Formation Model of Geothermal Water in Chaya of Tibet: Perspective from Hydrochemistry and Stable Isotopes

doi:10.19657/j.geoscience.1000-8527.2021.013

Abstract

Abstract:

Two occurrences of geothermal waters have been identified in Chaya of Tibet, and the one at Niangqu has a flow rate of 23,356 m ³/d and a temperature of 36 ℃. Understanding its hydrochemical and isotopic characteristics and groundwater circulation model is of great significance to tunnel design and construction. To clarify its hydrochemical characteristics and formation model, we analyzed the isotope hydrochemistry of water samples from these two geothermal water occurrences. The two geothermal waters contain main cations of Ca ²⁺ and Mg ²⁺, main anions of SO₄^2- and HCO₃^-. They are classified into SO₄-Ca·Mg and SO₄·HCO₃-Ca·Mg water-type, and have TDS content of 1,255 to 2,051 mg/L. Stable hydrogen and oxygen isotopes indicate that the main source of geothermal waters is meteoric precipitation, as featured by a ¹⁸O drift, reflecting O-isotope exchange between hot water and the wall rocks. Elevation of the recharge area is of 4,146 to 4,185 m, the temperature of the geothermal reservoir is about 53.1 to 61.0 ℃, and the water circulation depth is approximately 1,409 to 2,020 m. Formation model of the geothermal water is proposed as follows: after receiving recharge from meteoric water infiltration in high mountainous area from the northeast, groundwater may have flowed along the fractures between the karst layers and was heated by the geothermal heat flow through deep circulation. The water may have risen along faults due to the aquitard structure, mixed with 0.79 to 0.91 shallow groundwater, and formed springs in valley topographic incision. Integrating hydrogeology and tunnel location, the eastern karst-rich water area poses less threat on tunnel water incursion. The western karst-rich water area has tectonic karst water for the tunnel, and the risk of high-pressure water incursion should benoticed.

Key words: geothermal water, hydrochemistry, stable isotope, formation model

CLC Number:

P641.1

ZHANG Chunchao, LI Xiangquan, MA Jianfei, FU Changchang, BAI Zhanxue. Formation Model of Geothermal Water in Chaya of Tibet: Perspective from Hydrochemistry and Stable Isotopes[J]. Geoscience, 2021, 35(01): 199-208.

Figures/Tables 12

Fig.1 Location and simplified geological map of the study area

Fig.2 Hydrogeological profile AA' of the study area(profile’s location seeing in Fig.1)

Table 1 Elemental and hydrogen-oxygen isotopic compositions of water samples from the study area

