Úrkút Manganese Ore Formation
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| Úrkút Manganese Ore Formation | |
|---|---|
| Stratigraphic range: Toarcian ~ | |
 Ancient karst formation in an abandoned manganite quarry in Úrkút | |
| Type | Geological formation |
| Unit of | Úrkút Basin |
| Underlies | Épleny Limestone Formation |
| Overlies | Isztimér Formation |
| Thickness | 15 m (49 ft) |
| Lithology | |
| Primary | Manganese |
| Other | Rhodochrosite |
| Location | |
| Region | Central Mountains of Transdanubia |
| Country | Hungary |
| Extent | ~12 km (7.5 mi) by 4–6 km (2.5–3.7 mi) |
| Type section | |
| Named for | Úrkút |
| Named by | Drubina-Szabo[1] |
| Year defined | 1959 |
  Úrkút Manganese Ore Formation (Hungary) | |
The Úrkút Manganese Ore Formation is a Jurassic geologic formation in Hungary. It covers the Early Toarcian stage of the Early Jurassic, and it is one of the main regional units linked to the Toarcian Anoxic Events.[2][3] Different fossils heve been recovered on the locations, including marine life such as Ammonites Fish and terrestrial fossils, such as Palynomorphs and fossil wood.[4][5][6][7] Úrkút (17´38'E and 47´05'N) and Eplény (17´55'E and 47´12'N) are the main deposits of the Formation.[1] Are related to the Bakony Range, an ancient massif that was uplifted gradually and exposed to a long period of erosion, where the deposits of Úrkút appear to be a basin inclined gently to the north, while the highest point to the south is the basalt mass of Kab Mountain. Eplény region consists of a broad N-S trending open valley between fiat-topped, small hills.[1][8]
The Urkut Area is part of the Bakony Tectonic Block, with the abundant presence of faults dividing the region into several segments.[1] The terrain where the Manganese Ore is developed is characterised by a high fracturation, where the Jurassic beds and shale lent themselves readily to deformation, with minor folds, faults and shear zones.[9] During the geological evolution of the Bakony range a series of principal fractures were active repeatedly, yielding to vertical as well as horizontal forces that ultimately produced the structural make-up controlling the present topographic configuration of the area.[9] The Jurassic sediments, along the other Mesozoic aged strata were deposited in a branch of a Geosyncline, connected with the Alpine coeval biota.[1] On the Triassic-Jurassic boundary Kimmerian movements take place, as evidenced by the change observed on the texture of the local Calcareous sediments, interpreted as a gradual rising of the sea bottom.[9] To the end of the Lower Jurassic, on the Toarcian, there are several records of another series of pulses from Kimmerian movements, that resulted in partial emergence, which dates the beginning of Karst development on the Csirda Mountain. However, marine sedimentation continued over most of the region and the sea became more widespread.[1] On this time a global sea transgression occur, where on the Úrkút basin shallow-water sediments accumulated near the margins, and with progressive deepening of the sea bottom until the end of late Liassic time, sediments of correspondingly deeper water were deposited.[1] Due to a cut-off of water circulation there were a series of changes on the local development of the basin, which led to the accumulation of the manganese minerals.[1]
The Éplény Area shows a structure and geological development with minor differences from those of Úrkút, being considered overall identical. However, it suffered minor deformation during the late Kimmerian movements, and instead of the Austrian movements, the Subhercynian and Laramide movements produced important structures. After the Pyrenean and Savian movements, the Éplény area started to sink slowly and to receive marine sediments, emerging later on the Middle Miocene.[1] The manganese ore group of beds appears in an absolutely different way according to evolution in Eplény, where while in Úrkút 4 beds can be divided, in Eplény, the 3 beds appear usually with sharp boundary, in reduced thickness.[10]
Stratigraphy
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The oldest formations on the Úrkút basin are referred to the Upper Triassic Dolomite range and the Dachstein Limestone of Raetian age. After the deposition of the Triassic rocks a series of Jurassic strata successions have overlain the older deposits, with its lowermost contact found on the uppermost strata of the own Dachstein Limestone, developing a lower Liassic sequence that is a white, yellowish-gray or pink, dense Limestone resembling that of the Dachstein.[1] Over it, there is a series of younger liassic strata and a Crinoid-Brachiopod and Rhynchonellatan bearing reddish Limestone, that resembles the Sinemurian Hierlatz Limestone of the Csárda Mountain, that is the last unit under the coeval Manganese deposits from there. Late Pliensbachian strata is composed by nodular and cherty red limestone with abundant ammonites and brachiopods, that belong to the Isztimér Formation.