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Sources of Geothermal Water in Jiangxi Province, SE-China: Evidences from Hydrochemistry and Isotopic Composition
Available online at www.sciencedirect.com
ScienceDirect Procedia Earth and Planetary Science 17 (2017) 837 – 840
15th Water-Rock Interaction International Symposium, WRI-15
Sources of geothermal water in Jiangxi Province, SE-China: evidences from hydrochemistry and isotopic composition Jiale Lia, Bai Gaoa, Yihui Donga, Gongxin Chena, Zhanxue Suna,1 a
School of Water Resources and Environmental Engineering, East China University of Technology, Nanchang, 330013, China
Abstract Jiangxi Province is one of the regions where geothermal water is widely distributed in China, with discovered 96 hot springs and over 30 thermal water boreholes. Eleven geothermal water samples were collected and analyzed for hydrochemical and isotopic characteristics to distinguish the sources of geothermal water in Jiangxi Province, SE-China. Results showed that water temperatures varied from 32.0 to 80.8 ℃ with an average of 53.4 ℃ and the dominated compositions are Na-HCO type.The hydrogeochemical characteristics as well as isotopic compositions suggest the meteoric origin of geothermal water with recharge altitudes in the range of 400-995 m. Mixing with cold groundwater influences the hydrochemistry of geothermal water. This study furthers the understanding of sources of geothermal water and provides a theoretical basis for better exploitation of geothermal water in the province. 2017Published The Authors. Published by Elsevier B.V. © 2017 by Elsevier B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of WRI-15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 Keywords: geothermal water; Jiangxi Province; hydrochemistry; isotopic characteristics
1. Introduction Abundant geothermal reserves have been discovered in China and applied in electricity generating, heating, crops planting, floriculture, etc1. Jiangxi Province is one of the regions where geothermal water is widely distributed in China, and has attracted researchers’ attention on the forming condition and hydrochemical compositions for around three decades2,3. The objects of this study are to display the hydrochemical and isotopic characteristics, and to identify the sources of geothermal water. These results will be helpful for expanding our knowledge of geothermal water and better developing geothermal water in the province, China. * Corresponding author. Tel.: +86-791-83897597; fax: +86-791-83897320. E-mail address: [email protected]
1878-5220 © 2017 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2017.01.057
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Jiale Li et al. / Procedia Earth and Planetary Science 17 (2017) 837 – 840
2. Materials and methods 2.1. Study area Jiangxi Province, with an area of about 166,900 km 2, is located in the Southeast China Active Geothermal Zone. The province is well known for its abundant thermal water resources, where to date totally 96 hot springs and over 30 thermal water boreholes were reported 4 for the purposes of providing heat to buildings, recreational and therapeutic use, agriculture and aquaculture. The highest temperature of these hot springs reaches up to 84 ℃ with a total flow rate of 50-80 L/s1. The climate is humid, with an average annual precipitation of 1341-1940 mm. Annual average air temperature is 16.3-19.5 ℃. Well developed faults in this study area can be divided into four groups: the nearly E-Wtrending group, the NE-NEE trending group, the NNE-SN trending group and the N-W trending group, controlling the regional distributions of hot springs4. 2.2. Sampling and analysis A summary of 11 geothermal water samples including hot springs and boreholes were collected from Jiangxi Province (1 sample from Hunan Province, closed to Jiangxi Province), SE-China in October of 2015 (Fig.1).
