Sanjiang orogen is a NS-trending collisional orogenic belt between Indian plate and Yangtze block of the South China plate, and also an important metallogenetic belt in southwestern China. The collision process between Eurasia plate and Indian plate started from Mesozoic times, which resulted in strong and frequent magmatic activities then after. After Cenozoic, the stronger and more frequent tectono-magmatism and volcanic eruptions provided fracture spaces and plenty of heat sources for epithermal activity in this area. As an active geothermal field, the Rehai geothermal field situates in the southern part of the Sanjiang orogen, and is composed of two sub-scale geothermal fields-the Huanggua-qing-Liuhuang-tang in northeast and Reshui-tang in southwest. Rocks that outcrop in this geothermal field are mainly late Cretaceous granitoids with minor late Tertiary and Quaternary volcanics, sandstone and conglomerate. Strong volcanisms in Pliocene to Pleistocene were recognized and early Pleistocene dacite and andicitic terrestrial volcanics distribute in the Huanggua-qing-Liuhuangtang geothermal field (i.e. Rehai geothermal field in narrow sense). 62 hot spring groups occur along a NS-striking main fault in the Rehai geothermal field. Hydrochemical types of the spring water are mainly Na-Cl-HCO3 and Na-HCO3-Cl types, secondly Na-SO4 type, Na-Cl type, Ca-Na-HCO3-SO4 type and Mg-Ca-HCO3 type.Temperature of spring water on the surface is 24～102°C, and pH value is 2～9.8. Geothermometers of SiO2, Na/K, Na-K-Ca, and Na-K-Ca-Mg, of the hot spring waters in the Rehai geothermal field, were used to evaluate the reservoir temperature, which yielded results of >270～100℃ from below 600 m to the surface. The hydrothermal alteration and gold mineralization process are still going on in that area, and the Lianghe gold deposit was formed between the Zao-tang River and the Xiao-shui River in Liuhuang-tang-Huanggua-qing geothermal area in the northeast sector of the geothermal field. This deposit is about 6 km2 in area, with several kinds of spring sinter, hydrothermal alteration and breccia, and is one of the most recently formed hot spring-type gold deposits in China.Au content in hot spring water, surface sinter, bottom sinter, acid leaching zone, and stockwork quartz veins, is 0.01～0.16 ppb, 0.001～0.63 ppm, 0.004～0.17 ppm, 0.001～0.73 ppm, and 0.003～4.65 ppm, respectively. Ag content in silica cap reaches 0.001～54.5 ppm. Based on the average of Au and Ag content, Au/Ag ratio is always less that 0.1 (1 : 10～1 : 19）. δ18OH2O，δDH2O, and δ13CCO2, values of hot spring waters in the Tengchong Lianghe area are -12.3‰～-5.1‰, -68.9‰～-55.7‰，and -5.2‰～-1.6‰，respectively. δ34S values of hot spring water, native sulfur, and sulfides such as pyrite, are mainly -2‰～＋2‰. Liquid composition of fluid inclusions in quartz from breccia of Liuhuang tang area is H2O 72%, H2S 28%; vapor composition is CO2 67.1%, H2S 12.6%, and H2 20.3%. The δ18O values for quartz from quartz veins in the Lianghe gold deposit are between 5.0‰ and 8.8‰ (averaged 7.3‰ for 10 samples), and 2.3‰～12.4‰ (averaged 7.6‰ for 6 samples) for silicified Pliocene sandstone (whole rock). Soil and rock geochemical investigation results suggest a tendency of high concentration or anomalies of Bi, Li, Rb, As, Sb, Hg, and Sn in or near hot spring areas, and Mn, Ni, Co, Pb, and Zn around or out of hot spring areas.