The Madeng hot spring emerges in the central river valley in the northeastern Lanping Basin in Jianchuan county of Yunnan Province in China. Quaternary sand and gravel occur in the valley which is underlain by the red beds consisting of sandstone and mudstone. The temperature of the hot spring is 42.1°C. The spring water has a pH value of 6.41, TDS of 3.98 g/L, F contents of 3.08 mg/L, and H2SiO3 of 35.6 mg/L. The hot water is of SO4•Cl-Na•Ca type. There is a slight hydrogen sulfide odor in the spring water. Stable hydrogen and oxygen isotopes indicate that the hot water is of meteoric origin. It is estimated that the elevation of the recharge area of the hot spring is approximately 3800 m, the age of the hot water is some 140 years, the temperature of the geothermal reservoir is 75°C–80°C, the mixture ratio of cold water is approximately 80%, and the circulation depth of the thermal groundwater is 1870 m. After receiving recharge from infiltration of precipitation in the mountainous recharge areas, the groundwater undergoes a deep circulation, obtains heat from the heat flow, flows upward along the fractured zone, and emerges as an upflow spring through the Quaternary sand and gravel in the central low-lying river valley.
Hot springs display the thermal energy in the internal earth, and they can provide us important information on groundwater circulation and hydrochemistry at depth [
Hydrogeochemical studies of hot springs were carried out by many researchers. For example, Ellis and Mahon [
Stable 2H and 18O isotopes are often used to examine the origin of groundwater since Craig [
Geothermometers are used to estimate temperature of deep geothermal reservoirs. In the 1970s–1980s, several geothermometers were established to estimate the temperature of geothermal reservoirs [
In this paper, on the basis of field investigation and sample detection, we analyze the occurrence of the Madeng hot spring, examine the hydrochemical characteristics, and summarize the isotopic signature of the hot water. The origin of the geothermal water, residence time of the geothermal water, circulation depth, reservoir temperature, elevation and temperature of the recharge area, and mixture ratio of the hot water and cold water are also identified and estimated. The formation of the hot spring is further proposed.
The Madeng hot spring is located at the southeast of the Houdian village in Jianchuan County of Yunnan (Figure
Geological sketch map near the Madeng hot spring in Jianchuan of Yunnan Q—Quaternary gravel and sand; E—Eogene purple mudstone, siltstone, sandstone, and conglomerate; K—Cretaceous fine-grained sandstone, amaranth mudstone, and feldspar quartz sandstone; J—Jurassic red mudstone, siltstone; T—Triassic limestone, siltstone; P—Permian basalt and tuff breccia; C—Carboniferous quartz sandstone, limestone; D—Devonian dolomitic limestone and dolomite; O—Ordovician quartz sandstone; Pt2—Mesoproterozoic mica schist, dark cloud flash schist; F1—Lancangjiang river fault; F2—Weixi-Qiaohou fault; F3—Jinshajiang-Ailaoshan fault; F4—Lanping-Simao middle fault (Bijiang fault); F5—Duosong-Ludian fault; F6—Zhongdian-Jianchuan fault; F7—Annan-Jianchuan fault; F8—Jianchuan-Lijiang fault; F9—Heqing-Eryuan fault; F10—Honghe fault; 1—stratigraphic boundary; 2—strike-slip faults; 3—reverse fault; 4—rivers; 5—spring; 6—city; 7—county; 8—village and town; 9—mountain.