序号	样品编号	样品类型	水化学类型	pH值	水化学组分/(mg·L^-1)												同位素/‰
序号	样品编号	样品类型	水化学类型	pH值	溶解性总固体	K⁺	Na⁺	Ca²⁺	Mg²⁺	Cl^-	S $O 4 2 -$	HC $O 3 -$	F^-	偏硅酸	Sr²⁺		δD	δ¹⁸O
1	MKA15	鲁江热水(T₃b)	Ca-Mg-SO₄-HCO₃	7.18	1 255.0	2.40	14.54	271.10	58.90	4.89	754.00	263.20	1.60	19.66	6.99	-138			-16.3
2	MKA29	娘曲热水(T₃b)	Ca-Mg-SO₄	7.35	2 051.0	3.45	35.10	422.10	95.05	5.59	1 360.00	215.40	2.34	24.29	11.49	-139			-18.1
3	XMB33	岩溶泉水(T₃b)	Ca-HCO₃	7.99	159.1	0.45	1.77	48.61	4.70	1.75	14.36	155.40	0.17	8.73	0.09	-135			-17.7
4	MKA33	岩溶泉水(T₃b)	Ca-Mg-SO₄	7.17	2 562.0	0.63	5.59	586.20	100.10	2.10	1 752.00	203.80	1.70	12.48	12.95	-139			-18.2
5	XMB43	岩溶泉水(D₃z)	Ca-Mg-HCO₃-SO₄	7.63	286.5	0.66	3.98	57.95	22.01	1.75	102.30	178.70	0.21	7.34	0.41	-135			-18.2
6	MKA34	地表水	Ca-Mg-HCO₃	7.99	159.0	1.30	3.95	29.69	15.74	1.75	19.70	155.50	0.18	9.15	0.21	-126			-16.5
7	MKA41	地表水	Ca-Mg-HCO₃	7.83	124.3	1.77	10.16	25.21	6.09	1.75	4.38	131.00	0.19	7.79	0.13	-123			-16.2
8	MKA44	地表水	Ca-Mg-HCO₃	7.58	225.3	2.37	11.52	46.43	17.27	1.75	18.59	233.90	0.21	10.48	0.33	-131			-16.7
9	MKA01	地表水	Mg-Ca-HCO₃-SO₄	7.66	127.9	0.87	3.83	20.77	12.68	1.75	30.18	101.70	0.16	5.94	0.16	-122			-16.5
10	MKA08	地表水	Ca-Mg-HCO₃-SO₄	7.63	121.7	1.10	6.11	21.20	9.67	1.40	27.31	95.71	0.16	6.28	0.13	-123			-16.3
11	MKA12	地表水	Ca-Mg-HCO₃	7.85	135.8	1.04	5.48	30.73	9.18	1.40	12.57	137.60	0.16	6.03	0.15	-122			-16.3
12	MKA22	地表水	Ca-Mg-HCO₃	8.52	142.8	1.31	6.92	27.62	11.44	1.75	6.47	143.60	0.16	9.71	0.32	-131			-17.3
13	XMB41	地表水	Ca-Mg-HCO₃-SO₄	7.73	185.6	0.67	3.71	41.81	13.55	1.40	39.63	155.40	0.22	6.94	0.21	-128			-16.8
14	XMB48	地表水	Ca-Mg-HCO₃-SO₄	8.40	196.2	0.77	3.73	43.92	14.14	1.75	44.52	148.20	0.22	6.52	0.22	-128			-17.0
15	XMB49	地表水	Ca-Na-HCO₃	7.54	107.4	1.34	8.87	22.44	4.23	1.40	4.81	110.60	0.21	9.47	0.14	-125			-16.4
16	XMB50	地表水	Ca-Mg-HCO₃-SO₄	7.71	273.5	0.89	3.75	61.44	15.85	1.75	107.10	149.40	0.33	7.15	0.79	-123			-16.5
17	XMB52	地表水	Ca-Mg-HCO₃	7.49	197.5	1.38	5.13	52.81	9.12	1.75	24.25	188.40	0.20	7.79	0.16	-130			-17.1
18	XMB57	地表水	Ca-Mg-HCO₃	8.47	217.2	2.30	13.30	40.05	18.47	1.05	24.71	204.60	0.24	8.11	0.24	-126			-16.3
19	XMB58	地表水	Na-Mg-Ca-HCO₃	7.88	360.3	3.19	71.21	32.31	21.10	9.78	36.96	340.40	0.49	13.51	0.50	-129			-16.3
20	XMB63	地表水	Ca-Mg-HCO₃	7.66	217.0	2.04	10.16	41.28	18.41	1.75	21.25	221.30	0.28	10.46	0.66	-130			-16.7
21	XMB64	地表水	Ca-Mg-HCO₃	7.55	203.3	1.73	12.66	41.65	14.70	1.75	11.95	215.40	0.23	12.01	0.28	-132			-16.7
22	XMB66	地表水	Ca-Mg-HCO₃	7.89	120.8	1.28	8.36	24.30	7.59	1.75	4.31	125.60	0.19	10.32	0.20	-132			-17.1
23	XMB69	地表水	Ca-Mg-HCO₃-SO₄	7.23	130.5	1.20	3.78	25.32	10.93	1.75	23.02	113.70	0.16	6.91	0.13	-127			-16.9
24	XMB71	地表水	Mg-Ca-HCO₃	8.00	232.7	1.97	5.35	38.43	30.08	1.75	15.82	256.60	0.24	10.56	0.19	-134			-17.1
25	XMB73	地表水	Ca-Mg-HCO₃	7.19	115.7	1.46	5.99	19.33	9.47	1.75	10.73	110.70	0.17	11.54	0.15	-126			-16.8
26	CY01	雨水	Ca-HCO₃	6.54	12.1	0.45	0.22	0.39	0.09	1.75	2.07	8.97	<0.10	<1.00	0.01	-127			-16.9

Table 1 Elemental and hydrogen-oxygen isotopic compositions of water samples from the study area

