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Objective Yishu fault zone geothermal field and central Shandong uplift geothermal field are typical geothermal fields in south central Shandong Province. In order to investigated the distribution characteristics and mechanisms of fluorine enrichment in the geothermal water of the this area, Methods hydrochemical diagrams, geochemical simulations and principal component analysis were employed. Results The results show that the geothermal water in the study area is mainly Na-Ca-Cl-, Na-Ca-SO4-Cl- and Na-Cl-SO4-type water, dominated by weakly alkaline water. The predominant cation is the sodium ion, with fluorine concentration between 0.38 and 4.5 mg/L. Sodium-rich and weakly alkaline environments are faciliated to the enrichment of fluorine in the geothermal water. The fluorine concentration has significant positive correlations with the Na+, Cl- and TDS concentrations in the geothermal water. In addition, it has significant positive correlations with K+ and SO42- concentrations and significant negative correlations with Mg2+ and HCO3- concentrations in the geothermal water in the Yishu fault zone. The cation exchange effect in the geothermal water of the central Shandong uplift zone is stronger than that in the Yishu fault zone, and the reaction strength of Na+ is significantly stronger than that of Mg2+. The geothermal field of the central Shandong uplift and Yishu fault zones are both fracturing types. The thermal storage lithologies are limestone, limestone in the thermal alteration zone and ansanite in the broken belt, with strong water-rock interactions. The provenance of fluorine in the geothermal water is the dissolution reprecipitation of fluorine-containing minerals, and the fluorine concentration in the geothermal water is further increased by cation exchange and other water-rock interactions. High temperature and sodium-rich have a great influence on fluorine enrichment. Conclusion This research provides a reference for the exploitation and utilization of geothermal resources.

The lithospheric thermal structure has a profound indicative significance for the potential evaluation and exploration of geothermal resources. The Linyi geothermal field, located in the southern section of the Yishu fault in Shandong Province, boasts abundant geothermal resources. However, its origin is still unclear. This study analyzed the characteristics of terrestrial heat flow using the temperature logging of geothermal wells and measurements of thermal conductivity and heat production. Combined with the geophysical information of the Xiangshui (Jiangsu Province)-Mandula (Nei Mongol) geoscience transect and the lithology revealed by the geothermal wells, this study built a conceptual model of the lithospheric thermal structure using the one-dimensional steady-state heat conduction equation. Based on this model, the heat flow is 64.9 mW/m 2 , indicating a high geothermal setting in the study area. Furthermore, the ratio of crustal to mantle heat flow is

Jinggangshan City, which is located in the southwestern part of Jiangxi Province, is rich in hot springs. However, lack of geothermal studies has limited the exploration and utilization of the geothermal resources in this city. This study estimated the terrestrial heat flow in Jinggangshan City through well logging and analyses of rock thermal conductivity and heat production. Based on this and the surrounding geoscience transect and the Crust 1.0 model, this study constructed a one-dimensional lithospheric thermal structure by solving the steady-state heat conduction equation. Furthermore, the deep temperature distribution in Jinggangshan City was obtained to better understand the geodynamic condition of the geothermal resources in this city. The results show that the heat flow in this city is around 83.52 mW/m2, indicating the high heat background for the formation of geothermal resources. According to the lithospheric thermal structure of Jinggangshan City, the mantle contributes more to the terrestrial heat flow (qm/qc > 1) than the crust. The temperature of the Mohorovicic discontinuity (the Moho) is 671.7°C, which is consistent with that below the Tanlu deep fault (620–690°C). Moreover, the calculated depth of the Curie surface (585°C) is 27 km, which is consistent with the Curie isotherm depth estimated from aeromagnetic data. This consistency verifies the validity of the lithospheric thermal structure of Jinggangshan City constructed in this study. In summary, the high heat background plays an important role in the formation of geothermal resources in Jinggangshan City.

High-temperature hydrothermal activity areas in western Sichuan Province, China are ideal objects for studying deep Earth science, extreme ecological environments, and comprehensive geothermal utilization. To understand the geochemical characteristics of rare Earth elements (REEs) in the Chaluo hot springs in western Sichuan Province, the authors analyzed the composition and fractionation of REEs in the hot springs through hydrochemical analysis, REE tests, and North American Shale Composite-normalized REE patterns. Moreover, the composition and complex species of REEs in the geothermal water in the Chaluo area were determined through calculation and simulation analysis using the Visual MINTEQ 3.0 software. The results are as follows. In terms of hydrochemical type, all geothermal water in the Chaluo area is of the Na-HCO3 type. The cations in the geothermal water are mainly controlled by water-rock interactions and evaporation, the anions are determined by water-rock interactions, and the hydrochemical processes are primarily controlled by the dissolution of silicate minerals. The total REE content of the geothermal water in the Chaluo hot springs is 0.306 ± 0.103 ug/L. It is low compared to the Kangding area and is primarily affected by the reductive dissolution of Fe oxides/hydroxides, followed by pH. The geothermal water in the Chaluo area is rich in light rare Earth elements (LREEs) because of the presence of Fe oxides. It shows positive Eu and Ce anomalies due to the combined effects of the dissolution of Eh and Mn oxides and surface water. Furthermore, the positive Eu anomalies are also caused by the water-rock interactions between the Qugasi Formation and deep geothermal water. Similar to alkaline water bodies, the complex species of REEs in the geothermal water mainly include Ln(CO3)2−, LnCO3+, and LnOH2+, which is caused by the stability constants of complexation reactions.