Geochemistry of Geothermal Waters from the Gonghe Region, Northwestern China: Implications for Identification of the Heat Source

The Gonghe geothermal region, located in the northeastern part of Qinghai–Tibet Plateau, is the most geothermally active in Qinghai Province. The geothermal waters from three hydrothermal areas (Qiabuqia, Guide and Xinghai) of Gonghe are characterized with different hydrochemical types. Nevertheless, their δD and δ 18 O data suggest that they are all of meteoric origin. Most Gonghe samples are far away from the full equilibrium line in Na–K–Mg triangular diagram, implying that Na–K geothermometer is generally not suitable for calculating the reservoir temperatures. In comparison, silica geothermometers perform much better and give more accurate temperature estimations. The hydrochemistry of the Gonghe geothermal waters is distinctively different from that of the hot springs from Rehai, a well-known magmatic hydrothermal area located in the Tengchong volcanic region of Yunnan Province, southwestern China, indicating that the geothermal anomaly in Gonghe is not related to an underlying magma chamber. Instead, the strong hydrothermal manifestation there is more likely to be supported by the intense deep tectonic activities. Moreover, the possible existence of radioactive heat source can not be ruled out at this stage.