Some results of trials of airborne transient electromagnetic surveying for primary diamond deposit exploration

In autumn 2010, an integrated airborne geophysical survey at a scale of 1:5000 was conducted in the Arkhangelsk Region. The survey combined aeromagnetic prospecting and airborne transient electromagnetic surveying (ATEM). Its objectives were to search for primary diamond deposits and refine elements of the geological structure of the survey area.

ATEM employed the new Equator helicopter-borne electromagnetic system (Geotechnologii CJSC, Russia), which uses pulsed excitation at a frequency of 77 Hz. The system’s transmitting dipole is predominantly vertical and is towed by a helicopter on a dedicated platform, while receiver coils measuring all three spatial field components are mounted in a gondola towed on the same cable 40 m from the transmitter. Equator incorporates a specialized system for compensating systematic instrumental errors and the effects of conductivity in helicopter structural elements, as well as an additional-dipole system for high-accuracy relative positioning of transmitter and receiver. The system outputs the mean amplitude of the vertical and horizontal components of field B and the mean field derivative dB/dt in 14 time channels after the excitation signal is switched off.

The magnetic field was measured using a modern quantum magnetometer with a caesium sensor, providing a recording rate of up to 100 Hz and an instrumental error of 0.001 nT. The survey root-mean-square error, calculated at intersections of a specially flown diagonal line with regular survey lines where the horizontal gradient was below 50 nT/km, was no worse than 0.7 nT.

The survey used a Mi-8 helicopter as the platform, flying parallel east–west lines with general terrain following. Regular line spacing was 50 m. The mean flight height of the platform was 50 m.

Processing of ATEM data yielded effective resistivities for each delay time and decay constants, and identified local anomalies and linear conductive zones.

Specialized processing and interpretation focused on identifying the target objects—kimberlite pipes.