Fig.1. Maps showing the location of geothermal water samples
Electrical conductivity (EC), pH, water temperature (T), and oxidation-reduction potential (ORP), total dissolved solid (TDS) were measured in-situ using Hach Potable Analyzer (Hach, HQ40d). SiO 2 concentration was analyzed in site by Hach Potable Spectrophotometer (Hach, DR2800). Samples were filtered (<0.45μm) and stored in HDPE bottles for anions analysis, while were acidified to pH≤2 using ultra-pure HNO3 for cations analysis. Samples for isotope analysis were not filtered and directly kept in HDPE bottles with bubbles removed. All analysis was conducted within 7 days after sampling. Alkalinity was determined using the Gran titration method within 24 h after sampling. Cations and anions were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES, iCAP-7400) and ion chromatography (IC, ICS-1100), respectively. Oxygen and hydrogen stable isotopes were analyzed using a MAT 253 mass spectrometer and the results are expressed in standard δ notation representing per mille deviation from the VSMOW standard. Precision is better than 0.20‰ for δ18O and 2.0‰ for δ2H, respectively. All measurements were performed at the State Key Laboratory for Nuclear Resources and Environment, East China University of Technology.
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Jiale Li et al. / Procedia Earth and Planetary Science 17 (2017) 837 – 840
3. Results and discussion 3.1. Hydrochemical characteristics of geothermal water Results of major hydrochemical analysis of geothermal water, including both physical and chemical parameters, are shown in Table 1. Water temperatures vary from 32.0 to 80.8 ℃ with an average of 53.4 ℃. All waters are nearneutral to alkaline with pH ranging between 6.30 and 9.23. The dominant cations and anions are Na+ and HCO3-, respectively. Geothermal waters are classified into five types: Ca·Na-HCO3 (sample labelled as 1) and CaHCO3·SO4 (samples labelled as 2 and 3) waters in the central part of the province, Na-SO4 type (sample labelled as 4) in the east, Na-HCO3 (samples labelled as 5, 6, 7, 8, and 10) and Na-HCO3·SO4 (samples labelled as 9 and 11) in the south and west, consistent with previous studies1,5. Concentrations of SiO2 in geothermal waters reaches up to 117.0 mg/L in the sample with the highest content of TDS and the highest EC, indicating that SiO2 is of great importance to control the hydrochemistry of geothermal water. Water of Na-HCO3 type is mainly distributed in the area characterized by granite and acid volcanic and controlled by the regional faults. Because of the large amount of precipitation and good runoff condition, the meteoric water infiltrated into the faulted zone, then underwent an interaction with crystalline rock, resulting geothermal water of Na-HCO3 type containing CO2. Differently, water of Na-SO4 type is distributed in the area characterized by metamorphic and sedimentary rocks, in addition that gypsum and pyrite are often oversaturated and precipitated at the spring exposed site. In this study, the geothermal spring sample of Na-SO4 type had strongly pungent smell probably resulting from H2S. Index T EC pH TDS SiO2 F-
Table 1. Hydrochemical results of geothermal water samples from Jiangxi Province, SE-China (T in ℃; EC in μs/cm; ORP in mV; TDS and concentration of chemical composition in mg/L) Max. Min. Mean Index Max. Min. Mean Index Max. Min. 80.8 32.0 53.4 K+ 93.30 1.98 19.96 Cl28.90 2.05 3264 307 806 Na+ 703.00 8.44 136.10 SO42451.00 13.20 9.23 6.30 7.88 Ca+ 121.00 2.34 36.65 HCO3- 1820.00 31.50 2g+ 1330 129 365 M 11.80 0.02 2.14 CO3 16.20 <5 117.0 2.1 54.8 Fe 1.28 <0.03 0.13 NO31.22 <0.08 13.70 3.61 8.67 NH4+ 0.26 <0.025 0.06 PO431.15 <0.014
Mean 8.53 89.24 326.52 3.03 0.19 0.19
Cl is considered as an indicator to explain hydrogeochemical processes in geothermal system for its conservative behaviour. A positive linear correlation is found between Cl- concentration and Na+, HCO3-, and SiO2 concentrations, with correlation coefficient (R2) of 0.914, 0.656, and 0.487, respectively, while no obvious correlation between Cl and SO42-, suggesting the meteoric origin and mixing with cold groundwater (Fig.2).
