3D inversion of total magnetic intensity data for time-domain EM at the Lalor massive sulphide deposit
This case history follows the use of airborne and ground-based TDEM surveys to locate and characterize a deeply buried very massive sulphide deposit in the Flin Flon Greenbelt, Manitoba/Saskatchewan, Canada.
Thanks to the Society of Exploration Geophysicists for permission to reproduce figures and adapt text from the source material. This case history was adapted from “3D inversion of total magnetic intensity data for time-domain EM at the Lalor massive sulphide deposit” ([OY16]) and “Mine scale description of the mineralization at the Lalor deposit, Snow Lake, Manitoba, Canada” ([Tay14]).
The Lalor deposit is a massive sulphide that is characterized as a stack of conductive ore lenses buried more than 600 m deep. As of 2014, the deposit has a reserve of 15.2 Mt and an inferred resource of 10.1 Mt. Compared to typical Canadian gold deposits, the Lalor lake deposit has a grade 130% above the average.
In order to characterize the Lalor lake deposit, a helicopter sub-audio magnetic (HeliSAM) survey using a ground large transmitter loop and an airborne total magnetic intensity magnetometer receiver was employed to measure the time-domain EM responses of the conductive ore bodies. Using inversion, the Lalor ore lenses as well as small sulphide-bearing argillite units were successfully imaged in 3D. The successful inversion of the geophysical data was made possible through the use of warm-start and mesh refinement algorithms.