Mineralogical and textural evolution of the economic manganese mineralisation in western Rhodope massif, N. Greece

Abstract

The western Rhodope massif contains a significant number of 'battery grade' Mn-oxide deposits which are best developed in the area near Kato Nevrokopi, Drama district, N. Greece. Economic Mn-oxide ore concentrations are confined to fault zones and related karsts in marbles. The mineralisation has formed by weathering of hydrothermal veins that were genetically related to Oligocene magmatism.At Kato Nevrokopi, progressive and continuous weathering of primary, hydrothermal veins of rhodochrosite, mixed sulphide, quartz and 'black calcite' (calcite and todorokite) has resulted in the formation of the assemblage MnO-gel-(amorphous Mn-oxide)-todorokite-azurite-goethite-cerussite in the veins and the assemblage MnO-gel-nsutite--chalcophanite-birnessite-cryptomelane-pyrolusite and malachite and amorphous Fe-oxides in karstic cavities.The fs2 andfo2 of the hydrothermal fluids increased with time. The breakdown of the hypogene Mncarbonate was aided by the production of an acidic fluid due to the oxidation of sulphides. Precipitation of the supergene ores was caused by neutralisation of the fluids due to reaction with the host marble and to mixing of relatively reduced fluids with oxygenated surface water in a fluctuation water table regime. Zinc was also mobile during weathering and became concentrated in the intermediate Mn-oxides, effectively stabilising their structures. The mineral paragenesis records the progressive oxidation of the ore and the appearance of less hydrated Mn-oxides, low in alkalis and alkaline earths.

An EPMA and SEM study of the Mn-oxide mineralization of Kato Nevrokopi, Macedonia, northern Greece: Controls on formation of the Mn 4+ oxides

“…The latter series of mines are associated with veins which occupy small faults in the marbles. The mineralization is spatially and genetically related to the Oligocene granodiorite intrusives and andesite subvolcanics and has been confirmed as part of the mid-Tertiary hydrothermal event in northern Greece (Nimfopoulos et aL 1988).…”

“…The mineralogical evolution of the Kato Nevrokopi manganese mineralization, as given by Nimfopoulos & Pattrick (1991) and Nimfopoulos et al (this volume), is summarized in Fig. 3a.…”

“…Previous studies referred on descriptions of the mineralogy, mineral chemistry, textures, and parageneses of representative ore samples (Spathi 1964;Podufal 1971;Giovanoli 1980;Vacondios 1982;Nimfopoulos 1988, Nimfopoulos & Pattrick 1991.…”

“…On the basis of their setting and mineralogy, the ore zones have been divided into three categories (Nimfopoulos & Pattrick 1991).…”

Metallic mineral resources of Greece

“…The mineralization was formed by weathering of hydrothermal veins that are genetically related to Oligocene magmatism. The economically significant ore of Granitis Drama has a maximum thickness of 40 m, 70-90 m length and content in Mn 22-29% [51]. Occurrences of manganese deposits also exist in Thassos, Serres, Petroto Kozani, Mt Othrys, Mt Pindos, Zarko Trikala, Seskoulo Magnisia, Eretria Evia, Argolida, etc.…”