Magnetite-hematite Iron Ore Occurrences in the Triassic-paleozoic Metamorphic Complex of Medvednica Mountain, Croatia

Iron ore occurrences are situated on the south-eastern slopes of the Medvednica Mountain. They occur as discontinous, decameters long and 2-3.5 m thick bedded, poorly mineralized (15-35 % Fe) lenses. A narrow, 6 km long, ore zone strikes NE-SW from Tisova Peć to Pustodol-Adolfovac. It is spatially and genetically bounded to the basic volcanogenic-sedimentary series (SEDEX-type), metamorphosed in greenschists during Cretaceous under P 3-3.5 kbar and T 350-400°C. The main minerals of the paragenesis are: quartz, chlorite, hematite, magnetite, stilpnomelane, martite. Similar types of Neo-Proterozoic and Early Paleozoic iron deposits were found in eastern Bosnia western Serbia, western Macedonia and in the Serbo-Macedonian Mass. In the Triassic period of the Dinarides, magnetite-hematite deposits occur only as iron skarns or as short veins and small sized bodies of pneumatolytichydrothermal origin genetically bounded to gabbro-diorite or syenite stock and dykes. In the Triassic vulcanogenic-sedimentary complexes occur only bedded deposits of red hematite, siderite, as well as locally with Mn-oxide ores. The arguments pointing for the Paleozoic age of the Mt. Medvednica iron deposits are more convincing than those proposing theoretically possible Triassic age. The structures, textures and parageneses of the Mt. Medvednica magnetite-hematite occurrences are very similar only to the iron ores situated in the Early Paleozoic metamorphic complexes. Ključne riječi: željezna rudna ležišta, SEDEX-tip, donji paleozoik, Medvednica planina, Hrvatska