Bauxite formation on Tertiary sediments and Proterozoic bedrock in Suriname Bauxietvorming op Tertiaire sedimenten en Proterozoïsche gesteenten in Suriname (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof. dr. G.J. van der Zwaan, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op woensdag 24 januari 2018 des middags te 2.30 uur door Dewany Alice Monsels Geboren op 27 mei 1979 te Paramaribo, Suriname 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 1 Promotoren: Prof. dr. M.J.R. Wortel Prof. dr. Th.E. Wong Copromotor: Dr. M.J. van Bergen This thesis was accomplished with financial support from the Suriname Environmental and Mining Foundation (SEMIF). 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 2 Utrecht Studies in Earth Sciences 147 Bauxite formation on Tertiary sediments and Proterozoic bedrock in Suriname Dewany A. Monsels Utrecht 2018 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 3 Thesis assessment committee: Prof. dr. P.L. de Boer Faculteit Geowetenschappen Universiteit Utrecht Utrecht, Nederland Prof. dr. S.B. Kroonenberg Faculteit der Technologische Wetenschappen, Studierichting Delfstofproductie Anton de Kom Universiteit van Suriname Paramaribo, Suriname Prof. dr. M. Lima da Costa Instituto de Geosciências Universidade Federal do Pará Belém, Brasil Prof. dr. P.R.D. Mason Faculteit Geowetenschappen Universiteit Utrecht Utrecht, Nederland Dr. H. Théveniaut Bureau de Recherches Géologiques et Minières Orléans, France ISBN: 978-90-6266-495-5 Copyright © 2018 Dewany Alice Monsels Utrecht Studies in Earth Sciences: 147 All rights reserved. No part of this publication may be reproduced in any form, by print or photo print, microfilm or any other means, without the written permission of the author. Printed in the Netherlands by Ipskamp Printing, Enschede. 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 4 Table of Contents Chapter 1 Introduction 7 Chapter 2 Bauxite deposits in Suriname: Geological context and resource development 27 Chapter 3 Trace-element analysis of bauxite using laser ablation-inductively coupled 47 plasma-mass spectrometry on lithium borate glass beads Chapter 4 Bauxite formation on Proterozoic bedrock of Suriname 69 Chapter 5 Bauxite formation on Tertiary sediments in the coastal plain of Suriname 111 Chapter 6 Synopsis 165 Nederlandse samenvatting 171 Acknowledgements 175 About the Author 177 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 5 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 6 Chapter 1 Introduction 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 7 8 | Chapter 1 1.1 | Lateritic bauxites Bauxite is the world’s main economic source of aluminium, the second most abundant metallic element in the Earth’s crust after silicon. Bauxite was discovered in 1821 by the French scientist Pierre Berthier (Berthier, 1821) who originally named the material “beauxite” after a hill (“Colline des Beaux”) near the community of Les Baux in the Alpilles Mountains (Bouches du Rhône) in Southern France where it was found. In 1861 the term was recast into “bauxite” (Bárdossy, 1997). The ore belongs to the family of lateritic rocks that are products of strong weathering, accompanied by significant chemical and mineralogical modification occurring at or near the surface (Figure 1.1a). Hence, the following definition of laterites (Schellmann, 1983) also applies to bauxites: “Laterites are products of intense subaerial rock weathering. They consist predominantly of mineral assemblages of goethite, hematite, aluminium hydroxides, kaolinite minerals and quartz. The SiO2 : (Al2O3+Fe2O3) ratio of a laterite must be lower than that of the kaolinized parent rock in which all the alumina of the parent rock is present in the form of kaolinite, all the iron in the form of iron oxides, and which contains no more silica than fixed in the kaolinite plus the primary quartz. This definition includes all highly weathered materials, strongly depleted in silica and enriched in iron and alumina, regardless of their morphological and physical properties (fabric, colour, consistency, etc.)”