Márta POLGÁRI¹, Lóránt BÍRÓ², Elemér PÁL-MOLNÁR², Gábor DOBOSI¹, Bernadett BAJNÓCZI¹, Tibor NÉMETH¹, Viktória KOVÁCS KIS³ & Tamás VIGH^4
1Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, corresponding author: M. Polgári, e-mail: rodokrozit@gmail.com, Tel/Fax: +36 1 319-3137
²Szeged University, Dept. of Mineralogy, Geochemistry and Petrology, 6702 Szeged, Egyetem str. 2-6, Hungary
³Research Institute for Technical Physics and Materials Science, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege M. út 29-33., Hungary
⁴Mangán Ltd., H-8409, Úrkút, Hungary

RHODOCHROSITE-BEARING CONCRETIONS FROM A JURASSIC MANGANESE ORE MINERALIZATION – ÚRKÚT, HUNGARY

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Rhodochrosite concretions with fish and plant fossils occur in the Úrkút manganese carbonate deposit (Jurassic) and were investigated for mineralogy and geochemistry. These concretions are mainly composed of rhodochrosite and Mn-bearing calcite, but X-ray diffraction and electron microprobe analysis showed also the presence of Ca-rich kutnohorite. Cathodoluminescence microscopy revealed kutnohorite as luminescent mineral as infiltration and veinlets suggesting early diagenetic origin. Chrysotile needles were also detected in one of the kutnohorite veinlets by transmission electron microscopy. Stable C and O isotope results showed low-T very early diagenetic, bacterially mediated decomposition of organic matter and formation of Mn-carbonate in the ore section, which effect was the strongest around the organic remnants. Compared to the polarized light microscopy, cathodoluminescence microscopy was able to give visible picture about the texture of the very fine-grained Mn-carbonate concretions; therefore it was proved to be a useful method in study of diagenetic processes in manganese deposits.