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Geological Society, London, Special Publications; 1997; v. 119; p. 339-347;
DOI: 10.1144/GSL.SP.1997.119.01.22
© 1997 Geological Society of London

Geochemistry and Mineralogy

Zincian rancieite from the Kato Nevrokopi manganese deposits, Macedonia, northern Greece

M. K. Nimfopoulos1, K. M. Michailidis2 & G. Christofides2

1 Institute of Geology & Mineral Exploration, Thessaloniki Branch, 1 Fragon Street, 546 26 Thessaloniki, Macedonia, Greece
2 Department of Mineralogy, Petrology & Economic Geology, Aristotle University, 540 06 Thessaloniki, Macedonia, Greece

At the 25th km main Mn-mine of Kato Nevrokopi, Macedonia, northern Greece, rancieite forms flaky to laminated aggregates encrusting vugs, and replacing pyrolusite and todorokite in massive deposits of the Falakron marbles. It has an unusually high ZnO (1.53–3.07 wt%) content and therefore it was named ‘zincian rancieite’. The average (18 spots) chemical composition of rancieite by EPMA is (wt%): MnO2 62.01, CaO 6.83, ZnO 2.54, Al2O3 1.18, MgO 0.63 plus minor oxides (Fe2O3, K2O & SiO2), total of 73.98. Assuming H2O-content as 26.02 (100 – 73.98) wt%, these data reflect the following empirical formula: (Ca0.67Zn0.17Al0.12Mg0.09Fe0.023K0.02Si0.02)Mn3.904O97.9H2O. A high H2O-content is also evidenced by the XRD pattern, which together with optical microscopy and SEM, indicates a poor structural order. Rancieite formation at Kato Nevrokopi belongs to the last stage of mineral genesis, which took place at ambient P, low T (around 25°C) by percolating oxygen bearing, Ca-Zn rich, meteoric water through the host marble.