Atacama Desert Chile

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). 

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. 

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. 

Rech JA, Currie BS, Michalski G, Cowan AM (2006) Neogene climate change and uplift in the Atacama Desert, Chile. Geology 34(9) 761-764... 

Uncertainty in the depth history of a sample is a primary source of uncertainty for the cosmogenic-nuclide paleoaltimeter. Because of the >2000-fold difference in rock density versus atmospheric density, a 0.5-m uncertainty in depth is equivalent to >l-km uncertainty in altitude. Uncertainty in the depth of a sample during exposure is particularly problematic in regions where loess deposits may episodically bury a surface. For example, Hancock et al. (1999) find cosmogenic evidence of an ephemeral 0.5-1.5 m silt cap on currently uncapped, 600-ka terraces in the Wind River basin, Wyoming. The duration of time required to deposit a sedimentary layer may also result in a complex exposure history that can only be deduced with depth profiles and multiple nuclides (Riihimaki et al. 2006). However, Dunai et al. (2005) suggest that some deposits in the hyperarid Atacama Desert, Chile, have remained at the same depth without erosion or deposition for >20 Ma. 

Rech J. A., Quade J., and Hart B. (2002) Isotopic evidence for the source of Ca and S in soil gypsum, anhyrite and calcite in the Atacama desert, Chile. Geochim. Cosmochim. Acta 67(4), 575 -586. 

Goudie, A.S., Wright, E. Viles, H.A. (2002) The roles of salt (sodium nitrate) and fog in weathering a laboratory simulation of conditions in the northern Atacama Desert, Chile. Catena 48, 255-266. 

The search for surface deposits that preserve anomalous oxygen isotope fractionations led fi om improbable sites such as the hyper-arid, super-hot Atacama Desert, Chile, to super-cold sampling pits dug in snow at the South Pole. The proxy dragnet focused on these remote sites because aridity and freezing are two viable methods for preserving water-soluble, direct products of atmospheric chemistry for detailed investigations. Anomalously fractionated... 

K.L., Pointing, S.B. et al. (2006). Hypolithic cyanobacteria, dry limit of photosynthesis and microbial ecology in the hyperarid Atacama Desert, Chile. Microbial Ecology 52, 389-398. 

Ewing, S.A., Yang, W., DePaolo, D.J., Michalski, G., Kendall, C., Stewart, B.W., Thiemens, M and Amundson, R. (2008) Non-biological fractionation of stable Ca isotopes in soils of the Atacama Desert, Chile. Geochim. Cosmochim. Acta, 71, 1096-1110. 

Navarro-Gonzalez R, Rainey FA, Molina P, Bagaley DR, Hollen BJ, de la Rosa J, Small AM, Quinn RC, Grunthaner FJ, Caceres L, Gomez-Silva B, McKa CP (2003) Mars-like soils in the Atacama Desert, Chile, and the dry limit of microbial life. Science 302 1018-1021... 

Trippkeite is a copper arsenate mineral with composition CUAS2O4 (Sarp and Cemy, 2001). It forms as green-blue prismatic crystals in arsenic-bearing copper deposits such as those in the Atacama desert (Chile) from where it was first reported by vom Rath in 1880 it has also been found in the copper mines of Roua (Alpes-Maritimes, France) where it is associated with other copper minerals hrochantite, malachite and cuprite (qq.v). 

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. 

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. 

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.

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. 

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. 

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

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. 

Examples of especially dry environments on Earth include the Atacama Desert of northern Chile and the Dry Valleys of Antarctica. Dose et al. (2001) exposed spores, conidia, and cells of several microbes to 15 months of desiccation in the dark at two locations of the Atacama Desert. Bacillus subtilis (bacteria) spores (survival 15%) and Aspergillus niger (fungi) conidia (survival 30%) outlived other species. Deinococcus radiodurans (bacteria) did not survive the desert exposure because they were readily killed at RH between 40% and 80%, which occurred during desert nights (Dose et al. 2001). 

Occasionally, the extraction of arsenic forms can be conducted using demineralized water, but only in cases involving the release of stable compounds in solutions of varying pH. It has been employed, for example, in comparative analysis of the hair of 1000-year-old mummies recovered from the Atacama Desert in Chile, and in analyses of hair collected from contemporary residents of India inhabiting areas contaminated with arsenic [92]. Similar contents of dimethylarsinic acid [DMA(V)] and monomethylarsonic acid [MMA(V)] were found in both materials under study. 

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