Abstract The mine caves of Naica (Chihuahua, Mexico) are famous because they host large gypsum crystals. Mine works intersected new caves hosting the largest crystals in the world in the year 2000. From 2006 these caves became the object of a multidisciplinary research project with the goal of inferring their ages, the boundary conditions for their formation and the mechanisms inducing their development. Several other scientific aspects were also considered, including palynology, mineralogy, microbiology, physiology, hydrogeology and astrobiology. From 2006 to 2009, scientists and explorers tried to ensure the complete documentation of these natural wonders because they were expected to be accessible for only a few years. As a result of their location c. 160 m below the natural groundwater level, they were predicted to be flooded with thermal water as soon as dewatering of the mine ceased. This occurred at the end of 2015, so that the lower part of the mine is already submerged and in the near future the giant crystal caves will also disappear. Theoretically, it is still possible to maintain these incredible wonders for future generations, but this seems highly unlikely. Soon the crystals will be submerged below c. 150 m of hot water, restarting their incredible slow growth.

Abstract The Naica mining district is located in the municipality of Saucillo in south-central Chihuahua State, 110 km directly southeast of Chihuahua, the state capital, at an altitude of 1,382 m and geographic coordinates 27°52′00″N, 105°26′15″W (Fig. 1). Access to the district is by a 26-km-long paved road joining the Panamerican Highway at Conchos Station and another road, also paved, that runs for 40 km to Ciudad Delicias; the México- Ciudad Juárez Central Railroad stops at Conchos Station. The first mining concession in the district was granted in 1794 (Aldama, 1945). The deposits were discovered by prospectors, and small-scale mining began in 1828, during the rainy seasons only owing to the scarcity of water (Lambert, 1892). In the last years of the nineteenth century the Compañ×;a Minera de Naica, S. A., began industrial operations, which were later (1911) suspended when the mine reached ground-water level, and also because of the country's political instability at the time. In 1924 several companies renewed the extraction of oxidized ores. This work continued until 1951, when the Fresnillo Company acquired the Naica Mine and installed electric pumps and a 400 ton/day sulfide-processing flotation plant (in 1952), which doubled production capacity the following year. In 1956 the Fresnillo Company acquired all the deposits in the district and is presently the only producing company under title of Compañ×;a Fresnillo, S. A. de C. V.; since that date the plant capacity gradually increased to 3,000 tons/day in 1985.

Abstract The main item of interest is the visit to the Naica mine, which is reached by travelling southwards along valley floors to Delicias, and then southwestward to the mining community. The deposits comprise a lead-zinc-silver assemblage and are well developed in numerous mantos and breccia pipes that are located in Cretaceous carbonate host rocks. Felsic dikes, of Oligocene age, are associated with minor skarn development in their immediate vicinity. The latter part of the day will be spent by travelling southwards to Ciudad Camargo and Jimenez, and then west to Parral, located at the eastrn margin of Sierra Madre Occidental.