In the past 15 years several expeditions by French, American and especially Italian cavers have unveiled over 50 caves in the Cordillera de la Sal, close to San Pedro de Atacama village (Atacama Desert). Four caves are longer than 2 km, while total explored underground development has exceeded 20 km. These caves cross an Oligo-Miocene evaporite sequence, containing 20-60 m thick interbedded salt beds, sandwiched by an anticline structure between clastic and gypsiferous Cretaceous-Eocene sediments and a succession of Miocene to Pleistocene volcanics and continental, mostly alluvial, deposits. Despite the hyperarid climate, with annual rainfall of only a couple of mm/a, and often several years without any rain, short Niño-driven precipitation events are enough to trigger the dissolution of salt and the formation of underground meandering river passages. Caves are mostly through-passages, with large entrances both upstream and downstream, and often some skylights in between, creating a constant airflow through their entire length. In-cave temperature ranges between 15-18 °C, depending on altitude, cave depth below the surface, and size/number of their openings. Relative humidity is always very low, around 15%. These caves contain a variety of speleothems and minerals, two of which (atacamite and antarcticite) are new for the cave environment. Samples have been taken in six caves, at altitudes ranging between 2,348 m asl (the base of the Cordillera) and 2,550 m asl (the top of the anticline). Most secondary deposits are composed of halite, but also other halides, carbonates, sulphates, nitrates, phosphates, and silicates have been discovered. Among the seventeen observed minerals, beside the two new for the cave environment, darapskite, blodite, anhydrite are worth mentioning. The peculiar climate (extremely arid) and the very special environment, which is dominated by NaCl and CaSO4, allow local enrichment in Cu (of hydrothermal origin), Al and Mg (by volcanic source such as olivine, plagioclase, pyroxenes, and amphiboles) and nitrates (by bird guano), thus giving rise to the formation of the different observed mineral species.
Minerals from halite caves in the Atacama Desert (Chile)
Sanna Laura;
2016
Abstract
In the past 15 years several expeditions by French, American and especially Italian cavers have unveiled over 50 caves in the Cordillera de la Sal, close to San Pedro de Atacama village (Atacama Desert). Four caves are longer than 2 km, while total explored underground development has exceeded 20 km. These caves cross an Oligo-Miocene evaporite sequence, containing 20-60 m thick interbedded salt beds, sandwiched by an anticline structure between clastic and gypsiferous Cretaceous-Eocene sediments and a succession of Miocene to Pleistocene volcanics and continental, mostly alluvial, deposits. Despite the hyperarid climate, with annual rainfall of only a couple of mm/a, and often several years without any rain, short Niño-driven precipitation events are enough to trigger the dissolution of salt and the formation of underground meandering river passages. Caves are mostly through-passages, with large entrances both upstream and downstream, and often some skylights in between, creating a constant airflow through their entire length. In-cave temperature ranges between 15-18 °C, depending on altitude, cave depth below the surface, and size/number of their openings. Relative humidity is always very low, around 15%. These caves contain a variety of speleothems and minerals, two of which (atacamite and antarcticite) are new for the cave environment. Samples have been taken in six caves, at altitudes ranging between 2,348 m asl (the base of the Cordillera) and 2,550 m asl (the top of the anticline). Most secondary deposits are composed of halite, but also other halides, carbonates, sulphates, nitrates, phosphates, and silicates have been discovered. Among the seventeen observed minerals, beside the two new for the cave environment, darapskite, blodite, anhydrite are worth mentioning. The peculiar climate (extremely arid) and the very special environment, which is dominated by NaCl and CaSO4, allow local enrichment in Cu (of hydrothermal origin), Al and Mg (by volcanic source such as olivine, plagioclase, pyroxenes, and amphiboles) and nitrates (by bird guano), thus giving rise to the formation of the different observed mineral species.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
