Mine from Naica

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Green fluorite , framed by white calcite , from the Naica mine, excavated in the 1980s. Dimensions: 5.5 cm x 5.1 cm x 4.4 cm

The Naica Mine (Spanish: Mina de Naica ) is an ore mine near the city of Naica in the state of Chihuahua in northern Mexico . The mine gained worldwide fame due to the natural caverns in the mountain, which were discovered during the mine operation and contain giant crystals made of Marienglas (selenite), a variety of gypsum . One of these caverns, the “Cave of Crystals”, contains 14 meters long and up to 50 tons heavy crystals, the largest known crystals on earth.

history

Panorama of Naica

In 1794, Alejo Hernández, Vicente Ruiz, and Pedro Ramos found a small ore vein south of the capital Chihuahua at the foot of a mountain range known as Naica. They filed their claim and named the new mine San José del Sacramento . However, the first work did not begin until 1828 and then only to a limited extent. In 1896, Santiago Stopelli registered his claim on Mount Naica and the settlement was recognized as a village. Shortly thereafter, the Compañía Minera de Naica was founded and in 1900 mining began on a large scale. In 1911 the settlement had become so important that it achieved the status of a municipio (district town). Due to the Mexican civil war , however, the work had to be stopped and was only continued 13 years later under the Compañía Minera Peñoles . Between 1920 and 1961 the mine was run by American companies and since then by Grupo Peñoles . Mainly lead and zinc, but also gold, silver, copper as well as tungsten and molybdenum are mined in Naica.

In 1910 the Cave of Swords was discovered. In 2000, during exploration work in the mine, the cave of the crystals was found by chance . As the mine continues to expand, the mining company is now paying attention to the preservation of the crystal caves and protecting them against looters by laying tunnels and closing the entrances to the caves.

From 2006 to 2009, the Naica Caves were systematically explored by researchers from six different nations and eight disciplines. In addition to speleologists , geochemists , crystallographers , microbiologists , pollen researchers and immunologists were also involved. The aim of the investigations was to find out the formation conditions for this extraordinary giant growth of gypsum crystals. For security reasons, the caves have been closed to all visitor traffic since 2009. This applies to both researchers and journalists.

Single caves

Cave of Swords ( cueva de las espadas )

The cave is located at a depth of 120 meters and extends over a length of 70 to 80 meters. The floor, ceiling and walls are covered with large selenite crystals. Some of these crystals reach lengths of over a meter and resemble swords, which is what gave the cave its name. These crystals were believed to be the largest in the world until the other caves in Naica were discovered. In contrast to the newly discovered caves, the crystals of the Cave of Swords are pervaded by numerous growth disorders and are not transparent, but rather cloudy. This is explained by the greater proximity to the earth's surface and the resulting temperature fluctuations.

Cave of Crystals ( cueva de los cristales )

Giant crystals made of Marienglas (selenite) in the Cueva de los Cristales ("Cave of the Crystals"), note the person at the bottom right for the size comparison.

This cave is located at a depth of 290 meters, has a diameter of about 30 meters and was only discovered in April 2000. The crystals in this cave reach a length of up to 14 meters with a diameter of two meters. The largest of the crystals is believed to be 100,000 to 1,000,000 years old. The temperature in the cave is between 45 and 50 ° C and the humidity is 90 to 100%, which led to additional technical effort for the employees during the research.

In air at a temperature of 45–50 ° C that is almost saturated with water vapor, sweat no longer evaporates on the skin at 37 ° C, but rather, conversely, water vapor condenses on the skin and introduces thermal energy into the body. Countermeasures can be taken by breathing dry air and evaporation of body water in the respiratory tract, with water vapor-tight thermal insulation of the body. For technical and physical reasons, air from pressurized gas cylinders of 200 or 300 bar must be almost completely free of water. What sometimes cools down divers can be used here. Alternatively, only the surface of the body is flushed with dry air in order to cool by evaporation of sweat. The expansion of the air out of the bottle also cools the air.

