Geochemical discrimination of Early Palaeogene bauxites in Croatia

Two discriminant function models were created in order to distinguish between major- and trace-element geochemical patterns typical of Lower Palaeogene (Palaeocene, Pc) bauxites formed on the portion of the carbonate platform comprising the Karst or External Dinarides. Four groups of bauxites from Istria, North Adriatic Islands, North Dalmatia and Central Dalmatia have been distinguished, according to their specific combinations of major and trace elements, characteristic conditions of formation, and processes prevailing in the karst environment during subaerial exposure of the carbonate platform. Typically, in both models the first discriminant function explains most of the system variability. However, the trace-element model proves itself as a more helpful predictive tool, representing the straightforward example of classification of the samples into four pre-defined groups of Pc bauxites. Generally, both models follow a characteristic trend in geochemical signature related to the recent geographical position of the bauxite deposits, namely a decrease in K2O and an increase in the Cr content in a SE direction (from Istria to Dalmatia). This was most probably the result of environmental conditions during the AdCP Cretaceous-Palaeogene emergent stage (Istria), and emplacement of parent rocks (ophiolite belt) supplying the necessary material for bauxite genesis (Central Dalmatia).