[11] On the uppermost Pliensbachian strata there is a series of beds that consists of greenish-gray limestone and marl, which also contain crinoids and brachiopods, being the last unit under the Manganese Ore.[1] The Upper Liassic (Toarcian) sequence is composed mostly by the Úrkút Manganese and the Éplény Limestone (Late Toarcian-Aalenian), and starts with thick-bedded, gray, Radiolaria-bearing, argillaceous marl containing several intercalations of manganese carbonate, or rarely, manganese oxides, with the top of the sequence being a brown to purple nodular Limestone with light green spots.[1] Middle Jurassic overlaying these deposits, being mostly a series of cherty Marlstone containing the genus Posidonomya and several types of Radiolaria.[12] The Late Jurassic strata is vanished locally, with the Cretaceous sedimentation starting with several continental beds with Bauxite and accompanying Laterites.[1] Finally, on the Tertiary, the Lower Eocene continental clay and bauxite are overlain by gray carbonaceous clay and sandstone, with the Jurassic beds and manganiferous beds eroded.[1]
Lithology
The Manganese Ore is the main component of the formation, and its distinctive characteristic element.[13] The Úrkút Manganese ores occur on marine sedimentary rocks composed mainly of bioclastic Limestone, radiolarian Clay Marlstone, and dark-gray to Black Shale. The Origin of the Local Manganese Ores based on the presence of siliceous manganese ores and antauthigenic Silica points to the volcanogenic-sedimentary origin of this Mn-ore deposits[14] Manganese nodules are widely distributed in the area in Jurassic rocks, mainly on the Lower Jurassic, but younger nodules also occur.[13] The Black Shale with Mn-carbonate get its maximum deposition on the Toarcian, concretely during the Tenuicostatum–Falciferum Ammonite zones in the coeval Sachrang Formation, Strubberg Formation and Allgäu Formation in the Northern Calcareous Alps and the Eastern Alps (Austria, Germany and Switzerland), while Úrkút and related deposits were the regional equivalent in the Transdanubian Range.[13] There are other deposits with Shale and associated Mn particles on contemporaneous oxic deposits occur that formed under similar environmental conditions.[15] The Úrkút Manganese deposit has been investigated geologically, mineralogically and chemically.[16] It has several properties, including very fine grain size (~ 1 μm), an enrichment of metals over a geologically very short time (-500 thousand years). Both Metals and the Manganese have been related with local hydrothermal vent systems, where the metal enrichment was a result of microbial activity.[17] There are at least three types of Manganese deposits that occur close in proximity. The first, those with cherty Fe–Mn-oxide ore, developed on the margins of the much larger carbonate ore body, whose origin has been related with proximal fracture systems, being composed by varicolored metalliferous Claystone. Other type includes the so-called Csárda-hill, where it is very cherty and iron-rich, and is suggested as originated from a low-temperature fluid flow along an associated fracture zone. This deposit is associated with sedimentary dykes, filled with red Lime-Mudstone, varicoloured Claystone, carbonate debris, or Mn oxides. The last type is the Black Shale-hosted Mn-carbonate, considered a distal ore-forming environment, where the Mn-carbonate proto-ore sediment accumulated. A hydrothermal/exhalative source of metals may have contributed to the formation of the deposits of Black Shale.[18]
There is a rhodochrosite ore, composed of laminated gray, green, brown, and black sections, and is associated with a diagenetic origin.[19] Rhodochrosite concretions with fish and plant fossils are common on the strata, composed by Mn-bearing Calcite with traces of hydroxyl-apatite, kutnohorite, smectite, quartz, feldspar, barite, pyrite, and quartz-cristobalite.[19] Mineralized sections do not contain fossils or traces of benthic fauna, and contain only rarely fish remnants, planktonic organisms as well as silicified, manganized, or coalified plant fragments.[20]
Celadonite and smectite, especially the first, had particular importance for understanding the genesis of the Úrkút manganese ore.[21] Celadonite and nontronite indicate paleo-oxygen level variations in the environment. There are well-crystallised celadonite occurrences that was formed by primary precipitation, differing from the known celadonite occurrences in that it is not found in direct association with submarine basic volcanic rocks, although being any evidence for volcanic contribution to the local ore genesis.[22] The Smectite is also found on the lower Pliensbachian Limestone. Nearly every Sample on Úrkút contains interstratified Illite/smectite.[23]
The Rn220 and Rn222 concentration in the Úrkút Manganese Formation is anomalously high, and it causes health risk for the attendants of the Úrkút Manganese Mine, which is considered to be related to active fossil Biomat (bacterial action) which leads local minerals to adsorb different atoms or ions, whether they are radiogenic or not.[24]
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