Special Report 089
Significant amounts of placer gold, platinum and rare diamonds have been found in gravel deposits on the northern outskirts of Whitecourt, Alberta. These deposits are currently being worked for their cobble and gravel components, but test circuits have been set up to recover heavy minerals from the gravel washings. These minerals are recovered by various density-sensitive methods, such as a jig concentrator, shaking table, spiral concentrator and Knelson concentrator. Quartz, almandine garnet, magnetite, ilmenite, hematite, gold, zircon and monazite were the main minerals identified in these concentrates during this study, along with minor amounts of platinum, pyrite, dolomite, calcite, cerussite, lead, rutile, chromite and barite. Rare diamonds recovered from other samples were also shown to us, but not recovered from the samples used in this study.
A scanning electron microscope was used to determine the general morphological features of the heavy mineral grains, such as the degree of rounding, flattening and etching. These observations provide a qualitative measure of the degree of transport of grains and their environment of transport and deposition. Gold grains ranged in size between 0.1 and 1.5 mm.
Quantitative analysis of mineral grains was conducted with an electron microprobe. The fineness of the gold ranged between 550 and 790 in the cores of grains, but sharply defined rims had a much higher fineness of 940-980, with <0.1 wt.%="" cu.="" these="" gold="" grain="" compositions,="" as="" well="" as="" a="" number="" of="" the="" accompanying="" mineral="" constituents,="" indicate="" the="" gold="" is="" likely="" of="" epithermal,="" or="" possibly="" mesothermal,="">
Knight et al. have detailed a method whereby the flatness (ratio of length and breadth to thickness) of gold grains can be used to provide an estimate of the transport distance. The flatness ratio of grains from this study ranges between 40% and 50%, which suggests nearby derivation from as little as 3 to 8 km away.
The source of alluvial placer gold in Western Canada is an issue of contention because no viable sources have yet been identified. Similarly, the lack of diamond indicator minerals in this and similar deposits throughout Alberta provides no clues as to the source of the diamonds.
Mudaliar, G.G., Richards, J.P. and Eccles, D.R. (2007): Gold, platinum and diamond placer deposits in alluvial gravels, Whitecourt, Alberta; Alberta Energy and Utilities Board, EUB/AGS Special Report 89, 24 p.