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San Fenancio Mine, Estancia Anchilla, Tafí del Valle Department, Tucumán, Argentina

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Latitude & Longitude (WGS84): 26° 18' 42'' South , 66° 0' 52'' West
Latitude & Longitude (decimal): -26.31167,-66.01444
Köppen climate type:Cwc : Cold subtropical highland climate or subpolar oceanic climate with dry winters

During the last days of December 2012 a visit of exploration led by Raúl Tauber pegmatitics of local bodies was made Stay Anchilla a remote spot located on the eastern slope of the sierra de Quilmes to the Northwest of the province of Tucumán, particularly to a so-called sector San Fenancio Mine(26° 18´ 42.64" S - 66° 00´ 52.85" W, altitude 2403 m. asl), exploited in precarious shape sky opened by mica and currently abandoned.
Access to that site is performed from the town of Colalao del Valle about 6 kilometers westward by a double hand gravel road reaching a fork marked right hand as access to school El Arbolar, moves about 166 metres and appears another fork to the right that must be followed, being this one-hand of gravel that it is in good condition. It is follows this path by approximately four kilometres until its termination in an area of corrales stone for animals and where is a small house with two or three people (26° 18´ 58" S - 66° 01´ 09" W, altitude 2,245 m asl). From this point the access to the pegmatitic bodies must be on foot and climb up the hills and there are no marked paths, only in the first 200 meters from the House, and the ascent towards the sector of Mine San Fenancio lasts around 40 minutes reaching the 2,400 meters above the sea level.
The San Fenancio Mine consists of several bodies distributed pegmatitic in irregularly shaped and scattered in an area of 400 x 100 meters on the steep slopes of the hills of the place. On a painted rock can be seen a reference that indicates the name of the mine and that is owned by the company MICANORT S. R. L. On the site you can see on the land abundant scrap of mica Muscovite as a result of the exploitation of the same.

The mineralization found was the following:
Quartz: whitish and Milky good quality and idiomorphous crystals.
Quartz geodes with crystals in its interior (found in a sector of dry riverbed of the locality).
Feldspar: Anorthite-Albite Group, pink Microcline (excellent twined crystals).
Mica Group: Muscovite, Biotite, and others not yet identified.
Tourmaline Group: Schorl and dark brown tourmaline crystals.
Garnet Group: Almandine.
Copper minerals: malachite, native copper.
Manganese oxides.
Iron oxides/hydroxides: hematite, limonite.
Secondaries Uranium minerals.
Radioactive allanite + other minerals of the rare-earth group not yet identified.
With regard to this latter mineral commented as follows:
When performing a pegmatitic main body radiometric prospecting and its surroundings were detected radioactive anomalies in certain level especially in the area of contact metamorphic rocks with the body pegmatitic finding numerous samples of radioactive material identified Prima Facie as probable Allanite . Prospecting was carried out with a counter Geiger Müller designed and built by Raúl Tauber with art components (tubes and micro controller) with the peculiarity of using two selectable tubes, one internal for radiation β + γ and other external for α + β + γ of high sensitivity, this being the first time that was tested in the field with positive success.
Rigorous physical and chemical studies are to be done to determine exactly the species found.
The likely Allanite was found in small crystals and masses of several kilograms. In some specimens looks fresh with vitreous-resinous luster, translucent and opaque, with metamictic black coloration and Brown in the translucent edges. Measure hardness is around 5.5 to 6.0. The observable fracture is conchoidal. In some specimens were whitish crust with crystallization in the form of spheres millimetre perfect colours white beige, orange and green, believing that they could be dealt with in unidentified species even of rare earths as a product of alteration of ore or major minerals.
It is interesting to note that it is the first time that reported a discovery of radioactive minerals in the a group of rare earths in the province of Tucumán.

This rare phosphate, Jahnsite (CaMnMg), was found in a mass and nodules of several kilograms of weight and is probably radioactive by the presence of secondary minerals of uranium (the Group of the Autunite phosphates) fluorescent to ultraviolet light and rare earths. This mineral occurs in the area of contact between the pegmatitic body and the metamorphic rock in an area close to mine San Fenancio, not in it, but in a body pegmatitic which is part of the stay Anchilla set, in the vicinity of it and being the only one where I detect to date this place. Different samples were analyzed by XDR-TB in the Department of Earth & Environmental Sciences of New Orleans University, Louisiana, u. S. A. by Professor Alexander Falster. Another group of samples were also analyzed by XDR-TB by Dr. Alfredo Matías Kuck in the National University of Buenos Aires, Argentina, reaching the same conclusion in both cases.

Mineral List

14 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

541 - 1000 Ma

ID: 1376474
Neoproterozoic intrusive and metamorphic terranes

Age: Neoproterozoic (541 - 1000 Ma)

Comments: Mixtures of metamorphic and intrusive or plutonic rocks, tracts known as crystalline, migmatitic terranes, moderately to highly metamorphosed rocks of unknown origin with or without intrusions. This classification is inherently prone to variable interpretation, as other compilers might distinguish some packages by their metamorphic or gneissic protoliths, and the associated age ranges may be more variable.

Lithology: Intrusive and metamorphic terranes

Reference: Geological Survey of Canada. Generalized geological map of the world and linked databases. doi:10.4095/195142. Open File 2915d. [18]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

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R. J. Tauber Larry (2012). Visita a los cuerpos pegmatíticos de Estancia Anchilla, Departamento Tafí del Valle, Provincia de Tucumán.

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