Special Report 064

Special Report 064

SPE 064

Geophysical Signature of the Mountain Lake Intrusion: A Study to Support Future Kimberlite Exploration in Alberta

The Mountain Lake Intrusion in northwestern Alberta represents one of the most accessible kimberlitic pipes located to date within the Western Canadian Sedimentary Basin. As such, several practical exploration and orientation geophysical studies have been completed over the intrusion; the current report compiles more than 10 years' worth of geophysical data, including airborne magnetic and electromagnetic, ground magnetic and electromagnetic, gravity, seismic reflection and refraction, resistivity and borehole logs.

The Mountain Lake Intrusion has a distinct topographic, magnetic, resistivity and gravity response in comparison to its Upper Cretaceous host rocks. It produces a 10 nT magnetic anomaly, a 0.3 mGal Bouguer gravity anomaly and has a 50 m thick conductive core (< 10 ohm-m). Deeper parts of the intrusion (250 to 400 m) are modelled with magnetic and resistivity data to have subtly elevated magnetic susceptibility (10 mSI) and elevated resistivity values (30 ohm-m). The intrusive body can be recognized by the presence of strong seismic diffractions, which extend to depth in the seismic section and have apices coinciding with the topographical and other geophysical expressions of the intrusive.

The data collection not only provides the most up-to-date geophysical interpretation of the Mountain Lake area, but also a practical background dataset for reference in the continued exploration for kimberlite in sedimentary basins. For example, there is an unequivocal relationship between the physical properties derived from borehole logs, which are collected routinely by the oil and gas industry, and surface and airborne geophysical data. Thus, screening of vast oil and gas datasets may enable companies to investigate large areas of the prairies for possible kimberlite targets.

Kellett, R.L., Steensma, G.J. and Zahynacz, R.M. (2005): Geophysical signature of the Mountain Lake intrusion: a study to support future kimberlite exploration in Alberta; Alberta Energy and Utilities Board, EUB/AGS Special Report 64, 63 p.