Vipos deposit, Vipos, Tapia, Trancas Department, Tucumán Province, Argentinai

Regional Level Types
Vipos deposit	Deposit
Vipos	Village
Tapia	Municipality
Trancas Department	Department
Tucumán Province	Province
Argentina	Country

Gypsum deposit:
History: Gypsum in Tucuman is located within the stratigraphic column, in the upper strata of Tertiary, usually accompanying the oolitic limestone, interacting with clayey sediments of colour greenish-Brown.
Are presented in various varieties, such as fibrous concretional robes and partially crystallized type Selenite, saccharoid (Alabaster), etc...
The Tertiary of Tucumán presents the clay series that totals 11 bitumen, cinerites, marl, limestone and sandstone, interbedded with gypsum and limestone.
Gypsum banks reach thicknesses variables, coming in part to occur more than 1 meter.
Vipos Gypsum is interspersed in Brown argillite, which has certain desiccation cracks by where there are efflorescences of sodium sulfate (Mirabilite) in radiated groupings. The Selenite fill the subglacial of stratification of sediments in the form of thin slices.
In the area of Vipos, gypsum is presented en masse in the Brown Clay, with a variety of fine-grain medium and fibrous, being exploited today for supply of cement factories.
Chemical analysis of gypsum Vipos:
Silicon dioxide (SiO2): 7.46 g.%
Calcium sulfate (SO4Ca.2H2O): 84.28 g.%
Ferric oxides and aluminous ((Fe2O3 - Al2O3): 5.20 g.%
Indeterminate: 3.06 g.%

Mirabilite-Thenardite:
This sodium sulfate was presented in an outcrop of some centimetres, in the best of cases reaching 30 centimetres or more in the town of Vipos in the Trancas Department in the form of patches, powder of white colour on the surface, filling the cracks, especially marginal clay material.
This sulfate in contact with the foreign present efflorescence and pervades the sediment in the form of white powder, being common in the green-brown clay of training, especially in the wintertime.
The Mirabilite appears in a small Anticline near vertex Northwest to form the intersection of the Vipos River and the railway bridge, at distance 440 meters and direction on ground North - West 1.25 degrees and 790 m above sea level, of this point. The formation is represented by the upper part of the Tertiary, characterized by the presence of clay material from Brown and greenish, appear interspersed some banks of Gypsum in the brown clay especially.
As already mentioned the Mirabilite appears in the crevices of the material clay in the form of radiated and needle-like groupings. In contact with the surface, these efflorescence concentrations and they permeate the sediment of a white powder.
The presence of Thenardite as efflorescence on Gypsum and Clay is the product of dehydration of the Mirabilite which is dehydrated to Thenardite in dry air.

Chemical analysis of Vipos Mirabilite:
Sulphuric Acid (-SO3): 24.803%
Sodium Oxide (Na2O): 18.590%
Calcium Oxide (CaO): 0.163%
Water (H2O): 55.034%
Insoluble residue in water: 1.474%

The exact coordinates of the Anticline are:
Latitude: 26º 28´ 06" S.
Longitude: 65º 20´ 49" W.
Altitude: 790 m. above sea level.

Geodes:
Sediment Tertiary faults are geodes with boulders of sandstone, quartz and basic vulcanites. The geodes grow to 10 cm although in general, they are between 3 and 6 cm in diameter. There are two varieties, one of coarse-grained and microcrystalline. In the variety of coarse-grained quartz is transparent and well crystallized with Prism completed in a combination of rhombohedrons although some specimens have not developed the Prism. The crystals are between 2 and 4 mm and are in bands of microcrystalline quartz of bluish-grey to grey colour of 2 to 3 mm thick. In microcrystalline varieties, the texture is botryoidal and concentric bands of white, white colours grey and dark blue to black. Internally there may be small crystals.

Cinerite:
Cineritic material forming robes is located in the Vipos area, about 2 kilometres south of the local railroad station next to the same tracks. The area was visited in the 1960s being able to verify that this Cinerite is interspersed in despicable and partly Sandy silty material cloaks. You could count up to 6 sheets with an average thickness of 0.20 to 0.25 meters. Macroscopically is white, in parts quite pure and sometimes something gritty, with abundant lamellae of mica and gypsum sandwiched. Outliers have little visible expansion and an inclination which would oblige certain scale for a farm work.

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References