Naica Mine

The Naica Mine of the Mexican state of Chihuahua, is a lead, zinc and silver mine. Located in Naica in the municipality of Saucillo, the Naica Mine is owned by Industrias Peñoles, the world's largest silver producer. Caverns discovered during mining operations contain gigantic crystals of CaSO4 · 2 H2O (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.The peak underground air temperature was 58° C 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 and delivering fresh air for an easier breathing. The visits were limited to about half an hour, the time needed to melt the ice reserves.