Depth Of Circulation Research Articles

Assessment of geothermal potential of Kumaun Himalaya: A perspective for harnessing green energy

Energy is an essential part of human life, and its demand has exponentially increased after the industrial era, especially in developing countries. India has many geothermal springs (GTSs ∼340) in orogenic and non-orogenic belts, but their potential must be better known and utilized as an efficient green energy resource. Therefore, we attempted for the first time to estimate the reservoir temperature of geothermal springs (n = 17) using dissolved silica geothermometry along the Goriganga, Ramganga, and Kali rivers in the Kumaun Himalaya, Uttarakhand. The average and highest reservoir temperatures were 113 °C and 135 °C at Savildhar, respectively. The average reservoir and fluid circulation depths were ∼1.24 km and 1.27 km, respectively. An inverse relationship between reservoir temperatures and the distance of geothermal fields from the Main Central Thrust evinces structural control over the geothermal fields. Most of the studied GTSs (n = 14) have reservoir temperatures between 100 °C and 150 °C, making them medium enthalpy and suitable for Binary Organic Rankine Cycle power plants. Two springs with reservoir temperatures between 70 °C and 100 °C can be used for industrial, space heating, balneotherapy, and other direct uses. Since geothermal power plants do not require any fuel to produce electricity, this study emphasizes on exploiting the geothermal potential of Himalayan geothermal springs.

Both natural and anthropogenic factors control surface water and groundwater chemistry and quality in the Ningtiaota coalfield of Ordos Basin, Northwestern China.

An understanding of the vertical variations in hydrogeochemical processes in various aquifers and quality suitability assessment is crucial for the utilization of groundwater in the Ningtiaota coalfield of Ordos Basin, Northwestern China. Based on 39 water samples collected from surface water (SW), Quaternary pore water (QW), weathered fissure water (WW), and mine water (MW), we conducted self-organizing maps (SOM) algorithm, multivariate statistical analysis (MSA), and classical graphical methods to elucidate the mechanisms controlling the vertical spatial variations in SW and groundwater chemistry and conducted a health risk assessment. The findings indicated that the hydrogeochemical type showed a transition from the HCO3--Na+ type in SW to the HCO3--Ca2+ type in QW, then to the SO42--Mg2+ type in WW, and back to HCO3--Na+ type in MW. Water-rock interaction, silicate dissolution, and cation exchange were the main hydrogeochemical processes in the study area. Additionally, groundwater residence time and mining operations were critical external factors that affect water chemistry. Contrary to phreatic aquifers, confined aquifers featured greater circulation depth, water-rock interactions, and external interventions leading to worse quality and higher health risks. Water quality surrounding the coalfield was poor, causing it to be undrinkable, with excessive SO42-, arsenic (As), and F-, etc. Approximately 61.54% of SW, all of QW, 75% of WW, and 35.71% of MW can be used for irrigation.

Hydrogeochemical Study of Hot Springs along the Tingri—Nyima Rift: Relationship between Fluids and Earthquakes

Studying the hydrogeochemical characteristics of hot springs provides essential geochemical information for monitoring earthquake precursors and understanding the relationship between fluids, fractures, and earthquakes. This paper investigates the hydrogeochemical characteristics of hot springs along the Tingri–Nyima Rift (TNR) in southern Tibet, a seismically active zone at the collision front of the Indian and Asian-European plates. The major elements, hydrogen, and oxygen isotopes of seven thermal springs were analyzed from July 2019 to September 2021. The findings indicate that Mount Everest’s meteoric water, which has a recharge elevation of roughly 7.5–8.4 km, is the main source of recharge for the hot springs. The water samples have two main hydrochemical types: HCO3-Na and Cl-Na. The temperature of the geothermal reservoir is between 46.5 and 225.4 °C, while the circulation depth is between 1.2 and 5.0 km based on silica-enthalpy mixing models and traditional geothermometers. Furthermore, continuous measurements of major anions and cations at the Yundong Spring (T06) near Mount Everest reveal short-term (8 days) seismic precursor anomalies of hydrochemical compositions before an ML4.7 earthquake 64.36 km away from T06. Our study suggests that seismicity in the northern section of the TNR is controlled by both hydrothermal activity and tectonic activity, while seismicity in the southern section is mainly influenced by tectonic activity. In addition to magnitude and distance from the epicenter, geological forces from deep, large fissures also affect how hot springs react to seismic occurrences. A fluid circulation model is established in order to explain the process of groundwater circulation migration. The continuous hydrochemical monitoring of hot springs near Everest is critical for studying the coupling between hot springs, fractures, and earthquakes, as well as monitoring information on earthquake precursory anomalies near Everest.

