Geobotanical and biogeochemical nickel ore prospecting in Northern Finland

Category Medical geology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Uosukainen, Harry
Holding Date 27 September 2008

Geobotanical and biogeochemical investigations were carried out in an area where the nature of the bedrock is well known on account of previous drillings. The principal rock types of the area are granite, amphibolite and mica schist, with weakly mineralized serpentinites to be found between them. There are also some pyrite-bearing chert horizons in the schist zone. Powerful geophysical disturbances and Ni-mineralizations have been detected in the area. The average glacial transport distance for the till is 5-15 km, but there is also a large amount of quite local material. Attention was paid here to the species composition of the vegetation and heavy metal concentrations in the plants. Although the distributions of the most common forest and mire types, e.g. fresh heath forest, grass-herb forest etc., are evidently dependent mainly on the topography and moisture conditions, distinct eutrophicated patches are to be seen on the floor of the fresh heath forests in places in the serpentinite/skarn zones, accompanied by changes in the proportions of the main forest trees, reflecting the effects of the relative abundance of calcium in raising the nutrient status and reducing the toxic influence of the ultrabasic rocks to a minimum. The general indicator plants provided scarcely occur at all in the present area, but the species that are most typical of the eutrophicated patches observed here may be regarded in a sense as secondary indicators of certain rock types. Of the plants submitted to chemical analysis here, the birches, willows and horsetails (Equisetaceae) were the chief accumulators of heavy metals. Heavy metal concentrations in the needles of conifers were very small throughout. The highest concentrations of nickel were observed in Filipendula ulmaria, Juniperus communis and Equisetum limosum, those of cobalt in the Equisetaceae, those of copper and molybdenum in Rubus chamaemorus, and those of zinc in the birches and willows. No plants with a special tendency for lead enrichment were identified. The Ni mineralizations in the serpentinites were reflected more clearly in the birch samples than in those from coniferous trees, although even in the former the anomalies were weak along transects with a great depth of surficial deposits. Apart from nickel, the metal which showed major variation in the plant samples was zinc. The biogeochemical anomalies in the plant material were weaker than those in the humus and peat samples, but they did occur at more or less the same points. These investigations methods carried out here serve to demonstrate that such methods can provide significant information for ore prospecting purposes in areas where environment is somewhat similar to that of the present case. They may be particularly suitable for orientation in areas where there are few bedrock outcrops, especially since the sampling of plant material and the mapping of indicator species can be carried out at relatively little expense