La Esperanza Mine, Iruya, Salta, Argentina

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Introduction: Mineralized fault fissures. It is a hydrothermal deposit in veins. Ore mine "La Esperanza", located at 60 km NNE of the station Iturbe in the Iruya Department, found the existence of Pitchblende associated Chalcosine and Bornite in carbonate gangue(Dolomite) and also to Galena and Sphalerite in certain places. The seams of this mining property staying on slates Cambro-Ordovicics. The U3O8 tenors recorded on pieces of ore are very variable, coming in a case to 2%. This site was exploited mainly by copper ores in the past and had several underground and opening of new work.

Mine La Esperanza (ex - Chacabuco).
Location:
It is located in the Valley of the San Juan River, 85 km in a straight line to the northeast of the station Iturbe, FCGB in the Iruya Department, and 6 kilometers from the Iruya town and 2,600 meters above the sea level, located on the eastern slope of the lace of Zenta.

Laws, reserves and production:
100 Tonnes of ore with 30% of Cu and 150 tons of plumbo-copper ore were extracted during the rehabilitation carried out in 1944. Comprised mineral between - 18 and the surface, in the main grain, exploded in beginning of century undertakings and in the Decade of the 1930s. U3O8 laws vary between 0.14% and 0.37%, Zn between 9.75% and 10.3%, Pb meets tenors from 10% to 21% and Cu between 19% and 23%, always on the main vein. Uranium is also extracted during 1960. On that occasion the CNEA made prospecting radimetric in all accessible levels, without reaching values of interest. The mentioned agency acquired 17 tonnes of uranium ore to trials and carried out work in search of a supposed pitchblende nail, whose finding is frusto to locate the underground position filled with material already exploited. This work comes from the mine was worked to arrangements even more low than - 125 meters. CNEA came to the conclusion that a reservation of moderate dimension nuclear ore poor would be - 75 meters below the Chacabuco tunnel.

Operating system:
It has 4 main tasks, being the Chacabuco tunnel most important with 350 meters long and where will take place the most important tilling and the tunnel Santa Ana of 130 meters. The rest of the work include other washouts, piques, fireplaces and enhancement work. All are flooded and collapsed.

History of the tank:
It was discovered in 1870 and was named Mina Chacabuco in the first Chronicles. It was exploited for the first time in 1907 and 1935 on a smaller scale. In 1944 the Argentina mining holdings company proceeded to their temporary rehabilitation. In 1960 the CNEA performed geological surveys, exploration and geophysical work, identifying portions of the nail home, relatively rich in U3O8 is located 75 meters lower than the level Chacabuco (Lobos, 1960). View of the CNEA low stocks not compensate for the high costs of drain, Blaze and others. During the 1970s the Provincial direction of Salta mines, took scanning tasks that improve the knowledge of the mineralization concentrated in the area of the nail, registering a small mining activity. Since that date the mine remains inactive.

Legal background:
It was registered as a copper mine with the assignment of 2 membership of 300 x 300 meters (1941): Eda membership that covers the main grain and works in execution and Lilia membership covering other veins untapped distant approximately 1,000 meters from the previous.

Regional Geology:
The saw of Zenta, in whose eastern slope is implanted deposit, corresponds to the Cordillera Oriental morphostructure, in a sector characterized by Precambrian and Ordovician units. The first correspond to the Puncoviscana Formation metapelites. The latter are reddish psamites of the Meson group.
The tectonic main of this morphological unit consists of extensive North-South, slightly oriented northeast, high angle faults, with drawings of dips to the West. A plot of minor fractures crossing the previous ones with multiple addresses, being significant in density and intensity in the District of mine hope. With them are the Chacabuco veins, Potrerillos and Potrero. In the vicinity of the site there are reefs of basic rocks and clear andesites.

Geology of the deposit:
Lithology: Box of the mineralization is formed by rocks of Puncoviscana formation consisting of metagrauvacs, green slates and phyllites, and quartzites and Shales of the Cambrian–Ordovician reddish. They have general North-South direction and dip to the West.
Structure: The veins follow tectonic faulting of second and third order weft. The entire area comprising a high degree of cracking deposit presented by effect of the closed mesh of fractures.
Morphology: The site is vetiform and consists of two units, one predominantly copper and the other plumbiferous that concentrated the main mining activity and presents traces blotters at sharp angle (Angelelli, 1984) in General. Of these, the main grain is E15°S course pitches between 80-85 ° at its deepest level. It presents an average of 10 to 20 cm. level - 55 power, where its mineralized travel reaches 80 meters, of which the richest stretch reaches 50 meters. On surface, it reaches up to 1 meter in power. This grain, taking into account the tectonic intersection cited, forms an ore shoot with a vertical development that is inferred surpassed 125 meters, level that could have reached the old holdings (Lobos, 1960). This unit comes out 150 meters west of the top of the main gallery. The second vein blotting, plumbiferous, presents greater metaliferous expectations. All streaks present brechia structure. In the case of the second vein, appears to be more compact, with power up to 1 meter and well defined interface with box, formed by tailor's fault.
Mineralogy: Lode plumbiferous consists of Galena in Baryte gangue. The copper vein, is constituted by Chalcocite, Sphalerite and Tetrahedrite. The level - 55 dominated the bornite. Brodtkorb(1965, 1973) cites Pitchblende, Gersdorffite, Linneite, Bornite, Chalcopyrite, Tetrahedrite-Tennantite, Chalcocite, Covellite, Sphalerite and Galena.
The supergenics minerals include Azurite, Malachite, Chrysocolla, Limonite and ochre of uranium in a timely manner.
Gangue grain, copper, Dolomite, as is that of the grain plumbiferous, is Baryte.

Mineral List

Ankerite Azurite Baryte Bornite Calcite Chalcocite Chalcopyrite

Chrysocolla Covellite Dolomite Galena Gersdorffite Lead Limonite

Linnaeite Malachite Metazeunerite Millerite Quartz Sphalerite Tennantite

Tetrahedrite Ullmannite Uraninite var: Pitchblende Zeunerite

25 entries listed. 23 valid minerals.

References