Case history of Borehole Pulse EM surveys at the Falconbridge Lindsley discovery in Sudbury

CIM Bulletin, Vol. 85, No. 957, 1992

D. Crone, Crone Geophysics & Exploration Ltd., Mississauga, Ontario, and T. Watts, Falconbridge Ltd., Falconbridge, Ontario

The Lindsley project was a program of deep drilling to test the contact down-dip from two nickel-copper deposits, one uneconomical and the other mined out. The role of Borehole Pulse EM (PEM) was to detect the higher grade, more massive sulphide zones if they were missed by a drillhole, and to help determine geometry if the zones were intersected. Two problems appeared as the PEM survey progressed: (1) conductivity-thickness as measured by the PEM did not always relate to economic sulphides as determined by the market; (2) a pattern of unusual PEM anomalies was obtained that indicated something odd and big, but the cause was unknown. A large fold structure subsequently was indicated by a program of deepening previous holes, the third of which intersected high-grade mineralization below 1280 m. Falconbridge is in the process of shaft sinking and underground exploration.

Keywords: Exploration, Pulse EM surveys, Lindsley discovery, Falconbridge Ltd.