Pedogeochemical prospecting in a lacustrine clay environment

CIM Bulletin, Vol. 77, No. 862, 1984

J.-P. LALONDE et M. BEAUMIER Ministers de l'Energie et des Ressources Quebec

The results obtained from the study of soil geochemistry in 14 test areas as well as along six regional traverses clearly indicate that there are important variations in the trace-element content of the A1 soil horizon developed on glacio-lacusthne sediments. The observed dispersions are in all probability attributable to the same sources which are responsible for the anomalies in the groundwaters and the basal till. Of the fourteen test areas chosen, thirteen are clearly anomalous in the regional geochemical context and of these, ten are strongly anomalous. These figures suggest that a systematic regional soil survey would identify between 70 to 90% of the targets detected by geochemical surveys based on sampling at depth. The results of a systematic survey carried out in a 1000 km2 area also support this hypothesis. Consequently, the soils developed on glacio-lacustrine sediments are a very promising geochemical medium for a systematic evaluation of the mineral potential of large areas covered by lacustrine clays. The A1 horizon which consists of well decomposed organic matter as well as a certain mineral fraction is the most suitable horizon for this type of survey because it is easily sampled, it offers a guarantee of constancy in the sampled material, and finally, it has a greater base metal content. In this first study, the elements which appear to be the best regional indicators are Mn, Hg, Ni and Zn. However, it is still not possible to conclude that they will be the most useful because some may not be sufficiently specific. To progress in our comprehension of anomaly formation in this complex environment we must adopt a holistic approach which takes into consideration all interacting mechanisms operational before, during and after the deposition of the glacial and glacio-lacustrine overburden.

Keywords: Exploration, Exploration geochemistry, Pedogeochemistry. Soil, Humus, Glacio-lacustrine sediments, Till, Groundwaters.