountain

Tangyu town located in the piedmont of Qinling Mountain is typical recharge area of geothermal water in Guanzhong basin. Its hot springs are very famous. With the rapid development of hot spring tourism in recent years, geothermal water exploitation increased year by year leads to water level drop as deep as 69.16 m on average. Study of the origin and regeneration of Tangyu geothermal water is of great significance to the protection and sustainable development of geothermal resources in the piedmont Qinling Mountain and Guanzhong Basin.This aiticle focuses on the geothermal water in tangyu town and applies isotope and hydrogeochemistry methods combined with the conditions of geothermal geological structure to discuss the origin and occurrence characteristics of geothermal water, to evaluate the regeneration and quality of geothermal water, and to compare with geothermal water of Dongda and Xi’an depression.Geothermal water of Tangyu belongs to SO4-Na type, and is mainly influenced by mineral dissolution and cold water mixing in the process of formation; the average mixed quantity of cold water is 42.2%. Element proportional coefficient shows the structure in the study area is more developed and the environment of geothermal water is relative open. The interaction between water and rock is imbalance indicates that geothermal water may mix with cold water or mineral is still dissolving. The reservoir temperature is 70℃~90℃estimated by chalcedony geothermometer and multi-mineral balance method. The hydrothermal circulation depth is between 1036 m and 2528 m.Hydrogen and oxygen stable isotopic evidences indicate that geothermal water in the study area is mainly recharged by precipitation from the south Qinling Mountain with1550~1811m high. δ18O of geothermal water is very close and did not present oxygen drift phenomenon indicate that geothermal water is mainly affected by fault. 3H of geothermal water of different depth in the study area is from 2.5 TU to 8.9TU,indicating that geothermal water is mixed with cold water and water conducted by fault is the dominant factor. The average residence time of tritium model obtained is 66 a, indicating that the geothermal water’s renewable capacity is good. Helium isotope results show that geothermal water is mainly affected by crust and atmosphere, and influence degree of crust is dominated. This indicates that only small amount of deep mantle source material mixes to geothermal water. The comparison results of geothermal water from Tangyu, Dongda and Xi’an depression show that the genetic types of geothermal water are open-mixed type, semi-open-mixed type, semi-closed ancient infiltrating water, respectively. The renewable capacities of them are as follow: Tangyu>Dongda >Xi’an depression.Geothermal water in the study area is mainly medical mineral water which is rich in fluorine and silicon. It has high medicinal value and is very precious natural resources. Therefore we should pay attention to strengthen the implementation of cascade development and comprehensive utilization of geothermal water, and should carry out geothermal water reinjection as soon as possible in the process of using geothermal water. We should place equal stress on development and protection, so as to provide powerful guarantee the sustainable development and utilization of geothermal resources.