Formation of the crystals

The crystals could only arise because there was very little oversaturation in the solution with which the cave was filled over long periods of time . It is problematic to explain how it was possible to obtain such a low level of supersaturation without large fluctuations over such a long period of time. Analyzes of liquid inclusions in the crystals show that they grew from a solution with a low salt content at 55 ° C. This temperature is only slightly below 58 ° C, at which anhydrite precipitates instead of gypsum and thus no crystals are formed. Kinetic calculations for the formation of crystallization nuclei showed that crystal growth according to the present mechanism is only possible in this very narrow temperature range, as it was in the cave before its discovery.

The relatively high temperature in the cave results from the fact that there is a magma chamber just below the mine and a hydrothermal cycle could form above it. The layer of earth above the cave had a heat-insulating effect. Since the cave had no direct connection to the outside world, a constant temperature resulted, which depends on the distance to the magma chamber and the thickness of the insulating layer and does not fluctuate with the outside temperature. However, since the chamber was opened and a connection to the outside world was established, measurements have shown that the temperature has decreased by about half a degree every year.

Initially, volcanic activity 26 million years ago resulted in the formation of Mount Naica. In chambers filled with mineral-containing water, high-temperature anhydrite, the water-free variant of gypsum, was initially formed. Anhydrite is formed as a stable form at solution temperatures above 58 ° C, below this the selenite , which contains water of crystallization, is formed . As the magma slowly cooled below the mountain, the temperature dropped below 58 ° C and the anhydrite began to dissolve. This led to an accumulation of sulfates and calcium, which could be deposited as selenite crystals over long periods of time.

The Norwegian geologist Stein-Erik Lauritzen was able to estimate the age of the crystals to be around 350,000 years based on uranium-thorium dating . During the whole time the environmental conditions remained constant, as the cave system remained closed. So the water was exchanged slowly and the temperature hardly changed. Under these ideal conditions, the crystals had enough time to grow to the discovered dimensions.

However, the crystals under the earth are ephemeral: If the crystals were in a water bath during growth, they are now dry after pumping out due to mining activities. However, this dryness affects the crystals that have grown. Since 2006 researchers have been working intensively to collect as much knowledge as possible about the cave and to capture the beauty of the cave and gypsum crystals in pictures for posterity.

Cave Eye of the Queen ( cueva el ojo de la reina )

Similar to the Cave of Crystals, this cave is located at a depth of 300 meters, but is significantly smaller with a diameter of eight meters. It also contains very large crystals.

Cave of Candles ( cueva de las velas )

This fourth cave is also at a depth of about 300 meters and, like the Cave of Crystals, was discovered in 2000. Before the start of the mine work there were also large gypsum crystals, but also a porous layer of manganese and iron hydroxides. The large gypsum crystals are partially covered by tiny, candle-like gypsum crystals. Presumably, these fine crystals formed within a period of only one to two weeks, when the groundwater sank due to mining operations and the porous hydroxide layer had stored enough mineral-containing water to allow further crystal growth.

Web links

Commons : Mine by Naica  - collection of images, videos and audio files

Individual evidence

  1. ↑ GEO Magazine No. 05/08. Speleology: In the Chamber of Crystal Giants , p. 2 of 4
  2. ↑ a b Maravillas de Naica. ( Memento of March 21, 2009 in the Internet Archive ) México Desconocido. No. 287, January 2001 (Spanish)
  3. ^ Production details of the Naica mine from Industrias Peñoles
  4. ↑ GEO Magazine No. 05/08. Speleology: In the Chamber of the Crystal Giants , p. 3 of 4
  5. ^ Former websites of the Naica project - The Caves. (English) ( Memento from June 10, 2015 in the Internet Archive )
  6. ↑ Victoria Jaggard: Weird Life Found Trapped in Giant Underground Crystals nationalgeographic.com, February 17, 2017, accessed February 20, 2017.
  7. ↑ García-Ruiz et al. 2007, Geology (Geological Society of America), Formation of natural gypsum megacrystals in Naica, Mexico , (English) doi : 10.1130 / G23393A.1
  8. ↑ Broadcast Naica - Cave of Giant Crystals at Arte on March 6, 2010
  9. ^ National Geographic News
  10. ↑ GEO Magazine No. 05/08. Speleology: In the Chamber of Crystal Giants , p. 4 of 4
  11. ↑ Growth at a snail's pace. On: Wissenschaft.de from September 13, 2011.

Coordinates: 27 ° 50 ′ 42.9 "  N , 105 ° 30 ′ 24.1"  W.