engleski

Crystal chemistry of carbonates from Stari Trg mine, Trepča, Kosovo

More than 100 samples of carbonate minerals from Trepča, Stari trg mine, Kosovo were investigated. Samples were selected from Croatian Natural History Museum collection. The minerals were sampled from different areas in mine, so a great variability of these carbonates is observed. Due to their origin from hydrothermal veins in Pb-Zn mineral deposit, they occur mostly as a well developed crystals. They also occur as twins and penetration twins. An X-ray diffraction (XRD) analysis, SEM with EDS analysis and morphometric measurements were performed on these samples. X-ray diffraction data indicate carbonate phases, but it is difficult to distinguish the minerals with the calcite or dolomite structure if it is not possible to separate a single phase due to a great simmilarity of XRD patterns. The most valuable data were carried out with a scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). These data show that samples range amoung Ca, Mn, Fe and Mg (and in few samples also Zn) carbonate end members. According to the chemical composition it was difficult to divide carbonate minerals in groups precisely, because of a presence of 4 cations (Ca, Mn, Fe and Mg) in almost every sample. Only pure calcite is found. All other carbonate minerals have two or more important cations. So, the other carbonates are classified as manganoan calcite, ferroan rhodochrosite, manganoan siderite, kutnahorite, and ankerite. Only one sample was (Fe, Mn, Zn)-carbonate. Dolomite crystals, even refered many times in Trepè a mine, during this investigation there was no single undoubtful evidence of this mineral in studied samples. Such a variety in chemical composition of carbonate minerals from this mineral deposit reflects a variation in cations concentration in parent solution. According to their morphology, all samples were divided into 10 main groups and 5 more subgroups. It was not possible to perform morphometric measurement on representative crystals from each of these groups, because of the size of crystals or complicated twins or twin laws, especially when penetration twins are found. Results of morphometric measurements, which are compatible with the chemical composition of minerals are also usefull in determing chronology of crystallization of a particular mineral species. It is clear that only one method (in our case XRD) can not properly identifiy these minerals and determine their crystal chemistry. It is necessary to combine more analytical methods, especially SEM with EDS and in this case morphometric measurements as well. Unitt cell parameters calculated from XRD data also helped in interpretation of mineral species.

crystal chemistry; carbonates; Trepča

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