Geochemical Characteristics of Medium-high Temperature Geothermal Fluids in West Sichuan and Their Geological Implications

doi:10.19657/j.geoscience.1000-8527.2021.015

Abstract

Abstract:

West Sichuan is one of the main high-temperature geothermal resources distribution areas in China. The space-time distribution and material source of hydrothermal activities are closely related to hydrothermal diagenesis. The geochemical characteristics of geothermal fluid reflect the deep geochemical process information during the process of fluid rising to the surface. The fluid chemical characteristics of typical geothermal fields at Xianshuihe, Ganzi-Litang, and Jinshajiang along the fault zone are compared and analyzed. The results show that the groundwater type in the area is HCO₃-Na. K ⁺, Na ⁺, HCO₃ ^- and Mg ²⁺ in the geothermal water of Ganzi-Litang have similar material sources as Cl ^-, and they come from the deep earth besides mineral dissolution. The geothermal fluid runoff in the study area is long, with the depth of 2,189.93-5,620.52 m. The proportion of cold water mixed into geothermal fluid is 56%-78%, thus, the water rock interaction has not yet reached the equilibrium state. During the circulation process, it is affected by the dissolution of silicate minerals containing calcium and magnesium. The fluid path convergence and controlling factors are clarified. The results enhance the understanding of geothermal resource distribution patterns and genesis in west Sichuan, and provides reference for engineering construction in the region.

Key words: geochemistry, heat-transfer mechanism, genetic mechanism, west Sichuan

CLC Number:

P642

ZHANG Wei, WANG Guiling, ZHAO Jiayi, LIU Feng. Geochemical Characteristics of Medium-high Temperature Geothermal Fluids in West Sichuan and Their Geological Implications[J]. Geoscience, 2021, 35(01): 188-198.

Figures/Tables 15

Fig.1 Fault structure, distribution of geothermal zone and location of sampling points in the study area

Fig.2 Ion concentration of water samples from the study area

Table 1 Hydrochemical parameters of groundwater samples from the study area

区域	编号	水温/℃	pH	K⁺	Na⁺	Ca²⁺	Mg²⁺	Cl^-	S $O 4 2 -$	HC $O 3 -$	TDS
鲜水河地热带	KD01	68.0	6.8	31.00	320.00	86.17	23.32	85.10	19.04	1 159.30	1 268.20
	KD02	47.0	6.9	30.00	270.00	71.14	16.42	64.89	6.48	897.00	1 009.30
	KD03	26.0	7.1	26.00	200.00	62.12	26.14	46.80	3.76	784.10	846.50
	KD04	32.0	6.8	12.00	185.00	40.08	4.26	35.45	3.00	549.20	584.10
	KD05	47.0	7.0	34.00	290.00	45.09	7.90	76.22	8.60	915.30	1 132.00
	KD06	61.0	7.1	36.00	370.00	90.18	21.28	85.09	2.90	1 305.80	1 222.00
	KD07	46.0	7.4	34.00	338.00	86.17	22.50	88.63	1.35	1 220.30	1 275.40
	KD08	70.0	8.7	56.00	550.00	12.02	29.18	260.60	<0.10	1 019.00	1 649.60
	KD09	81.0	7.6	55.00	400.00	40.08	14.59	294.30	75.80	720.00	1 430.80
甘孜—理塘地热带	LT10	54.0	8.2	1.92	53.57	3.92	0.18	7.00	16.50	128.10	202.80
	LT11	72.0	8.1	2.48	63.66	3.82	0.02	1.75	15.28	140.30	238.00
	LT12	76.0	8.0	2.63	65.40	4.06	0.03	1.75	16.66	146.40	253.90
	LT13	75.0	7.9	2.80	72.32	3.36	0.03	1.75	15.30	161.70	275.10
	LT14	79.7	7.8	2.80	72.01	4.32	0.01	1.75	14.55	158.60	272.60
	LT15	80.0	7.1	57.69	477.50	27.52	10.92	68.28	7.72	1 522.00	1 585.00
	LT16	84.0	7.0	57.40	480.20	24.05	10.43	65.83	12.07	1 483.00	1 564.00
	LT17		7.1	62.41	525.70	23.44	10.53	68.28	10.97	1 488.00	1 618.00
	LT18	56.0	6.8	53.60	443.60	29.66	12.93	61.97	10.41	1 327.00	1 442.00
	LT19	64.0	6.7	54.57	446.60	29.79	12.97	59.52	11.00	1 422.00	1 469.00
金沙江地热带	BT20	94.0	8.6	19.94	267.20	5.60	0.23	40.88	70.14	516.60	871.50
	BT21	88.0	9.3	29.86	333.20	1.02	0.06	17.77	28.81	319.80	992.30
	BT22	90.0	9.3	29.98	324.80	2.06	0.08	47.99	52.71	418.80	1 047.00
	BT23	89.0	9.2	34.53	358.90	1.34	0.02	19.19	32.84	379.10	1 079.00
	BT24	81.0	9.3	29.81	317.00	0.81	<0.013	39.10	30.17	365.00	991.20
	BT25	90.0	8.4	27.62	290.80	4.02	0.21	42.65	42.06	617.50	909.00
	BT26	88.0	9.4	30.48	321.80	0.69	<0.013	51.54	27.50	209.70	1 065.00
	BT27	91.0	9.6	31.36	335.80	0.80	<0.013	51.54	46.19	190.10	1 105.00
	BT28	89.0	9.0	28.86	343.80	0.65	<0.013	51.90	25.45	428.00	1 041.00
	BT29	48.0	8.4	2.60	104.50	9.34	0.70	8.89	16.33	226.20	332.10
	BT30	53.0	8.3	2.41	90.24	11.61	0.81	8.89	20.74	217.00	305.50
	BT31	64.0	7.8	6.21	124.80	16.30	0.35	16.00	25.46	314.90	476.60
	BT32	75.0	7.5	6.69	128.90	17.11	0.39	13.86	23.52	342.40	483.20
	BT33	86.0	8.2	26.00	353.20	6.41	2.92	33.77	19.47	679.30	1 071.00
	BT34	90.0	9.1	26.23	351.60	0.77	0.10	23.10	20.30	114.30	1 039.00
	BT35	90.0	7.8	26.80	358.20	1.67	0.20	33.77	42.62	885.90	1 071.00
	BT36	90.0	8.0	25.24	345.20	0.80	0.10	33.06	42.09	862.10	1 033.00
	BT37	70.0	7.6	30.51	380.40	7.77	2.51	32.70	25.90	1 015.00	1 179.00

