Enormous gypsum crystals (CaSO
4 · 2 H
2O) in the most spectacular Naica cavern, found during mining. Note the size of the person at the bottom right for the scale.

The Naica Mine of the Mexican state of Chihuahua, is a lead, zinc and silver mine.[1][2] Located in Naica in the municipality of Saucillo, the Naica Mine is owned by Industrias Peñoles,[3] the world's largest silver producer.[4][5] Caverns discovered during mining operations contain gigantic crystals of CaSO
4 · 2 H
2O (calcium sulfate dihydrate, gypsum, also sometimes called selenite. Peñoles announced in October 2015 that it was indefinitely suspending operations due to uncontrollable flooding at the Naica Mine.[6]

The peak underground air temperature was 58°C (136°F) with 100% relative humidity, which rapidly exposed the visitors to hyperthermia hazard and caused breathing difficulties. Because of the heat, unprotected researchers could only stay up to 10 minutes inside the cave. Longer visits required the use of a special suit fitted with a cooling system (ice reserve in a backpack with cooled water recirculating in polymer tubes installed over all the body surface) and delivering fresh air for easier breathing. The visits were limited to about half an hour, the time needed to melt the ice reserves.

Cave of the Crystals

Location of the Swords and Crystal caves with the gypsum crystals within the conceptual block diagram of Naica mine

The Cave of Crystals is a cave approximately 300 m (1,000 ft) below the surface in the limestone host rock of the mine, about 109-metre (358 ft) long, with a volume of 5,000 to 6,000 cubic metres (180,000 to 210,000 cu ft).[7] The chamber contains giant selenite crystals, some of the largest natural crystals ever found.[8][9] The largest is 11.40 metres (37.4 ft), with a volume of about 5 cubic metres (180 cu ft), and an estimated mass of 12 tonnes.[7] The selenite crystals were formed by hydrothermal fluids heated by the magma chamber below. The cavern was discovered while the miners were drilling through a newly drained area. The caves are closed to the public, and remain closed after a worker tried to enter the cave to steal some of the selenite, only to suffocate and die in the cave's humid and inhospitable atmosphere.[10]

Reports in 2017 stated that scientists had found "long-dormant microbes" in the crystals and removed them for further research. The cave was closed in 2015 and some of the chambers were allowed to flood again to continue the process of crystal growth.[11] If the mining company decides to open another entrance, researchers might again enter to continue their work, according to a February 2019 report.[12]

The Cave of Swords

The Cave of Swords (Cueva de Espadas) is the second-largest chamber in the Naica Mine, at 104-metre (341 ft) long, with a volume of 1,400 cubic metres (49,000 cu ft).[7] It also containing gypsum crystals but each "only" about a meter long, due to the fact that these crystals are younger and had been growing for much less time by the time they were discovered in 1910.[9]

References

  1. ↑ García-Ruiz, Juan Manuel; Villasuso, Roberto; Ayora, Carlos; Canals, Angels; Otálora, Fermín (2007). "Formation of natural gypsum megacrystals in Naica, Mexico". Geology. 35 (4): 327. Bibcode:2007Geo....35..327G. doi:10.1130/G23393A.1. hdl:10261/3439.
  2. ↑ Van Driessche, A. E. S.; Garcia-Ruiz, J. M.; Tsukamoto, K.; Patino-Lopez, L. D.; Satoh, H. (2011). "Ultraslow growth rates of giant gypsum crystals". PNAS. 108 (38): 15721–6. doi:10.1073/pnas.1105233108. PMC 3179101. PMID 21911400.
  3. ↑ "The Naica Mina". Archived from the original on 2010-11-25.{{cite web}}: CS1 maint: unfit URL (link)
  4. ↑ "Peñoles, the world's top producer of refined silver", Corporate profile, Retrieved June 15, 2019
  5. ↑ Maple mine, known also as Naica, "under Peñoles control since 1964.", Corporate mining operations, Retrieved June 15, 2019
  6. ↑ "Penoles suspends operations at Naica mine in northern Mexico". Reuters. 13 October 2015. Retrieved 14 October 2015.
  7. 1 2 3 Badino, Giovanni; Sanna, Laura (1 July 2009). "The Naica caves survey". International Congress of SpeleologyProceceedings: 1764–1769. Retrieved 18 April 2021.
  8. ↑ National Geographic, 2008. Cavern of Crystal Giants
  9. 1 2 National Geographic, 2007. Giant Crystal Cave's Mystery Solved
  10. ↑ "Danger and wonder in Nat Geo's "Giant Crystal Cave"".
  11. ↑ Naica's crystal caves hold long-dormant life
  12. ↑ Naica's crystal cave captivates chemists
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