Exploring high-resolution targeting till geochemical data in central Lapland, Finland

The targeting till geochemical dataset of Finland was collected during the 1970s and early 1980s by the Geological Survey of Finland (GTK). The dataset covers central Finnish Lapland and some areas in Ostrobothnia and eastern Finland. A subset of data from central Lapland has been examined in this study. The goal of this study is to present a detailed description of the high-resolution targeting till geochemical data, together with data preprocessing and preliminary data analysis. The geochemical data are considered to be compositional data. Box plots, original concentration maps, and quantile-quantile (Q-Q) plots were used to explore the data and original and centred log-ratio (clr) transformed concentration maps with lithological units, heat maps and principal component analysis (PCA) plots were used as analytical tools. The data analysis revealed mismatches between neighbouring map sheets which were caused by the problems related to till sampling, analytical methods, and the complex levelling problems of elements. A better insight into the data could be obtained by analysing clr-transformed data rather than by analysing raw data. A PCA biplot is a powerful tool for identifying the important patterns in the area and correlating them to the underlying geology.