Exploration and Discovery
with the Geotech VTEM
Versatile time domain EM
Airborne System Specifications
30 Hz Primary Frequency
Bi-polar 16.6 millisecond half cycle
Pulse duration 4.6 to 7.5 milliseconds
Dipole moment 425,000 to 600,000 + nIA
Horizontal central loop or in-loop system
Transmitter - 26.1 m diameter 4 turn loop
Receiver – 1.1 m diameter 100 turn coil
0.1 second sampling, minimum 25 channels
dB/dt finite impulse response
B-field and Deconvolved options
Transient Decay- Bounded Object
Langmuir L3520
3
2
1
A~e¯(t/τ)
Ln(pV/(Amp x m^4)
Ln(A) = -(t/τ)
Tau = Slope = Δt / Ln ΔA
0
-1
-2
-3
-4
-5
0
1000
2000
3000
4000
Time (microseconds)
5000
6000
7000
Examples
Document the early stages of a New Ni-Cu-PGE
Discovery in Langmuir Twp (35 Km south-east of
Timmins).
Show how Late Time analysis, CDI
computations and BHEM can help orientate the
drilling program.
Using an example of Poorly Conducting
Sphalerite mineralization, show how Early Time
analysis can assist in priorizing the exploration
program.
Langmuir Area Geology
Section of survey – 2VD image + conductor
symbols (75 m line spacing).
Conductivity-depth Image – L3520
Conductivity-depth Image – L3515
Bore Hole 3-comp TEM
Z - Component
X - Component
Prism Model Results
Line
Conductance
VTEM Tau
3510
2.8 S/m x 25 m
60 m
82.5 (N)
3515
2.5 S/m x 60 m
90 m
70(N)
3520
3.0 S/m x 60 m
75 m
85(S)
3525
3.0 S/m x 65 m
90 m
72.5(S)
3530
3.5 S/m x 40 m
95 m
90
4.24 ms
BH Tau
4.6 ms
Depth
Dip/Direction
Low Conductance Targets
(known sphalerite occurrences)
Early Time Channels (70,90,110 &
130 µsec)
Mid Time Channel (1130 µsec)
Computed Conductance & Tau
Values for weak Targets
Area
Conductance S
Tau millisecond
Range
Range
Mean
Mean
A
0.5-1.0
0.8
----
<0.01
B
0.2-0.5
0.4
----
<0.01
C
1.5-4.0
2.8
0.01-1.6 1.1
D
4.2-5.9
4.3
4.5-4.9
E
0.4-0.9
0.5
0.01-0.6 0.2
F
0.3-1.8
1.1
0.01-1.5 0.1
4.7
Summary - Langmuir
Both geology and Ni-Cu-PGE
mineralization similar to Kambalda –w Aus
VTEM provided “low noise” late time data
required for accurate determination of
conductance and Tau values and modeling
Summary – Langmuir cont’d
VTEM data provided CDI’s showing
confirming evidence for a wide zone of
mineralization and low amplitude folding to
the south of the discovery zone
3 component bore hole data provided an
accurate logging of the limits of the overall
zone(s) and of the higher grade sections
within
Summary – Low Conductance
Targets
VTEM maps very early time expression of
low conductance sphalerite mineralized
zones providing accurate contrasting of
weak conductances and Tau values
Selection of targets can be assisted by
early time imaging, conductance and Tau
values