Tabataud quarry

Coordinates: 45 ° 31 ′ 30 ″  N , 0 ° 40 ′ 31 ″  E

Tabataud quarry​

France

The Tabataud quarry is an interesting mineral discovery site in the northwestern Massif Central of France . Granodiorite was once mined here. It has become known among mineral collectors as a good site.

geography

The Tabataud quarry (sometimes also written Tabateaud) is located just one kilometer southeast of the city center of Nontron , on the left side of the Bandiat valley at around 165 meters above sea level. The D 707 from Nontron to Saint-Pardoux-la-Rivière passes it. The actual quarry also has two other, smaller quarries in the immediate vicinity, the Maspeyrot-Lagarde quarry and the Moulin Blanc quarry , both of which are, however, older. All of these quarries, which have now been closed, can be reached from the D 707. It is dangerous to enter it because of falling rocks and the risk of collapse.

geology

Heavily weathered galena coating on granodiorite

The Tabataud quarry and the other two quarries are located in the Piégut-Pluviers granodiorite , namely in its fine-grained, dark, biotite and amphibole- bearing marginal facies. Because of its pale bluish color, this rock is known locally as granite bleu (blue granite). The extreme west of the quarry is traversed by an NNE-SSW-trending fault zone , which separates the granodiorite from the plagioclase- bearing paragneiss . The granodiorite in the quarry area is interspersed with a mineralized vein storey consisting of 17 relatively thin (1 to 3 centimeters thick), generally northwest-southeast trending veins . The Puyssechet corridor near Moulin Blanc, which was only temporarily dismantled, cuts east-west and is at least 30 centimeters thick. In addition to the ore veins, smaller pegmatite veins also occur in the quarry .

mineralogy

The tunnels belong to the typical sphalerite - pyrite - galena - chalcopyrite - mineralization, with the galena clearly coming to the fore. It is hydrothermal mineralization in the medium temperature range (300 to 150 ° C), analogous to the Cantonnier vein . In the Tabataud quarry, however, the main focus is on the primary galena and not on the secondary minerals .

Gang minerals in the veins are quartz and / or barite . Calcite and dolomite are added to the common minerals . Secondary minerals are the lead minerals angelsite , cerussite , pyromorphite and wulfenite as well as the iron sulfides marcasite and pyrite. A rarity that occurs Bituminous pseudo mineral ozokerite on.

The pegmatite tunnels lead beautifully formed, 2 millimeter large garnets and tourmalines (here: Schörl ) in the millimeter range and up to 5 millimeters, asparagus green apatites .

The ore minerals in detail:

• Anglesite (Pb [SO ₄ ]): rare; millimeter-sized, colorless prisms .
• Barite (Ba [SO ₄ ]): common; Gait; leafy habit; white documents, spherical balls, usually occurring together with galena (and marcasite).
• Galena ( lead gloss ) (PbS): very common; Crystal size up to several centimeters; mostly weathered (iron oxide coating), often matt (oxidation), but occasionally of extremely brilliant, excellent quality in cracks; Cube and octahedron; growing on quartz, sometimes also on calcite, dolomite or barite; overgrown by cerussite, pyrite, marcasite, quartz and ozokerite.
• Cerussite (Pb [CO ₃ ]): occurring locally; crystallizes on galena as its conversion product; forms decimeter-sized coatings with crystals in the millimeter, rarely also in the centimeter range; crossed habitus, prisms, mainly crystals stretched along the a-axis, sometimes also along the c-axis; white single crystals and twins .
• Dolomite (CaMg [CO ₃ ] ₂ ): relatively rare; associated with galena; Millimeter-large, pink rhombohedra, occasionally in a saddle-shaped habit.
• Calcite (Ca [CO ₃ ]): frequent late stage of fissures; associated with galena; pointed (reflective) and flat (matte) rhombohedra; milky single crystals can be up to 5.5 centimeters in size.
• Gypsum (Ca [SO ₄ ] • 2H ₂ O)
• Marcasite (FeS ₂ ): extremely common low temperature mineral; very susceptible to weathering; overgrows the lead sheen, often in beautiful, well-formed individual crystals in the millimeter range; Crust formation up to a square decimeter; Cockscomb habit; Twinning according to (110).
• Ozokerite (or smelling wax): associated with quartz and galena; Brown bitumen balls up to 0.09 millimeters in size (a mixture of volatile and solid hydrocarbons of the methane series ).
• Pyrite (FeS ₂ ): relatively rare; spherical crystal aggregates from millimeter-sized single crystals on quartz, sometimes also on dolomite.
• Pyromorphite (Pb ₅ [Cl | (PO ₄ ) ₃ ]): common; however, beautiful crystals are rare; forms crusts on heavily attacked galena; Occasionally the lead gloss disappears completely, the pyromorphite then assumes a boxwork habit ; pale yellow to deep green crystals; light green, needle-shaped pyromorphite sometimes grows in very different crevices in the granodiorite.
• Quartz (SiO ₂ ): frequent gait; very beautiful, 5 to 8 millimeter large single crystals (with double ends) on galena; can in turn be covered by a thin skin of green pyromorphite and also carry microcrystals of wulfenite; otherwise mostly classic habitus with poorly developed prisms, colorless to milky; slightly smoky, amethyst-like individuals also occur.
• Sphalerite (ZnS): not very common; Microcrystals associated with galena.
• Wulfenite (Pb [MoO ₄ ]): very rare; sits on dull green pyromorphite; orange, tabular, 2 to 3 millimeters, very rarely 1 centimeter large single crystals; originated near the surface; the molybdenum should come from the very finely distributed molybdenite in the granodiorite .

history

Work on the Tabataud quarry began in the 1890s. The ore from mining was collected, but it was not the focus of mining activities. The granodiorite was initially much more a sought-after building stone and paving stone, later the stone was mainly ground into gravel and granules. In 2003, work in the quarry was finally stopped, since then the quarry has served as a storage place for the countless tree trunks uprooted in the area by Hurricane Lothar in 1999.

meaning

The Tabataud quarry is likely to contain the most beautiful galena crystals in France . It is also one of the very rare finds in France for wulfenite and also carries the rarity ozokerite . The cerussite is of exceptional quality and has a rich variety of shapes.

The numerous pegmatites , veins and fissures indicate a tectonically induced expansion phase in the granodiorite, which must have taken place after it had cooled down and which enabled the mineral-laden pneumatolytic and hydrothermal solutions to separate out the metals (especially lead), although the higher temperature pegmatite stage is likely to be older . A radiometric age study on the galena using the uranium-lead method revealed a sub-permean age of 300 to 250 million years BP for the mineralization. The spatial orientation of the corridors suggests a SE-NW, transtensioned , dextral shear .

literature

• J.-L. Duthou et al. a .: Les gisements plombo-zincifères du seuil du Poitou et de sa bordure Limousine . In: Bulletin du BRGM, section II . No. 1 , 1974, p. 453-474 .
• J.-P. Floc'h u. a .: Feuille Nontron . In: Carte géologique de la France at 1/50 000 . BRGM, Orléans.
• J. Guillemot, J. Lebocey, N. Legrand: Minéralogie de la carrière Tabataud, Nontron, Dordogne . In: Le Règne Minéral . tape 84 , 2008, p. 27-33 .

Web links

• Mindat - description of the location and mineral list of "Tabataud quarry, Nontron, Dordogne, Aquitaine, France" (English, with links to picture galleries of individual minerals)