Heninga Lake, Nunavut, Canada

... conventional geophysics had aided in delineating the near-surface mineralization but there was the potential of finding other zones at greater depth. A UTEM survey was carried out with deep penetration in mind.

Two new zones were detected by the 1979 UTEM2 survey - the AB-II Deep Zone and the deeper UTEM Zone. The UTEM Zone was interpreted to be very deep and located within the areal extent of the shallower main zone. A routine plot of the UTEM data on Line 240W revealed a broad, slowly-decaying, negative anomaly of very small amplitude (less than 2%) that attracted attention. Detailing with longer averaging times (increased signal-to-noise) and increased station spacing (the broadness of the original anomaly) included a crossline. The response was interpreted to indicate a depth-to-top of 270m with both depth-extent and strike limited to about 200m.

Based on the UTEM interpretation, a drill hole was recommended to test the source of the anomaly. The hole intersected massive sulphides - mainly pyrite with significant sphalerite - at 483m (300m vertical depth). Three subsequent holes drilled based on the original UTEM interpretation all intersected massive sulphides and indicated that the true dip was about 70° to the South.