Geo-Note 2005-02

Geo-Note 2005-02

GEO 2005-02

Kimberlite-Indicator Mineral Till Survey of the Sawn Lake Area (NTS 84B/13), Southern Buffalo Head Hills, Alberta

The Sawn Lake (NTS 84B/13) map area covers the northwestern part of the Buffalo Head Hills kimberlite field, within which 38 kimberlites have been discovered since 1997. During the 2002 program, 55 till samples (with an average weight of 29 kg) were collected within map area 84B/13, representing an average density of approximately one sample per 16 km2. Heavy mineral concentrates were prepared and picked for kimberlite-indicator minerals, including pyrope, eclogitic garnet, Cr-diopside, olivine, picroilmenite and chromite. In addition, data were obtained on epidote, spinel, apatite, tourmaline, chlorite, rutile, monazite, sulphide and Cr-amphibole.

Within the central and southwestern parts of the Sawn Lake map area, high counts of pyrope, chromite and olivine grains in till occur in a west-southwest-trending zone up to 6 km wide with a minimum length of 15 km. The most anomalous sample returned 418 pyropes, 190 chromites and 137 olivines (picked grain counts). To the south and east of the anomalous pyrope-chromite-olivine trend, the kimberlite-indicator mineral assemblage tends to be dominated by olivine (50% to 100% olivine) with counts of up to 150 picked olivine grains per sample.

The northeastern part of map area 84B/13, which contains a number of kimberlites, including the K252 kimberlite (estimated diamond grade of 55 carats per hundred tonnes), is characterized by tills lacking pyrope and containing relatively modest amounts of olivine +/- chromite +/- Cr-diopside (up to 20 picked olivine grains per sample).

A strong pyrope-olivine-chromite anomaly in till was identified east of Sawn Lake, in the north-central part of NTS map area 84B/13 (123 pyrope, 53 olivine and 28 chromite grains recovered from one sample). These grains may indicate the presence of an undiscovered kimberlite nearby. Glacial dispersal is most likely to have been in a southwesterly direction, and there are no known kimberlites northeast of this anomaly.

Prior, G.J., Paulen, R.C., Pawlowicz, J.G. and Fenton, M.M. (2005): Kimberlite-indicator mineral till survey of the Sawn Lake area (NTS 84B/13), southern Buffalo Head Hills, Alberta; Alberta Energy and Utilities Board, EUB/AGS Geo-Note 2005-02, 110 p.