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Kaolinization of Bauxite: A Study in the Vlasenica Bauxite Area, Yugoslavia. I. Alteration of Matrix

Published online by Cambridge University Press:  02 April 2024

Adam Dangić
Adam Dangić*
Affiliation:
Faculty of Mining and Geology, University of Belgrade, Djušina 7, 11000 Belgrade, Yugoslavia
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Abstract

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The kaolinization of bauxite has generally been thought to be a simple process of epigenetic resilification. A study of the karstic boehmitic bauxites in the Vlasenica region of Yugoslavia, however, shows that kaohnization took place in a rather complex manner, in which the alteration was caused by the percolation of siliceous water descending through the deposit by means of cracks, fissures, etc. The matrix of one such Vlasenica deposit was found to be more highly kaolinized than the oolitic fraction. Based on a mineralogical and geochemical examination of matrix material, the following pattern of zoned alteration was identified: kaolinitic zone-boehmite enrichment zone-original bauxite. In the kaolinitic zone, well-crystallized kaolinite, formed by the reaction of dissolved silica with boehmite, has replaced all other minerals in the matrix. This Si metasomatism was accompanied by an outward migration of Al and resulted in the formation of a transition zone in which new boehmite partly replaces both kaolinite and hematite (Al remobilization). A thermodynamic model of the process has been established on the basis of stability diagrams calculated for the mineral assemblages in the alteration zones and in the deposit as a whole.

Rezime

Rezime

Opšteprihvaćeno je shvatanje da je kaolinizacija boksita jednostavan proces epigenetske resilifikacije. Proučavanja karsnih bemitskih boksita u regionu Vlasenice u Jugoslaviji pokazala su, medjutim, da kaolinizacija predstavlja deo složenijeg procesa alteracije koji nastaje pri perkolaciji voda obogaćenih rastvorenom silicijom kroz pukotine, rasedne zone i sl. u ležištima boksita. Detaljna proučavanja u jednom takvom ležištu u ovom regionu pokazala su da je osnova boksita mnogo jaće kaolinisana nego ooliti. Na osnovu mineraloškog i geohemijskog proućavanja osnove boksita identifikovan je sledeći tip zonarne alteracije: kaolinitska zona-bemitska zona-originalni boksit. U kaolinitskoj zoni dobro iskristalisali kaolinit, obrazovan kroz reakciju silicije iz rastvora sa bemitom, potisnuo je sve minerale u osnovi. Ova Si-metasomatoza je bila udružena sa migracijom Al dublje u boksit, što je dovelo do obrazovanja prelazne zone, u kojoj je neo-bemit delom potisnuo hematit i kaolinit (Al-remobilizacija). Proraćunati su i razmotreni dijagrami stabilnosti mineralnih asocijacija u zonama alteracije i u samon ležisštu, a na osnovu toga postavljen je i termodinamićki model procesa.

Keywords

AluminumBauxiteBoehmiteKaoliniteResilificationSilica
Type
Research Article
Information
Clays and Clay Minerals , Volume 33 , Issue 6 , December 1985 , pp. 517 - 524
Copyright
Copyright © 1985, The Clay Minerals Society

Footnotes

1

Presented at the 5th ICSOBA Congress in Zagreb, Yugoslavia, September 1983, under the title “Kaolinization of Bauxite—a Study in the Vlasenica Bauxite-bearing Area, Yugoslavia.”

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