Minette (ore)

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The minette is an iron ore of sedimentary origin that was deposited in the Upper Lower Jurassic and Lower Central Jurassic in the extreme south of Luxembourg and Lorraine .

etymology

Minette is a term from the vocabulary of French miners. It is a diminutive of la mine and means something like "small mine, small colliery", but also "small vein, small vein" in view of the relatively low iron content of 28 to 34%.

The term minette is also used in geology for a igneous rock , the minette gangue .

description

The minette is a brownish iron-olite heart with a silica content of over 20%. The ooids , tiny spheres with concentric layers, consist of limonite (brown iron stone) and are held together by a cement rich in carbonate (high lime content of 5 to 20%). They were deposited as sloping and finely stratified bodies of sand together with quartz and mussel shill under shallow marine conditions. The sediment structure suggests current transport and wave movement. The grain sizes of the ooids increase towards the hanging wall , which can be interpreted as a gradual regression of the former Flachsee. Lime concretions and Fe 2+ minerals such as chlorite (leptochlorite), pyrite , siderite and subordinate berthierite and thuringite formed diagenetically . Apatite was also formed , which means that the minette has a fairly high phosphorus content of 0.5 to 1.0%.

Geological overview

In the Lias there was a transgression over the deeply eroded Variscan basement of the Rhenish Slate Mountains , the Vindelician Sill and the Bohemian Massif . In the Lorraine region (southern Luxembourg and eastern France), a fairly shallow bay, the so-called Gulf of Lorraine , was created between the Rhenish Slate Mountains in the north and the Vosges / Black Forest in the south between the Toarcium and Aalenium . In this shallow marine sedimentation area, traversed by strong currents, the minetteooids were deposited in relative proximity to the coast.

The iron ores are now contained in the Jura sediments as twelve layers of seams, the thickness of which is two to three, maximum nine meters. Their sedimentation took place in the hanging wall of a coarse and gradually falling mega-sequence. In terms of their characteristics, the minette sediments are very similar to the Ordovician iron ores of the Clinton type . The seams emerge on the eastern slope of the Moselle valley between Metz and Thionville ; they dip one or two degrees to the south and west. This occurrence continues to the south of Luxembourg. Another deposit with a lower iron content is located in the north and west of Nancy .

The formation of similar iron ores took place at the same time in many areas of the European Jurassic Sea . For example, the Dogger ores were deposited in southern Germany and Switzerland around the same time .

At Ougney-Douvot in the French Jura department and at Change - Mazeney east of Chagny in the Saône-et-Loire department , similar ore deposits were already formed in the older Hettangium . These Hettang ores were mined there until 1921, the total production amounted to 7.33 million tons.

history

The deposit is likely to be one of the most important iron ore deposits on earth; the reserves were estimated at six billion tons of ore with an iron content of around two billion tons. The high phosphorus content of the minette prevented industrial mining for a long time, which started relatively late after the introduction of the Thomas process .

After the Franco-Prussian War of 1870/71, parts of Lorraine fell to the German Empire. The limit was set in such a way that large parts of the well-known Minette occurrence were in what was now the German Alsace-Lorraine . The geologist Wilhelm Hauchecorne , who was a member of the border regulation commission, had campaigned for this. Although the German authorities granted considerably more mining concessions than the French ones before, ore production hardly increased until 1879. This changed from the 1880s, among other things through better development of the Minette area by railways and the construction of a railway line from Diedenhofen to Völklingen , which enabled a direct connection to the Saarland industrial area from 1883. Drilling in the 1880s revealed that the Minette deposits extended further west than previously thought, increasing in thickness and iron content with increasing depth. By 1909 , 16 mines had been built in the French part of Lorraine, the department of Meurthe-et-Moselle , especially in the Briey basin , which mined minette.

After the First World War , all of Lorraine was again part of France. In 1919 the annual production exceeded 41 million tons, 21 million tons in the Moselle department and 20 million tons in the Meurthe-et-Moselle department . At that time, Lorraine was the world's second largest iron producer after the United States . The ore production peaked in 1960 with 62 million tonnes in France and 6 million tonnes in Luxembourg. In the meantime, after almost 150 years of ore mining, a total of around 3 billion tons of ore has been mined. However, the relatively low iron content meant that Lorraine Minette ore was successively replaced by more highly concentrated imported ores (with an iron content of around 60%). As a result, more and more mines were shut down. The last mine in Luxembourg ( Differdange ) closed in 1981, the last in France at Audun-le-Tiche in the Moselle department in 1997.

Formation and origin of iron

One possible interpretation is the formation in the context of the weathering of tropical soils under lateritic conditions. Siehl & Thein (1978) interpret the ooids as a shallow marine transformation from the iron hydroxide goethite . They were then eroded again, transported to deeper basin areas and relocated, sorted and concentrated ( accumulation ) as geological soap deposits in the shallow shelf area by multiple tidal currents . In the subsequent diagenesis under reducing conditions, the goethite was converted to chamosite , magnetite , pyrite and siderite . The model explains the origin and transport of iron in an up-to-date manner and is in line with geochemical similarities between laterites and minette ores.

In addition, an authigenic , biogenic ooid formation in the still water area using mycelial mats is also being considered. The microbiocenoses act as catalysts and metal traps .

Individual evidence

  1. ↑ L. Bubenicek: Étude sédimentologique du minerai de fer oolithique de Lorraine. In: GC Amstutz: Sedimentology and ore genesis. Elsevier, Amsterdam 1964, pp. 113-122.
  2. ^ A b Roland Walter et al.: Geology of Central Europe . 5th edition. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 1992, ISBN 3-510-65149-9 , pp. 345 .
  3. ^ Helmut Frühauf: Iron industry and hard coal mining in the Neunkirchen / Saar area. (= Research on German regional studies . Volume 217). Central Committee for German Cultural Studies, Trier 1980, ISBN 3-88143-010-5 , p. 52ff.
  4. ↑ Tom McCann (Ed.): The Geology of Central Europe . Volume 2: Mesozoic and Cenozoic . The Geological Society of London , 2008, ISBN 978-1-86239-265-6 , pp. 1397 .
  5. ^ H. Frühauf: Eisenindustrie und Steinkohlenbergbau ... 1980, p. 56.
  6. ^ H. Frühauf: Eisenindustrie und Steinkohlenbergbau ... 1980, p. 59, 74. Funding statistics also with Stefanie van de Kerkhof: The industrialization of the Lorraine-Luxembourg Minette region. In: Toni Pierenkemper : The industrialization of European mining regions in the 19th century. Steiner, Stuttgart 2002, ISBN 3-515-07841-X , pp. 225–276, here p. 271. (online)
  7. ↑ H. Frühauf: Eisenindustrie und Steinkohlenbergbau ... 1980, pp. 75f.
  8. ^ A. Siehl, J. Thein: Geochemical Trends in the Minette (Jura, Luxembourg, Lorraine). In: Geologische Rundschau. 67, 1978, pp. 1052-1077.
  9. ↑ K. Dahayanake, WE Krumbein: Microbial structures in oolitic iron formations. In: Miner. Deposit. 21, Heidelberg 1985, pp. 85-94.

literature

  • Hans Füchtbauer (Ed.): Sediments and sedimentary rocks . Schweizerbart, Stuttgart 1988, ISBN 3-510-65138-3 .

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