Mountains graphic with white diamonds on itGeoscience and Exploration

Extremely Low Frequency (ELF) Passive EM Survey for Conductivity Mapping Over Known Sulphide Deposits in Bathurst, NB

Thursday, November 21, 2019 - 9:40am to 10:00am Theatre One
(Student abstract)


A. Furlan (Presenting)
Brock University
H. Ugalde
Brock University
W.A. Morris
Brock University
D. White
Aurora Geosciences Ltd.

Volcanogenic massive sulphide (VMS) deposits have been mined in northern New Brunswick since their initial discovery in the 1950’s. Geological and geophysical methods were used to find 46 known deposits including the famous Brunswick 6 mine. Past exploration efforts during the last 2 decades (mostly through the EXTECH2 and TGI3 programs) have resulted in a large database of high-resolution airborne and ground geophysical data, consisting mostly of magnetic, gravity and conventional DC IP and resistivity surveys. Although this database did not succeed in reaching early levels of success in Bathurst, it provides us with a collection of geophysical signatures over known deposits that can be used to test new instrumentation. The pyrrhotite-rich sulphide deposits in the area have strong conductivity contrasts with the host rock and can be identified using electromagnetic (EM) survey methods.

Recently, Aurora Geosciences Ltd. has being using an extremely low frequency (ELF) passive EM system to map conductivity structures. A similar airborne system, ZTEM (developed by Geotech), has already proven its usefulness mapping porphyry deposits around the world. The ELF system measures horizontal and vertical components of the Earth’s geomagnetic field. Tilt angle, otherwise known as the tipper, is comprised of these components and recorded for eight frequencies between 11 and 1440 Hz. While dependent on the conductivity in the top-most layers (skin depth), the ELF system can image up to 2km depth. A deep penetrating EM method, such as the ELF, is a perfect use case for the overburden covered deposits of northern New Brunswick.

Several transects were collected using the ELF system over known VMS deposits at Key Anacon Mine. Using the currently mapped deposits from Osisko Base Metals, three survey locations were selected; one over the ‘Titan Zone’ & two over the ‘Main Zone’. This presentation focuses on the preliminary results derived from the surveys. Total divergence (DT), total phase rotation (TPR), and tipper vectors for both in-phase and quadrature components were computed. These data are compared with known geology & legacy datasets to associate ELF data with real world structures and geophysical signatures typical of VMS deposits.