Hostname: page-component-cd9895bd7-p9bg8 Total loading time: 0 Render date: 2024-12-18T07:00:08.241Z Has data issue: false hasContentIssue false
  • English
  • Français

A preliminary petrographic study of the Chilean nitrates

Published online by Cambridge University Press:  01 May 2009

Alison Searl  and
Sharon Rankin
Alison Searl
Affiliation:
School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K.
Sharon Rankin
Affiliation:
School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

The nitrate deposits of the northern Atacama Desert occurin a narrow zone between the low-lying Pampa del Tamarugal to the east and the hills of the Coastal Range to the west. High purity nitrate ore occurs as stratiform seams about 20 cm thick, present at depths of 3–7 m below thedesert surface. The ore is hosted by a variety of lithologies and overlain by salt-cemented regolith. The ore is largely composed of nitratite (= sodanitre or Chilean salt peter) and halite with locally abundant humberstonite, polyhalite and mirabilite. Other salts present include Ca iodates and a variety of sulphate, borate and chromate minerals. Textural relationships can be used to deduce paragenetic sequences for individual salt samples and these combined to produce a generalized paragenetic web for the nitrate ore.These textural data can be combined with published solubility data to investigate the course of fluid evolution during ore genesis. The multiplicity of paragenetic relationships within the ore reflects the derivation of precipitating fluids from a variety of sources: westwards flowing Andean groundwater, coastal fogs, occasional rainfall and Andean-derived surface floodwaters. The unusual mineralogy of the nitrate ore reflects the extreme chemical evolution of the precipitating brines through multiple episodes of salt precipitation and remobilization during transport to the nitrate horizons. The formation of high purity nitrate ore appears to be the result of multiple phases of dissolution, reprecipitation and recrystallization, that have separated the highly soluble nitrate salts from less soluble salts in the overlying profile. Salts have largely accumulated through displacive growth, but some of the host silicate and carbonate lithologies have also undergonea small degree of salt replacement.

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 3 , May 1993 , pp. 319 - 333
Copyright
Copyright © Cambridge University Press 1993

