Geochemical Evidence Constraining Genesis and Mineral Scaling of the Yangbajing Geothermal Field, Southwestern China

Abstract

The Yangbajing geothermal field, a renowned high-temperature geothermal resource in Tibet of southwestern China, has been utilized for power generation for several decades. To improve geothermal exploitation in the Yangbajing, genesis and mineral scaling have yet to be further revealed. In this study, hydrochemistry and D-O-Sr isotopy were employed for analyzing genesis and mineral scaling in the Yangbajing geothermal field. The geothermal waters were weakly alkaline and had a high TDS content (1400–2900 mg/L) with the Cl-Na, Cl·HCO3-Na, and HCO3·Cl-Na types. The dissolution of silicate minerals (sodium and potassium feldspars) and positive cation exchange controlled the hydrogeochemical process. The geothermal water was recharged from snow-melted water and meteoric water originating from the Nyainqentanglh Mountains and Tangshan Mountains. The geothermal waters possessed the highest reservoir temperature of 299 °C and the largest circulation depth of 2010 m according to various geothermometers. The geothermal waters can produce CaCO3 and SiO2 scaling during vertical and horizontal transport. These achievements can provide a scientific basis for the sustainable development and conservation of the high-temperature geothermal resources in Yangbajing and elsewhere.

Representative High-Temperature Hydrothermal Activities in the Himalaya Geothermal Belt (HGB): A Review and Future Perspectives

“…These three sets of faults in the geothermal field are the main channels for geothermal fluid migration [45,46]. [19], Gudui (b) [43], and Rehai (c) [47]. The red circles in the figure represent the locations of some of the geothermal water samples.…”

“…At a depth of 7 km below the Rehai geothermal field, there is a magma chamber that retains water and has a thickness of 20 km. This magma chamber serves as a heat source and [19], Gudui (b) [43], and Rehai (c) [47]. The red circles in the figure represent the locations of some of the geothermal water samples.…”

“…where H(m) is the recharge elevation, δR(‰) is the δD value of the geothermal spring sample, δP(‰) is the δD value of the shallow groundwater sample, K(‰/100 m) is the isotopic elevation gradient of the atmospheric precipitation, and h(m) is the elevation of the shallow groundwater sample. The contribution of different recharge waters was also estimated using a mixing model [19,61] (Equations ( 2)-( 5)).…”

“…Based on previous research results, the global meteoric water line (GMWL: δD = 8δ 18 O + 10) [65] and the local meteoric water line (LMWL: δD = 8.01δ 18 O + 11.8) [56] were drawn. The sources of recharge for geothermal water in Yangbajing may consist of three end-members: magmatic water (rectangle A) [60], meteoric water (rectangle B) [8], and snow-melt water (rectangle C) [19]. The shallow groundwater in Yangbajing is situated on the LMWL and is closed to the meteoric water end, indicating the shallow groundwater mainly comes from atmospheric precipitation (Figure 5).…”

“…Thermal springs are a natural outlet for geothermal water. Studying their hydrochemical and isotopic characteristics can provide a profound understanding of geothermal systems [18][19][20]. This includes revealing the source, circulation mechanism, and reservoir characteristics of geothermal water [21][22][23].…”