Table 1 Hydrochemical parameters of groundwater samples from the study area

区域	编号	水温/℃	pH	K⁺	Na⁺	Ca²⁺	Mg²⁺	Cl^-	S $O 4 2 -$	HC $O 3 -$	TDS
鲜水河地热带	KD01	68.0	6.8	31.00	320.00	86.17	23.32	85.10	19.04	1 159.30	1 268.20
	KD02	47.0	6.9	30.00	270.00	71.14	16.42	64.89	6.48	897.00	1 009.30
	KD03	26.0	7.1	26.00	200.00	62.12	26.14	46.80	3.76	784.10	846.50
	KD04	32.0	6.8	12.00	185.00	40.08	4.26	35.45	3.00	549.20	584.10
	KD05	47.0	7.0	34.00	290.00	45.09	7.90	76.22	8.60	915.30	1 132.00
	KD06	61.0	7.1	36.00	370.00	90.18	21.28	85.09	2.90	1 305.80	1 222.00
	KD07	46.0	7.4	34.00	338.00	86.17	22.50	88.63	1.35	1 220.30	1 275.40
	KD08	70.0	8.7	56.00	550.00	12.02	29.18	260.60	<0.10	1 019.00	1 649.60
	KD09	81.0	7.6	55.00	400.00	40.08	14.59	294.30	75.80	720.00	1 430.80
甘孜—理塘地热带	LT10	54.0	8.2	1.92	53.57	3.92	0.18	7.00	16.50	128.10	202.80
	LT11	72.0	8.1	2.48	63.66	3.82	0.02	1.75	15.28	140.30	238.00
	LT12	76.0	8.0	2.63	65.40	4.06	0.03	1.75	16.66	146.40	253.90
	LT13	75.0	7.9	2.80	72.32	3.36	0.03	1.75	15.30	161.70	275.10
	LT14	79.7	7.8	2.80	72.01	4.32	0.01	1.75	14.55	158.60	272.60
	LT15	80.0	7.1	57.69	477.50	27.52	10.92	68.28	7.72	1 522.00	1 585.00
	LT16	84.0	7.0	57.40	480.20	24.05	10.43	65.83	12.07	1 483.00	1 564.00
	LT17		7.1	62.41	525.70	23.44	10.53	68.28	10.97	1 488.00	1 618.00
	LT18	56.0	6.8	53.60	443.60	29.66	12.93	61.97	10.41	1 327.00	1 442.00
	LT19	64.0	6.7	54.57	446.60	29.79	12.97	59.52	11.00	1 422.00	1 469.00
金沙江地热带	BT20	94.0	8.6	19.94	267.20	5.60	0.23	40.88	70.14	516.60	871.50
	BT21	88.0	9.3	29.86	333.20	1.02	0.06	17.77	28.81	319.80	992.30
	BT22	90.0	9.3	29.98	324.80	2.06	0.08	47.99	52.71	418.80	1 047.00
	BT23	89.0	9.2	34.53	358.90	1.34	0.02	19.19	32.84	379.10	1 079.00
	BT24	81.0	9.3	29.81	317.00	0.81	<0.013	39.10	30.17	365.00	991.20
	BT25	90.0	8.4	27.62	290.80	4.02	0.21	42.65	42.06	617.50	909.00
	BT26	88.0	9.4	30.48	321.80	0.69	<0.013	51.54	27.50	209.70	1 065.00
	BT27	91.0	9.6	31.36	335.80	0.80	<0.013	51.54	46.19	190.10	1 105.00
	BT28	89.0	9.0	28.86	343.80	0.65	<0.013	51.90	25.45	428.00	1 041.00
	BT29	48.0	8.4	2.60	104.50	9.34	0.70	8.89	16.33	226.20	332.10
	BT30	53.0	8.3	2.41	90.24	11.61	0.81	8.89	20.74	217.00	305.50
	BT31	64.0	7.8	6.21	124.80	16.30	0.35	16.00	25.46	314.90	476.60
	BT32	75.0	7.5	6.69	128.90	17.11	0.39	13.86	23.52	342.40	483.20
	BT33	86.0	8.2	26.00	353.20	6.41	2.92	33.77	19.47	679.30	1 071.00
	BT34	90.0	9.1	26.23	351.60	0.77	0.10	23.10	20.30	114.30	1 039.00
	BT35	90.0	7.8	26.80	358.20	1.67	0.20	33.77	42.62	885.90	1 071.00
	BT36	90.0	8.0	25.24	345.20	0.80	0.10	33.06	42.09	862.10	1 033.00
	BT37	70.0	7.6	30.51	380.40	7.77	2.51	32.70	25.90	1 015.00	1 179.00

