Geologia Croatica (Jun 2014)
Geochemical characteristics and genesis of Mačje Jame and Vranjski Potok As-Cu-bearing iron occurrences west and southwest of the town of Busovača, Mid-Bosnian Schist Mountains
Abstract
In this study two small, but genetically very interesting iron carbonate deposits Mačje Jame and Vranjski Potok, south west of Busovača (MBSM), located in the pre-Devonian metamorphic complex were investigated in detail. The analyses of the main chemical components, trace elements, REE, isotope composition of C, O, S, 87Sr/86Sr ratio of rhyolite, plot of REE normalized to CI chondrites and a microscopic study of thin and polished sections were performed. Three mineralization phases were identified: the oldest is the main phase (90-95 wt %) with Fe (Ca, Mg, Mn) carbonates (siderite, ankerite, Fe-dolomite) as the predominant minerals whereas magnetite, hematite, albite, allanite, pyrite I, quartz I represent subordinate minerals. The second phase is the pneumatolytic-kathathermal phase (5-10 wt %) characterized by pyrrhotite relicts, pyrite II, quartz II, arsenopyrite and some supposed accessory minerals such as cassiterite, wolframite, gersdorffite, columbite. The youngest is the katha-mezo-epithermal-hydatogene phase (<1 wt %) which gave quartz III-chalcedony as gangue minerals and marmatite, chalcopyrite, boulangerite, gel-pyrite-marcasite, sphalerite, enargite, tetrahedrite, galena, cosalite, bismuth and sternbergite as ore minerals. Almost an identical paragenesis has been found in the oldest ore deposit of the Gemericum Paleozoic metamorphic complex (RADVANEC and BARTALSKY, 1987).The first and second mineralization phase of both ore deposits formed in the Carboniferous from metamorphogeno-hydrothermal fluids generated from S-granitoid magmatic rocks and their protoliths. This claim is strongly supported by very similar REE and their interior disposition between these deposits and metarhyolites as well as by the obtained values of strontium ratios. The third, youngest phase is the product of a very weak overprint of the Late Variscan (290-260 Ma and in the Upper Permian-Lower Triassic (260-240 Ma) time) hydrothermal activity.
Keywords
