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Airborne electromagnetic and horizontal-gradient magnetic survey of the central Slave craton area, Northwest Territories

Airborne electromagnetic and horizontal-gradient magnetic survey of the central Slave craton area, Northwest Territories

Helicopter-borne system used for electromagnetic and horizontal-gradient magnetic survey of the central Slave craton area, Northwest Territories. (Credit: NTGS)

Description

Electromagnetic data can illustrate the presence of certain rock types or structures in the bedrock where a mineral deposit may have formed. To achieve this objective, a high-resolution helicopter-borne electromagnetic and horizontal-gradient magnetic survey was performed with specifications such as, nominal traverse line spacing 75 m with east-west direction and control lines spacing 750 m with north-south direction. The nominal helicopter terrain clearance was 60 m with bird height 25 m. A total of 4,578 line-km data was acquired.

Location of EM survey blocks in the central Slave craton area, Northwest Territories (Covering parts of NTS map sheets 75M, N, and 76D)

Location

The survey area is located in the Slave craton of the Northwest Territories, covering six blocks of ground on parts of NTS map sheets 75M, N, and 76D.

Apparent resistivity 7200Hz image of the Blue Block, central Slave craton area, Northwest Territories.

Justification

Previous to this study, there is no electromagnetic data available for the central Slave craton area, only low-resolution regional aeromagnetic data which is of insufficient detail to assist our clients. These data are intended for subsequent use during detailed bedrock geologic mapping. The EM geophysical data are expected to stimulate private sector activity and investment by providing insight into possible locations of intrusions and fault structures that could be related to mineralization of interest, especially kimberlite.

CGG Dighem EM System bird used for electromagnetic and horizontal-gradient magnetic survey of the central Slave craton area, Northwest Territories, (Credit: NTGS)

Approach

CGG’s DIGHEM system was selected to perform the survey. The DIGHEM system consists of two magnetometers located on booms with a lateral separation of 5.212 m and EM receiver which measure in-phase and quadrature components at five frequencies. There were two vertical coaxial coil-pairs operating at 1000 Hz and 5500 Hz, while three horizontal coplanar coil-pairs operated at 900 Hz, 7200 Hz and 56 000 Hz. The data products were provided in Geosoft’s database and grids along with Geotiffs and PDF formats.

CGG Dighem electromagnetic and horizontal-gradient magnetic system with Helicopter at Yellowknife airport, Northwest Territories. (Credit: NTGS)

Schedule

All six blocks were flown between February 19 and March 31, 2017, with Kelvin Camp and MacKay Lake Lodge as bases of operations. The data was published by Northwest Territories Geological Survey (NTGS) as NWT open report 2017-015 (Mirza and Elliott, 2017) in July 2017.

Apparent resistivity 900Hz of the MacKay Lake, central Slave craton area, Northwest Territories.

Partners and Support

The work was funded by a joint-agreement between the NTGS and the Canadian Northern Development Agency (CanNor).

CGG Canada Services Ltd. carried out this survey.

Keywords

Airborne Geophysics, helicopter-borne, magnetic, Electromagnetic, EM Anomaly, Munn Lake, MacKay Lake, Margaret Lake, Zyena Lake, Big Blue Block, LdG West Block, central Slave craton area,  Lac de Gras, DIGHEM system