megaVTEM response over the Caber Deposit
September 16, 2009
VTEM detects the Night Hawk Lake conductor from 705 m above.
Read the case study (PDF)
January 26, 2009
Geoscience BC Releases new Analysis of the QUEST Geochemical Dataset, Z-TEM Data from Mt. Milligan and Preliminary QUEST Project Area Till Geochemistry
"... Geoscience BC is also pleased to announce the release of Geoscience BC Report 2009-7: "Helicopter-Borne Z-Axis Tipper Electromagnetic (ZTEM) and Aeromagnetic Geophysical Survey -- Mt. Milligan Test Block." The release includes a final report for the project, databases and grids, and maps in PDF format, all of which will be available from Geoscience BC's website. Z-TEM is a passive airborne electromagnetic system. It uses the natural time varying changes in the earth's magnetic field to detect conductors, map geology and explore for large poorly conductive features such as regional faults and porphyry copper deposits. Geoscience BC and Terrane Metals Corp partnered on the Z-TEM survey of the Mt Milligan property, which was flown at a 250 m line spacing by Geotech Ltd."
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Equipment
A typical Geotech airborne geophysical system consists of the following main components:
- A time-domain electromagnetic system (VTEM)
- A high-sensitivity cesium magnetometer
- A GPS navigation system
- A radar altimeter
- A cesium magnetometer base station
1. VTEM System
Geotech's time-domain electromagnetic system (VTEM) utilizes modern advances in digital electronics and signal processing along with recent company research in the area of precision electromagnetic measurements.
1.1 The system was designed to have very low-noise characteristics. This low-noise level is as important as the large transmitter dipole-moment in determining the capabilities of the system:
- Deep penetration
- High spatial resolution
- Excellent resistivity discrimination
- Detection of weak anomalies
Recent surveys flown with the Geotech system have picked up a number of anomalies left undetected by previous airborne EM surveys. The Geotech VTEM system flew the Reid-Mahaffy, Caber, Perseverance and Montcalm test ranges. The results of the tests have demonstrated that Geotech VTEM system provides the industries highest signal/noise ratio and spatial resolution of conductors. The receiver and transmitter coils are concentric and Z-direction oriented.
1.2 The system was designed to be versatile and adaptable to different geophysical priorities such as deep penetration or for different resistivity ranges.
1.3 The system is easily transportable. It can be packaged into relatively small units for shipping to distant survey areas. The transmitter-loop can be assembled or disassembled in 3-4 hours.
1.4 The system is completely modular, allowing for easy replacement of any part in the field. This is extremely useful if the EM loop sustains damage.
2. Magnetometer
A Geometrics/Scintrex split-beam total-field magnetic sensor, with a sampling interval of 0.1 seconds and an in-flight sensitivity of 0.02 nT, is utilized. The magnetometer will perform continuously in areas of high magnetic gradient with the ambient range of the sensor approximately 20k-100k nt.
3. Electronic Navigation - GPS
A Geotech GPS navigation system utilizing NovAtel's WAAS (Wide Area Augmentation System) enabled OEM4-G2-3151W GPS receiver provides in-flight navigation control. This system determines the absolute position of the helicopter in three dimensions by monitoring the ranges to orbiting satellites. As many as 11 GPS and two WAAS satellites may be monitored at any one time. The positional accuracy or circular error probability (CEP) is 1.8 m, with WAAS active, it is 1.2 m.
4. Altimeter
A radar altimeter system records the ground clearance to an accuracy of approximately 1 m.
5. Data Acquisition/Recording System
A custom Geotech data acquisition system is used. Data is recorded onto PCMCIA flash cards.
6. Field Computer Workstation
A dedicated PC-based computer workstation is used in the field for purposes of displaying geophysical data for quality control, calculating and displaying the navigation, producing preliminary EM anomaly information and magnetic maps, and copying/verifying the digital data.
7. Base station
A dedicated computer including high-sensitivity base station cesium magnetometer is employed to record magnetic diurnal activity.