Geophysical interpretation of the central Slave craton aeromagnetic survey area

Geophysical interpretation of the central Slave craton aeromagnetic survey area, Northwest Territories, parts of NTS map sheets 075M and 075N

Description

This publication describes the geophysical interpretation of an aeromagnetic survey conducted in the central Slave craton area (CSC), Northwest Territories (NWT). The objective of the geophysical interpretation is an aid to define and map structures that are prospective for hosting mineral deposit, with a specific focus on identifying kimberlite targets for future diamond exploration. The interpretation can also constrain the geometrical signature and structural orientation of magnetic anomalies that could relate to other commodities of interest, such as gold and VMS occurrences as well as the definition of targets and areas of interest for future follow-up. A compilation map was produced as a synthesis from the interpretative layers, all calculated geophysical products, of the central Slave craton aeromagnetic survey area.

Location

This survey area is located approximately 235 km northeast of Yellowknife, in the Slave craton. It covers a large portion of the National Topographic System map sheets 075M and a small portion of 075N.

Justification

Geophysical interpretation generates plausible combinations of body shapes and magnetic properties of the bedrock in the survey area that would explain the observed magnetic field, allowing the geologist to choose a realistic explanation for the observed anomalies. Various processing and interpretation techniques were applied to the CSC aeromagnetic dataset to create high-quality products, including grids of magnetic field reduced to the magnetic pole, vertical derivatives, tilt derivative, and apparent magnetic susceptibility. Other techniques applied to the CSC dataset were the Keating method, Euler deconvolution, a local wavenumber method, and three-dimensional inversion to enhance the value of the data for mineral exploration.

Approach

This geophysical interpretation is based on a multi-dataset stacking technique in which the expression of features was compared across various geophysical data layers, and interpreted features were manually traced on a series of colour- stretched and shaded-relief grids. The structural interpretation of magnetic data in terms of basic geological features such as lineaments, faults, contacts, and dykes are provided. The two-dimensional filtering, Grav/Mag Interpretation, and VOXI extensions of Seequent's Geosoft Oasis MontajTM geoscience software were used to apply Keating correlation coefficients, Euler three-dimensional deconvolution, local wavenumber depth-determination, and three-dimensional inversion techniques to the aeromagnetic data. Ninety-eight out of two hundred and forty of the best potential kimberlite targets were selected as the highest priority on the geophysical interpretation map for follow-up. The targets are ranked based on Keating correlation percentage, error, amplitude, correlation of anomalies defined by the Keating and Euler techniques, estimated depths derived from a local wavenumber technique, and associated structural features (interpreted dykes, contacts, lineaments, or faults). The highest priority targets are assigned a rank of 1, whereas the lowest priority targets are assigned a rank of 5. Three-dimensional unconstrained magnetic inversions were also performed to enhance visualisation of dominant magnetic bodies and structural features. The model presented herein is the simplest model to satisfy the available geophysical data and includes a collection of source geometries and magnetic susceptibilities that could plausibly explain the observed magnetic field.

Schedule

During the winter of 2017, a high-resolution total field aeromagnetic survey of the central Slave craton area was flown for NTGS. The detail of survey data equipments, acquisition, data processing and logistics can be found at previously published NTGS survey from NWT Open Report 2017-014 (Mirza and Elliott 2017). All advance data processing and geophysical interpretation are described in this publication NWT Open File 2024-01.

Keywords

Airborne Geophysics, magnetic, Central Slave Craton, Slave Craton, Slave Geological Province, kimberlite, fixed wing, aeromagnetic, Interpretation, 75M and 75N, Great Slave Lake, Keating Coefficients, Structures, Euler 3D deconvolution, and Source Parameter ImagingTM techniques, 3D magnetic inversions, Susceptibility Model, Voxels & Iso-surfaces