Kaolin deposits from the northern sector of the Cunene anorthosite complex (southern Angola)

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doi: 10.1346/CCMN.2005.0530613
Authors:Saviano, Giovanna; Violo, Maurizio; Pieruccini, Umberto; da Silva, Emidio Tertulliano Lopes
Author Affiliations:Primary:
Universita di Roma "La Sapienza", Dipartimento Ingegneria Chimica dei Materiali, Rome, Italy
Universita di Siena, Italy
"A. Neto" University, Italy
Volume Title:Clays and Clay Minerals
Source:Clays and Clay Minerals, 53(6), p.674-685. Publisher: Clay Minerals Society, Clarkson, NY, United States. ISSN: 0009-8604
Publication Date:2005
Note:In English. 61 refs.; illus., incl. 4 tables
Summary:The Mevaiela kaolin deposits are located in the northern part of the anorthositic-gabbro massif within the Cunene complex (southern Angola) and were formed by the alteration of basic anorthosites and gabbros. The Mevaiela area is part of an elevated region which is located between two extensive NNW-SSE fracture systems. Several kaolinite samples were collected from a quarry (main excavation) and from drill-holes as well as from surficial occurrences in the Cunene complex. Chemical analyses, X-ray diffraction, differential thermal analysis, scanning electron microscopy and isotope analyses were performed in order to model the kaolinite occurrences. The alteration of the anorthosite to kaolin approaching the main excavation is characterized by significant decrease in alkaline-earth and transition metals (Ca, Mg, Fe, Co, Ni and Mn) between the average anorthosite and the kaolin. The crystallinity indices suggest that the kaolin contains kaolinite with a reasonably well ordered structure and near the transition between T (triclinic) and pM (pseudo monoclinic). Mineral exploration tools have been evaluated during this study to assist in future kaolin exploration in the Cunene anorthosite complex. Isotopic analysis of O and D indicates that Ca-feldspar alteration is essentially due to meteoric fluids, over a different range of temperatures. Furthermore, the presence of quartz-feldspar veinlets in the kaolinite bodies could be the result of hydrothermal activity linked to post-anorthosite granite intrusions of the so-called "red granite". Kaolinite from Cunene plots on or close to the kaolinite line into the "warm temperature in tropical region" area (surficial samples). Samples from drill-holes plot on the left and show the largest displacement from the KS line; these samples also have a relatively reduced δD range of values (-65 to -98 per mil). However, if supergene processes take place in the presence of waters of meteoric origin at temperatures similar to typical surface temperatures, the clays thus formed should plot either in the vicinity of the KS line or be displaced towards lower δO18 and higher δD, depending on both the temperature and relative proportion of clay to water.
Sections:Clay minerals
Subsections:Petrology; weathering; soils
Subjects:Anorthosite; Clay minerals; Complexes; Gabbros; Hydrothermal alteration; Igneous rocks; Kaolin deposits; Kaolinite; Metasomatism; Mineral deposits, genesis; Ore-forming fluids; Plutonic rocks; Sheet silicates; Silicates; Africa; Angola; Central Africa; Cunene Complex; Mevaiela Deposit; Southern Angola
Coordinates:S160000 S160000 E0140000 E0140000
Abstract Numbers:06M/597
Record ID:2006011146
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Clay Minerals Society, Reference includes data from GeoScienceWorld, Alexandria, VA, United States
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