Neuil mine

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The Neuil Mine, in French Mine de Neuil, is a mine emplaced in paragneisses of the northwestern Massif Central. The mine is part of the commune of Saint-Pardoux-la-Rivière in the Dordogne. Extracted from the mine was galena, slightly enriched in silver.

French language Romance language

French is a Romance language of the Indo-European family. It descended from the Vulgar Latin of the Roman Empire, as did all Romance languages. French evolved from Gallo-Romance, the spoken Latin in Gaul, and more specifically in Northern Gaul. Its closest relatives are the other langues d'oïl—languages historically spoken in northern France and in southern Belgium, which French (Francien) has largely supplanted. French was also influenced by native Celtic languages of Northern Roman Gaul like Gallia Belgica and by the (Germanic) Frankish language of the post-Roman Frankish invaders. Today, owing to France's past overseas expansion, there are numerous French-based creole languages, most notably Haitian Creole. A French-speaking person or nation may be referred to as Francophone in both English and French.

Mining The extraction of valuable minerals or other geological materials from the earth

Mining is the extraction of valuable minerals or other geological materials from the earth, usually from an ore body, lode, vein, seam, reef or placer deposit. These deposits form a mineralized package that is of economic interest to the miner.

Contents

Geography

The mine is situated about 1 kilometer north of Neuil, a small hamlet in the commune of Saint-Pardoux-la-Rivière. The main production shaft, at an elevation of 250 meters above sea level, can be reached by following a small valley on the left side of the D 707 Nontron- Thiviers just before arriving at Neuil. The shaft is located on the right-hand side of the small stream; it is fenced in and closed to the public because of its hazardous nature.

Saint-Pardoux-la-Rivière Commune in Nouvelle-Aquitaine, France

Saint-Pardoux-la-Rivière , in occitan Sent Pardol la Ribiera, is a commune in the Dordogne department in Nouvelle-Aquitaine in southwestern France. It forms part of the Parc naturel régional Périgord Limousin.

Nontron Subprefecture and commune in Nouvelle-Aquitaine, France

Nontron is a commune in the Dordogne department in Nouvelle-Aquitaine in southwestern France.

Thiviers Commune in Nouvelle-Aquitaine, France

Thiviers is a commune in the Dordogne department in Nouvelle-Aquitaine in southwestern France.

Mine works

The partially collapsed main shaft was once 47.50 meters deep and led to three exploitation levels. An additional horizontal access is now flooded.

The ore was taken to Nègrecombe, washed and then transported by train (on the now redundant railway line Angoulême-Thiviers) to a smeltering plant.

Angoulême Prefecture and commune in Nouvelle-Aquitaine, France

Angoulême is a commune, the capital of the Charente department, in the Nouvelle-Aquitaine region of southwestern France.

History

The mine was in operation mainly between 1921 and 1928, between 1956 and 1959 and once more between 1976 and 1984. Several hundred tons of ore were mined. The reserves are estimated at several thousand tons.

Ore rock with valuable metals, minerals and elements

An ore is a natural occurrence of rock or sediment that contains sufficient minerals with economically important elements, typically metals, that can be economically extracted from the deposit. The ores are extracted at a profit from the earth through mining; they are then refined to extract the valuable element, or elements.

Geology

The Neuil Mine is emplaced in Neoproterozoic paragneisses of the Variscan basement of the northwestern Massif Central. The in places tightly folded paragneisses strike mainly N 130 and dip 35° to the northeast. The ore-bearing lodes crosscut the strike of the paragneisses, their orientation varying between N 045 and N 065. Their dip is generally 65° to the north. The lodes are therefore roughly parallel with the boundary fault of the Massif Central north of Saint-Pardoux-la-Rivière.

The Neoproterozoic Era is the unit of geologic time from 1,000 to 541 million years ago.

Variscan orogeny

The Variscan or Hercynianorogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea.

Basement (geology) Metamorphic or igneous rocks below a sedimentary platform or cover

In geology, basement and crystalline basement are the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover".

The lodes of the Neuil Mine are no single occurrence. To the northwest (towards Nontron) several other lodes follow, which were also mined (Le Puy Mine, Cantonnier Lode, Tabataud Quarry among others).

The le Puy Mine is an ancient lead mine in the northwestern Massif Central, France. The mine produced mainly silver-bearing galena.

The Cantonnier lode formed in the Piégut-Pluviers Granodiorite, part of the basement rocks of the northwestern Massif Central in France. Its importance is highlighted by very rare mineral parageneses.

The Tabataud Quarry is situated in the northwestern French Massif Central. The quarry used to be mined for its granodiorite.

Mineralogy

The central part of the lode consists of a quartz matrix enriched more or less in baryte. The baryte can become very abundant so that it completely replaces the quartz. Abundant fractures cut through the quartz-baryte core. The sulfides galena, sphalerite and marcasite are enclosed within the quartz/baryte. The galena forms mats of octahedral crystals, the sphalerite is dense and anhedral and the marcasite powdery or displays its coxcomb habit. The lodes are mylonitized at the edges; the sulfide mineral aggregates within this zone are sheared. Secondary mineralisations cover the central fracture surfaces and the mylonitic edges. In the core region geodes of quartz and of chalcedony can occur. In the quartz geodes the habit of quartz is hexagonal-pyramidal but can show occasional bipyramids. Druses in baryte can be clad with gypsum. Apple green pyromorphite occurs forming hexagonal prisms.

The mineralisation is due to hydrothermal circulation in the temperature range 150 – 300 °C. The ores were deposited in two stages, each with a characteristic paragenesis: a higher temperature stage with galena and quartz and a lower temperature stage with baryte and marcasite. These minerals are accompanied by sphalerite, pyrite and chalcopyrite. The ore therefore belongs to the mineralisation type sphalerite-pyrite-galena-chalcopyrite.

Age

A radiometric lead isotope study on the basement lodes yielded an age of 300 to 250 million years BP (Lougnon, J. et al. 1974). The lodes belong clearly to a late Variscan phase and were definitely formed after the intrusion of the Piégut-Pluviers Granodiorite into the paragneisses during the late Pennsylvanian (elsewhere lodes can be found that also formed within the granodiorite). Yet the metal impregnation is most likely genetically related to the granodiorite.

Conclusion

The spatial arrangement of the lodes points towards local southeasterly extension within the basement rocks. By that time the paragneisses had cooled down to below 300° C. Additionally the lodes experienced shearing motions as shown be the mylonitized edges. This fact combined with the variations in strike possibly hints at a shear zone oriented southeast: the lodes following N 065 can then be interpreted as antithetic surfaces, whereas the lodes following N 045 are probably R'- Riedel shears. Furthermore the fairly steep northwesterly dip of the lodes hints at a top to the southeast sense of motion (“bookshelfing”).

The mineralizing hydrothermal solutions most likely came from the Piégut-Pluviers Granodiorite.

Literature

Coordinates: 45°30′10″N0°43′03″E / 45.5028°N 0.7175°E / 45.5028; 0.7175

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