Fig.2. Relationship between Cl- and Na+, HCO3-, SiO2, and SO42- in geothermal water samples
3.2. Isotopic composition of geothermal water δ18O and δ2H values of geothermal waters vary from -8‰ to -6.1‰, and from -66.6‰ to -47.9‰, respectively. The relationship of δ18O and δ2H values shows samples are closed to global meteoric water line (GMWL) and local meteoric water line (LMWL, expressed as δ2H=8.31δ18O+11.36 with R2=0.97, Fig.3)6, demonstrating the geothermal water is of local meteoric origin, rather than the cold groundwater (<22ć)7.
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Jiale Li et al. / Procedia Earth and Planetary Science 17 (2017) 837 – 840
Fig.3. Isotopic compositions of geothermal waters of different types
The slight oxygen shift possibly results from the interaction between groundwater and the bedrock. Several bubbles were obviously observed in geothermal waters numbered 2, 6, 7, 9 when sampling. Due to the observation of oxygen shift in most samples, it can be concluded that the high content of CO2 which probably provide more protons for water-rock interaction8 leads to oxygen isotopic exchange. According to the correlation between altitude and isotopic composition of local precipitation defined as the following equations 3: δ2H = - 25.11 – 0.047H δ18O = - 4.82 – 0.0032H
(1) (2)
Based on the isotopic compositions of these geothermal waters, the recharge altitudes of the geothermal waters are in the range of 400-995 m. 4. Conclusions A summary of 11 geothermal water samples including hot springs and boreholes were collected from Jiangxi Province, SE-China for hydrochemical and isotopic analysis. Results showed that the geothermal water temperatures ranged from 32.0 to 80.8 ℃ with an average of 53.4 ℃ and dominated cations and anions are Na+ and HCO3-, respectively. The hydrochemical types differ in the different areas due to the geological structure and lithology and experienced processes. The hydrochemical and isotopic compositions suggest the meteoric origin of geothermal water with recharge altitudes in the range of 400-995 m. Mixing with cold groundwater as well as SiO2 content influence the hydrochemistry of geothermal waters. Acknowledgements This study is supported by China National Foundation of Natural Sciences (No. 41511130031) and Doctoral Scientific Research Foundation of East China University of Technology (No. DHBK 2015307) . References 1. Gao B, Sun ZX, Liu JH. Exploitation and protection of geothermal hotsprings in Jiangxi Province. Water Resources Protection 2006; 22: 9294 (in Chinese with English abstract). 2. Sun ZX. The formation conditions of hot springs in Jiangxi Province, SE-China. East China Geological Institute, Fuzhou, 1988 (in Chinese). 3. Sun ZX, Li XL. Studies of geothermal waters in Jiangxi Province using isotope techniques. Science in China (Series E) 2001; 44: 144-150. 4. Sun ZX, Liu JH, Gao B. Hydrogeochemistry and direct use of hot springs in Jiangxi Province, SE-China. Proceedings of the Proceedings World Geothermal Congress, Bali: Indonesia; 2010. 5. Sun ZX, Zhang WM. Subsurface temperature estimation of geochermal reserviors in the Hengjing hot spring area, Jiangxi Province, SE-China. Proceedings of the Proceedings World Geochermal Congress, Antalya: Turkey; 2005. 6. Sun ZX, Li XL, Shi WJ. Isopotic hydrogeochemistry of mid-low temperature geothermal water in Jiangxi Province. Journal of East China Geological Institute 1992; 15: 243-248 (in Chinese with English abstract). 7. Chen GX, Wang GC, Sun ZX, Liu JH. The isotopic and chemical characteristics of geothermal fluids from two selected hot spring areas in Jiangxi Province, SE-China. Proceedings of the World Geothermal Congress, Bali: Indonesia; 2010. 8. Zhang WM, Wang YX, Sun ZX. A study of the CO2 genesis of the carbonated hot springs in Hengjing, southern Jiangxin. Hydrogeology and Engeerning Geology 2005; 6: 6-9 (in Chinese with English abstract).
