Mangan Ltd.

Úrkút, Hungary

Mangan Ltd.

Úrkút, Hungary

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Polgari M.,Eszterházy Károly College | Hein J.R.,U.S. Geological Survey | Biro L.,Hungarian Academy of Sciences | Gyollai I.,Hungarian Academy of Sciences | And 7 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

Toarcian black shale that hosts Mn-carbonate microbialites at Úrkút, Hungary was investigated by mineralogical, inorganic, and organic geochemical methods for characterization and comparison with other European black shales representative of the Toarcian Oceanic Anoxic Event. Based on the authigenic mineral composition, calculations were made to estimate environmental conditions during sediment accumulation and early diagenesis. Geochemical and petrographic results of organic, carbonate, and REE multiple-proxy analyses revealed a strong congruence between the host black shale and the Mn-carbonate ore beds. The Úrkút black shale is really a gray shale with moderate to low TOC contents that accumulated in a starved basin. The organic matter and anoxic characteristics resulted from rapid accumulation of organic matter from microbial booms, accompanied by a geothermally generated hydrothermal circulation system, and a high rate of authigenic mineral formation (clay minerals and proto-ore minerals). The inferred enzymatic Mn and Fe oxidation blocked carbonate formation by decreasing the pH. The system remained suboxic via syngenetic mineral accumulation (Fe-rich biomats), and became anoxic during diagenesis in conjunction with pyrite generation. The separation of black shale beds and Mn-ore beds is not distinct through the section. Instead, a distal hydrothermally induced clay-rich authigenic assemblage (marlstone) best describes the black shale, in which Mn-oxide proto-ore beds (Mn-rich laminae) formed from the beginning of black shale deposition, when the oxygen supply in the sedimentary basin was insufficient for enzymatic Mn(II) oxidation. Mn-oxide proto-ore was transformed to Mn-carbonate ore during microbially mediated processes during early diagenesis. The drivers for Mn-bearing organic matter-rich marlstones were most probably a combination of regional and local processes, with generation of a tectonic rift system that promoted geothermally generated hydrothermal fluids, which initiated microbial blooms. Black shale mineralogy, geochemistry, and organic matter at Úrkút differ from those of the epicontinental shelf black shales of the Tethyan Ocean. © 2016 Elsevier B.V.


Polgari M.,Hungarian Academy of Sciences | Polgari M.,Eszterházy Károly College | Nemeth T.,Hungarian Academy of Sciences | Pal-Molnar E.,University of Szeged | And 4 more authors.
Gondwana Research | Year: 2015

The genesis of a suite of Jurassic (Lias) microbialites at the Úrkút black shale-hosted manganese carbonate ore body (central Hungary) is described by a two-step microbial formation model that uses mineral chemistry combined with whole-profile (up section) textural context and sulfur isotopic compositions of associated pyrite and barite. Petrogenetic analysis and paleo-environmental reconstructions show that the sedimentary regime of the Úrkút microbialites mostly behaved as an open system during deposition of black shale under early diagenetic conditions. Sulfur isotopes and other chemostratigraphic indicators, however, reveal that the Mn ore bed horizons reached semi-closed/closed conditions which modulated sedimentation rate and organic matter burial. Barite horizons within Mn-carbonate layers preserve δ34SVCDT values that average +22.2‰, with a maximum at +35.2‰. Barite formation occurred under semi-closed/closed conditions at diagenesis, and the Ba source is attributable to the decomposition of organic matter derived from plankton and other marine organisms, as well as transformation of biogenic silica. Pyritiferous horizons host equant, framboidal and euhedral morphotypes. The distribution and size of euhedral and framboidal sulfide habits is consistent with later diagenetic sulfate reduction under an oxic water column; more equant types occur at the contact zone of black shale and Mn-carbonate horizons. The microbialites of Úrkút bear strong similarities to ore bodies at Molango (Upper Jurassic, Mexico) and Tao Jiang (Middle Ordovician, China). Manganese supply and trace metal contents (Co, Ni, Zn, Cd and As) of the sulfides also point to the effects of distal hydrothermal fluid sources to the system. © 2014 International Association for Gondwana Research.


Polgari M.,Hungarian Academy of Sciences | Hein J.R.,U.S. Geological Survey | Toth M.,Hungarian Academy of Sciences | Brukner-Wein A.,Hungarian Academy of Sciences | And 3 more authors.
Journal of the Geological Society | Year: 2010

Mineralogy and chemical composition are presented for a chert-ironstone bed that overlies the Úrkút Mn deposit. This bed is mottled green-brown in its lower and upper parts, which are composed of quartz, goethite and celadonite. These parts of the bed are interpreted to be strongly altered tuffs, reflecting oxidic, low-temperature alteration of a hydrated, Fe-rich, Al-poor tuff, and K and Mg uptake from seawater. The middle part of the bed is a mineralized bacterial mat (quartz, goethite). Textures resembling bacterial cells and colonies are common, with wavy, bulbous laminations composed of mounds overlying a mesh-work stromatolite-like texture constructed of micrometre-size Fe oxides. This bed is concordant with the underlying Mn deposit and marks the termination of Mn accumulation. Although no genetic connection exists between the two, the rocks adjacent to the contact record the oceanographic and bottom-water conditions extant when accumulation of one of the major Mn deposits of Europe ended, when the Transdanubian Range was located in the middle of the Adria-Apulian microcontinent between the Neotethys and Atlantic-Ligurian seaways. A pyroclastic origin for part of the bed has significance for the Toarcian of Central Europe because evidence of volcanism occurring at that time is otherwise sparse. © 2010 Geological Society of London.


