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Secondary minerals of Pb-Zn Stan Terg skarn deposit, Kosovo - X-Ray Diffraction and Raman spectroscopy study

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Kołodziejczyk J. , Janicka U. , Prsek J.

tom Vol. 38, no. 4

486--87

Stan Terg deposit, one of numerous occurrences within the Vardar Zone on the Balkan Peninsula, is located in the north-eastern part of Kosovo. The formation of the deposit was controlled by metasomatic processes between carbonates and volcanic intrusive rocks. Ore bodies are located on the contact between Tertiary volcanic breccias, and Triassic metamorphic Trepca Series (represented by schists and carbonates). Significant number of ore precipitated from hydrothermal fluids in paleokarst cavities. Galena, sphalerite, pyrite, pyrrhotite and arsenopyrite are the main components of the primary ore assemblage (Forgan 1950, Schumacher 1950, Palinkas et al. 2013). The weathering zone is not well developed in the deposit. Development of weathering zone was stopped by tuff series overlaying the area after volcanic activity. Gossan occurs, but it is seldom (Forgan 1950). However, the circulating water through the karstic system could have dissolved sulphides, as well as neighboring rocks, which led to the precipitation and formation of secondary minerals on the galleries walls inside the mine. The aim of the study is identification and description of secondary minerals paragenesis that is present on the corridor walls inside the mine. The knowledge about this kind of secondary minerals may led to determination of weathering conditions in the deposit. Secondary minerals described in this study occur in minor amounts and should be regarded rather as a curiosity and as a supplement of knowledge about Stan Terg deposit. Samples were collected at 6 level of the mine. 20 samples were investigated using of X-Ray Diffraction (XRD) and 5 samples by Raman spectroscopy. Secondary minerals occur mainly in form of fine-grained crystals, dripstones or incrustations. Among them copiapite, roemerite, epsomite, bianchite, melanterite, rozenite and gypsum have been recognized. Copiapite is present in form of yellow and yellowish fine-grained crystals. It is most common secondary mineral in the mine. It occurs together with roemerite and epsomite. Roemerite, macroscopically not visible, occurs in minor amounts. Epsomite occurs in form of fine-grained, fibrous aggregates, crusts or dripstones. It exhibits white color, but may be also orange, if mixed with copiapite. Small amounts of bianchite were found (using XRD) within fine-grained crusts of epsomite. Melanterite occurs as crusts and stalactites. It builds clear phases or occurs together with other, yet not recognized minerals. A further study of melanterite is needed for successful characterization this additional phases. Rozenite was confirmed only by XRD. This mineral occurs in greenish-white fine-grained aggregates. Gypsum is a widespread mineral in the deposit. It occurs as single phases (with fibrous, fine-grained, needle-like or tabular crystals habit) or in lesser amounts with all other secondary minerals. Weathering of primary ore minerals is related to underground water circulating through karst cavities and fractures within the Stan Terg deposit. Recognized secondary minerals are being an effect of metal sulfides oxidation when oxygen and water are present in the environment. Highly soluble sulphates are formed in such condition. Copiapite, rozenite, melanterite, roemerite, bianchite may be caused by quickly oxidization of pyrite to aqueous Fe2+ and SO42- . The source of zinc in bianchite is sphalerite, whereas the presence of the magnesium in epsomite may be linked to Mg-reach carbonates. All of described minerals precipitated from the solution.