A new massive deposit of allophane raw material in Ecuador
Kaufhold, Stephan (BGR Bundesanstalt für Geowissenschaften un Rohstoffe)
Kaufhold, Annette (Martin-Luther-University Halle-Wittenberg. Institute for Soil Sciences and Plant Nutrition)
Jahn, Reinhold (Martin-Luther-University Halle-Wittenberg. Institute for Soil Sciences and Plant Nutrition)
Brito, Salomón (SGN Servicio Geológico Nacional)
Dohrmann, Reiner (LBEG Landesamt für Bergbau Energie und Geologie)
Hoffmann, Reiner (BGR Bundesanstalt für Geowissenschaften un Rohstoffe)
Gliemann, Hartmut. (ITC-WGT. Abteilung Nanomineralogie. Forschungszentrum Karlsruhe)
Weidler, Peter (ITC-WGT. Abteilung Nanomineralogie. Forschungszentrum Karlsruhe)
Frechen, Manfred (GGA. Institut für Geowissenschaftliche Gemeinschaftsaufgaben)

Data:	2009
Resum:	In Ecuador, DINAGE (known today as the Servicio Geológico Nacional) and the German Federal Institute for Geosciences and Natural Resources have discovered a huge allophane deposit covering an area of >4000 km. This study presents the results from an investigation of a 16-m thick vertical sequence from this deposit, supposedly the weathering product of two different volcanic ash deposits. In particular, the distribution of alkali metals within the uppermost layer indicates that the weathering process is still ongoing. According to the mineralogical composition, an allophane-rich layer (allophane facies) could be distinguished from the underlying halloysite-rich layer (halloysite facies). A 2-m thick transition zone is characterized by the presence of gibbsite and intermediate specific surface area values. Only a few imogolite fibers could be identified (by scanning electron microscopy), indicating the dominance of allophane over imogolite in the allophane facies. Single allophane particles were investigated by atomic force microscopy, though this method was less accurate than transmission electron microscopy with respect to the determination of the primary particle diameter. Carbon isotope analysis (C) suggested an age of ∼20,000 y for the allophane layer. Within the allophane facies, a 4-m thick layer occurs containing 70-80 wt. % allophane with an N-BET specific surface area of >300 m/g. Based on infrared and energy-dispersive X-ray diffraction measurements, an Al/Si ratio of 1. 3-1. 4 was established for this allophane, which is between Al-rich and Si-rich allophane. The allophane layer may be of economic value due to the large allophane content, the small amount of organic matter, and the significant thickness of the deposit.
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Publicat a:	Clays and Clay Minerals, Vol. 57, Núm. 1 (2009) , p. 72-81, ISSN 1552-8367

DOI: 10.1346/CCMN.2009.0570107

10 p, 1.8 MB  Accés restringit a la UAB

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