Introduction

In view of a recent kimberlite discovery in the Wekusko Lake area and active diamond prospecting during the past 5 years in north-central Manitoba, a reconnaissance kimberlite indicator mineral sampling program was carried out as part of a regional surficial mapping and drift prospecting project centred in the Flin Flon-Snow Lake area. This project was initiated in 1991 under the NATMAP Shield Margin Program by the Geological Survey of Canada. Heavy mineral concentrates were recovered from 60 large bulk till samples collected in 1992 over a 4000 km2 area. The chemistry of potential kimberlite indicator minerals was confirmed by microprobe analysis and published in the GSC Open File Report 2844 in 1994.

Results

Non-ferromagnetic heavy mineral concentrates were recovered from 60 large bulk samples collected in the Wekusko Lake area, and a total of 78 potential kimberlite indicator minerals were recovered. Three peridotitic garnets were identified and particularly one high-Cr pyrope G9 was found in the northeast part of the study area. All other garnets appeared to have a crustal origin. Cr-diopsides with high CaO content and Cr2O3 > 0.5 wt% are abundant in the study area, with high concentrations SE of Wekusko Lake and particularly north of North Moose Lake, where the diopsides are highly enriched in Cr2O3 (> 1.4 wt%). Mg-ilmenites with high MgO content (> 3.0 wt%) that would indicate a good degree of diamond preservation are concentrated at 4 sites directly south of Wekusko Lake. All other ilmenites and all chromites did not have high MgO content and were considered to have a crustal origin. From the 60 sites sampled, 4 sites have more than one type of indicator mineral, and two of these sites are located immediately south of Wekusko Lake. The greatest concentration of indicator minerals occurs at three sites north of North Moose Lake where 20 high-Cr diopsides (Cr2O3 > 1.4 wt%) were recovered.

Future Work

In addition to the 60 samples collected in the Wekusko Lake area, 100 large bulk till samples collected on the Paleozoic cover over the entire study area in Manitoba and Saskatchewan and 45 till samples collected in the Amisk Lake area, Saskatchewan, were recently analysed for kimberlite indicator minerals. The chemical results from potential kimberlite grains will be published in a second GSC Open file report in 1997.

Author: Isabelle McMartin