Special Report 087

Special Report 087

SPE 087

Chemistry of Kimberlite Indicator Minerals and Sphalerite Derived from Glacial Sediments of Northwest Alberta

Previous AGS and GSC work have reported the presence of kimberlite indicator minerals (KIMs), sphalerite and galena in glacial sediments from northwest Alberta. Most of the KIMs, originally identified from optical properties alone, are confirmed following more detailed electron microprobe analyses with the exception of 1) 15 grains, originally classified as low Cr-diopside, are re-interpreted as KIMs because of their Cr2O3 content that exceeds 0.5 wt. % and 2) one grain originally identified as chromite is re-evaluated as crustal ilmenite. These new results confirm the presence of anomalous concentrations of KIMs in 3 glacial sediment (till) samples (6, 7 and 9 KIMs) and suggest an unknown kimberlitic source is reflected in the glacial sediments of northwest Alberta. Electron microprobe analyses (N=180) were completed on 15 sphalerite grains recovered from the region of the sphalerite anomaly (Plouffe et al., 2006a). Sphalerite has an average composition of 33.4 wt % S, 65.4 wt % Zn, 0.7 wt % Fe, 0.43 wt % Cd and traces amount (0.3 to 0.1 wt %) of Cu, Ag, Se and In. A negative correlation exists between Fe and Zn in sphalerite, suggesting the substitution of Fe for Zn in the sphalerite lattice.

Plouffe, A., Paulen, R.C. and Smith, I.R. (2007): Chemistry of kimberlite indicator minerals and sphalerite derived from glacial sediments of northwest Alberta; Alberta Energy and Utilities Board, EUB/AGS Special Report 87, 40 p.