ScienceDirect Procedia Earth and Planetary Science 17 (2017) 837 – 840
15th Water-Rock Interaction International Symposium, WRI-15
Sources of geothermal water in Jiangxi Province, SE-China: evidences from hydrochemistry and isotopic composition Jiale Lia, Bai Gaoa, Yihui Donga, Gongxin Chena, Zhanxue Suna,1 a
School of Water Resources and Environmental Engineering, East China University of Technology, Nanchang, 330013, China
Abstract Jiangxi Province is one of the regions where geothermal water is widely distributed in China, with discovered 96 hot springs and over 30 thermal water boreholes. Eleven geothermal water samples were collected and analyzed for hydrochemical and isotopic characteristics to distinguish the sources of geothermal water in Jiangxi Province, SE-China. Results showed that water temperatures varied from 32.0 to 80.8 ℃ with an average of 53.4 ℃ and the dominated compositions are Na-HCO type.The hydrogeochemical characteristics as well as isotopic compositions suggest the meteoric origin of geothermal water with recharge altitudes in the range of 400-995 m. Mixing with cold groundwater influences the hydrochemistry of geothermal water. This study furthers the understanding of sources of geothermal water and provides a theoretical basis for better exploitation of geothermal water in the province. 2017Published The Authors. Published by Elsevier B.V. © 2017 by Elsevier B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of WRI-15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 Keywords: geothermal water; Jiangxi Province; hydrochemistry; isotopic characteristics
1. Introduction Abundant geothermal reserves have been discovered in China and applied in electricity generating, heating, crops planting, floriculture, etc1. Jiangxi Province is one of the regions where geothermal water is widely distributed in China, and has attracted researchers’ attention on the forming condition and hydrochemical compositions for around three decades2,3. The objects of this study are to display the hydrochemical and isotopic characteristics, and to identify the sources of geothermal water. These results will be helpful for expanding our knowledge of geothermal water and better developing geothermal water in the province, China. * Corresponding author. Tel.: +86-791-83897597; fax: +86-791-83897320. E-mail address: [email protected]
1878-5220 © 2017 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2017.01.057
838
Jiale Li et al. / Procedia Earth and Planetary Science 17 (2017) 837 – 840
2. Materials and methods 2.1. Study area Jiangxi Province, with an area of about 166,900 km 2, is located in the Southeast China Active Geothermal Zone. The province is well known for its abundant thermal water resources, where to date totally 96 hot springs and over 30 thermal water boreholes were reported 4 for the purposes of providing heat to buildings, recreational and therapeutic use, agriculture and aquaculture. The highest temperature of these hot springs reaches up to 84 ℃ with a total flow rate of 50-80 L/s1. The climate is humid, with an average annual precipitation of 1341-1940 mm. Annual average air temperature is 16.3-19.5 ℃. Well developed faults in this study area can be divided into four groups: the nearly E-Wtrending group, the NE-NEE trending group, the NNE-SN trending group and the N-W trending group, controlling the regional distributions of hot springs4. 2.2. Sampling and analysis A summary of 11 geothermal water samples including hot springs and boreholes were collected from Jiangxi Province (1 sample from Hunan Province, closed to Jiangxi Province), SE-China in October of 2015 (Fig.1).