. Throughout this thesis we will use “laterite” loosely as a geologic term for a rock that experienced intense subaerial weathering, consists predominantly of goethite, hematite, aluminium hydroxides, kaolinite and quartz, and has a SiO2/(Al2O3 + Fe2O3) ratio lower than that of the associated kaolinized parent rock. The term “bauxite” will be referred to using a combination of definitions (Bárdossy and Aleva, 1990; Aleva, 1994; Tardy, 1997): Bauxite is an Al-rich laterite characterized by a particular enrichment of free aluminium hydroxide minerals such as gibbsite, boehmite, diaspore and nordstrandite. It can form from many different parent rocks, which preferably have a high aluminium content and relatively low iron content. Bauxite is basically an economic term, as it is a raw material for the aluminium industry when its grade and other economic parameters allow profitable extraction. Different classification schemes for bauxites have been developed over the years, based on factors such as chemical and mineralogical composition, age, genetic history, shape and location (Valeton, 1972; Bárdossy and Aleva, 1990; Patterson et al., 1997; Tardy, 1997; Bogatrev et al., 2009). Three main genetic types can be distinguished when considering mineralogy, chemistry and host-rock lithology (Bárdossy and Aleva, 1990): 1. Lateritic bauxites — residual deposits derived from underlying alumosilicate rocks. 2. Karst-bauxites — deposits overlying karstified surfaces of carbonate rocks. 3. Tikhvin-type bauxites — detrital deposits of eroded lateritic bauxites. Bogatyrev et al. (2009) classified this type as “sedimentary bauxites”. 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 8 Introduction | 9 Approximately 88% of the global bauxite resources belong to the lateritic bauxites, 11.5% to the karst bauxites and approximately 0.5% to the Tikhvin-type deposits (Bárdossy and Aleva, 1990). 1 Figure 1.1 | (a) Ternary compositional diagram, illustrating the nomenclature of weathering products in humid tropical climates (modified after Valeton, 1972; Bárdossy and Aleva, 1990; Aleva, 1994); (b) Sketch of a typical bauxite-bearing laterite profile. A typical complete weathering profile of lateritic bauxite starts with a weathered parent rock at the bottom (saprolite, also known as kaolin), grades into an Al-accumulation horizon (bauxite) and is topped by a hard iron-rich cap (duricrust) and soil (Figure 1.1b). Sometimes horizons are absent in weathering profiles because of erosion of elevated areas in a landscape. Transition zones may separate horizons, but abrupt changes between bauxite and parent rock have also been described. The formation of lateritic bauxite requires a set of favourable conditions that include climate, time, hydrogeology, parent rock composition, geomorphology, petrophysics and biological factors (Aleva, 1984; Bárdossy and Aleva, 1990; Tardy, 1997; Bogatyrev et al., 2009 and references therein). Key requisites are: – Wet tropical and subtropical conditions with mean annual temperature above 20oC and rainfall above 1200 mm/yr, is the reason why many Cretaceous and Tertiary lateritic bauxite deposits in South America, Africa, India and Australia are found in (paleo-)coastal plains where humidity is usually higher than in continental interiors. – Parent rock with suitable composition (e.g., Al2O3-content ≥ 10%, SiO2-content is variable but preferably quartz-free) and sufficient porosity and permeability to allow fluids to percolate, leach out and transport dissolvable components. 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 9 10 | Chapter 1 Figure 1.2 | Relationship between bauxitization, climate conditions and sea-level changes during Phanerozoic times (modified after Bogatyrev et al., 2009). Figure 1.3 | Average Al2O3 -content and reserves of important lateritic bauxite deposits worldwide. Surinamese deposits are indicated by circular symbols and italic labels. See Table 1.1 for details and references.*= resource. 516008-L-bw-monsels Processed on: 21-12-2017 PDF page: 10 Introduction | 11 – Long-term tectonic stability with quiet vertical uplifts as the only disturbance, favouring the formation of an elevated fault-dissected landscape with well-drained flat areas such as plateaus or peneplains (planation surfaces), since mature bauxite deposits mainly develop when the chemical weathering rate is higher than the rate of mechanical erosion. Passive continental margins often fulfill this requirement. – Favourable pH and Eh gradients that allow fluid-rock interactions involving mineral dissolution and precipitation. Vegetation and metabolic products of micro-organisms may provide the acidity needed to accelerate the decomposition of aluminosilicate minerals (pH < 5), whereas new aluminium phases precipitate at pH 5.5–8.0. Likewise, the oxidation state of the system exerts a strong control on the (im-)mobility of Fe. 1 Certain periods in the Earth’s history were clearly more favourable for bauxitization than others, as is demonstrated by the strong link with climate conditions and regressions (Figure 1.2). A productive period was the Cretaceous–Eocene epoch when bauxite formed in Gondwana and Laurasia. 1.2 | Geomorphological setting of bauxite in the Guiana Shield region The Precambrian core of the Guiana Shield is surrounded and unconformably