Geochemical characteristics of barite occurrences in the Palaeozoic complex of South-eastern Bosnia and their relationship to the barite deposits of the Mid-Bosnian Schist Mountains

In Palaeozoic rocks of South-eastern Bosnia (SEB) there are numerous, but very small vein and replacement barite ore deposits containing up to 10% Pb-Zn-Fe-Cu sulphides. Their geochemical characteristics are compared with large barite monosulphide (Hg-tetrahedrite) ore deposits in Mid-Bosnian Schist Mountains (MBSM). The 87Sr/86Sr isotope ratios in the barites of both areas are very similar, (0.710972 and 0.714170 in SEB, 0.711764 and 0.712548 in MBSM), and indicate the epigenetic hydrothermal origin of the barite ore deposits. This conclusion is supported by the elevated Sr content in barites of both areas (0.48 to 2.83% in SEB, 1.44% in MBSM) and the δ13C and δ18O values in calcite and siderite of barite ore deposits which are shifted toward lower values relative to typical values occurring in the Devonian host rock. The δ18O values in barites from SEB (+14.2‰ to +15.6‰) are remarkably lower than those from MBSM (+15.8‰ to +22.4‰). This can be explained by the lower temperature and lower salinity of mineralisation fl uids in barite ore deposits of SEB. The δ34S values in barites of SEB are positive (+11.6‰ to 17.7‰), and enriched in heavy sulphur isotopes in comparison with sulphides of SEB (–0.41 to +4.26‰), whereas those in tetrahedrites are negative (–4.95 in SEB, –5.50 to –15.40‰ in MBSM) indicating two remarkably different sulphur sources and times of formation. Barite ore deposits of both areas, SEB and MBSM, have been genetically linked to fl uids that originated during Late Variscan S-type magmatism and metamorphism of Upper Proterozoic and Lower Palaeozoic rock complexes. However, later Post Variscan/Eoalpine heating processes affected signifi cant parts of barite ore deposits in MBSM. They caused fl uidization of sulphides in barite deposits, ascension of subcrustal deepseated fl uids enriched in H2S and mercury (± fl uorine), which passed through Upper Proterozoic and Caledonian ore deposits amalgamating their Au and Ag content leading to formation of a new mineral, Hg-tetrahedrite rich in Au (10–50 g/t) and Ag (1000 do 3000g/t).