Rare earth element distribution and mineralization in Sweden: An application of principal component analysis to FOREGS soil geochemistry

Abstract

This paper presents results of statistical analyses and spatial interpretations of distributions of rare earth elements (REEs) in Sweden using the Forum of European Geological Surveys (FOREGS) geochemical database of topsoil, subsoil and stream sediment compositions. Raster maps depicting spatial distributions of individual REEs were created by interpolation of uni-element data and then principal component (PC) analysis was carried out on the REE data to identify geochemical anomalies associated with bedrock lithology and known mineralizations. The spatial distributions of REEs in Sweden are studied using only the Swedish data subset and the entire European data set. The light rare earth elements (LREEs) La, Ce, Nd and Sm show good correlations among each other but not with Eu. The heavy rare earth elements (HREEs) including Tb, Dy, Ho, Er, Tm, Yb and Lu also show good correlations among each other but not necessarily with the LREE. La, Ce and Nd are the most abundant REEs in all the studied media (topsoils, subsoils and stream sediments), with average median concentrations of 25.3mg/kg, 53.6mg/kg and 23.9mg/kg, respectively. The total explained variances of the first two PCs of each of the REE dataset for topsoils, subsoils, and stream sediments are 95.4%, 95.8% and 95.2%, respectively. Biplots of the first two PCs of each of the REE dataset for topsoils, subsoils, and stream sediments commonly reveal two distinct groupings – HREEs and LREEs – whereas biplots of PC1 versus PC3 of these datasets commonly reveal three distinct groupings – Eu, Ce and other REEs. The main difference between the distribution patterns of LREE and HREE is likely due to enrichment of the LREEs in the Archean bedrock underlying northern Sweden. HREE concentrations in the Archean to Paleoproterozoic metasediments are rather low. Color composites of PC maps produced from the topsoil and subsoil datasets clearly reflect the Archean rocks in northern Sweden and outline the second phase of the Svecokarelian orogen.