Naica Mine

(Saucillo Municipality, Chihuahua, Mexico)

https://www.mindat.org/loc-16778.html

Mine Information: Naica began operations in 1794 and was taken over completely by Grupo Peñoles in 1955.

The underground mine is serviced by a number of shafts, declines, and spiral ramps and processes are highly automated.

Ore is crushed underground and transported to the surface by conveyer.

Naica mine, ore loading bridge for railway wagons, 1911

Water is the big challenge for the mine; 60,000 l/min is pumped out to avoid flooding.

The groundwater is 110 m below the adit level: production when the mine flooded in 2015 was up to 900m below that.

The caves were not seen by modern-era humans until the year 2000.

Miners Pedro & Juan Sanchez — two brothers with the Peñoles Mining Company— became the first people to lay eyes on its crystals when they entered the drying cave on foot. It soon became clear that Crystal Cave was an inhospitable place:

https://cen.acs.org/physical-chemistry/geochemistry/Naicas-crystal-cave-captivates-chemists/97/i6

Do not attempt to access the Naica Mine without professional guides & supervision.

Not only does the temperature climb as high as 136 degrees Fahrenheit (58.3 degrees Celsius), but the humidity levels are close to 100 percent.

The cave is so humid that anyone who enters will have fluids condense in his or her lungs, which can be fatal.

Geology:

The mine is situated on a structural dome measuring about 12 km by 7 km.

Country rock is a thickly bedded Cretaceous limestone.

The ore deposits occur in limestones of the Finlay, Lagrima and Benigno Formations (Aurora Group, which is over 1000m thick.

The limestone sequence may be overthickened by thrust faulting.

Alteration of the limestone is typically limited to a few centimeters to 8m of recrystallization or marbelization.

Overlying the Finlay limestones are calcareous shales of the Benavides Formation and limestones of the Lorna de Plata Formation.

Some of the smaller caverns can be accessed without protective equipment:

Hydrothermally altered Tertiary (30.2 Ma) felsites occur as thin discontinuous dikes and sills that localize the ore and cut the limestone.

These coalesce to the west and ultimately merge into a granitic stock west of the historic part of the mine.

Virtually no alteration or mineralization extended through the Benavides, suggesting that it formed an effective seal on the system that caused the orefluids to spread out laterally below it-creating near-surface orebodies with a pattern like the roots of an inverted tree.

Block diagram with deep levels and sequence of mineralization, indicating general depth of each cave system & location of the Swords and Crystal caves within the conceptual block diagram of Naica mine

Sulfide minerals are mostly pyrite, galena and sphalerite with lesser amounts of chalcopyrite, arsenopyrite, pyrrhotite, matildite, kobellite-tintinaite and molybdenite.

Scheelite occurs in economic concentrations.

Fluorite, quartz, adularia and calcite seem to be in part contemporaneous with the sulfides but also occur as crystals in vugs in the sulfide and silicate ore.

NASA Astrobiology Institute director Penelope Boston journeyed into the Giant Crystal Cave in 2008, and again in 2009.

She helped discover microbial life forms that had been trapped inside one of the crystals.

Suspended in an air bubble, the tiny organisms may have laid dormant for up to 50,000 years before Boston and company came along.

The ores show the kind of complex repeated paragenesis typical of large, long-lived skarn-replacement systems: gold, silver, lead, zinc, and much smaller amounts of copper and tungsten.

Mercury was historically recovered from some of the near-surface gossans.

The cave hosts selenite crystals up to 14m x 2m in length and width, respectively.

These crystals formed underwater where the hot and calcium carbonate and sulfides saturated fluids transported through the Naica fault, mixed with colder fluids originating from the surface.

It is estimated that the crystals have been growing for about one million years.

google.com/maps/@27.855399,-105.4878993,15z/

The mine was allowed to re-flood in October 2015, making it completely inaccessible for exploration.

Currently (2023) the mine appears to be moving slowly back towards production, but the ramp-up is expected to take several years.

http://www.nags.net/stein/2009/3-2009-Lauritzen.pdf

www.unige.ch/sciences/terre/mineral/MexicoFieldGuide.pdf

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