Biro L.,University of Szeged | Biro L.,Hungarian Academy of Sciences | Polgari M.,Hungarian Academy of Sciences | M. Toth T.,University of Szeged | And 3 more authors.
Journal of Radioanalytical and Nuclear Chemistry | Year: 2015

The presence of anomalous terrestrial radioisotopes must be suspected in black shale-hosted manganese ore deposits, based on high organic matter content, which is useful tool in genetic, among them paleoenvironmental investigations. Our work aims at the characterization of the paleoredox conditions of the Úrkút Manganese Formation based on comparison of terrestrial radioisotopes and selected element ratios. Paleoredox indicators were estimated on U/Th, δU, Ni/Co, V/Cr, V/(V + Ni) and Ce*. The results of paleoredox indicator element ratios show, that these methods must be used with caution (microbial selective element enrichments, mobilizations), and the complex interpretation using mineralogy and microtexture can be recommended. © 2015, Akadémiai Kiadó, Budapest, Hungary.


Kavasi N.,Japan National Institute of Radiological Sciences | Vigh T.,Mangan Ltd. | Sorimachi A.,Japan National Institute of Radiological Sciences | Ishikawa T.,Japan National Institute of Radiological Sciences | And 2 more authors.
Radiation Protection Dosimetry | Year: 2010

In this study, short-term radon (RnDP) and thoron (TnDP) progeny measurements and dose estimation were carried out in winter and summer in a manganese mine, Hungary. Gamma-ray dose rate originating from external sources and 222Rn and 226Ra contents of spring-water from a mine was also measured. During working hours RnDP and TnDP concentration values changed between 12.1-175 and 0.14-0.42 Bq m-3, respectively. The 222Rn and 226Ra concentration values in the karst spring-water were ~6 Bq dm-3 and 16 mBq dm-3, respectively. The radiation dose resulting from the consumption of karst spring-water was negligible. The doses from the inhalation of TnDP and external gamma radiation were of the same magnitude, ~0.1 mSv y-1, which was rather negligible related to the estimated radiation dose of 5 mSv y-1 from RnDP. © The Author 2010. Published by Oxford University Press. All rights reserved.


Polgari M.,Hungarian Academy of Sciences | Hein J.R.,U.S. Geological Survey | Toth A.L.,Research Institute for Technical Physics and Materials Science | Pal-Molnar E.,University of Szeged | And 3 more authors.
Geology | Year: 2012

The Úrkút (Hungary) manganese (Mn) ore, hosted by Jurassic black shale, was studied using high-resolution mineralogical, microtextural, and chemical methods. Two independent superimposed biostructures were identifi ed consisting of rhythmic laminations that provide important proxies for paleoenvironments and duration of ore formation. Millimeter-scale laminae refl ect a depositional series of Fe-rich biomats, mineralized microbially produced sedimentary structures. These biomats formed at the sediment-water interface under dysoxic and neutral pH conditions by enzymatic Fe 2+ oxidizing processes that may have developed on a daily to weekly growth cycle. The early diagenetic sedimentary ore is composed of Ca rhodochrosite, celadonite, and smectite, and also shows a 100- m-scale element oscillation that produces Mn(Ca)-rich and Si(Fe clay)-rich microlaminae. This microlamination may refl ect a 10 h to daily rhythmicity produced by the growth of microbial communities. If true, then the giant Úrkút ore deposit may have formed over hundreds of years, rather than hundreds of thousands of years as previously thought. © 2012 Geological Society of America.


Biro L.,University of Szeged | Biro L.,Hungarian Academy of Sciences | Polgari M.,Hungarian Academy of Sciences | Vigh T.,Mangan Ltd | And 2 more authors.
Journal of Radioanalytical and Nuclear Chemistry | Year: 2015

The presence of anomalous terrestrial radioisotopes must be suspected in black shale-hosted manganese ore deposits, based on high organic matter content, which is useful tool in genetic, among them paleoenvironmental investigations. Our work aims at the characterization of the paleoredox conditions of the Úrkút Manganese Formation based on comparison of terrestrial radioisotopes and selected element ratios. Paleoredox indicators were estimated on U/Th, δU, Ni/Co, V/Cr, V/(V + Ni) and Ce*. The results of paleoredox indicator element ratios show, that these methods must be used with caution (microbial selective element enrichments, mobilizations), and the complex interpretation using mineralogy and microtexture can be recommended. © 2015, Akadémiai Kiadó, Budapest, Hungary.

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