Application of Controlled-Source Audio Magnetotellurics for Geothermal Water Resource Exploration: A Case Study

 

Concept Introduction

CSAMT stands for Controlled-Source Audio Magnetotellurics. It is a geophysical method used for subsurface exploration. By transmitting controlled audio-frequency electromagnetic signals into the ground and measuring the resulting electrical and magnetic field responses, CSAMT provides valuable information about the subsurface resistivity structure. This technique helps in identifying geological features and assessing mineral resources and groundwater reservoirs. CSAMT is a non-invasive and high-resolution imaging method widely used in geothermal surveys and resource exploration projects.

Equipment Used

GD-5 Ultra-wideband Electromagnetic Equipment

Result

The total length of the survey line is 580 meters. At the shallow depth, there is a small amount of Quaternary cover layer with a resistivity less than 200 Ω∙m. Below that, there is a uniform distribution of strongly weathered and moderately weathered gneiss, with resistivity ranging from 500 to 3000 Ω∙m. Further down, there is weakly weathered gneiss, which is cut by two northeast-trending faults, F2 and F4. At the bottom, there is a fault zone with fragmented and granulated rocks, rich in geothermal water. A verification borehole, ZK5, was designed at the 75-meter position along the survey line to investigate the fault zone. The borehole was designed to a depth of 600 meters, but the actual drilling reached a depth of 530 meters, yielding water with a temperature of 62℃ and a flow rate close to 2000 cubic meters per day.