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Mineralogy, Geochemistry, and Origin of the Underclays of the Central Coal Basin, Asturias, Spain

Published online by Cambridge University Press:  02 April 2024

Olga Elvira Alonso  and
Covadonga Brime
Olga Elvira Alonso
Affiliation:
Departemente de Geología, Universidad de Oviedo, Arias de Velasco s/n, 33005 Oviedo, Spain
Covadonga Brime
Affiliation:
Departemente de Geología, Universidad de Oviedo, Arias de Velasco s/n, 33005 Oviedo, Spain
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Abstract

Samples of underclays corresponding to nine different coal beds of the María Luisa coal seam in the Aller valley (Asturias, Spain) were collected to determine whether their mineralogy and geochemistry could be used for correlation. The underclays are dominated by illite, with an average abundance of 46%, and contain smaller amounts of chlorite, kaolinite (chlorite always more abundant), paragonite, pyrophyllite, mixed-layer illite/smectite (I/S), and mixed-layer muscovite/paragonite. This mineralogical association along with the illite “crystallinity” values (mean values of “crystallinity” in air-dried and ethylene glycol-solvated illite are 0.48° and 0.35°2θ, respectively) suggest that the samples have undergone very low-grade metamorphism. No consistent variation in the mineral components with increasing depth below the coal was noted. The presence of chlorite and K-feldspar precludes the development of the underclays by extensive leaching by acid swamp waters and thereby suggests that their mineral composition was determined largely by provenance.

Thirty-seven mineralogical and geochemical variables were treated by stepwise discriminant analysis. The variables that best served as discriminators between the underclays were: illite + I/S contents of both the whole rock and clay fraction, illite “crystallinity” of the clay fraction in both air-dried and glycolated patterns, pH of the samples, and the elements (in order of atomic number) Na, Al, K, Ca, Ti, V, Sr, Zr, Nb, Ba. The Molino underclay is clearly distinct from the other eight underclays, suggesting its potential use in regional correlation.

Keywords

ChloriteDiagenesisIlliteIllite/smectiteParagonitePyrophylliteUnderclay
Type
Research Article
Information
Clays and Clay Minerals , Volume 38 , Issue 3 , June 1990 , pp. 265 - 276
Copyright
Copyright © 1990, The Clay Minerals Society

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