The mean annual precipitation in Jianchuan county is 731.1 mm (1990–2010). The main outcropping formations in the study area are related to the Devonian dolomitic limestone and dolomite, Permian tuff, Triassic siltstone, basaltic sandstone, limestone sandstone and carbonaceous shale, Jurassic red mudstone, marl, siltstone and fine sandstone, Cretaceous amaranth mudstone and feldspar quartz sandstone, Paleogene amaranth mudstone, siltstone, sandstone and conglomerate, and Quaternary sandy clay, gravel and grit (Figure
Tectonically, Yunnan Province is located in the Indian Ocean Plate and Eurasian Plate collision zone and its affected area. From east to west, Yunnan and Tibet geothermal zone can be divided into the Ailaoshan anticlinorium, Lanping-Simao depression, Changning-Lancang anticlinorium, Baoshan synclinorium, and Tengchong-Gaoligong mountain anticlinorium [
Special geological and geographical conditions make the Yunnan Province abundant in geothermal resources in China. There is a very close relationship between the formation of geothermal resources and the geological background. From the point of view of geothermal geology background, Yunnan Province can be divided into two areas by the Jinshajiang-Ailaoshan fault zone. The west is a high-temperature hydrothermal area where some boiling hot springs and hot springs of low to moderate temperature occur, and the east is a low-temperature hydrothermal area where boiling hot springs are seldom encountered. High-temperature hydrothermal activities in the Western Yunnan are in the south band of the Yunnan and Tibet geothermal band. The high-temperature geothermal systems in the region are obviously controlled by the distribution of the activity of the basement and depression layout and the tectonic uplift.
The Madeng hot spring (YJ2) is located in the west of Jianchuan county of Yunnan with an elevation of 2356 m. There are six vents in the hot spring, and the hot spring is an upflow spring. The upflow spring is a kind of genetic types of springs when the aquifer is covered by unconsolidated sediments of poor permeability or buried under an aquitard and when the hydraulic head in the aquifer is higher than the ground surface. Groundwater will flow through the upper unconsolidated sediments or aquitard and emerges on the land surface [
Sampling was conducted for the Madeng hot spring in Jianchuan county of Yunnan on August 19, 2014. The chemical analyses were conducted at the laboratory of the Beijing Brigade of Hydrogeology and Engineering Geology, using the following methods: K, Na, Li, Sr, Zn, and Mn by the flame atomic absorption; Ba, Al, Pb, Cd, and Ag by the atomic absorption of the plumbago furnace; Cl, SO4, and NO3 by the ion chromatogram; NH4, Fe2, Fe3, NO2, F, Br, I, Cr(6), H2SiO3, HBO2, and HPO3 by the spectrophotometer; Hg, Se, and HAsO3 by the atomic fluorescence; Ca, Mg, and hardness by the volumetric method (EDTA titration); HCO3, CO3, and total alkalinity by the volumetric method (HCl titration); total acidity by the volumetric method (NaOH titration); H2S by the volumetric method (sodium hyposulfite titration); and 226Ra and 222Rn with the radioactive radon-thorium analyser. 2H and 18O were detected at the Analysis Center of the Beijing Research Institute of Uranium Geology by the zinc reduction method for hydrogen isotopes and the carbon dioxide—water equilibrium method for oxygen isotopes. The chemical constituents were tested for accuracy by calculating the normalized inorganic charge balance which was less than 2.22% for the YJ2 sample and 0.17% for the YJ2-A sample, respectively.
The chemical analyses of the hot spring (YJ2) and those reported in the “Hot Springs’ Records in Yunnan Province’ Records” (YJ2-A) are listed in Table
Chemical analyses of the Madeng hot spring (mg/L).
Composition | YJ2 | YJ2-A |
---|---|---|
K | 11.4 | 17.9 |
Na | 802 | 733 |
Ca | 378 | 185 |
Mg | 37.9 | 35.5 |
NH4 | <0.02 | 0.701 |
Fe | 0.116 | / |
HCO3 | 663 | 287 |
Cl | 810 | 595 |
SO4 | 1.24 × 103 | 1.05 × 103 |
F | 3.08 | 2.32 |
NO3 | 3.7 | / |
226Ra (Bq/L) | 0.420 | / |
222Rn (Bq/L) | 7.21 | / |
Ba | 0.051 | / |
Cr (6) | <0.001 | / |
Pb | <0.0008 | / |
Mn | 0.024 | / |
Al | 0.060 | / |
Li | 0.246 | 0.25 |
Sr | 12.4 | / |
Br | 0.17 | / |
I | <0.02 | / |
Zn | 0.026 | / |
Se | 0.0003 | / |
Ag | <0.0005 | / |
H2SiO3 | 35.6 | / |
HAsO3 | 0.016 | / |
HBO2 | 3.60 | 2.75 |
HPO3 | <0.01 | / |
NO2 | 0.078 | / |
Free CO2 | 91.5 | / |
TDS | 3.98 × 103 | 2.82 × 103 |
Total alkalinity | 543 | / |
Total acidity | 104 | / |
Total hardness | 1.10 × 103 | / |
H2S | <0.05 | / |
pH | 6.41 | 7.65 |
Temperature (°C) | 42.1 | 42 |
YJ2 represents the sample collected in August 2014; YJ2-A represents the data recorded in the “Hot Springs’ Records in Yunnan Province’ Records” in 1999.
