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Geophysical Services Are Being Developed – Now Testing an Electromagnetic Transmitter That Improves the Data Quality Down to 500 Meters

Electromagnetic group of Geological Survey of Finland (GTK) tested in September new equipment that enables improved visibility deeper to the earth’s crust without drilling. Controlled source electromagnetic (CSEM) transmitter enables improved data quality for deep (around 500 m) exploration surveys i.e, higher data quality (higher S/N ratios) for deep mineral exploration depths.

The testing is part of GTK’s project for developing the geophysical services. It develops geophysical services, i.e. various packages from measurement to data processing, interpretation and 2D/3D modelling, combining various methods. The survey and testing with CSEM transmitter is one part of the development. First in the focus is to develop the entire workflow of the CSEM method from safe and efficient field work procedures to modelling and interpretation aspects. In the future GTK aims to apply this new technology for various applications such as mineral prospecting, groundwater and geothermal studies.

GTK crew in field work
GTK measurement crew in field work
A large generator in the field
We rented a 3-phase 20kW motor generator to power up the transmitter.
Controlled source electromagnetic (CSEM) transmitter in action in a van.
The actual transmitter (box on the left) generates the signal. Box on the right is the control unit including emergency shut down. The 3-phase transformer (300 kg) is situated in the back. For safety reasons galvanic decoupling of the motor generator and transmitter is required.
CSEM control unit in action.
CSEM control unit in action
People in the swamp prepairing equipments for testing
The signal of the transmitter is injected into the ground at three grounding points (approximately 800m apart of each other). Thus, we laid out 1.6km of cable connecting the transmitter and electrodes.
The grounding area is surrounded with line in the forest
We fenced the area to avoid people getting close to the grounding points while they are under voltage.
3 persons installing transmitter to the swamp.
Transmitter electrode installation. In order to achieve good electrical coupling to the ground, we installed metal sheets in the swamp which are then connected to the transmitter with long cable.
Person measuring on the ground.
We measured electric and magnetic fields generated by the transmitter with 26 receiver stations. Stations were between 2-5 km away from the transmitter. At the centre of the receiver line is the GTK Deep hole.
The eequipment on the ground on top of a cover.
Datalogger records and stores the received signal.
People installing the equipment to the ground.
Installing of the datalogger.
Equipment on the ground
Magnetometer recording magnetic fields.
Assembling the pipe to protect the equipment.
Magnetometer have to be protected from wind, rain, temperature change and other external influences.

 

More information

Geophysical applications

Jochen Kamm
Phone +358295032228
jochen.kamm@gtk.fi