Fig.1. Maps showing the location of geothermal water samples
Electrical conductivity (EC), pH, water temperature (T), and oxidation-reduction potential (ORP), total dissolved solid (TDS) were measured in-situ using Hach Potable Analyzer (Hach, HQ40d). SiO 2 concentration was analyzed in site by Hach Potable Spectrophotometer (Hach, DR2800). Samples were filtered (<0.45μm) and stored in HDPE bottles for anions analysis, while were acidified to pH≤2 using ultra-pure HNO3 for cations analysis. Samples for isotope analysis were not filtered and directly kept in HDPE bottles with bubbles removed. All analysis was conducted within 7 days after sampling. Alkalinity was determined using the Gran titration method within 24 h after sampling. Cations and anions were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES, iCAP-7400) and ion chromatography (IC, ICS-1100), respectively. Oxygen and hydrogen stable isotopes were analyzed using a MAT 253 mass spectrometer and the results are expressed in standard δ notation representing per mille deviation from the VSMOW standard. Precision is better than 0.20‰ for δ18O and 2.0‰ for δ2H, respectively. All measurements were performed at the State Key Laboratory for Nuclear Resources and Environment, East China University of Technology.
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Jiale Li et al. / Procedia Earth and Planetary Science 17 (2017) 837 – 840
3. Results and discussion 3.1. Hydrochemical characteristics of geothermal water Results of major hydrochemical analysis of geothermal water, including both physical and chemical parameters, are shown in Table 1. Water temperatures vary from 32.0 to 80.8 ℃ with an average of 53.4 ℃. All waters are nearneutral to alkaline with pH ranging between 6.30 and 9.23. The dominant cations and anions are Na+ and HCO3-, respectively. Geothermal waters are classified into five types: Ca·Na-HCO3 (sample labelled as 1) and CaHCO3·SO4 (samples labelled as 2 and 3) waters in the central part of the province, Na-SO4 type (sample labelled as 4) in the east, Na-HCO3 (samples labelled as 5, 6, 7, 8, and 10) and Na-HCO3·SO4 (samples labelled as 9 and 11) in the south and west, consistent with previous studies1,5. Concentrations of SiO2 in geothermal waters reaches up to 117.0 mg/L in the sample with the highest content of TDS and the highest EC, indicating that SiO2 is of great importance to control the hydrochemistry of geothermal water. Water of Na-HCO3 type is mainly distributed in the area characterized by granite and acid volcanic and controlled by the regional faults. Because of the large amount of precipitation and good runoff condition, the meteoric water infiltrated into the faulted zone, then underwent an interaction with crystalline rock, resulting geothermal water of Na-HCO3 type containing CO2. Differently, water of Na-SO4 type is distributed in the area characterized by metamorphic and sedimentary rocks, in addition that gypsum and pyrite are often oversaturated and precipitated at the spring exposed site. In this study, the geothermal spring sample of Na-SO4 type had strongly pungent smell probably resulting from H2S. Index T EC pH TDS SiO2 F-
Table 1. Hydrochemical results of geothermal water samples from Jiangxi Province, SE-China (T in ℃; EC in μs/cm; ORP in mV; TDS and concentration of chemical composition in mg/L) Max. Min. Mean Index Max. Min. Mean Index Max. Min. 80.8 32.0 53.4 K+ 93.30 1.98 19.96 Cl28.90 2.05 3264 307 806 Na+ 703.00 8.44 136.10 SO42451.00 13.20 9.23 6.30 7.88 Ca+ 121.00 2.34 36.65 HCO3- 1820.00 31.50 2g+ 1330 129 365 M 11.80 0.02 2.14 CO3 16.20 <5 117.0 2.1 54.8 Fe 1.28 <0.03 0.13 NO31.22 <0.08 13.70 3.61 8.67 NH4+ 0.26 <0.025 0.06 PO431.15 <0.014
Mean 8.53 89.24 326.52 3.03 0.19 0.19
Cl is considered as an indicator to explain hydrogeochemical processes in geothermal system for its conservative behaviour. A positive linear correlation is found between Cl- concentration and Na+, HCO3-, and SiO2 concentrations, with correlation coefficient (R2) of 0.914, 0.656, and 0.487, respectively, while no obvious correlation between Cl and SO42-, suggesting the meteoric origin and mixing with cold groundwater (Fig.2).