The content of F in the hot spring water is 3.08 mg/L, which is greater than that in the“Hot Springs’ Records in Yunnan Province’ Records” (2.23 mg/L) (Figure
Durov diagram showing the Madeng hot spring water samples—YJ2: water sample of the hot spring taken in 2014; YJ2-A: water sample of the hot spring from Local Chronicles Compilation Committee of Yunnan Province [
The pH of the hot spring water is 6.41, and the hot water is weakly acidic. As shown in Table
Craig [
Data of
Name of hot spring | Madeng hot spring | Xinhe hot spring | Wenxing hot spring | Lajing hot spring | Niujie hot spring |
---|---|---|---|---|---|
Serial number | YJ2 | YJ1 | YY11 | YLP1 | YE1 |
T (°C) | 42.1 | 42.7 | 40 | 46.1 | 76.1 |
−120.4 | −128.6 | −118 | −112.4 | −88.5 | |
−18.5 | −19.2 | −19.1 | −17.6 | −11.4 |
Plot of
As mentioned previously, the geothermal water was originated from meteoric water in the study area. On the mainland, the
The relationship between the values of the isotope and the altitude in Sichuan, Guizhou, and Tibetan areas in China [
The equation describing the relationship between the values of
Yu [
The temperature effect of the values of
According to (
226Ra and 222Rn are of uranium series isotopes. 226Ra is formed after the decay of uranium, and it becomes 222Rn after further decay of 226Ra. According to the contents of 226Ra and 222Rn in the hot water, the resident time (age) of the thermal water can be estimated by using the following equation [
The contents of 226Ra and 222Rn of the hot water are 0.42 Bq/L and 7.21 Bq/L, respectively. According to (
Surface temperature of hot water usually can be observed in the field, but the surface temperature does not stand for the reservoir temperature of the thermal water [
Triangular diagram of Na-K-Mg1/2. YJ2: water sample of the hot spring taken in 2014; YJ2-A: water sample of the hot spring from Local Chronicles Compilation Committee of Yunnan Province [
SiO2 mineral is widespread in geothermal water. When the hot water temperature drops, the process of SiO2 deposition is very slow. When the temperature is lower than 300°C, the pressure and salinity have little impact on the solubility of quartz and amorphous SiO2, and the dissolved SiO2 in the water is generally not affected by other ions. These characteristics of SiO2 make it suitable as a geothermometer and extensive applications. There are five commonly used silica geothermometer equations as follows [ Quartz geothermometer—without steam separation or mixing action:
Quartz geothermometer—without steam loss (0–250°C):
Quartz geothermometer—largest steam loss at 100°C (0–250°C): Chalcedony geothermometer—without steam loss (0–250°C):
The reservoir temperature is estimated as 76.2°C, 75.7°C, 79.8°C, 26°C, and 44.1°C by using (
After receiving recharge from infiltration of precipitation, the groundwater is heated during a deep circulation, flows upward to the surface, and emerges in the form of the hot spring. The temperature of the geothermal water is mainly derived from geothermal heating in the process of deep circulation. The geothermal water often can reach as deep as thousands of meters [
According to the “Jianchuan County Annals” published in 1999, we can obtain
The mixing between hot water and cold water in geothermal systems is very common, which may occur in the whole process of the geothermal fluid circulation. It is very important to recognize the formation conditions and the reservoir temperature of geothermal water by examining the mixing effect [
Assuming that the dissolved SiO2 of the deep geothermal water is in a saturated state, the initial enthalpy and SiO2 content in the deep hot water at the beginning are inevitably converted into final enthalpy and SiO2 content of hot spring water at last during the process of cold water and hot water mixing [
Substituting the enthalpy of different temperatures and the content of SiO2 (Table
Relationship between the hot water temperature, enthalpy, SiO2 content, and ratio of cold water (X).
