3D inversion of total magnetic intensity data for time-domain EM at the Lalor massive sulphide deposit
In this case study, TDEM is used to image a massive sulphide ore deposit. Material presented here has been 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.