Kaolinization of Bauxite: A Study in the Vlasenica Bauxite Area, Yugoslavia. I. Alteration of Matrix1

Adam Dangić
Faculty of Mining and Geology, University of Belgrade Djušina 7, 11000 Belgrade, Yugoslavia
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.”

Abstract: 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 kaolinization 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.

Key Words: Aluminum • Bauxite • Boehmite • Kaolinite • Resilification • Silica

Clays and Clay Minerals; December 1985 v. 33; no. 6; p. 517-524; DOI: 10.1346/CCMN.1985.0330606
© 1985, The Clay Minerals Society
Clay Minerals Society (www.clays.org)