T (°C) | X1 | X2 | ||
---|---|---|---|---|
50 | 50 | 13.5 | 0.255 | −3.966 |
75 | 75 | 26.6 | 0.588 | −0.047 |
100 | 100.1 | 48 | 0.715 | 0.543 |
125 | 125.1 | 80 | 0.782 | 0.752 |
150 | 151 | 125 | 0.825 | 0.849 |
175 | 177 | 185 | 0.854 | 0.901 |
200 | 203.6 | 265 | 0.875 | 0.932 |
225 | 230.9 | 365 | 0.891 | 0.951 |
250 | 259.2 | 486 | 0.904 | 0.963 |
275 | 289 | 614 | 0.914 | 0.971 |
300 | 321 | 692 | 0.924 | 0.975 |
The relationship between the hot water temperature, enthalpy, and SiO2 content is quoted from Fournier and Truesdell [
Relationship between temperature of hot water and ratio of cold water
Tectonically, the Madeng area in Jianchuan county is located in the west of the Weixi-Qiaohou fault zone and in the east of the Lanping-Simao fracture (Bijiang fault), which formed an inverted triangle. Fractured zones are observed in the red beds in the western of Yunnan and could provide good circulation conditions for the formation of the hot spring. The Madeng hot spring emerges in the center of the river valley in the northeastern Lanping Basin. Quaternary sand and gravel occur in the valley, and the underlying strata are the red beds of sandstone and mudstone. After receiving recharge from infiltration of precipitation in the recharge area in the surrounding mountains (Figure
Schematic diagram showing the formation (a regional scale) of the Madeng hot spring in Jianchuan county, Yunnan. 1—hot spring; 2—snow and ice; 3—meteoric water; 4—flow line; 5—heat flow.
Schematic profile showing the formation (near the vent) of the Madeng hot spring in Jianchuan county, Yunnan. 1—sand and gravel; 2—sandstone; 3—mudstone; 4—fracture zone; 5—hot spring; 6—thermal ground water flow; 7—heat flow; 8—water table.
The Madeng hot spring emerges in the central river valley in the eastern Lanping Basin of Yunnan in China. Temperature of the hot spring water is 42.1°C, belonging to geothermal water of low temperature. The total hardness is 1100 mg/L belonging to the especially hard water according to the classification of hardness. The TDS is 3.98 g/L, indicating the brackish water. The hot water has a pH value of 6.41, belonging to weakly acidic water, which can express that the ability to neutralize the alkali is greater than the acid in the hot spring water in the study area.
The cations of the hot water are predominated by Na, K, Ca, and Mg and the anions of the hot water by SO4, HCO3, and Cl. The minor ions of the hot water include NH4, NO3, and Fe. H2SiO3 of the hot water is 35.6 mg/L and F content is 3.08 mg/L, which are greater than the drinking water standard of China and are not suitable for drinking. The hot water is of SO4•Cl-Na•Ca type.
The values of the
SiO2 geothermometer is used to estimate the thermal reservoir temperature of the hot spring in the study area, and the temperature of the geothermal reservoir in the study area ranges from 75°C to 80°C. The mixing ratio of cold water is approximately 80%, and the circulation depth of the hot water, approximately 1870 m. After receiving recharge from infiltration of precipitation in the recharge area, the groundwater is heated during a deep circulation, flows upward along the fractured zone, and emerges as an upflow spring through the Quaternary sand and gravel in the central low-lying river valley.
Given the key information of hydrochemistry and formation hypothesis of the Madeng hot spring in this article, it could provide some insights into the potential and development of thermal groundwater resources in Western Yunnan. Future studies of further explanation of the solutes and isotopic features of the hot spring are required to better understand the substance migration of thermal groundwater occurring in red bed areas.
The authors declare that they have no conflicts of interest.
This work was cooperatively supported by the Natural Science Foundation of China (41572223, 41772261) and the Fundamental Research Funds for the Central Universities of China (2652015245). The authors want to thank Dr. Haiyan Zhou and Dr. Juan Guo for their help in improving the manuscript. The authors are also grateful for the critical comments and suggestions by the editors and anonymous reviewers.