Assessing the geochemical variability of oil shale in the Attarat Um Ghudran deposit, Jordan

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.