| Nowadays, the non-renewable energy sources such as oil, coal and natural gas are being exhausted, therefore, the exploitation of new energy and renewable energy is a premise for sustainable development of world economy. The exploitation of shallow geothermal energy, a new renewable clean energy and a special mineral resources, is very important for building a Resource-conserving and Environment-friendly Society, ensuring national energy safety, adjusting the existing energy structure, and promoting the achievement of the goals of energy saving and green house gas mitigation. Chongqing City, the only municipality in southwestern China, is rich in shallow geothermal energy, which is mostly distributed in the area of eastern Sichuan parallel Ridge and Valley. Its exploitation currently is mainly for the Spa leisure tourism, so Chongqing is named as "A Spa city of China" in2011, and is expected to be "A Spa city in the world" in2012. So, it is very important to carry out the researches on the origin of the geothermal water, water-rock interaction, ions'source and migration of the shallow geothermal energy. In this study, the underground thermal water (including natural outcrops and manual drilling) in the area of eastern Sichuan parallel Ridge and Valley were measured and sampled in fields, and then analyzed in the Laboratory. And a conceptual model of recharge, streamflow and discharge of the thermal water in Carbonate Reservoir in Triassic was established through the study on the recharge regional, runoff process and matter resources of the thermal water in Carbonate Reservoir in Triassic in Chongqing.Shallow geothermal water in Chongqing City is the underground thermal water of Triassic Carbonate reservoir. Its geological features are shown that the reservoir bed is located in the carbonate rocks in Jialingjiang formation in Lower Triassic, covered by the sandstone and shale in Xujiahe formation in Upper Triassic as the cap rock, and the Clastic rocks with carbonate rocks in Feixianguan formation in Lower Triassic as the bottom rock. The best reservoir structure made the eastern Sichuan parallel Ridge and Valley a huge Heat reservoir with hot springs found in many gorges.It was found that the hydrochemical properties of most of the underground thermal waters are the similar featured by neutral pH, high Electrical Conductivity(EC) and temperature ranging among30℃to50℃, which were identified to low-medium temperature shallow geothermal water. The major cations of these thermal water are Ca2+and Mg2+and the major anions are SO42-and HCO3-, so the chemical types of theses underground thermal water are SO4-Ca (Mg) type, which is a kind of typical Triassic Carbonate Reservoir thermal water. The concentration of SO42-and Ca2+,Mg2+varies slightly by time but significantly by the space. The concentration of SO42-and Ca2+,Mg2+in two springs in Qingmuguan are lower than those in others because of the outcroping geology environment. The calcite and dolomite in the underground thermal water are under the critical state of saturated to unsaturated, and there is no obvious phenomenon of travertine deposition. Na-K-Mg-Ca diagram shows the thermal water in Carbonate Reservoir in Triassic in Chongqing haven't reach the water-rock equilibrium, and the sources of the matters in thermal water are basically the same in each season.The value of δD about the thermal water in Carbonate Reservoir in Triassic in Chongqing is between-63.08%o and-48.62%o, while the value of δ18O varies from-9.5%o to-6.47%o. The linear relationship between δD (‰) and δ18O (‰) is δD=(7.666±0.283) δ18O+(6.88±2.35) δD, which is mostly closed to global meteoric water line, therefore, it is confirmed that the source of the thermal water in Carbonate Reservoir in Triassic in Chongqing is from meteoric water. As the difference in temperature between the thermal water and external environment is small, there is no apparent drift of the δ18O in water-rock interaction. Therefore, the value of d is about d=0‰and d=20‰, mainly concentrating in the vicinity of d=10‰.The value of δ18O about the thermal water in Carbonate Reservoir in Triassic in Chongqing is between-9.5%o and-6.47%o and the recharging area of this thermal water is at an altitude of460m～1605m. Taking into account together with the Yangzi River and Jialing River which control the underground water circulation in the anticlines in eastern Sichuan parallel Ridge and Valley, it can be realized that the recharging area of the thermal water are the karst areas on the north of the eastern Sichuan parallel Ridge and Valley and the Karst valley in eastern