The geochemical correlation between coarse and fine fractions of till in southern Finland

Abstract

Since the 1950s, the <0.06 mm fraction of till samples has been sieved off and analysed, for purposes of mapping the geochemistry of Finland. The primary objective of the mapping was reconnaissance, regional and local scale exploration. The data are now stored and readily available from the relational ALKEMIA databases at the Geological Survey of Finland (GSF). Data on the natural distribution of nutrients, base cations and trace metals are also important for addressing environmental issues. However, a coarser fraction (< 2 mm) has been preferred in several environmental studies. To evaluate the usefulness of the old data in modern environmental studies, the element concentrations in the fine and coarse fractions of 618 till samples from southern Finland were compared using four data sets: 1. analyses based on total dissolution of the fine till fraction, as published in the Geochemical Atlas of Finland; 2. aqua regia soluble concentrations of the fine till fraction; 3. analyses based on total dissolution of the coarse till fraction; and 4. aqua regia soluble concentrations of elements in the coarse till fraction. The total concentrations of Na, Ca and K in the coarse till fraction reflected well the chemical composition of the underlying bedrock, while the distribution of the same elements in the fine fraction was ambiguous. By contrast, the concentrations of trace elements in the two fractions correlated well, although the concentrations were higher in the fine fraction. With the aid of linear relationship functions, the analytical results from the fine fraction of till can be used to estimate the natural distribution of trace elements in the coarser till fraction.