Hydrogeochemical characteristics and genesis of geothermal water in northern Zhangqiu.

The northern part of Zhangqiu district in Jinnan City has developed a thick sedimentary formation from the late Paleozoic to the Cenozoic. In this district, relatively well-developed fault structures and magmatic rocks provide good geothermal conditions. Abundant geothermal resources have been discovered in the study area, with three geothermal wells located near the fault zone. Therefore, establishing the genesis model of geothermal resources is significant for their future sustainable development and utilization. Based on hydrochemical and isotopic data of the study area, hydrochemical characteristics, water-rock interaction process, recharge source and formation age of geothermal water have been analyzed in this study. Besides, the elevation of the recharge area, thermal reservoir temperature, and depth of hot water circulation have also been calculated. Research findings show that geothermal water in the study area is composed of Cl·SO₄-Na·Ca or SO₄·Cl-Ca·Na, whose hydrochemical components mainly come from water-rock dissolution in the similar hydrogeochemical process. The source of water recharge is supplied by atmospheric precipitation, at an elevation from +563 m to +616 m. The ¹⁴C apparent age ranges from 5.55 ka to 29.71 ka. The geothermal water is mixed with modern water and ancient water. The chalcedony temperature scale shows that the temperature of geothermal reservoir is at 41.9-52.4 °, with the circulation depth of geothermal water at 622-1,565 m. The study area is a small-opened karst hot reservoir with deep circulation, during which geothermal water is heated up. Formation and enrichment of geothermal water are significantly controlled by fault structures. The geothermal reservoir is of stratified and banded type, belonging to geothermal resources at medium-low temperature. [ABSTRACT FROM AUTHOR]