Environmental Stable and Radioactive Isotopes in the Assessment of Thermomineral Waters in Lisbon Region (Portugal): Contributions for a Conceptual Model

The existence of thermomineral waters in the Lisbon region (western Portugal), has been known for centuries. Several authors have investigated the characteristics of these thermomineral waters, but their conceptual model (recharge zone, processes controlling the origin and chemical evolution, depth of circulation, etc.) remains unknown. This work highlights the advantages of assessing the conceptual model in urban coastal areas, where different saline sources coexist, combining chemical analyses with environmental isotopes and geochemical modeling. The final physicochemical composition of thermomineral waters seems to be mainly controlled by water–rock interaction processes and different mixing degrees between HCO3-Ca regional groundwaters, cold dilute shallow groundwaters and highly salinized fluid (brackish or brine or non-recent seawater) probably trapped at depth. Based on these results, neither the contribution of polluted water nor the leaching of evaporite rocks seems to be the main salinization factor of the warmer and saline waters. A positive correlation exists between the lowest radiocarbon activities (average apparent ages ~6 ka BP) and highest water temperature and salinity (up to 39 °C and 6.3 g/L), suggesting progressive salinization and deeper circulation (up to 1200 m depth) into the hosting formations, where mixing with trapped salinized fluids probably took place, as confirmed by geochemical modeling. Finally, very favorable geological conditions in the Estoril region allow for fast rising and the occurrence of these thermomineral waters at relatively shallow depths.

Assessment of possibility of finding geothermal energy resources around Mount Meru in northern Tanzania using classical solute geothermometry

This study uses classical solute geothermometry analysis to estimate the temperature and circulation depth of the geothermal reservoir around Mount Meru. Five springs affected by magmatic gases from a deep magmatic heat source are investigated; these include two hydrothermal springs. Results from silica geothermometers show that estimated reservoir temperatures range from 70 to 110 °C; this corresponds to a low-temperature hydrothermal system. Since Mount Meru is an active volcano, one would expect a high-temperature hydrothermal system; the low temperatures are ascribed to the mixing of hydrothermal and cold recharge waters. The geothermal reservoir is estimated to be about 1.3–1.4 km deep. Thus, the study shows that a low-temperature geothermal energy resource can be found on the eastern flank of Mount Meru.

Magmatic fluid input controlling the geochemical and isotopic characteristics of geothermal waters along the Yadong-Gulu rift, southern Tibetan Plateau

Geothermal resources, regarded as sustainable green energy, are attracting increasing attention. The southern Tibetan Plateau possesses the most abundant intermediate-high geothermal resources in China and has enormous potential for geothermal exploration. Geothermal waters from the Yadong-Gulu Rift (YGR), which is considered as the most active geothermal belt of the plateau, are studied based on hydrochemical and isotopic characteristics to understand the spatial variations of fluid origin, evolution, and circulation mechanism as well as heat sources. The hydrochemical characteristics of cold springs and surface waters are consistently characterized by Ca-HCO3 dominated (Ca-HCO3 and Ca-HCO3·SO4) waters while those of geothermal springs present extensive variability with Na-Cl dominated (Na-Cl·HCO3, Na-HCO3·Cl, Na·Ca-Cl·HCO3) and Na-HCO3 waters. The main geochemical processes controlling the geothermal springs are combinations of silicate weathering, carbonate dissolution, and cation exchange. The characteristics of trace alkali metals and B indicate they undergone common/similar deep process and the potential input of magmatic degassing. The δD and δ18O values suggest that cold springs and surface waters are recharged by meteoric water, and geothermal springs are replenished by meteoric water, snow-melt, and magmatic fluid. The mass balance model reveal that dominant carbon sources for geothermal waters can be deeply derived CO2 (i.e., magmatic source and metamorphic source), contributing from 77% to 99%. Based on empirical chemical geothermometers, Si-Enthalpy mixing model, and geothermometrical modelling, the calculated reservoir temperatures are highly variable (137-312 °C). The circulation depths of geothermal waters are 2.45-6.85 km. A conceptual model is proposed to reveal the deep groundwater circulation.

