Diamond Geology and Exploration

Airborne Mag/EM Data Integration of Slave Province Kimberlites, NWT

Tuesday, November 20, 2018 - 11:00 to 11:19 Theatre 1


H. Ugalde (Presenting)
Brock University

B. Milkereit
University of Toronto

I. Lenauer
Golder Associates

W.A. Morris
McMaster University

A.M. Mirza
Northwest Territories Geological Survey

B. Elliott
Northwest Territories Geological Survey

As part of the Slave Province Geophysical, Surficial Materials and Permafrost Study, the Northwest Territories Geological Survey (NTGS) commissioned high resolution geophysical surveys in the Slave Geological Province (SGP). This work focuses on the analysis of six horizontal gradient magnetic and frequency domain EM (FDEM) surveys that were flown from February to March 2017 (Munn Lake, Margaret Lake, Zyena Lake, Lac de Gras West, Big Blue and Mackay Lake). All surveys were acquired at 75 m line spacing with nominal terrain clearance of 60 m to maintain bird height of 25 m. They total 4,580 line-km. We use the FDEM data to locate areas of potential remanent magnetization, and thus additional areas that could be related to kimberlite bodies.

The area is part of the central Slave Craton, which is dominated by Archean granitoid rocks and Archean metasedimentary rocks. Heaman et al (2013) identifies several distinct domains based on kimberlite ages in the area. Central Slave is characterized by Tertiary/Cretaceous age kimberlites, whereas the southern part exhibits kimberlites of Cambrian age. This have important implications for the orientation of the remanent magnetization vector.

The methodology involves the use of a homogeneous half-space model to invert the data for dielectric permittivity, relative magnetic permeability, apparent resistivity and magnetic susceptibility. Using this model, we calculated Conductivity-Depth-Images (CDIs) for all the EM data. The susceptibility distribution from the EM data (MagEM) is then plotted against an apparent susceptibility derived from the total field data for the main survey via standard FFT calculation (MagTMI). Major differences between both distributions are usually associated to remanence. Once we identify areas of potential remanent magnetization, we use Helbig analysis to estimate the direction of magnetization. The validity of this model is verified by comparison of the computed remanence direction with the appropriate Apparent Polar Wander Path (APWP). We find a good correlation of APWP directions with the estimated remanence, however, a viscous remanence component subparallel to the present’s day Earth field is sometimes required.

Finally, we show the integration of these results with a structural interpretation of the aeromagnetic data and potential alteration zones derived from Aster imagery for all 6 blocks.