Postorogenic volcanic rocks of different Tertiary ages are very common in the Sava-Vardar Zone of the Dinarides and in the southeastern part of adjoing Pannonian Basin. South of the Sava-Vardar Zone, in central Bosnia, Tertiary volcanic rocks occur within ophiolite sequences and genetically related sedimentary formations of the Dinaride Ophiolite Zone. Central Bosnia volcanic rocks are mostly dacites, and highly subordinately andesites as the members of the high-K calc-alkaline series.It appears from the mineralogical and petrographic characteristics obtained some insight into the processes that occurred during the genesis of the rocks. The presence of primary igneous minerals: clinopyroxene, orthopyroxene, hornblende and biotite from ferromagnesian minerals, and plagioclase, sanidine and quartz, indicates that the fractional crystallization played a significant role in the genesis of the rocks. Reaction edge on many rounded quartz phenocrysts indicates the possibility of magma mixing with the formation of Tertiary volcanic rocks of the central Bosnia. On magma mixing different temperature and chemical composition also indicates the existence of zoned plagioclase and amphibole phenocrysts.Complex compositional and zoning patterns of biotite and plagioclase phenocrysts and disequilibrium microstructures of plagioclase and quartz phenocrysts suggest interaction of fractionating, mantle derived melts with continental crust during a shalow level pre-eruptive stage and mixing with small amount of devolatilized phlogopite-phyric mafic magma before eruption.
In Bosnia and Herzegovina, Tertiary volcanic rocks occur within two geotectonically different areas: (1) in northeastern Bosnia, the wider area of Srebrenica and, (2) to a lesser extent in central Bosnia, the wider areas of Maglaj, Teslić and Nemila (Kolići). The major and trace element variations in the rocks surrounding Maglaj indicate their high-K calc-alkaline character, and are consistent with fractionation of the observed phenocryst assemblages (plagioclase, sanidine, biotite and hornblende). The scatter in some graphs cannot be explained by simple crystal fractionation from a common parent magma. More likely, such variations are affected by variable contribution and assimilation of continental crust within the magmas generated in the mantle. The presence of reverse zoned plagioclase phenocrysts, as well as a resorbed rim enclosing the coexisting quartz phenocrysts, can be interpreted by mixing of magmas with different temperatures and compositions.All analyzed rocks show enrichment of the LILEs over the HFSEs and have significant negative Ta-Nb, P and Ti anomalies, and positive U and Pb anomalies, which are characteristic of subduction-related volcanic rocks generated in (post) collisional zones. Chondrite-normalized REE patterns exibit enrichment on the LREEs over the HREEs with (La/Yb) cn ranging from 21.4 to 21.9. All analyzed rocks have small negative Eu anomalies (Eu/Eu * =0.86-0.89) which suggests that plagioclase fractionation played a minor role in the genesis of the dacites. Ratios of some diagnostic elements versus SiO 2 diagrams are best explained as a result of assimilation of varying degree in the continental crust during magma ascent and continuing fractional crystallization. High values of LILE/HFSE ratios in K/Ti (6.6 to 11.9), K/Zr (124-169), K/Nb (1598-2692) and Ba/Nb (44-65) and negative anomalies of Ti and Nb in the volcanic rocks surrounding Maglaj can be explained as the result of complex processes in the magmatic system originally derived from a mantle wedge.
Magmatic rocks of post-Late Eocene magmatic formation are widespread in the Sava segment of Sava- Vardar suture zone and adjoin areas. The rocks formed as a response to transpressional-transtensional tectonic activity preceded by the Cretaceous-Eocene compression of the Internal Dinarides and Tisia Unit as fragments of Eurasian continental lithosphere. Central Bosnia Tertiary volcanic rocks (CBTVR), erupted as dacites in Lower Oligocene, are peculiar rocks of this formation either by their location (southernmost distal outcrops) or geological setting (extrusive within the melange of the Internal Dinaride Ophiolite Belt). Major element composition of the CBTVR reveals high-K calc-alkaline geochemical affinity whereas trace element discriminate the rocks as shoshonitic. The rocks are LILE-enriched and show negative Ta- Nb, P and Ti anomalies, and positive Pb anomalies typical of subduction related volcanic rocks. Chondrite-normalized REE patterns exhibit significant LREE/HREE enrichment [(La/Yb)cn = 21.4 - 33.4]. Geochemical affinity of the CBTVR combined with tectonic position of extrusions suggests derivation of the melts from the subcontinental mantle which had inherited strong orogenic signature during an ancient subduction.
SUMMARYQualitative characteristics of bauxite deposit "Oštrelj" are defined through extensive laboratory testing of chemical and mineralogical-petrographic composition, and geomechanical characteristics. Chemical composition has shown that it is a relative poor bauxite with low Al/Si module (2,28). Low values of Al/Si module are result of lower Al 2 O 3 concentration (48 %), and higher SiO 2 concentration (21 %), what these bauxites define as high silicic or »acidic«. Identified are increased concentrations of larger number of analyzed trace elements (B, Co, Cr, Li, Mn, Ni, Sn, V, Zn) comparing to the medium content in the Earth's crust. Mineralogical composition, structure and texture are uniform.Holders of Al mineralization are bemite and diaspor (to a lesser extent) as crypto-crystalline phases of rock matrix. Lower Cretaceous age (K 1 ) of roof layers over bauxite deposit is paleontologicaly documented, while in the bauxite any fossils are not registrated. Values of geomechanical paramers of layers under and over bauxite is uniform. In bauxite value of compressive strength is increased, which is equivalent to chemical and mineralogical composition, and structural and textural characteristics of tested bauxite samples.
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