Hydrogeochemistry of Fault-Related Hot Springs in the Qaidam Basin, China

Hydrogeochemical characterization studies are regarded as an important method for determining the origin of hot springs. The major elements, trace elements, and stable isotopes of four groups of hot spring water samples and two groups of gas samples collected from the intersection of the Altyn Tagh fault zone and the East Kunlun fault belt were investigated in this study. The hot spring water temperature ranged between 6 °C and 14 °C. The water chemistry types of the hot springs were Na·Mg-Cl, Mg·Na-Cl·HCO3, Na-Cl·SO4, and Na-Cl·HCO3. The δD values ranged from −50.00% to −68.60%, while the δ18O values ranged from −6.90% to −8.60%. The hot spring water was recharged mainly by infiltrating precipitation, with a recharge elevation of 3390~3676 m. The heat storage temperature ranged from 66.7 to 164.9 °C. The circulation depth was estimated to range between 1043 and 2679 m. The strontium isotopic composition of the water samples in response to the main weathering sources comprised carbonate and sulfate. CO2 was the main component in the hot spring gas in the study region, and its content was over 95%. The 3He/4He-R/Ra relationship diagram revealed that the mantle-sourced helium from the Yitunbulake spring was 3.06%. In comparison, that from the Aiken spring was 7.38%, which indicated an intrusion of mantle-source material mixed into the hot springs in the study region. The crustal marine limestone contributed significantly to the carbon inventory of the hot spring gas samples (>75%). The dissolution of the marl aquifer resulted in the release of CO2. Carbon was primarily obtained through metamorphism and hydrothermal reactions in the basement lithologies. The Yitunbulake and Aiken hot springs are found near the intersection of the Arjin and East Kunlun fractures, where the water–rock response is relatively strong and the depth of circulation and thermal storage temperature are both high. This causes relatively high ambient pressure to be released from the deep fluid, resulting in microseismic activity in this region. The continuous observation of Aiken spring water chemistry allows for the monitoring of fracture activity in the region. The results of the study could serve as a foundation for further exploration of the relationship between geothermal water and deep faults, shallow geological formations, hydrogeological conditions, and geothermal resource development in the region.

Relationship between hydrogeochemical characteristics of hot springs and seismic activity in the Jinshajiang fault zone, Southeast Tibetan Plateau

Significant anomalous hydrogeochemical changes in hot spring water are detected during strong seismic cycles. It is now necessary to clarify the relationship between tectonic movements, earthquakes and the evolution of hot springs. In this paper, laboratory analyses of major, trace elements, δD, δ18O and 87Sr/86Sr values of 28 hot spring waters in the Jinshajiang fault zone (JSJFZ) in the northwestern boundary of the Sichuan-Yunnan block were conducted. The results showed that the primary source of water for JSJFZ hot springs was atmospheric precipitation. The geothermal reservoir temperature variation based on the silicon enthalpy mixing model ranged from 73 to 272°C. And the circulation depth range was 1.2–5.4 km. The segmentation characteristics of the 87Sr/86Sr values were related to the influence of source rocks on groundwater cycle processes. A conceptual model of the hydrologic cycle of hot springs explained the spatial distribution of earthquakes associated with tectonic movements. The Batang segment had the strongest water-rock reaction, the highest reservoir temperature and the deepest circulation depth; meanwhile, it was also an earthquake prone area. The fluid circulation of the JSJFZ corresponds well with the seismicity, which indicates that the hydrological characteristics of the hot spring water in a fracture zone play a crucial role in receiving information on seismic activity.

