Evolution of VTEM

Evolution of VTEM
Evolution of VTEM
The objective of this presentation is to showcase the VTEM system
improvement in achieving the low system noise together with increasing
dipole moment.
Some modeling and real examples are depicted in support of the study.
Outline
Evolution of VTEM
– VTEM landmarks
– technical improvements
– latest VTEM fleet
Significance of Low System Noise?
– Illustration of a simple model
– how system noise influence depth of investigations
Case Study – Caber and Caber North tests 2003 through 2012
Conclusions
Evolution of VTEM
Introduction
VTEM – Versatile Time-domain
Electro-Magnetic
• Developed in 2002 and now
leading the helicopter-borne TEM
industry
• Mining magazine award winner
• A fleet of 30 systems flying
worldwide
• three significant features of the
VTEM system are
a) lowest noise levels
b) large dipole moment and
c) in-loop Tx-Rx configuration
VTEM plus
Evolution of VTEM
VTEM Landmarks – 2002 to 2012
18 m diameter with
125,000 NIA dipole
moment
26m diameter with
improved S/N
2002
B-field introduced with
ZX (Y) components
2005
2008
35 m Tx loop with
800,000 NIA dipole
moment
2009
VTEM max
18m
dBz/dt
26m
dBzx/dt
Bzx-field
26m
dBz/dt
35m
dBzx(±y)/dt
Bzx(±y)-field
Improved S/N and horizontal
magnetic gradiometer
2010
Horizontal
MagneticGradiometer
with GPS and
inclinometer
26m
dBzx(±y)/dt
Bzx(±y)-field
VTEM plus
2011
Full waveform
option for
VTEM system
2012
VTEM max
35 m Tx loop with 1.3
million NIA dipole
moment and improved
S/N
35m
Technical Improvements
2003
2005
2007
2009
2012
Noise Level (pV/Am4)
0.01
0.0015
0.0009
0.0003
0.00005
Dipole Moment (NIA)
148 000
380 000
425 000
866 000
1 600 000
Transmitter Coil Diameter (m)
18
26
26
35
35
Base Frequency (Hz)
30
30
30
30
30
Peak Current (A)
110
180
200
230
420
Dipole Moment
40
VTEM Signal-to-Noise Ratio for 7036 µs Time
Gate and Noise Levels
37.4
0.01
1000000
800000
20
600000
400000
For Target Plate with
dip of 75°, depth of
150m, depth extent of
150m and length 200m
10
2003
2005
2007
2009
Year
2010
2012
0.001
0.0001
6.2
200000
0
4
190x
Noise Level (pV/Am )
30
1200000
Signal-to-Noise Ratio
Tx Dipole moment (NIA)
1400000
0.2
1.2
2.1
0
2003
2005
2007
2009
VTEM System Iteration
0.00001
2012
Signal-to-Noise
Calculated response from a synthetic model
•
S/N ratio determines depth of investigation and the system ability to
discriminate the targets based on their conductance.
Modeling Responses – dB/dt VTEM max response vs depth
Forward model VTEM max responses for conductive plate dipping 50 degrees at depths 400, 800,
1200 m using Maxwell EMIT. The plate parameters: thickness 50 m; conductance 150 S; depth
extent 250 m (Athabasca graphite mineralization type of conductor)
VTEM dB/dT response vs. Conductance Nomogram
VTEM max noise level
For Target Plate with dip of 75°, depth of 150m, depth
extent of 150m and length 200m
•
•
•
Measureable response, above the system noise level, is represented
within boxes
Horizontal extent of boxes represents range of conductance sensitivity
Decrease in noise level leads to a wider conductance sensitivity range
Evolution of VTEM based on tests over Caber
and Caber North VMS deposits
• Caber and Caber North deposits are located in the Matagami
mining camp of Western Quebec, Canada within the Abitibi
Greenstone Belt
• VTEM has flown over the Caber deposit since 2003
Caber Geology
The deposit is sphalerite-rich,
cigar-shaped, ~30m wide x
~250m strike, steeply SW-dipping
and buried at ~120-350m, below
~30m of conductive clay
overburden. It was discovered,
based on favorable geology, using
air + ground magnetics, IP and
borehole TEM follow-up Undetected by EM, ground or air.
• Excellent for testing EM system quality due to:
–
–
–
–
–
Small and moderately conductive
Overlain by conductive overburden
150 meters depth to top of mineralization
Sub-vertical dipping at around 75-85°
Depth extent of 150 meters
Resistivity Depth Imaging Comparison for
Caber Deposit
2003
2005
200 meters
DOI 150 meters
2007
2009
250 meters
350 meters
2012
•
650 meters
•
Decreased noise levels and increased dipole
moment has increased depth of investigation
from 150 meters to 650 meters at Caber
VTEM’s increased depth of investigation allows
for exploration of deeper targets with airborne
EM
The transformation scheme (Meju, 1998) Deff(app, t), where the Deff – effective depth of investigation,
app – apparent (effective) resistivity, t – time after turn-off transmitter current, provides resistivity depth sections
from time-domain data. The RDIs illustrate the improved depth of investigation of VTEM system over time.
Caber Plate Modeling
dB/dT
•
•
dB/dT
•
•
•
VTEM’s high target
sensitivity allows for
accurate modeling of late
time gates
Time gates from 14324987 µs used for
modeling
Significantly increased X
component sensitivity
Model plate has depth of
178 meters, dip of 86.5°
and depth extent of 100
meters
Model plate coincides with
depth, dip and location of
mineralization which
would allow for accurate
drill-hole targeting
Caber North Geology
• The Caber North deposit is located 2km NW of the Caber deposit
• Caber North is:
– More than 300 meters depth to the top, which is about double the
Caber depth;
– Completely overlain by conductive overburden
– Near vertical body of mineralization
Caber North Modeling
dB/dT
InfiniTEM Results
•
•
•
•
First airborne EM system to detect Caber North deposit
Time gates from 1891-6581 µs used for modeling
Model plate has depth of 333 meters, dip of 88° and depth extent of 200 meters
High signal-to-noise ratio allows for accurate modeling of deep conductors
Conclusions
• Constant improvement to VTEM’s low noise levels and
increasing dipole moment allows for a wider range of
conductance sensitivity
• Increasing the signal-to-noise ratio leads to greater depths
of investigation and accurate modeling of targets in difficult
environments
• VTEM data over the Caber deposit has demonstrated an
increase in depth of investigation and target sensitivity
• VTEM’s high signal-to-noise ratio and target sensitivity
allowed for the detection and modeling of the Caber North
deposit at over 300 meters depth below conductive
overburden
Evolution of VTEM
Latest VTEM Fleet – various configurations
VTEM mini
VTEM
240,000 NIA
(optional Spectrometer)
17.6 m diameter
dB/dt &B-field
Z, X coils
VTEM max
>1,300,000 NIA
Deep exploration
35 m diameter
dB/dt & B-field
Z, X (±Y) coils
VTEM plus
450 - 600,000 NIA
horizontal magnetic gradiometer
Unique in the industry
26 m diameter
dB/dt & B-field
Z, X (±Y) coils
VTEM Full Waveform
Optional for any system
Ideal for groundwater and layered geology