Thirty-one soil samples were collected from one east west transect line orientated roughly perpendicular to the larger of two north- south-trending positive magnetic anomalies interpreted to be possible kimberlites. The samples were treated using the enzyme leach process and the leachate was analyzed by inductively coupled plasma-mass spectrometry (ICP-MS).
Since the Mountain Lake Diatreme is near surface and forms a topographic high, the morphology of the enzyme leach-based geochemical signature is expected to yield an oxidation halo profile only. However, the geochemical signature over the Mountain Lake Diatreme combines a moderately strong to strong oxidation halo profile with a sharply defined apical geochemical profile. The high contrasting apical signature is formed from a "single" reproducible sample (Re-Ml97-015). Although apical responses generally indicate an anomalous source at depth, it is likely that the apical signature generated in this study is a
A multi-element geochemical response, with contrasts of up to 29 times background, was obtained in soil above the Mountain Lake Diatreme. Elements that are elevated >4 times background include: As, Ce, Co, Cr, Cs, Cu, Ga, Hf, La, Mn, Mo, Nb, Ni, P, Pb, Pd, Sb, Sn, Th, Ti, U, V, W, Y, Yb, Zn and Zr. While the overall geochemical signature is indicative of an ultramafic source, apical and oxidation halo geochemical responses yield elevated concentrations of Co, Cr, Cu and Ni with the presence of high Ba, Ga, Hf, PO4, Rb, Ta, Ti and light rare earth elements suggestive of a kimberlite or lamproite body. direct indication the top of the diatreme is close to surface. Since altered ultra basic volcanic rocks were observed at a depth of 1.8 m and represent the parent material to the soil, the geochemical abnormality at RE-ML97-015 may express the soil development profile that forms on top of kimberlitic and lamproitic bodies. The resultant apical profile from sample RE-ML97-015, in combination with an oxidation halo profile, is potentially something explorationists in Alberta should be aware of since diatremes discovered to date have been defined as predominantly topographic highs.
The results from analysis of the geochemical data indicate that the enzyme leach technique can be used as an exploration tool for kimberlite pipes, and that exploration companies may expand the method from base- and precious-metal exploration to include kimberlite, lamproite and related rocks. Furthermore, enzyme leach-based soil geochemical surveys may have a significant impact on exploration for kimberlite, lamproite and related rocks in Alberta by providing industry with a useful and cost effective tool to probe blind and/or buried anomalies identified by airborne and ground magnetic surveys in areas of complex glacially-derived overburden.
Eccles, D.R. (1998): Enzyme leach-based soil geochemistry of the Mountain Lake diatreme, Alberta; Alberta Energy and Utilities Board, EUB/AGS Open File Report 1998-01, 34 p.