Sphalerite and kimberlite indicator minerals in till from the Zama Lake region, northwest Alberta (NTS 84L and 84M)

Abstract

This report presents the results and interpretations of the heavy mineral assemblages and pebble lithologies of 19 bulk till samples collected in northwest Alberta, from the region of a sphalerite dispersal train originally reported by Plouffe et al. (2006a). Indurated pebbles in the 4-8 mm sized fraction of till dominantly consist of distally-derived bedrock lithologies: Canadian Shield rocks, Paleozoic carbonates, and quartzite. Three till samples contain mineralized clasts with visible pyrite and marcasite. Kimberlite indicator minerals (KIMs) in till, including Cr-pyrope, Cr-diopside and chromite are present in trace amounts (1 to 2 grains) in nine samples. Although the KIM counts are low, the samples with KIMs do cluster in the Zama Lake - Zama City area. The source, proximal or distal, is unknown and remains to be identified. Seven out of the 19 till samples contain sand-sized sphalerite grains, with the strongest anomaly consisting of 989 sphalerite grains recovered from a 34 kg till sample. The sphalerite is dominantly in the 0.25 to 0.5 mm fraction (900 grains) with smaller amounts (89 grains) in the 0.5 to 1.0 mm size range. The new data indicate that the sphalerite dispersal train first identified by Plouffe et al. (2006a) could cover an area of over 4000 km2. The bedrock source(s) of the sphalerite in till remains to be discovered.