Exploration for hydrothermal geological reservoirs by geophysical methods in the Mongol-Baikal region

The paper presents the study on the prospects of the exploration for hydrothermal geological reservoirs in the Mongol-Baikal region using geophysical methods. For the purpose of the study, the following methods have been used: transient electromagnetic sounding, vertical electromagnetic sounding, and induced polarization method. The above methods have proved effective in the selecting the objects with contrast resistivity at various depths. The low resistance (5-10 Om·m) of the hard rock can be caused by the presence of fractured zones with high-temperature mineralized solutions, i.e hydrothermal reservoirs. As a result of the surface geophysical studies carried out at different depths at the reference site (Shivert hydrotherm deposit, Arkhangai aimak, Mongolia) and at the prospective site in the vicinity of Sangiyin-Tolgoi volcano (7-8 km from the regional center Tsetserlag), hydrothermal geological reservoirs isolated from the day surface have been identified. The Shivert hydrothermal deposits with a temperature of 67 °С have been brought to the surface with shallow boreholes up to 78 m deep. At the prospective site located within the internal deflection of the Khangai synclinorium, the hydrothermal geological reservoir is at a depth of over 700 m. A 400 m deep borehole drilled in this section brought the pressure water with a temperature of up to 16 ºС to the surface in spite of the cold water influx in the lower 100-meter interval. The thermal state of the underground hydrosphere of the Khangai arch uplift has been estimated using hydrogeochemical geothermometers, based on the chemical composition of more than 20 thermal sources. The underground hydrosphere of the Khangai arch uplift with its high temperatures associated with magmatogene thermal anomaly is of great practical interest. The thermal waters of the Mongol-Baikal region are concentrated in the thermal effluent fault zones and in the presence of overlapping sedimentary deposits, do not always make their way to the day surface. The above geophysical methods are suitable for the exploration for such hydrothermal reservoirs.

hydrothermal geological resources, thermal waters, geoelectric section, mineralized-solution zones, hydrogeochemical geothermometers