Hydrogeochemistry Of Hot Springs In Yichun Area Of Jiangxi Province

Yichun area is rich in geothermal resources,which is one of the typical mid-low temperature geothermal areas of Jiangxi province.The study of hydrogeochemical characteristics of hot springs in this area is of great significance to its sustainable development and utilization of geothermal resources.The author selects 10 hot springs in Yichun area for the study.Through field investigation and sample analysis,the chemical composition and isotopic characteristics and the evaluation of heat storage temperature of hot spring resources in this area are discussed using geothermal geochemistry,Aquachem and Phreeqc software.The studies of water chemistry showed that:the hot springs in Yichun area are neutral or weak alkaline.The water chemistry types of hot springs in that area mainly include HCO₃-Na type and HCO₃-Ca type(distributed in the vicinity of major faults in southern Yichun,SO₄-HCO₃-Na type(exposed in the northern region of the magmatite.Most hot springs have circulated for long time,and experienced high degrees of metamorphism.The results of gas component analysis showed that the hot springs in the study area belong to the nitrogen type hot springs.Isotopic compositions of hydrogen,oxygen and strontium indicated that the hot water is of meteoric origin.The geothermal water was formed by Water-rock interactions.The hot springs are formed by deep circulation of precipitation through the granite and heated by geoheat from the depth.The recharge altitude of the hot springs of HCO₃-Na type and SO₄-HCO₃-Na type estimate about 900-1700m,and the recharge altitude of the hot springs of HCO₃-Ca type is lower,which is about 200-700m.The ¹⁴C age of SO₄-HCO₃-Na hot springs exposed to magmatic rocks is greater than 6000a,much higher than that?about2000a?of HCO₃-Na type distributed near faults.This indicated that the hot water recharge path in magmatic rocks is relatively long and groundwater runoff is slow.By comparing results of severa kinds of geothermometer,which indicated that the geothermal reservoir temperature calculated by quartz and chalcedony is more in line with the physical truth of underground hot water in deep reservoir.The temperature of the geothermal reservoir of HCO₃-Na type hot springs are about 80-100?.The temperature of the geothermal reservoir of HCO₃-Ca type hot springs are about 40-60?.The temperature of the geothermal reservoir of SO₄-HCO₃-Na type hot springs are about 90-120?.The circulation depth of the hot water in HCO₃-Na type and SO₄-HCO₃-Na type are estimated about 2000m,and that of HCO₃-Ca type is lower,which is about 1000m.The heavy metal concentrations of some geothermal waters in Yichun area are higher than those of drinking water standard.The contents of F and SiO₂ in some hot springs are high,which have medical value.We should pay attention to the rational utilization of geothermal waters and the environmental protection in the hot spring area.