Analysis of the Formation Mechanism of Medium and Low-Temperature Geothermal Water in Wuhan Based on Hydrochemical Characteristics

Wuhan and its surrounding areas have obvious geothermal spring outcrops, which are unexplored potential geothermal resources. The degree of geothermal resource development in Wuhan is low, and there is a lack of systematic research on their hydrochemical characteristics and formation mechanism. The Wuhan area is bounded by the Xiang-Guang fault, the South Qinling-Dabie orogenic belt in the north, and the Yangtze landmass in the south, with Silurian and Quaternary outcrops and little bedrock outcrops. The Silurian is the main water barrier in the region, which separates the upper Triassic and Paleogene as shallow aquifers and the lower Cambrian and Ordovician as deep aquifers. Different strata are connected by a series of fault structures, which constitute Wuhan’s unique groundwater water-bearing system. Eleven geothermal water (23~52 °C) and six surface water samples (around 22 °C) were collected from the study area. The geothermal water in the study area is weakly alkaline, with a pH of 7.04~8.24. The chemical type of geothermal water is mainly deep SO42− with a higher TDS and shallow HCO3− type water with a lower TDS. Isotopic analysis indicates that atmospheric precipitation and water-rock interaction are the main ionic sources of geothermal water. The chemical composition of geothermal water is dominated by ion-exchange interactions and the dissolution of carbonates and silicates. The characteristic coefficients, correlation analysis, water chemistry type, recharge elevation, geothermal water age, reservoir temperature, and cycle depth were also analyzed. The performance was similar in the same geothermal reservoir, which could be judged as an obviously deep and shallow geothermal fluid reservoir, and the genetic conceptual model of Wuhan geothermal was preliminarily deduced. DXR-8 and DXR-9 had the best reservoir conditions, hydrodynamic conditions, rapid alternation of water bodies, and large circulation depth, which is a favorable location for geothermal resource development and will bring considerable economic and social benefits.

Structural controls of the northern Red River Fault Zone on the intensity of hydrothermal activity and distribution of hot springs in the Yunnan-Tibet geothermal belt

Deep, large faults are well-developed in the Red River Fault Zone in Yunnan in southwest China. This study uses a classification approach and macro-scale analysis of faults and hot springs with data from the literatures and field work. By examining 68 hot springs, 6 faults, and 12 Quaternary basins in this area, controls of the northern Red River Fault Zone on the intensity of hydrothermal activity (temperature and flow rates) and distribution of hot springs are summarized. The results show that topography-related hydraulic gradients can cause geothermal water to rise after circulation. The hot springs are easy to occur along the active faults (76%), especially at fault intersections (37%). The circulation depth and elevated temperature of hot springs in the study area are positively correlated. The highest temperature hot springs correspond to low flow rates, and hot springs with the highest flow rate have low temperatures. The results are of practical significance for the search for thermal groundwater and for understanding geothermal resources potential in this area and similar areas.

Earthquake-induced impulsive release of water in the fractured aquifer system: Insights from the long-term hydrochemical monitoring of hot springs in the Southeast Tibetan Plateau

The outpouring hot spring water is deep circulated groundwater and its chemical constituents act as information carriers of the hydrological setting, including the recharge source, circulation path, and reservoir properties. However, the temporal variation in hydrochemical components and their inducing mechanisms remain to be elucidated. In this study, hot springs along the Anninghe-Zemuhe Fault, a controlling fault on the eastern edge of the Tibetan Plateau, were investigated. According to the spatial chemical variations of the sixteen hot springs and the two-year hydrochemical monitoring results of four hot springs, the aquifers in such fault-controlled regions exhibit heterogeneous anisotropy and elastic properties. Earthquake activities were found to play a significant role in both spatial and temporal changes in chemical compositions. We found that the waters with the highest reservoir temperatures (∼100 °C) and deepest circulation depth (∼3 km) outcropped in the north of the fault, where earthquakes occur more intensively, deeply, and stronger than those in other parts of the fault. During the stress accumulating and releasing processes in the earthquake sequence, the fractured aquifer systems are elastic and subject to impulsive mixing with subordinate fracture waters which induced hydrochemical changes at different levels. The chemical constituents responded to seismic energy densities as low as 6.5 × 10−4 J/m3, showing superiority over the groundwater monitoring wells. However, earthquakes that occurred in a tectonically independent area or with an inappropriate stress loading-unloading direction could fail to trigger a distinguishable mixing process with apparent chemical fluctuations. These findings provide insights into the hydrochemical response to earthquakes in orogenic areas and further draw attention to hydrochemical changes in hot spring waters in seismic studies.