序号	样品编号	样品类型	水化学类型	pH值	水化学组分/(mg·L^-1)												同位素/‰
序号	样品编号	样品类型	水化学类型	pH值	溶解性总固体	K⁺	Na⁺	Ca²⁺	Mg²⁺	Cl^-	S $O 4 2 -$	HC $O 3 -$	F^-	偏硅酸	Sr²⁺		δD	δ¹⁸O
1	MKA15	鲁江热水(T₃b)	Ca-Mg-SO₄-HCO₃	7.18	1 255.0	2.40	14.54	271.10	58.90	4.89	754.00	263.20	1.60	19.66	6.99	-138			-16.3
2	MKA29	娘曲热水(T₃b)	Ca-Mg-SO₄	7.35	2 051.0	3.45	35.10	422.10	95.05	5.59	1 360.00	215.40	2.34	24.29	11.49	-139			-18.1
3	XMB33	岩溶泉水(T₃b)	Ca-HCO₃	7.99	159.1	0.45	1.77	48.61	4.70	1.75	14.36	155.40	0.17	8.73	0.09	-135			-17.7
4	MKA33	岩溶泉水(T₃b)	Ca-Mg-SO₄	7.17	2 562.0	0.63	5.59	586.20	100.10	2.10	1 752.00	203.80	1.70	12.48	12.95	-139			-18.2
5	XMB43	岩溶泉水(D₃z)	Ca-Mg-HCO₃-SO₄	7.63	286.5	0.66	3.98	57.95	22.01	1.75	102.30	178.70	0.21	7.34	0.41	-135			-18.2
6	MKA34	地表水	Ca-Mg-HCO₃	7.99	159.0	1.30	3.95	29.69	15.74	1.75	19.70	155.50	0.18	9.15	0.21	-126			-16.5
7	MKA41	地表水	Ca-Mg-HCO₃	7.83	124.3	1.77	10.16	25.21	6.09	1.75	4.38	131.00	0.19	7.79	0.13	-123			-16.2
8	MKA44	地表水	Ca-Mg-HCO₃	7.58	225.3	2.37	11.52	46.43	17.27	1.75	18.59	233.90	0.21	10.48	0.33	-131			-16.7
9	MKA01	地表水	Mg-Ca-HCO₃-SO₄	7.66	127.9	0.87	3.83	20.77	12.68	1.75	30.18	101.70	0.16	5.94	0.16	-122			-16.5
10	MKA08	地表水	Ca-Mg-HCO₃-SO₄	7.63	121.7	1.10	6.11	21.20	9.67	1.40	27.31	95.71	0.16	6.28	0.13	-123			-16.3
11	MKA12	地表水	Ca-Mg-HCO₃	7.85	135.8	1.04	5.48	30.73	9.18	1.40	12.57	137.60	0.16	6.03	0.15	-122			-16.3
12	MKA22	地表水	Ca-Mg-HCO₃	8.52	142.8	1.31	6.92	27.62	11.44	1.75	6.47	143.60	0.16	9.71	0.32	-131			-17.3
13	XMB41	地表水	Ca-Mg-HCO₃-SO₄	7.73	185.6	0.67	3.71	41.81	13.55	1.40	39.63	155.40	0.22	6.94	0.21	-128			-16.8
14	XMB48	地表水	Ca-Mg-HCO₃-SO₄	8.40	196.2	0.77	3.73	43.92	14.14	1.75	44.52	148.20	0.22	6.52	0.22	-128			-17.0
15	XMB49	地表水	Ca-Na-HCO₃	7.54	107.4	1.34	8.87	22.44	4.23	1.40	4.81	110.60	0.21	9.47	0.14	-125			-16.4
16	XMB50	地表水	Ca-Mg-HCO₃-SO₄	7.71	273.5	0.89	3.75	61.44	15.85	1.75	107.10	149.40	0.33	7.15	0.79	-123			-16.5
17	XMB52	地表水	Ca-Mg-HCO₃	7.49	197.5	1.38	5.13	52.81	9.12	1.75	24.25	188.40	0.20	7.79	0.16	-130			-17.1
18	XMB57	地表水	Ca-Mg-HCO₃	8.47	217.2	2.30	13.30	40.05	18.47	1.05	24.71	204.60	0.24	8.11	0.24	-126			-16.3
19	XMB58	地表水	Na-Mg-Ca-HCO₃	7.88	360.3	3.19	71.21	32.31	21.10	9.78	36.96	340.40	0.49	13.51	0.50	-129			-16.3
20	XMB63	地表水	Ca-Mg-HCO₃	7.66	217.0	2.04	10.16	41.28	18.41	1.75	21.25	221.30	0.28	10.46	0.66	-130			-16.7
21	XMB64	地表水	Ca-Mg-HCO₃	7.55	203.3	1.73	12.66	41.65	14.70	1.75	11.95	215.40	0.23	12.01	0.28	-132			-16.7
22	XMB66	地表水	Ca-Mg-HCO₃	7.89	120.8	1.28	8.36	24.30	7.59	1.75	4.31	125.60	0.19	10.32	0.20	-132			-17.1
23	XMB69	地表水	Ca-Mg-HCO₃-SO₄	7.23	130.5	1.20	3.78	25.32	10.93	1.75	23.02	113.70	0.16	6.91	0.13	-127			-16.9
24	XMB71	地表水	Mg-Ca-HCO₃	8.00	232.7	1.97	5.35	38.43	30.08	1.75	15.82	256.60	0.24	10.56	0.19	-134			-17.1
25	XMB73	地表水	Ca-Mg-HCO₃	7.19	115.7	1.46	5.99	19.33	9.47	1.75	10.73	110.70	0.17	11.54	0.15	-126			-16.8
26	CY01	雨水	Ca-HCO₃	6.54	12.1	0.45	0.22	0.39	0.09	1.75	2.07	8.97	<0.10	<1.00	0.01	-127			-16.9

