Abstract: The aim of this thesis was to define mineralogical, sedimentological and geochemical characteristics of iron ore and its underlying and overlying carbonate sediments from the historical mine Kotlenice near Trilj in the hinterland of middle Dalmatia, Croatia. Iron ore was formed on the uplifted carbonate platform during the emersion phase in the transition from lower to upper Cretaceous. The duration of the emersion phase can not be determined with certainty. The bedrock of iron ore is composed of micritic limestones with fenestral fabric. Lateritic soils formed on the uplifted carbonate platform during the emersion phase were weathered, transported and deposited in the depressions of the paleorelief. Iron ore was formed in specific, locally restricted environment, in which reductive and slightly acidic geochemical conditions prevailed (e.g. lake, swamp or marsh). Overlying sediments are composed of fine grained, partially recrystalized reddish micritic limestones impregnated by goethite and hematite originated from iron ore, which was weathered during the transgression. Dominant mineral phases in the iron ore are goethite and haematite. From the bottom to the top of iron ore profile the amount of clay minerals, which are mainly kaolinite, mica minerals, 14Å philosilicates and irregulary interstratificated clay minerals, is generally increasing. In the upper part of iron ore profile gibbsite was determined. Minor mineral phases found in ore are anatase and calcite. The presence of kaolinite and gibbsite may indicate that the lateritic soils formed on the uplifted carbonate platform were weathered and transported into the depressions of the paleorelief in which reductive conditions prevailed. The results of chemical analysis of major elements are in good corellation with the results of mineralogical analyses of ore. Trace elements and rare earth elements distribution along the iron ore profile implicates that reductive and slightly acidic geochemical conditions prevailed during the formation of iron ore. High concentrations of some trace elements (in particular vanadium) probably indicate that the processes of biomineralization might have had significant influence on the formation of iron mineral phases.