Hydrogeochemical origin and circulation of spring waters along the Karakorum fault, Western Tibetan Plateau: Implications for interaction between hydrosphere and lithosphere

Geochemical investigation on the origin and circulation of geothermal water is crucial for better understanding the interaction between hydrosphere and lithosphere. Previous studies on the Himalayan geothermal belt mainly distributed in the central and eastern Tibetan Plateau. In this study, water samples (8 hot springs and 1 cold spring) from the Karakorum fault (KKF) zone of western Tibetan Plateau were analyzed for the hydrogeochemical characteristics and isotopic compositions. Three types of spring water along the KKF were classified on basis of ionic concentration and Sr isotopic composition: type A water (HCO3–Mg or Ca), type B water (HCO3–Na) and type C water (Cl–Na). Type A water is originated from the infiltration of meteoric water and the dissolution of silicate/evaporite. Type B water is mainly leached from the metamorphic and granitoid rocks. Type C water is formed by the dissolution of chlorides and sulphates. δD and δ18O isotopes indicate that geothermal fluid along the fault zone was mainly recharged by local precipitation. Moreover, reservoir temperatures of 144.2–208.6°C were estimated by the silica–enthalpy mixing model, and the thermal waters have a relatively deep circulation depth (≥ 7.0 km). Meanwhile, the thermal waters are characterized by extremely high Li, B, Fe and As concentrations and earthquakes frequently happened in the vicinity, suggesting that the KKF is a deep and active fault, which also indicates that the thermal fluids are strongly associated with seismicity. Therefore, thermal fluid can potentially be used as continuous monitoring sites for earthquake forecasting.

Genesis Mechanisms of Geothermal Resources in Mangkang Geothermal Field, Tibet, China: Evidence from Hydrochemical Characteristics of Geothermal Water

The Mangkang geothermal field, distributed in the Mediterranean–Himalayas geothermal belt, hosts abundant hot springs whose geneses remain unclear. To determine the hydrochemical characteristics, reservoir temperature, circulation and recharge depths, and water–rock interactions of the geothermal water in the geothermal field, this study analyzed hydrochemical compositions and isotopes (2H, 3H, and 18O), conducted a PHREEQC simulation, and established a conceptual model to illustrate the genesis of geothermal resources in the Mangkang field. Based on the study of hot springs in Meipu, Qvzika, and Zulongpu villages and Rumei town, the following results are reported: The orifice temperatures of these hot springs vary between 18 °C and 67.5 °C. The hydrochemical composition analysis results indicate that the geothermal water in the hot springs is of hydrochemical type HCO3-Ca·Mg. Moreover, the geothermal water has high HBO2 and Na+ concentrations, suggesting protracted water runoff and strong water–rock interactions during its evolution. According to the mineral–water solubility equilibrium and silica geothermometers, it is estimated that the reservoir temperature of the Zulongpu hot spring is 47 °C and other hot springs have much higher reservoir temperatures of 116–130 °C. As indicated by geothermal gradients, annual temperatures, and reservoir temperatures, the geothermal water in Meipu and Qvzika villages has the greatest circulation depth, up to 3600–4300 m, followed by that in Rumei town (3700–4000 m) and Zulongpu village (~1500 m). The 2H-18O isotopic analysis of the geothermal surface water revealed that the geothermal water originates from meteoric water. The recharge elevation was inferred to be ~4700–4900 m. Moreover, the low 3H values (<1 Tu) suggest that the geothermal water is older than 40 years. The PHREEQC inverse simulation results indicated that the variation in the hydrochemical composition of the geothermal water results from the precipitation of chalcedony and dolomite, the absorption of NaX, and the loss of CaX2 during migration and storage.

