A Study Of The Formation And Evolution Of The Wenluo Hot Spring And Precipitation Mechanism For The Nearby Tufa In Bobai, Guangxi

Hot springs, as the emergence of the thermal groundwater, have special evolution mechanism. In the southeast of Guangxi occur 5 hot springs . The temperature of the springs range from 40℃ to 78℃. AH of them emerge from hard rocks, and are directly or indirectly controlled by faults, and consist of different chemical compositions. The Wenluo hot spring, in particular, occurs in clastic rocks, has chemical characteristics different from the other 4 springs. In addition, tufa is found near the Wenluo hot spring. This paper places its emphasis on the formation and evolution of the Wenluo hot spring and precipitation mechanism of the tufa in Bobai, Guangxi.Based on the hydrological conditions, geochemical methods and isotope methods are used to analyze the geochemical characteristics and the isotopic features, and to study the evolution mechanism of the Wenluo hot spring and the formation mechanism of the tufa .Using the isotope method, we got the results: the hot spring is recharged from precipitation in the recharge area with elevation of 507 m. The depth of water circulation of the hot spring is estimated about 3 km. The thermal groundwater obtains heat during the long period of circulation, reactes with the rock, and is the primary transmutative water. Several kinds of geothermometers are used to predict the temperature of the geothermal reservoir, and the temperature ranges between 70℃ and 90℃. The temperature, discharge and chemical compositions of the Wenluo hot spring did not change very much during the past decades. The ocuurence of the Wenluo hot spring is controlled by the Luchuan-Cenxi fault.Formation of the tufa is affected by temperature, pressure, hydrodynamic conditions, biological action, and chemical compositions of the hot solution. The water solution saturated with carbonate is the basic condition for precipitation of the tufa. It is only the necessary condition, but is not the sufficient condition. The rise in temperature, decrease in pressure, quick flow of hot water, attenuation of the flow, large interface between the gas and the liquid, are all helpful in precipitation and formation of the tufa. Tiny physiognomy and plant roots can alter the hydrodynamic conditions, accelerate the transgression of CO₂. In addition, the plants roots are important to the sculpture of the tufa. Isotopic data indicate that the major origin of CO₂ in the hot water is from biological contribution.Chemical model is set up to calculate water composition consistency changes in the course of travertine precipitation. Although the changes are so little, simulation calculations provide quantitative results.