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The Jõhvi magnetite quartzites (MagQ) occur as subvertical beds with a complicated structural outline in biotite-garnet-cordierite and pyroxene gneisses which in places also contain high concentrations of iron. Drill core study shows that the complex of MagQ and magnetite-rich gneisses may be up to 100 m thick. The MagQ provide a wide range of chemical composition: SiO2 ranges between 40.3 and 60.1 wt%, Al2O3 between 1.7 and 19.7 wt% and total iron between 15 and 45.2 wt%. This study also revealed unusually high manganese contents of 1â6 wt%. The rare earth element (REE) patterns of MagQ and the surrounding gneisses partly overlap. Cutting granitoids form two different REE patterns. Magnetite occurs as anhedral grains elongated along rock fabric, as rounded inclusions in other minerals or as tiny platelets along grain edges and along cleavage planes of amphibole and biotite. Sulphides are present as pyrite, pyrrhotite and other minor sulphide minerals (chalcopyrite, galena and sphalerite). Analysis of the magnetite grains from drill core J-1 shows that classifying Jõhvi magnetites into a certain deposit type is not unambiguous. The garnetâbiotite geothermometer revealed metamorphic temperatures between 650 and 750 ºC. The garnetâbiotiteâplagioclaseâquartz geobarometer yielded the pressure range of 2.9 to 4.9 kbar. However, having in mind that the entire Jõhvi ore complex may be a result of repeated metasomatic events, which have influenced the primary volcanic-sedimentary sequences, the estimate of primary pressureâtemperature conditions might not be a straightforward task. The current understanding of the geological-geochemical correlation hints at geological similarities between the Bergslagen area in Sweden and the Jõhvi Zone in Estonia.

The Cretaceous to Palaeogene oil shale (OS) of Jordan is predominantly calcareous mudstone with intervals of mostly siliceous minerals, quartz and cristobalite–tridymite. Oil shale is rich in organic sulphur and trace elements. According to preliminary micropalaeontological data, the OS succession of the studied area, the south-central part of the Attarat Um Ghudran (AUG) deposit in central Jordan, is of Maastrichtian age. A representative collection of 392 samples from 9 drill cores reliably characterizes the sequence of the OS seam, on average 70 m thick. The composition of AUG OS varies significantly. The major compounds CaO and SiO2 range within 3–70 wt% and 10–50 wt%, respectively, and also the contents of organic matter, MgO, P2O5, Al2O3 and S change. The concentrations of metals (especially Zn, V, Cr, Ni and Mo) change many dozens of times in the cross section. The aim of our statistical analysis was to determine the most significant OS types and their positions in the OS sequence. Two multivariate statistical analysis methods, principal components analysis (PCA) and hierarchical clustering of PCA groups, gave an interpretable result. Four principal components account for 88.6% of data variability. Variation in six main chemical components or groups of components is reflected in parameters of the four principal components. The component PC1 accounts for 47% of the data variance, expressing the highest correlation with organic matter, S, Cr, Cu, Ni, Zn, Mo, and PC2 accounts for 22.82% of the data variability, being strongly correlated with TiO2, Al2O3, Fe2O3, SiO2 and K2O and negatively correlated with CaO. The next two significant component groups express covariance with CaO and MgO. The applied statistical analysis proves to be a powerful tool for the interpretation of the chemically variable structure of the OS unit when using a representative enough sample collection. In the complex study of the OS unit, variation in the chemical composition is of interest, especially in the context of genetic and mining aspects.

The high-resolution study of vertical geochemical variability of shallow-water Tremadocian black shales of the Türisalu Formation targeted two drill core sections from Suur-Pakri Island, NW Estonia. Altogether 374 samples from 4.6 m thick shale were analysed by XRF. The metalliferous and organic-rich black shales revealed significant centimetre-scale variation in the concentration of redox-sensitive trace metals – U, Mo and V. The V profiles show cyclic variations in half a metre- to metre-scale and the strongest correlation with loss on ignition (LOI) 500 °C (interpreted to reflect organic matter abundance). The abundance of Mo presents high values near the lower and upper contacts of black shale and otherwise moderate covariance with LOI. The distribution of U is not coupled with LOI, being characterized by irregular local enrichment anomalies in the profiles of both sections. This suggests that sequestration of U may have been time-dependent and possibly favoured by dissimilatory U-reduction at the sediment–water interface under iron-reducing conditions. Significant depositional variability of the studied organic-rich muds apparently supported dynamic physicochemical and biological microenvironments at the sediment–water interface and thus temporally and spatially diversified the paths and efficiency of synsedimentary redox-sensitive trace element enrichment.