During the 1990s, ultramafic diatremes were discovered in three separate areas of northern Alberta. In 1990, Monopros Limited discovered the Mountain Lake diatreme located northeast of Grande Prairie. In 1997, Ashton Mining of Canada Inc., in conjunction with Alberta Energy Company and Pure Gold Resources Ltd., discovered kimberlites on the southeastern flanks of the Buffalo Head Hills. To date, Ashton has discovered 36 pipes. In 1998, Kennecott Exploration Canada Inc., in conjunction with Montello Resources Ltd., discovered seven kimberlites in the Birch Mountains of northeastern Alberta. In December 2000, New Blue Ribbon Resources Ltd. discovered an eighth kimberlite in the Birch Mountains.
Although regional till sampling has been conducted in southern Alberta for extraction and analysis of kimberlite indicator minerals, most of the discoveries in northern Alberta were made with airborne and ground geophysical techniques, including seismic, magnetics and gravity. In northern Alberta, indicator mineral analysis may not be effective for detecting kimberlites because kimberlites are decoupled from streams draining upland areas by thick till cover, and the remoteness of northern Alberta makes basal till collection difficult and prohibitively expensive. Instead of pursuing mechanically dispersed anomalies from buried kimberlite pipes, this program focused on searching for pathfinder elements in plant tissue, soil, till and bog sediments that have been chemically dispersed from weathered kimberlites under glacial drift.
A total of 806 samples were collected during detailed orientation surveys at Mountain Lake (1 pipe), Buffalo Head Hills (3 pipes) and Birch Mountains (1 pipe). Samples collected over the pipes included white and black spruce top twigs, ground level aspen bark, willow twigs, spruce needles, A- and B-horizon soils, C-horizon till, peat, and subpeat sediments. The vegetation samples were dried and ashed at the Geological Survey of Canada (GSC), and the ash samples were sent to Acme Laboratories for acid digestion and multi-element Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) analysis (Group 1VE). The A-horizon soil samples were dried and sieved at the GSC and sent to Acme Laboratories for acid digestion and multi-element ICP-MS analysis (Group 1F), loss on ignition (LOI), pH and conductivity. Peat, subpeat sediments, B-horizon soil and C-horizon till were dried and sieved at the Alberta Geological Survey (AGS) Laboratory and sent to Acme Laboratories for acid digestion and multi-element ICP-MS analysis (Group 1F), pH and conductivity. Splits of the same B- and C-horizon samples were submitted to Activation Laboratories for Enhanced Enzyme Leach and multi-element ICP-MS analysis.
The results of the 2000 fiscal year geochemical program are summarized below. In general, the quality of the analytical data are good, but the precision shown by enzyme extractable elements in reference materials and field samples is inferior to that shown by Group 1F extractable elements.
As expected, the within-site variability comprises a significant proportion of the total variability. Variability decreases considerably within the samples, and sieving of the samples further decreases the variability. These observations indicate that source minerals susceptible to attack by the Group 1F analysis and enzyme leach are more uniformly distributed within 1 kg samples than within the sample sites themselves.
The three main suites of elements that are anomalous in various sample media over kimberlite pipes covered by shallow (<2 m), moderate (10-15 m) and very thick (>30 m) glacial drift are:
{PEA} Primary Element Association (Ni, Co, Cu, Cr, Ti, V, Mg, Mn, Fe).
{SEA} Secondary Element Association (H+, Nb, Rb, Zr, Y, Sc, Th, U, Cs, REE, P, Al, K, Na, Ca, Ba, Sn, Mo, W, Cd, Zn, Pb, B, Hf, Ga).
{TEA} Tertiary Element Association (Au, Ag, Re, Te, Se, Sb, Bi, S).
Anomaly contrast for elements in the three associations decreases markedly from ultramafic diatremes under shallow cover (<2 m) to those under intermediate (10-15 m) to very deep cover (>30 m). For most sample media, the contrast shown by elements of the TEA and SEA suites is typically higher than those of the PEA suite. Enzyme extractable elements show higher contrast than Group 1F extractable elements in B-horizon soil, C-horizon till and subpeat sediments.
The anomaly patterns examined in this study suggest there is very little, if any, chemical dispersion of kimberlite pathfinder elements downslope and/or down-ice from buried pipes. As such, these methods should be used for classifying airborne or ground geophysical targets by sampling of plant tissue, soil, till, peat and/or subpeat sediments at short intervals (<50 m). Sampling at larger intervals (e.g., 1 km) in a regional geochemical survey could potentially miss buried kimberlite pipes, although it may succeed in identifying kimberlite clusters for more focused follow up.
In the case of shallow glacial drift (<2 m), high contrast, Group 1F multi-element anomalies over buried kimberlite are evident in trembling aspen bark, twigs, stems (Eccles, 1998a), A- and B-horizon soil, and C-horizon till. In the interest of time and cost for ground-truthing geophysical anomalies, it is recommended that trembling aspen or spruce tissue be sampled at short intervals (<50 m) and analyzed by Group 1F analysis.
In the case of moderately deep glacial drift (10-15 m), low to moderate contrast, Group 1F and/or enzyme multi-element anomalies over buried kimberlite are evident in white and black spruce-top twigs, ground-level spruce needles, A- and B-horizon soil, and C-horizon till. In the interest of time and cost for ground-truthing geophysical anomalies, it is recommended that white or black spruce tissue be samples on the ground or from a helicopter at short intervals (<50 m) and analyzed by Group 1F analysis.
In the case of deep glacial drift (>30 m), low to moderate contrast, Group 1F and/or enzyme multi-element anomalies over buried kimberlite are evident in white and black spruce-top twigs, ground-level willow twigs, A- and B-horizon soil, C-horizon till, peat and subpeat sediments. In the interest of time and cost for ground-truthing geophysical anomalies, it is recommended that white or black spruce tissue be sampled on the ground or from a helicopter at short intervals (<50 m) and analyzed by Group 1F analysis.
The main objective of the program was to identify sample media and analytical techniques that could be used to explore for diamonds and other commodities both on regional and detailed scales.