Sichuan parallel Ridge and Valley, but mostly is the karst area on the north.A high-resolution automatic detection instrument (CDTP) was used to monitor the pH, temperature, EC and runoff of rain gauge. A lot of data were collected. The data in2009and2010showed that the pH, temperature, EC and runoff in outcropped springs were stable, but the runoff of the spring is larger in dry season and smaller in rainy season. Research on extreme geological events is a common way to study underground thermal water. The hydrocheimcal features of the north spring (BWQ) were measured during the earthquake in Sichuan on May12,2008. The results showed that fissures in the cap rock and reservoir bed turned to be more after the earthquake and the allogenic water filtered into the reservoir bed and lead to the change of the temperature, water quantity and chemical characteristics of BWQ.The most striking feature of the thermal water in Carbonate Reservoir in Triassic in Chongqing is high concentration of SO42-and low concentration of HCO3-, and it is the key point for studying the water-rock interaction. There is a negative correlation between the concentration of HCO3-and that of Ca, HCO3-, Mg and of Sr; the concentration of HCO3-are also in strong negative correlation with SO42-. It can be realized that the concentration of Ca, Mg, Sr and SO42-in thermal water restrict the concentration of HCO3-in thermal water. The values of δ13C.DIC in the thermal water are between-9.73‰and-3.12‰, which means that the source of CO2joined in the water-rock interaction are from both biological and mantle sources. The ratio of the value of3He/4He about the thermal water and the value of3He/He about air is bigger than1, which also means that there are some matters from mantle. It was calculated that of the total CO2that were active in the water-rock interaction,25.2%～68.73%is from the soil and31.27%～74.8%from the mantle.The concentration of SO42-in thermal water in the Carbonate Reservoir in Triassic in Chongqing is very high and the value of δ34S-SO42-is very heavy which is about29.70‰～34.32‰. The reason for the high concentration of the SO42-is the solution of the gypsum in the carbonate rock in the study area. And the reason for the heavy value of δ34S-SO42-is because of the salt lake in the second period of Jialingling formation in Lower Triassic. Evaporate rocks were formed with strong evaporation, and the sulfate touched with organic matter, decomposing to H2S and CO2under the reducing action of the Anaerobic microorganisms. That is the reducing action of the bacterial made the oxygen get out of the sulfate-ion and release the H2S with more32S than sulfate. This process enriched the34S in the sulfate and made the value of δ34S-SO42-heavy.The Value of87Sr/86Sr and δ13C in thermal water in Carbonate Reservoir in Triassic in Chongqing is light and the value of δ34S is heavy. The high value of δ34S means the source of SO42-is the gypsum in the second section of Jialingjiang formation in lower Triassic. Due to the surface runoff and sandstone water filter into cracks in cap rock and mixed with thermal water, resulting in seasonal differences of the value of isotopes in underground thermal water. The value of87Sr/86Sr means the source of Sr is carbonate rock. The value of δ34S is lighter in rain season and the value of δ13C is heavier in rain season.A conceptual model of recharge, streamflow and discharge of the thermal water in Carbonate Reservoir in Triassic was established through the study on the recharge regional, runoff process and matter resources of the thermal water in Carbonate Reservoir in Triassic in Chongqing. On the area of the karst area on the north of the eastern Sichuan parallel Ridge and Valley and the karst valley in eastern Sichuan parallel Ridge and Valley that at the altitude of460m to1605m, the precipitation and surface runoff infiltrate into the a Carbonate Reservoir system with the carbonate reservoir bed, sandstone and shale cap rock, and the clastic rocks as carbonate rocks bottom. Water in this aquifer has experienced long flow paths, constantly absorbing the heat from the surrounding rock, mixing with the matters from the mantle and dissolving the gypsum, weathering the carbonate rock with CO2and H2O. During the progress of runoff, the underground thermal water is suffocated by the fault or the valley that were deep dissected by Yangzi river and Jialing River, and then upward moving, mixing with the cold karst water and sandstone water, at last discharged as natural outcropping springs and manual drilling springs.
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