Fig.3 Piper diagrams of water samples from the study area

Fig.4 δD vs. δ18O plot of water samples from the study area

Table 2 Elevation calculation for hot-spring recharge area

水样类型	标高/m	δD/‰	补给高程/m (据δD值)	取值/m
鲁江热水	3 660	-138	4 146	4 146
娘曲热水	3 670	-139	4 185	4 185

Table 3 Temperature calculation of the geothermal reservoir

水样类型	水温/℃	计算热储温度/℃		公式(3)和(4) 平均温度
水样类型	水温/℃	公式(3)	公式(4)	公式(3)和(4) 平均温度
鲁江热水	24	53.0	53.3	53.1
娘曲热水	36	61.0	60.9	61.0

Table 4 Empirical values of temperature, enthalpy and SiO2 contents of thermal groundwater[19]

温度/ ℃	焓/ (4.1868 J/g)	SiO₂含量/ (mg/L)	温度/ ℃	焓/ (4.1868 J/g)	SiO₂含量/ (mg/L)
50	50.0	13.5	200	203.6	265
75	75.0	26.6	225	230.9	365
100	100.1	48.0	250	259.2	486
125	125.4	80.0	275	289.0	614
150	151.0	125.0	300	321.0	692
175	177.0	185.0

Table 5 Mixing ratio calculation results for the Lujiang thermal groundwater

温度 /℃	S_c	S_h	S_s	C(SiO₂)	S(SiO₂)	h(SiO₂)	X₁	X₂
50	4.15	50.0	18.1	3	15.1	13.5	0.70	-0.15
75	4.15	75.0	18.1	3	15.1	26.6	0.80	0.49
100	4.15	100.1	18.1	3	15.1	48.0	0.85	0.73
125	4.15	125.4	18.1	3	15.1	80.0	0.88	0.84
150	4.15	151.0	18.1	3	15.1	125.0	0.91	0.90
175	4.15	177.0	18.1	3	15.1	185.0	0.92	0.93
200	4.15	203.6	18.1	3	15.1	265.0	0.93	0.95
225	4.15	230.9	18.1	3	15.1	365.0	0.94	0.97
250	4.15	259.2	18.1	3	15.1	486.0	0.95	0.97
275	4.15	289.0	18.1	3	15.1	614.0	0.95	0.98
300	4.15	321.0	18.1	3	15.1	692.0	0.96	0.98

Table 6 Mixing ratio calculation results for the Niangqu thermal groundwater

温度 /℃	S_c	S_h	S_s	C(SiO₂)	S(SiO₂)	h(SiO₂)	X₁	X₂
50	4.15	50.0	30.98	3	18.7	13.5	0.41	-0.50
75	4.15	75.0	30.98	3	18.7	26.6	0.62	0.33
100	4.15	100.1	30.98	3	18.7	48.0	0.72	0.65
125	4.15	125.4	30.98	3	18.7	80.0	0.78	0.80
150	4.15	151.0	30.98	3	18.7	125.0	0.82	0.87
175	4.15	177.0	30.98	3	18.7	185.0	0.84	0.91
200	4.15	203.6	30.98	3	18.7	265.0	0.87	0.94
225	4.15	230.9	30.98	3	18.7	365.0	0.88	0.96
250	4.15	259.2	30.98	3	18.7	486.0	0.89	0.97
275	4.15	289.0	30.98	3	18.7	614.0	0.91	0.97
300	4.15	321.0	30.98	3	18.7	692.0	0.92	0.98

Fig.5 Mixing ratio of cold water in the Lujiang (a) and Niangqu (b) thermal groundwater

Fig.6 Formation model of the Niangqu geothermal water in Wangka, Chaya

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