Determination of the circulation depth and reservoir temperatures of thermal waters in the southern Spitsbergen using geothermometry

Determination of the circulation depth and reservoir temperatures of thermal waters in the southern Spitsbergen using geothermometry

A data-driven modeling approach for the sustainable remediation of persistent arsenic (As) groundwater contamination in a fractured rock aquifer through a groundwater recirculation well (IEG-GCW®)

Persistent arsenic (As) pollution sources from anthropogenic activities pose a serious threat to groundwater quality. This work aims to illustrate the application of an innovative remediation technology to remove As from a heavily contaminated fractured aquifer at a historically polluted industrial site. Groundwater circulation well (GCW) technology was tested to significantly increase and accelerate the mobilization and removal of As in the source area. The GCW extracts and re-injects groundwater at different depths of a vertical circulation well. By pumping out and reinjecting in different screen sections of the well, the resulting vertical hydraulic gradients create recirculation cells and affect and mobilize trapped contaminants that cannot be influenced by traditional pumping systems. The first 45-m deep IEG-GCW® system was installed in 2020, equipped with 4 screen sections at different depths and with an above-ground As removal system by oxidation and filtration on Macrolite (Enki). A geomodeling approach supports both remediation and multi-source data interpretation. The first months of operation demonstrate the hydraulic effectiveness of the IEG-GCW® system in the fractured rock aquifer and the ability to significantly enhance As removal compared to conventional pumping wells currently feeding a centralized treatment system. The recirculation flow rate amounts to about 2 m3/h. Water pumped and treated by the GCW system is reintroduced with As concentrations reduced by an average of 20%–60%. During the pilot test, the recirculating system removed 23 kg As whilst the entire central pump-and-treat (P&T) system removed 129 kg, although it treated 100 times more water volume. The P&T plant removed 259 mg As per m3 of pumped and treated groundwater while the GCW removed 4814 mg As per m3 of the treated groundwater. The results offer the opportunity for a more environmentally sustainable remediation approach by actively attacking the contamination source rather than containing the plume.

Research on the Genetic Mechanism of High-Temperature Groundwater in the Geothermal Anomalous Area of Gold Deposit-Application to the Copper Mine Area of Yinan Gold Mine.

Geothermal energy is new, environmentally friendly, and clean energy, which is of great significance to realize energy saving and emission reduction. The study of the genesis mechanism of geothermal water is the key to its rational development and utilization. In this study, based on 14 sets of water samples from the eastern section of the copper well mining area of Yinan Gold Mine, mineral saturation index, isotope analysis (δ18O, δD), Si-enthalpy mixing equation, and geochemical geothermal temperature scale were used to analyze the thermal storage temperature, recharge characteristics, mixing ratio, circulation depth, and fluid passage to reveal the geothermal water fugitive transmission pattern and genesis mechanism in the study area and to propose a geothermal water genesis model. The study shows that the water supply elevation in the area is between 687.22 and 1164.15 m and a large amount of cold water recharged it. It is inferred that the recharge area is the precipitation in the Northwest Mountain range and surrounding atmosphere. Groundwater flows along the fracture zone in a south-easterly direction. It receives heating from the surrounding rocks, where the water level rises at the fracture zone intersection and is stored in the lower and middle Cambrian thermal reservoirs and continues to receive heating from deeper heat sources. Based on this study and previous regional research data, the fault structure in this area is within the influence range of the energy field of the Yishu fault zone. Yishu fault zone becomes the heating source under the background of cold water. It is inferred that the east-east Yishu fault zone in the study area may also be the recharge area.

A Joint Method Based on Geochemistry and Magnetotelluric Sounding for Exploring Geothermal Resources in Sedimentary Basins and Its Application

The precise exploration of the characteristics of geothermal fields in sedimentary basins, such as the temperature and burial depth of their deep geothermal reservoirs, is of great significance for improving the probability of penetration and reducing exploration risks and development costs. This study proposed a joint exploration method combining magnetotelluric (MT) sounding and geothermometers. Using this method, this study estimated the geothermal reservoirs’ temperature and the circulation depth of geothermal water in the Xianxian geothermal field, a typical geothermal field in a large sedimentary basin in northern China, and prepared the temperature and depth maps of the geothermal reservoirs. The main results are as follows. First, the bedrock’s geothermal reservoirs with karst fissures in the Xianxian geothermal field have great potential for development. Among them, geothermal reservoirs in the Jixianian Wumishan formation have a top depth of 1100–1500 m and a thickness of 700–1700 m, and the geothermal reservoirs in the Jixianian Gaoyuzhuang formation have a top depth of 3700–4000 m and a maximum drilled thickness of 400 m. The geothermal reservoirs of the Xianxian geothermal field mainly have medium and low temperatures of 138–160 °C and the circulation depth of the geothermal water is 5873 m.

