Hydrochemical Characteristics And Origin Of The Deep-formation Brines And Hot Springs Occurring In The Triassic Strata In The High-fold Belts Of The Eastern Sichuan Basin

In recent years, with the development of economy and agriculture, the lack of potashresources is valued and a large-scale of potash exploration jobs have been launched in ourcountry. The Sichuan Basin is a famous and large sedimentary basin, and abundant in brineresources. Many of them are high-salinity and K-rich brines. K-rich brines had been foundin the Xuanhan area in the east of Sichuan basin. Studies of hydrogeochemicalcharacteristics and origin on the deep brines and hot springs occurring in the Triassic stratain the high-fold belts of the eastern Sichuan basin can play an additional role in theexploration of potash. It also provides evidence for the utilization of geothermal resourcesof the eastern Sichuan basin.In this paper, the reservoir characteristics and distribution of deep-formation brinesand hot springs in the high-fold belts of the eastern Sichuan basin have been discussed indetail. The analysis of brines and hot springs is from formations and strata, which are twodifferent angels. Anticline structures are deep-buried, and with a good enclosed condition.They are good for the preservation of brines. Conversely, in the half-open-open anticlineformation, the core of anticline was weathered and denuded seriously. The strata of Triassicare exposed in surface and accepts recharge from atmospheric precipitation. They are notbenefit for the preservation of brines. In the lower place, geothermal water occurs and hotsprings emerge through the cracks or faults.This paper uses a variety of methods to do hydrochemical analysis for thedeep-formation brine in the Luojiaping structure and the Wolonghe structue, such as theway of routine components analysis, ion proportional coefficient, and comparison with thecurve of evaporating seawater, and so on. The results show that the hydrochemical type ofthe deep-formation brines are of Cl-Na type, and are enriched in microelement orcomposition, such as Br-、Li-、Sr2-、I-、B2O3and so on. Among these brines, the Chuan25well is the rarely K-rich brine which has high total dissolved solids. It has reachedsedimentary stage of epsomit, and its salinity is352.693g/L, and the content of K is as high as25.955g/L。With the routine component analyses of geothermal water in the Xiannvshan andTongjing hot springs, we conclude that the geothermal water is dominated by the SO4-Catype, and have a high concentrations of Sr2+, F-, metasilicic acid and dehydrated boric acid.It is calculated out by mean of the altitude effectiveness of2H, that the elevation ofrecharge area is about1036-1084m. Through the analyses of radioactive isotopes ofradium-radon, we calculate geothermal water age is only about20a. The geothermalreservoir temperature is estimated at79℃-85℃using SiO2geothermometers. Thecirculation depth is estimated as about2000m.The stable isotopes of δD and δ18O of the brines show that they are of paleo-marineorigin. Ratios of ions such as rNa/Cl and Br×103/Cl show that the origin of the deep brinesof the eastern Sichuan basin are related to the deposition water. Comparision of thehydrochemical composition of brines with the corresponding phase on the curve ofevaporating seawater indicates that the deep-formation brines are not simply concentratedby the evaporation of seawater. Stable isotopic analyses indicate that the Xiannvshan andTongjing hot springs are of meteoric origin. Combining with the supply elevation andterrain, the recharge areas of geothermal water probably are the outcrops of karst in thenorth of the high-fold belts of the eastern Sichuan basin.