Occurrence, genesis and travertine deposition of the Adong hot springs in northwestern Yunnan of China

Abstract

The Adong hot springs in the Meso-Proterozoic metamorphic rocks are located in Deqin county in northwestern Yunnan of China in the Yunnan-Tibet geothermal belt with travertine deposition. Different from many other hot springs which emerge along rivers or in valleys in Yunnan, the springs emerge on the mountain slope about 100 m above the local River. Little is known about the genesis and state of travertine deposition in the hot springs. The study of the hot springs will be helpful to enrich the understanding of research on geothermal resources and travertine deposition in northwestern Yunnan and the application of hydrogeochemical and isotopic methods to research on geothermal water and travertine. The results show that: (1) the major hydrogeochemical processes are the dissolution of Na-feldspar, carbonate rocks, oxidation of H2S, precipitation of calcite and geothermal and cold water mixing, and sodium sulfate minerals could be a source of Na and SO4. (2) The isotope data indicates that the geothermal water is meteoric in origin with a slight “18O shift” and a reservoir depth of 4525-4750 m is also estimated. (3) A reservoir temperature (190-199 ℃) is attained with the quartz geothermometers and silica-enthalpy graphic method. (4) The groundwater circulates deeply along the flow paths after receiving the recharge from infiltration of precipitation or snow melt water from the Cali and Jiawu snow mountains, and then ascends toward the land surface in the form of hot springs after heated by the heat flow and mixed by cold water with mixing ratios of about 75%-80%. (5) Comparative analyses of the hydrochemistry of the spring waters illustrate that the Adong hot springs are more easy to deposit travertine in wet season and vents YN1, YN2 and YN3 still tend to deposit travertine.