Latitude: 43°26'29"N
Longitude: 5°36'29"W
Mina La Viesca, Huergo, Zona minera de La Collada, Siero, Asturias, España
LA VIESCA MINE
La Viesca Mine, which is currently owned by Preparación Minera del Norte - Preminor S. L., is located near the town of Huergo, at km. 13 of the As-248 road, in a hollow known by the villagers by the same name. (43º 26’ 27,77’’ N; 5º 36’ 46,58’’ W).
The first company which obtained rights to work this concession was Felgueroso Hermanos, who were Asturian entrepreneurs closely related to coal mining. Although this mining concession was originally made for coal, it was always mined for Fluor spar, firstly by Fluoruros S.A. and then by the current owner, Preminor S. L.
In 2004, after a long period of inactivity, the mine workings started again by Preminor, through an inclined ramp that now measures about 5 km.
The main crystalline shapes from this locality are cubic, however rhombododecahedron faces can be found as well, but with more limited development than in La Collada. Specimens with icositetrahedron and tetrahexahedron habit have been seen on rare occasions. What is common is the appearance on the faces of the cube of intergrowths that cause rather complex mosaic surfaces producing a loss of brilliance of the crystals due to the optical effect of the reflections.
The most frequent paragenesis is a combination of Fluorite with Calcite, Quartz, Dolomite and various sulfides (Sphalerite, Pyrite, Chalcopyrite, Galena, etc). In the finds made here, the Fluorite features colors varying from absolute transparency to nearly black through all shades of blue and violet. The crystals can reach 30 cm. across.
The associated Calcite crystals, usually scalenohedrons, can also be large. The Calcite in this mine sometimes adopts very complex forms in combination with the rhombohedron providing pseudo-spherical crystals.
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In may 2010 a pocket of worldclass fluorites was discovered. The pocket was baptised "Geoda de Las Monjas" and produced about 400 specimens, the largest one measured 70 x 70 cm and weighed 135 kg, and the smallest one 4 x 4 cm with a weight of 10 gr.
References
- Gutiérrez, M., Luque, C., García, J.R. y Rodríguez, L.M. (2009). La Fluorita. Un Siglo de Minería de Asturias. Universidad de Oviedo.565 págs.
- Calvo, M. (2006) Minerales y Minas de España. Vol. III. Halogenuros. Museo de Ciencias Naturales de Álava. 267 pp.
- García Álvarez, J.R. (2011): Las Monjas: une géode de fluorine exceptionnelle de la mine La Viesca, Asturies, Espagne. Le Règne Minéral. 97: 7-10
External Links
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http://www.mineral-forum.com/message-board/viewtopic.php?t=1753
The history of the finds (external and internal) made at the La Viesca Mine with description and pictures for each pocket. Written by José Ramón García & Jordi Fabre. Translation slightly abbreviated by James Catmur. To see the full Spanish text follow the link below
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http://www.foro-minerales.com/forum/viewtopic.php?t=5934 (original full text in Spanish language)
Mineral List
8 entries listed. 8 valid minerals.
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