THE GEOCHEMICAL CORRELATION BETWEEN COARSE AND FINE FRACTIONS OF TILLIN SOUTHERN FINLAND

Since the 1950s, the < 0.06 mm fraction of till samples has been sieve d off and analysed, for purposes of mapping the geochemistry of Finlan d. The primary objective of the mapping was reconnaissance, regional a nd local scale exploration. The data are now stored and readily availa ble from the relational ALKEMIA databases at the Geological Survey of Finland (GSF). Data on the natural distribution of nutrients, base cat ions and trace metals are also important for addressing environmental issues. However, a coarser fraction (< 2 mm) has been preferred in sev eral environmental studies. To evaluate the usefulness of the old data in modern environmental studies, the element concentrations in the fi ne 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 F inland; 2. aqua regia soluble concentrations of the fine till fraction ; 3. analytes based on total dissolution of the coarse till fraction; and 4. aqua regia soluble concentrations of elements in the coarse til l fraction. The total concentrations of Na, Ca and K in the coarse til l fraction reflected well the chemical composition of the underlying b edrock, while the distribution of the same elements in the fine fracti on was ambiguous. By contrast, the concentrations of trace elements in the two fractions correlated well, although the concentrations were h igher in the fine fraction. With the aid of linear relationship functi ons, 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.