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A new massive deposit of allophane raw material in Ecuador

Published online by Cambridge University Press:  01 January 2024

Stephan Kaufhold ,
Annette Kaufhold ,
Reinhold Jahn ,
Salomón Brito ,
Reiner Dohrmann ,
Rainer Hoffmann ,
Hartmut Gliemann ,
Peter Weidler  and
Manfred Frechen
Stephan Kaufhold*
Affiliation:
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany
Annette Kaufhold
Affiliation:
Martin-Luther-University Halle-Wittenberg, Institute for Soil Sciences and Plant Nutrition, Weidenplan 14, D-06108 Halle, Germany
Reinhold Jahn
Affiliation:
Martin-Luther-University Halle-Wittenberg, Institute for Soil Sciences and Plant Nutrition, Weidenplan 14, D-06108 Halle, Germany
Salomón Brito
Affiliation:
SGN, Servicio Geológico Nacional, Juan León Mera y Orellana (esquina), Quito, Ecuador
Reiner Dohrmann
Affiliation:
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany LBEG, Landesamt für Bergbau, Energie und Geologie, Stilleweg 2, D-30655 Hannover, Germany
Rainer Hoffmann
Affiliation:
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany
Hartmut Gliemann
Affiliation:
ITC-WGT, Abteilung Nanomineralogie, Forschungszentrum Karlsruhe, Forschungszentrum Karlsruhe GmbH, Herman-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
Peter Weidler
Affiliation:
ITC-WGT, Abteilung Nanomineralogie, Forschungszentrum Karlsruhe, Forschungszentrum Karlsruhe GmbH, Herman-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
Manfred Frechen
Affiliation:
GGA, Institut für Geowissenschaftliche Gemeinschaftsaufgaben, Stilleweg 2, D-30655 Hannover, Germany
*
* E-mail address of corresponding author: [email protected]
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Abstract

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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 km2. 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 (14C) 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 N2-BET specific surface area of >300 m2/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.

Keywords

AFMAllophaneEcuadorNanoparticleSpecial Clay
Type
Article
Information
Clays and Clay Minerals , Volume 57 , Issue 1 , February 2009 , pp. 72 - 81
Copyright
Copyright © The Clay Minerals Society 2009

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