Fig.3 Piper diagram of groundwater samples from the study area (unit :%)

Fig.4 Relations between(Ca2++Mg2+)and(K++Na+) cation alternation adsorption diagram of water samples from the study area

Fig.5 Relations between (Ca2++Mg2+) and (SO42-+HCO3-) of water samples in the study area

Fig.6 Relations between (Na++K+) and Cl- of water samples in the study area

Fig.7 Relations among major ions and Cl- of groundwater samples from the study area

Fig.8 Ternary plot of Na-K-Mg for groundwater from the study area (unit:%)

Table 2 Estimated temperatures of the geothermal reservoir (℃)

地理位置	T_石英(无损)	T_石英(最大蒸汽损失)	T_玉髓
鲜水河地热带	121.75~172.27	119.65~161.85	93.49~150.00
甘孜—理塘地热带	101.85~132.36	102.59~128.64	71.92~105.14
金沙江地热带	98.81~185.92	99.96~173.00	68.66~165.74

Table 3 Relations between temperature, enthalpy and SiO2 content

温度/℃	焓/(J/g)	SiO₂/(mg/L)	温度/℃	焓/(J/g)	SiO₂ /(mg/L)	温度/℃	焓/(J/g)	SiO₂/(mg/L)
50	50.0	13.5	150	151.0	125.0	250	259.2	486.0
75	75.0	26.6	175	177.0	185.0	275	289.0	614.0
100	100.1	48.0	200	203.6	265.0	300	321.0	692.0
125	125.1	80.0	225	230.9	365.0

Fig.9 Si-enthalpy model of thermal reservoir in the study area

Fig.10 Relations between δD and δ18O of groundwater samples from the study area

Fig.11 Relations between δ18O and Cl- concentration of groundwater samples from the study area

Table 4 Calculation results of the thermal cycle depth in west Sichuan

区域	冷水混入比例/%	循环深度范围/m	混入前循环深度/m
鲜水河地热带	72~78	1 925.02~3 114.82	3 866.12~5 620.52
甘孜—理塘地热带	56~65	1 470.95~3 160.92	2 189.93~3 624.05
金沙江地热带	65~68	1 402.41~3 446.09	3 318.15~5 471.50

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