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Alonso, R. N., Jordan, T. E., Tabbutt, K. T. & Van-dervoot, D. S. 1991. Giant evaporite belts of the Neogene Central Andes. Geology 19, 401–4.2.3.CO;2>CrossRefGoogle Scholar
Bathurst, R. G. C. 1975. Carbonate Sediments and their Diagenesis. 658 pp. Amsterdam: Elsevier.Google Scholar
Chong, G. 1988. The Cenozoic saline deposits of the Chilean Andes between 18°00 and 27°00 South. In The Southern Central Andes (eds Bahlburg, H., Breitkreuz, Ch. and Giese, P.), pp. 135–51. Berlin: Springer-Verlag.Google Scholar
Christ, C. L., Truesdell, A. H. & Erd, R. C. 1967. Borate mineral assemblages in the system Na2O-CaO-MgO-B2O3-H20. Geochimica et Cosmochimica Acta 31, 313–37.CrossRefGoogle Scholar
Coton, F. A., Wilkinson, G. & Gaus, P. L. 1986. Basic Inorganic Chemistry, 2nd ed. J. Wiley & Sons. 708 pp.Google Scholar
Ericksen, G. E. 1963. Geology of the salt deposits and the salt industryof northern Chile. U.S. Geological Survey open file report, 164 pp.CrossRefGoogle Scholar
Ericksen, G. E. 1981. Geology and origin of the Chilean nitrate deposits. U.S. Geological Survey professional Paper No. 1188. 37 pp.CrossRefGoogle Scholar
Ericksen, G. E. 1986. Meditations on the origin of the Chilean nitrate deposits. U.S. Geological Survey Open-File Report 86–361, 27 pp.Google Scholar
Ericksen, G. E. & Mrose, M. E. 1970. Mineralogical studies of the nitrate deposits of Chile. II. Darapskite. American Mineralogist 55, 1500–17.Google Scholar
Ericksen, G. E., Mrose, M. E. & Marinenko, J. W. 1974. Mineralogical studies of the nitrate deposits of Chile. IV. Bruggerite Ca(I03)2 H2O. United States Geological Survey, Journal of Research 2, 471–8.Google Scholar
Ericksen, G. E., Mrose, M. E., Marinenko, J. W. & McGee, J. J. 1986. Mineralogical studies of the nitrate deposits of Chile. V. Iquiqueite Na4K3Mg(CrO4)B24 O39(OH). 12H2O. American Mineralogist 71, 830–6.Google Scholar
Eriksson, E. 1985. Principles and Applications of Hydro-chemistry. London: Chapman and Hall. 187 pp.Google Scholar
Esteban, M. & Klappa, C. F. 1983. Subaerial exposure. In Carbonate Depositional Environments (eds Scholle, P. A., Bebout, D. G. and Moore, C. H.), pp. 1–55. American Association of Petroleum Geologists Memoir no. 33.Google Scholar
Eugster, H. P. & Hardie, L. A. 1978. Saline lakes. In Lakes Chemistry, Geology and Physics (ed Lerman, A.), pp. 237–93. New York: Springer-Verlag.Google Scholar
Eugster, H. P. & Jones, B. F. 1979. Behavior of major solutes during closed-basin brine evolution. American Journal of Science 279, 609–31.Google Scholar
Eugster, H. P., Harvie, C. E. & Weare, J. H. 1980. Mineral equilibrium in a six-component seawater system Na-KMg-Ca-SO4-Cl-H2O at 25 °C. Geochimica et Cosmochimica Acta 44, 135–47.CrossRefGoogle Scholar
Harker, A. 1932. Metamorphism: A Study of the Transformation of Rock Masses. London: Chapman & Hall, 362 pp.Google Scholar
Harvie, C. E. & Weare, J. H. 1980. The prediction of mineral solubilities in natural waters: the Na-K-Mg-Ca-SO4-Cl-H2O system from zero to high concentrations at 25 °C. Geochimica et Cosmochimica Acta 44, 981–97.CrossRefGoogle Scholar
Hawxhurst, R. 1926. Genesis of the Chilean nitrate (discussion). Engineering and Mining Journal 122, 182–3.Google Scholar
Keys, J. R. & Williams, K. 1981. Origin of crystalline, cold desert salts in the McMurdo region, Antarctica. Geochimica et Cosmochimica Acta 45, 2299–309.Google Scholar
Krauskopf, K. B. 1979. An introduction to Geochemistry, 2nd ed. New York: McGraw-Hill. 617 pp.Google Scholar
Mrose, M. E., Fahey, J. F. & Ericksen, G. E. 1970. Mineralogical studies of the nitrate deposits of Chile III. Humberstonite K3Na7Mg2(SO4)6(NO3)2 6H2O, a new saline mineral. American Mineralogist 55, 1518–33.Google Scholar
Pettijohn, P. J. 1975. Sedimentary Rocks, 3rd ed. New York: Harper & Row. 628 pp.Google Scholar
Risacher, F. & Fritz, B. 1991. Geochemistry of Bolivian salars, Lipez, southern Altiplano: Origin of solutes and brine evolution. Geochimica etCosmochimica Acta 55, 687–705.CrossRefGoogle Scholar
Sonnenfeld, P. 1984. Brines and Evaporites. Orlando: Academic Press. 613 pp.Google Scholar
Spencer, R. J., Moller, N. & Wears, J. H. 1990. The prediction of mineral solubilities in natural waters: A chemical equilibrium model for the Na-K-Ca-Mg-Cl-SO4-H2O system at temperatures below 25 °C. Geochimica et Cosmochimica Acta 54, 575–90.CrossRefGoogle Scholar
Stewart, F. H. 1949. The petrology of the evaporites of the Eksdale No. boring, East Yorkshire; part 1. The lower evaporite bed. Mineralogical Magazine 28, 621–75.Google Scholar
Stewart, F. H. 1956. Replacements involving early carnallite in the potassium-bearing evaporites of Yorkshire. Mineralogical Magazine 31, 127–35.Google Scholar
Stewart, F. H. 1965. Mineralogy of the British Permian Evaporites. Mineralogical Magazine 34, 460–70.Google Scholar
Winchell, A. N. 1933. Elements of Optical Mineralogy: Part II. New York: John Wiley & Sons. 459 pp.Google Scholar
Wright, V. P. 1982. Calcrete paleosols from the Lower Carboniferous Llanelly Formation, South Wales. Sedimentary Geology 33, 1–33.Google Scholar