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Naica Mine, Naica, Mun. de Saucillo, Chihuahua, Mexico

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Mine Information: Naica began operations in 1794 and was taken over by Grupo Peñoles in 1952. The underground mine is serviced by a number of shafts, declines, and spiral ramps. Processes are highly automated. Ore is crushed underground and transported to the surface by conveyer.

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 surface: current [2013] production is 740m below that.

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 reef-facies carbonates of the Aurora Formation, which is about 800m thick. Overlying the Aurora limestones are calcareous shales of the Benavides Formation and limestones of the Lorna de Plata Formation. Hydrothermally altered Tertiary felsites occur as thin discontinuous dikes and sills that localize the ore and cut the limestone. Here, the Aurora Formation limestone has been metamorphosed to white/light grey marble.

The deposit consists of mantos and chimneys, but unlike most replacement massive sulfide deposits in Mexico where mantos and chimneys are distinguished by their geometry, at Naica the difference is by ore silica content. True skams consisting of calc-silicates with disseminated sulfides make up the mantos, whereas the opposite is true for the chimneys. Many of the mantos are cored by felsite dikes which seem to be replaced by mineralization. There is a clear relationship between the silicate-rich mantos and the silicate-poor chimneys; the chimneys originate from mantos.

The area is cut by 3 main faults, and the ore is found between these structures. Generally, the chimneys are controlled by the fractures and the mantos seem to be localized by the dikes. While mineralization is largely structurally controlled, the geometry of certain chimneys indicates that some limestone horizons are more favorable for mineralization. Post-mineralization faults are sometimes lined with large (up to a few feet) gypsum crystals.

Sulfide minerals are mostly pyrite, galena and sphalerite with lesser amounts of chalcopyrite, arsenopyrite, pyrrhotite, matildite, cosalite, 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. The ores are gold, silver, lead, zinc, and much smaller amounts of copper.



In 2000, a cave was encountered while driving a communication tunnel. 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.

Mineral List

Mineral list contains entries from the region specified including sub-localities


93 entries listed. 86 valid minerals.

Localities in this Region

Mexico

The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10111567 & 10181941.

Werner, A.B.T., Sinclair, W.D., and Amey, E.B. (1998): International Strategic Mineral Issues Summary Report - Tungsten. US Geological Survey Circular 930-O.

Panczner(1987): 98, 109, 121, 166, 168, 171, 182, 195, 201, 221, 267, 277, 311, 351

Mining Annual Review (1985): 332-333.

Geology and Geochemistry of Naica, Chihuahua, Mexico, Ruiz, Barton, SME-AIME, 1985


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