Atacama Desert

Mineral Deposits. The only iodine obtained from minerals has been a by-product of the processing of nitrate ores in Chile. CaUche occurs in the Atacama desert of Northern Chile and west of the Andes mountains. The Atacama desert is known as the driest of the world s deserts, where measurable (>1 mm) rainfalls may be as infrequent as once every 5—29 years (58). The caUche deposits occur in an area averaging 700 km (north—south) by 30 km (east—west). The iodine may total over 5 x 10 t (59). 

The Chilean nitrate deposits are located in the north of Chile, in a plateau between the coastal range and the Andes mountains, in the Atacama desert. These deposits are scattered across an area extending some 700 km in length, and ranging in width from a few kilometers to about 50 km. Most deposits are in areas of low rehef, about 1200 m above sea level. The nitrate ore, caUche, is a conglomerate of insoluble and barren material such as breccia, sands, and clays (qv), firmly cemented by soluble oxidized salts that are predominandy sulfates, nitrates, and chlorides of sodium, potassium, and magnesium. Cahche also contains significant quantities of borates, chromates, chlorates, perchlorates, and iodates. 

Numerous theories exist as to how the Chilean deposits formed and survived. It has been postulated that the unique nitrate-rich caUche deposits of northern Chile owe their existence to an environment favorable to accumulation and preservation of the deposits, rather than to any unusual source of the saline materials (2). The essential conditions are an extremely arid climate similar to that of the Atacama desert in the 1990s, slow accumulation during the late Tertiary and Quaternary periods, and a paucity of nitrate-utilizing plants and soil microorganisms. 

Occurrence. Iodine [7553-56-2] is widely distributed in the Hthosphere at low concentrations (about 0.3 ppm) (32). It is present in seawater at a concentration of 0.05 ppm (33). Certain marine plants concentrate iodine to higher levels than occur in the sea brine these plants have been used for their iodine content. A significant source of iodine is caUche deposits of the Atacama Desert, Chile. About 40% of the free world s iodine was produced in Japan from natural gas wells (34), but production from Atacama Desert caUche deposits is relatively inexpensive and on the increase. By 1992, Chile was the primary world producer. In the United States, underground brine is the sole commercial source of iodine (35). Such brine can be found in the northern Oklahoma oil fields originating in the Mississippian geological system (see Iodine and iodine compounds). 

A large reserve of caUche ore bearing iodine is being processed in the Atacama Desert. Production of iodine there is relatively inexpensive. About 40% of the world supply of iodine is made from these Chilean deposits. The process consists of leaching the caUche with water. Brine is stripped of iodine using an organic solvent. The iodine is then removed from the solvent to form a slurry. SoHd-phase iodine is separated from the slurry in conventional flotation cells, dried, and packaged. Details of the process are proprietary. 

Figure 8-2. The Chuquicamata copper mine is iocated in the Atacama desert in Chiie.

Important weather details are not only provided by the newest information from the Cassini orbiter the Very Large Telescope in the Atacama desert and the W. M. Keck Observatory on Hawaii are also involved. Near-IR spectra show increased cloudiness in the Titanian troposphere on the morning side, i.e., there are methane clouds at a height of about 30 km and methane drizzle at the surface (Adamkovics et al., 2007). 

South America has two major areas, separated by the Andes Mountain ridges, where arid and semi-arid zones dominate. In the barren, coastal Atacama desert of Peru and northern Chile, precipitation is extremely limited and comes as winter mists or drizzles. In the rain shadow east of the Andes in Argentina, arid zones are widespread. South America apparently has only a slightly greater proportion of dry zones than North America. 

Asymmetric substrate, 13 664-665 Asymmetric synthesis, via chiral organoboranes, 13 664-671 ATI receptor, 5 158 Atacama Desert, sodium nitrate in, 22 844-845 Atacamite, 7 769... 

Fig. 1. Distribution of copper deposits in northern Chile including those containing atacamite in the oxide zone. DFZ is the Domeyko Fault Zone and ACL is Antofagasta-Calama Lineament. The land between the High Andes and the coast is the hyper-arid central Atacama Desert.

The metallogenic evolution of the copper porphyry deposits of the Atacama Desert included a long phase of supergene... 

Arancibia, G., Matthews, S.J., Perez De Arce, C. 2006. K-Ar and °Ar Ar geochronology of supergene processes in the Atacama Desert, Northern Chile tectonic and climatic relations. Journal Geological Society London, 163, 107-118. 

Leybourne, M.I. Cameron, E.M. 2006. Composition of groundwaters associated with porphyry-Cu deposits, Atacama Desert, Chile Elemental and isotopic constraints on water sources and water-rock reactions. Geochimica et Cosmochimica Acta, 70, 1616-1635. 

Palacios, C., Guerra, N., Townley, B., Lahsen, A. Parada, M. 2005. Copper geochemistry in salt from evaporate soils, Coastal Range of the Atacama Desert, northern Chile an exploration tool for blind Cu deposits. Geochemistry Exploration, Environment, Analysis, 5, 371-378. 

Reich, M., Palacios, C., Parada, M.A., Fehn, U., Cameron, E.M., Leybourne, M.I. Zuniga, A. 2008. Fluid inclusion, groundwater geochemistry, TEM and 36CI. Evidence for a genetic link between basinal brines and atacamite formation, Atacama Desert, Chile. Mineralium Deposita, 43, 663-675. 

Lithogeochemistry of the Quebrada Blanca Porphyry Cu Deposit, Atacama Desert, Northern Chile... 

The Quebrada Blanca (QB) porphyry Cu deposit (21°24 S, 68°55 W) is located 1,500 km north of Santiago in the Tocopilla Province, Chiie (Region 1). Located at 4,300 m eievation in the Atacama Desert, QB is iess than 10 km west of the Rosario and Ujina porphyry Cu deposits, which together with QB make up the Coiiahuasi porphyry Cu district. QB is aiso iocated east of the West Fissure within the Domeyko fauit system, a major crustai structure controiiing the iocation of iarge economic porphyry Cu deposits, inciuding the Chuquicamata porphyry Cu deposit iocated 150 km south of QB. 

Perchlorate is another anthropogenic compound, which may contaminate surface and gronnd waters. The occurrence of natural perchlorate is limited to extremely dry environments, snch as the Atacama desert. Large kinetic isotope effects during microbial rednction of perchlorate have been observed by Sturchio et al. (2003) and Ader et al. (2008), which may be used to document in-situ bioremediation. 

CALICHE (Nitrate). The gravel, rock. soil, or alluvium cemented with soluble salts of sodium in the nitrate deposits of the Atacama Desert of northern Chile and Peru. The material contains from 14 to 25% sodium nitrate, 2 to 3% potassium nitrate, and up to I i sodium iodaic. plus some sodium chloride, sulfate, and borate. At one time, this was an important natural fertilizer. 

Figure 1. (a) Elevations of the Central Andean plateau between 15°S and 26°S, constructed with SRTM30 dataset. White circles show our late Oligocene to late Miocene sites discussed in the text. White boxes enclose study sites for modem soil carbonate in the Atacama Desert in Quade et al. (2007) (b) study locations in the Himalayan-Tibet orogen (Himalaya/Hindu Kush shaded). 

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