Methods exploiting natural electromagnetic fields in the audio frequency range significantly increase depth of investigation in any geoelectrical conditions and sensitivity to a wide range of resistivity contrasts including in the range of thousands of ohm-ms. A brief history of the development of the natural field airborne technology is discussed and accompanied by a comparison of the systems technical specifications. Field examples from the latest development in the airborne electromagnetic natural fields’ domain, MobileMT, demonstrate its exploration capabilities in both conductive and resistive environments, sensitivity to any direction of geoelectrical boundary, and detectability of near-surface discrete targets along with deeper structures.

1. THE HISTORY OF THE DEVELOPMENT OF NATURAL FIELD AIRBORNE
ELECTROMAGNETICS AND MODERN EXPLORATION ADVANTAGES
A L E X A N D E R P R I K H O D K O * , A N D R E I B A G R I A N S K I , P E T R K U Z M I N , A A M N A S I R O H E Y
E X P E R T G E O P H Y S I C S L I M I T E D
K E G S 2 0 2 2
S Y M P O S I U M
2022 PLATINUM
SPONSOR

2.  Milestones of the airborne natural EM fields method development
 Technical parameters progress of commercially used systems
 Field examples of the latest natural field EM system development
PRESENTATION OUTLINE

3. 2001
2003
2006
2009
2018
1959
1985

4. characteristic AFMAG (1958) ZTEM (2006) MobileMT (2018)
Detector type 2 inductive coils in the air at 450 to the
horizontal and to each other in the
direction of flight. The components are
compared electronically (H-field)1.
1 vertical field inductive coil in the air
(H-field);
2 horizontal field inductive coils on
the ground (H-field).
3 orthogonal inductive coils in the air
(H-field);
2 pairs perpendicular grounded electric
lines (E-field).
Output data Tilt component of the magnetic field
along the line direction. Deflections are
proportional to the tilt of the plane of
polarization1.
Tipper data Admittance data (apparent
conductivity)
frequency bands (Hz) Typical 150; 510 1 32, 45, 90, 180, 360, 7203,4 Up to 30 frequency windows in the
20-26,000 Hz range
Data recording sampling (Hz) No digital recording 20005 73728
Bird tilting motion
compensation
Yes Yes Not required
Signal bias problem Yes Yes No
Sensitivity to subsurface
geoelectrical differentiations
It is difficult or impossible to recover
conductors with parallel axes to the
direction of the inducing field 1
lack of ability to image layered
geology2
Sensitivity “to current density
variations caused by conductivity
contrasts, but not to the absolute
conductivities themselves” 2
Sensitive to the absolute conductivities
and to geoelectrical boundaries of any
direction
1-(Ward et.al., 1966); 2- (Jansen, Cristall, 2017); 3-(Legault et. al. 2009); 4-(Lo et al., 2009); 5-(Lo and Zang, 2008).
Technical parameters progress

5. MobileMT towed bird configuration
Three XYZ H-field components
Two pairs of XY E-field lines
(‘reference’ and ‘signal’)
MobileMT base station configuration
MobileMT configuration

6. Ground TAMT (EMpulse Geophysics)
Airborne AFMAG (Expert Geophysics)
Comparison between EM natural fields ground
(TAMT) and airborne (MobileMT)
Kianna Zone, Shea Creek,
Athabasca Basin

7. copper-cobalt deposits at Elizabeth Creek (Emmie Bluff)
Olympic Dam region (South Australia)
0.001 - 250 Hz with a
site spacing ~500 m.
27-445 Hz with a station
spacing ~12-15 m

8. MobileMT – ground IP (resistivity) comparison (British Colombia)
MobileMT apparent conductivity 103 Hz Ground DC-IP resistivity
(~400 m depth slice from surface)

9. known sulfide
mineralization
Papua New Guinea, The Kainantu Gold Project

10. an epithermal to gold-porphyry system with evidence for low-sulphidation and high-
sulphidation overprints
Thorn Project (British Colombia)
The Trapper Target is a deep-rooted multi-phase gold porphyry system
Hole THN21-186 (Trapper Target) yielded 11.0m of
19.25 g/t gold from 50m within 139.0m of 2.14 g/t Au

11. L1330
high-grade epithermal deposit Broadview
Magnetic field profile
nT
the Thor Ag-Au-Pb-Zn-Cu epithermal
mineral deposit located near Trout Lake, SE
of British Columbia
Thor Project (SE of BC)

12. Megagossan – 40% iron, Ore-grade Ni and Co in soil samples
L1060
Magnetic field profile
nT
Meters,
ASL Thor Project (SE of BC)

13. CENTERRA GOLD INC.
TECHNICAL REPORT ON THE
KUMTOR MINE, KYRGYZ REPUBLIC
NI 43-101 Technical Report, 2021
southern Tien Shan
metallogenic belt (Central Asia)
Sediment hosted intrusion
related orogenic gold
Orogenic gold
Central Asia, Tien Shan

14. southern Tien Shan
metallogenic belt (Central
Asia)
Sediment hosted intrusion
related orogenic gold
MobileMT resistivity sections
Orogenic gold
Central Asia, Tien Shan

15. NEAR SURFACE CAPABILITIES
Northern Ontario, KL-22 kimberlite
pipe (30 m from surface)
Northern Ontario, KL-01
kimberlite pipe (on surface)
Inversion of MobileMT
high frequencies set

16. Holdsworth Project: Wawa, Ontario, Au bearing shear zone
NEAR SURFACE CAPABILITIES

17. Conclusions
The main advantages of the principle includes:
- depth of investigation exceeding all other airborne EM principles in any
conditions;
- Sensitivity to geoelectrical differentiations in very broad resistivity range;
- much less dependent on terrain clearance above the ground comparing to
systems with controlled field sources.
- Other advantages, with corresponded technical solutions, include sensitivity
to any direction of geoelectric boundaries; a broad depth range of
investigation beginning from near-surface; output data in absolute
conductivity units.
All the advantages make the method very attractive for exploration of different
commodities and in the wide range of geological and geoelectrical environment.

18. THANK YOU