Fig.2. Relationship between Cl- and Na+, HCO3-, SiO2, and SO42- in geothermal water samples
3.2. Isotopic composition of geothermal water δ18O and δ2H values of geothermal waters vary from -8‰ to -6.1‰, and from -66.6‰ to -47.9‰, respectively. The relationship of δ18O and δ2H values shows samples are closed to global meteoric water line (GMWL) and local meteoric water line (LMWL, expressed as δ2H=8.31δ18O+11.36 with R2=0.97, Fig.3)6, demonstrating the geothermal water is of local meteoric origin, rather than the cold groundwater (<22ć)7.
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Jiale Li et al. / Procedia Earth and Planetary Science 17 (2017) 837 – 840
Fig.3. Isotopic compositions of geothermal waters of different types
The slight oxygen shift possibly results from the interaction between groundwater and the bedrock. Several bubbles were obviously observed in geothermal waters numbered 2, 6, 7, 9 when sampling. Due to the observation of oxygen shift in most samples, it can be concluded that the high content of CO2 which probably provide more protons for water-rock interaction8 leads to oxygen isotopic exchange. According to the correlation between altitude and isotopic composition of local precipitation defined as the following equations 3: δ2H = - 25.11 – 0.047H δ18O = - 4.82 – 0.0032H
(1) (2)
Based on the isotopic compositions of these geothermal waters, the recharge altitudes of the geothermal waters are in the range of 400-995 m. 4. Conclusions A summary of 11 geothermal water samples including hot springs and boreholes were collected from Jiangxi Province, SE-China for hydrochemical and isotopic analysis. Results showed that the geothermal water temperatures ranged from 32.0 to 80.8 ℃ with an average of 53.4 ℃ and dominated cations and anions are Na+ and HCO3-, respectively. The hydrochemical types differ in the different areas due to the geological structure and lithology and experienced processes. The hydrochemical and isotopic compositions suggest the meteoric origin of geothermal water with recharge altitudes in the range of 400-995 m. Mixing with cold groundwater as well as SiO2 content influence the hydrochemistry of geothermal waters. Acknowledgements This study is supported by China National Foundation of Natural Sciences (No. 41511130031) and Doctoral Scientific Research Foundation of East China University of Technology (No. DHBK 2015307) . References 1. Gao B, Sun ZX, Liu JH. Exploitation and protection of geothermal hotsprings in Jiangxi Province. Water Resources Protection 2006; 22: 9294 (in Chinese with English abstract). 2. Sun ZX. The formation conditions of hot springs in Jiangxi Province, SE-China. East China Geological Institute, Fuzhou, 1988 (in Chinese). 3. Sun ZX, Li XL. Studies of geothermal waters in Jiangxi Province using isotope techniques. Science in China (Series E) 2001; 44: 144-150. 4. Sun ZX, Liu JH, Gao B. Hydrogeochemistry and direct use of hot springs in Jiangxi Province, SE-China. Proceedings of the Proceedings World Geothermal Congress, Bali: Indonesia; 2010. 5. Sun ZX, Zhang WM. Subsurface temperature estimation of geochermal reserviors in the Hengjing hot spring area, Jiangxi Province, SE-China. Proceedings of the Proceedings World Geochermal Congress, Antalya: Turkey; 2005. 6. Sun ZX, Li XL, Shi WJ. Isopotic hydrogeochemistry of mid-low temperature geothermal water in Jiangxi Province. Journal of East China Geological Institute 1992; 15: 243-248 (in Chinese with English abstract). 7. Chen GX, Wang GC, Sun ZX, Liu JH. The isotopic and chemical characteristics of geothermal fluids from two selected hot spring areas in Jiangxi Province, SE-China. Proceedings of the World Geothermal Congress, Bali: Indonesia; 2010. 8. Zhang WM, Wang YX, Sun ZX. A study of the CO2 genesis of the carbonated hot springs in Hengjing, southern Jiangxin. Hydrogeology and Engeerning Geology 2005; 6: 6-9 (in Chinese with English abstract).