HIGH PRECISION FDIP EXPLORATION IN PRODUCTIVE MINE WITH STRONG EM INTERFERENCE

Geophysical exploration in productive mine is a challenging problem. There are many sources to produce strong electromagnetic interference to prevent the qualified data acquisition of IP, MT, AMT, TEM, and CSAMT exploration. Chinese Bureau of Geological Survey organized a geophysical data acquisition in productive mine applying different geophysical instruments and different geophysical methods, such as IP, CSAMT, and TEM. Because of strong EM interference, no instrument or method can satisfy the data quality requirement of geophysical exploration. Baiying (Silver) mine in Gansu province of northwest of China is a productive mine. Geophysical exploration with time domain induced polarization (TDIP) method cannot get good quality data when the spacing between current electrode and potential electrode is large because of the strong EM interference. To solve above problem, we carried out a testing to evaluate technologies needed for good quality data acquisition. We acquired a lot of data when the current injection was off to get the detailed characteristic of EM interference. Distributed high precision data acquisition station, spread spectrum technology, GPS synchronization, correlation detection, strong injected current, robust processing, frequency domain IP (FDIP), and longtime data acquisition are adopted to improve the data quality of IP exploration with the depth of exploration as about 1000m. We find that 30A of injected current is enough when above technologies are adopted, and the time of data acquisition is about 120s. If 8A of injected current is applied, the time of data acquisition for good quality data will be 1800s or more. At last, we carried out a 2D FIP exploration with minim potential electrode spacing as 20m, maxim current electrode spacing as 5200m, maxim injected current as 30A. The overall data quality is satisfactory, and the average measurement error of apparent resistivity is 0.3%.