Minette (ore)

The Minette is an ore of sedimentary origin, which came to be deposited in the upper Jurassic and lower Middle Jurassic in the extreme south of Luxembourg and Lorraine.

Etymology

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

The term Minette is used in geology for an igneous rock, the gangue Minette.

Description

Minette which is a brownish Eisenoolitherz having a silica content of over 20%. The ooids, tiny, concentric- ply constructed beads consist of limonite ( limonite ) and are from a carbonate-rich cement held together ( high lime content 5-20 %). They were sold as obliquely and finely stratified sand body along with quartz and shell Schill under shallow marine conditions. The sedimentary structures suggest flow transport and wave motion. The grain sizes of the ooids take the hanging wall to go, what is to be interpreted as a gradual regression of the former shallow lake. Diagenetically were formed carbonate concretions and Fe2 - minerals such as chlorite ( Leptochlorite ), pyrite, siderite and subordinate Berthierite and thuringite. It also was apatite, whereby the Minette having a relatively high phosphorus content of 0.5 to 1.0%.

Geological Survey

In the Lias was a transgression on the deeply eroded Variscan basement rocks of the Rhenish Massif, the Vindelician threshold and the Bohemian Massif. In the region of Lorraine ( eastern France and southern Luxembourg ) was created during the time period Toarcian to Aalenian between the Rhenish Slate Mountains in the north and the Vosges / Black Forest in the south quite a shallow bay, the so-called Gulf of Lorraine. In this shallow marine, crossed by strong currents, sedimentation the Minetteooide came to deposit in relative coast.

Iron ores are now twelve Flözlagen included in the Jurassic sediments, whose thickness is two to three, no more than nine meters. Your sedimentation took place in the hanging ends of a coarsening and gradually falling flat mega sequence. In its form, the Minettesedimente are very similar to the Ordovician iron ores of the Clinton - type. The seams outcrop on the eastern slopes of the Mosel Valley between Metz and Thionville; they fall to the south and west, with one to two degrees. This occurrence continues to the south of Luxembourg. Another occurrence with lower iron content is located in the northern and western outskirts of Nancy.

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

In Ougney - Douvot in the French Jura and in change Mazeney east of Chagny in the department of Saône -et -Loire similar ore deposits were already in the older Hettangian to training. This hettangischen ores were mined there until 1921, the total production of this amounted to 7.33 million tons.

History

The deposit is probably one of the most important iron ore deposits in the world; the reserves were estimated at six billion tonnes of ore with an iron content of about two billion tons. The high phosphorus content of the Minette prevented long time industrial mining, which is then relatively late introduction of the Thomas process began.

After the Franco-German War of 1870/71 were part of Lorraine to the German Empire. The limit was set so that large parts of the known Minettevorkommens were in German territory. For this purpose, among others, the geologist Wilhelm Hauchecorne had used, who was a member of the Border Regulatory Commission. Although the German authorities considerably more mining concessions granted than before the French, the ore mining hardly increased until 1879. This changed in the 1880s, including through the development of better Minettegebiets by railways and the construction of a railway line from Thionville to Völklingen which enabled a direct connection to the Saar industrial region from 1883. Holes in the 1880s showed that the Minettevorkommen extended further west than previously thought, and this increased with increasing depth in thickness and iron content. By 1909, emerged in the French part of Lorraine, the department of Meurthe -et -Moselle, in particular in the Basin of Briey, 16 mines that promoted Minette in the shaft operation.

After the First World War was quite Lorraine back to France. 1919 exceeded the annual production of 41 million tons, 21 million tons in the department of Moselle and 20 million tons in the department of Meurthe -et -Moselle. Lorraine was behind the United States at this time internationally the second largest producer of iron. The high point in the Ore production was achieved with 62 million tons in France and 6 million tonnes in Luxembourg in 1960. Meanwhile likely to have been promoted after almost 150 years of mining of ore a total of around 3 billion tonnes of ore. The relatively low iron content, however, led to Lorraine minette ore was successively ( with an iron content of 60% ) replaced by highly concentrated Importerze. As a result, then more and more mines were shut down. The last colliery in Luxembourg ( Differdange ) closed in 1981, the last French at Audun -le- Tiche in Moselle 1997.

Development and origin of iron

One possible interpretation is the emergence in the context of weathering of tropical soils under lateritic conditions. Siehl & THEIN (1978 ) interpret the ooids as shallow marine conversion from the ferric hydroxide goethite. They were then eroded again transported into the deeper basin areas and rearranged as geological soap deposits in the shallow shelf area through multiple tidal currents, sorted and concentrated ( accumulation ). In the subsequent diagenesis under reducing conditions of goethite to chamosite, magnetite, pyrite and siderite was converted. The model explains the origin and movement of iron to actualistic manner and is consistent with geochemical similarities of laterites and Minette ores.

In addition, an authigenic, biogenic Ooidbildung in the quiet water area is drawn by mycelial mats into consideration. The Mikrobiozönosen this act as catalysts and metal traps.