Hydrogeochemical Characteristics and Genesis of the Chazi Geothermal Field Area in Tibet

The Chazi geothermal field area is located in the large region of Shigatse in southern Tibet. The geothermal resources in this area are abundant, but their exploitation and utilization are low. By studying the water chemistry and isotope characteristics of geochemical fluids in the study area, information on water chemistry, heat storage temperature, recharge source, recharge elevation, and circulation depth was obtained. These results provide a scientific theoretical basis for improving the genetic mechanism of high-temperature geothermal systems in the study area. The type of geothermal fluid hydrochemicals in this area is mainly HCO3–Na. The isotopic geochemical method was used to determine that the recharge source of geothermal fluids was atmospheric precipitation, and the recharge elevation was 5200–6000 m. The geochemical thermometer, Na–K–Mg equilibrium diagram, and silica-enthalpy mixed model indicated the shallow and deep thermal storage temperatures of approximately 150 and 200°C, respectively, and the average circulation depth of 1163.38 m in the study area. Combined with the fracture structure and magmatic activity characteristics of the southwest Qinghai-Tibet Plateau, the source, storage, cover, and general situation of the area were preliminarily summarised, and the conceptual model of geothermal origin was established. The results can provide a scientific theoretical basis for the mechanism of high-temperature geothermal systems and subsequent drilling and resource development.

Role of Atmospheric Temperature and Seismic Activity in Spring Water Hydrogeochemistry in Urumqi, China.

Springs offer insight into the sources and mechanisms of groundwater recharge and can be used to characterize fluid migration during earthquakes. However, few reports provide sufficient annual hydrochemical and isotopic data to compare the variation characteristics and mechanisms with both atmospheric temperature and seismic effects. In this study, we used continuous δ2H, δ18O, and major ion data from four springs over 1 year to understand the groundwater origin, recharge sources, circulation characteristics, and coupling relationships with atmospheric temperature and earthquakes. We found that (1) atmospheric temperatures above and below 0 °C can cause significant changes in ion concentrations and water circulation depth, resulting in the mixing of fresh and old water in the aquifer, but it cannot cause changes in δ2H and δ18O. (2) Earthquakes of magnitude ≥ 4.8 within a 66 km epicentral distance can alter fault zone characteristics (e.g., permeability) and aggravate water–rock reactions, resulting in significant changes in δ2H, δ18O, and hydrochemical ion concentrations. (3) Hydrogen and oxygen isotopes are the most sensitive precursory seismic indicators. The results of this study offer a reference for the establishment of long-term hydrochemical and isotopic monitoring, with the potential for use in earthquake forecasting.

Hydrogeochemical characteristics of thermal springs in the Qilian–Haiyuan fault zone at the northeast Tibetan Plateau: Role of fluids and seismic activity

The Qilian–Haiyuan fault zone (QHF) is located in a highly deformed and seismically active area of the northeastern margin of the Tibetan Plateau. This study investigated the major elements, strontium, hydrogen, and oxygen isotopes of 22 sites in the thermal springs along the QHF from October to November 2020. The QHF hydrochemical system is recharged by meteoric water primarily infiltrating between 2.8 and 4.4 km a.s.l. Based on quartz geothermometers, the geothermal reservoir temperature variation ranged from 25.5 to 111.3°C, and the circulation depth ranged from 1.3 to 5.6 km. In the QHF zone, the highest spring water temperature values were correlated with deep groundwater circulation circuits in areas where earthquake foci are concentrated. A conceptual model of the hydrologic cycle of thermal springs explains the spatial distribution of earthquakes associated with tectonic movements. The fluid circulation of the QHF corresponds well with the seismicity, which indicates that the hydrological characteristics of the thermal spring in a fault zone are vital in receiving information on seismic activity to assess the seismic risk of the QHF in the future.