A geometallurgical evaluation of the ores of the northern Kalahari manganese deposit, South Africa

D. Phil.The Kalahari Manganese Deposit (KMD) is the largest of five erosional relics of the Hotazel Formation that are located near Kuruman in the Northern Cape Province of South Africa. Manganese ores are exploited from the lowermost of three manganiferous beds that are interbedded with banded iron-formation (BIF) and hematite lutite, that together constitute the Hotazel Formation. Two major ore types have been delineated previously, viz. low grade braunite lutite of the Mamatwan-type, and high grade oxidic ores of the Wessels-type, with the latter spatially restricted to the northern KMD. Genesis of the ores was temporally distinct, with the Mamatwan-type ore considered as a sedimentary-diagenetic precursor to the hydrothermally altered Wessels-type ore. Drill core samples from the Nchwaning-Gloria area of the northern KMD were analysed, with the aim to better characterise ore genesis, with emphasis on ore alteration. A second part of the study aimed at the application of mineralogical and geochemical information to aspects of ore smelting for the production of Mn alloy for use in the steel industry. Methods employed were drill core logging, X-ray diffraction (XRD), petrography, electron probe microanalysis (EPMA), major and trace element (including REE) analysis (employing artificial neural networks for evaluation of elemental trends), and stable isotope (C and O) analysis. Significant effort was invested in method development for quantitative mineralogical modal analysis using Rietveld refinement of XRD data. The study shows that a number of ore types can be differentiated in the northern KMD on the basis of mineral assemblage, grade, texture and geochemical characteristics. The ores are broadly classified into least altered (LA), partially altered (PA) and advanced altered (AA) types. The LA ores are low grade (45 wt%Mn), are recorded. Trace elements of significance include Zn, associated with hausmannite, B, associated with massive braunite and a number of trace minerals, and P, typically present in trace quantities of apatite. In terms of ore genesis, mineralogical, geochemical and geological considerations suggest that Mn (and Fe) originated from submarine hydrothermal vents, from which it travelled in hydrothermal plumes, prior to rapid deposition ~2.2 Ga ago. Diagenesis followed soon after deposition, through redox reactions involving organic matter and higher oxides of Mn to produce the braunite-carbonate assemblage primarily observed in LA ores. The carbonate:oxide ratio and nature of the carbonates varied slightly depending on fluctuations in organic matter flux to the sediment, as well as marine bicarbonate concentrations. Metamorphism, in relation to diagenesis and metasomatism, is poorly understood, but is perceived to have resulted in serpentine formation, as observed in LA and PA ores

Geochemical fingerprinting of carbonate wall rock alteration at major base metal sulphide deposits in the Otavi Mountain Land, Namibia

Bibliography: leaves 134-147.The Otavi Mountain Land is a base metal ore province in which base metal sulphide deposits are hosted by platform carbonates in a foreland fold-and-thrust belt on the northern edge of the PanAfrican Damara Belt. Deposits have been classified as the Berg Aukas- and Tsumeb- types, based on differences in ore association, stratigraphic position and geochemistry of ores and gangue carbonates. Mineralisation at each of these deposits is accompanied by carbonate alteration in the form of dolomite and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Optical cathodoluminescence imaging, electron probe micro analysis, X-ray fluorescence spectrometry, X-ray diffraction, high performance ion chromatography, proton probe micro analysis, stable isotope techniques, and fluid inclusion microthermometry were employed (i) to differentiate between carbonate generations associated with the alteration and mineralisation, particularly for the more economic Tsumeb-type deposits, represented by Tsumeb and Kombat, as well as in comparing between Berg Aukas- and Tsumeb-type deposits; (ii) to set constraints on the fluids effecting such alteration and associated mineralisation; (iii) to determine the relationship of the Khasib Springs deposit, for which little geochemical data exists, to deposits of the Tsumeb-type, and (iv) to identify those parameters which are diagnostic of Tsumeb-type mineralisation

Acid-Gangue Interactions in Heap Leach Operations: A Review of the Role of Mineralogy for Predicting Ore Behaviour

Heap leaching accounts for a fifth of global copper production, sourced primarily from porphyry ores, yet metal recoveries are often not optimal. Gangue, and its interaction with acid, plays an important role in such processes. Thus, a proper understanding of gangue minerals present in the ore, their textural relationships relative to particle size distribution, reactivity with acid under different conditions, and relationship to lithotypes and geological alteration in the orebody, is necessary to predict ore behaviour in the comminution, agglomeration, curing and heap leach unit operations. Mineralogical tools available for characterisation are routine X-ray diffraction, optical microscopy, automated scanning electron microscopy, and electron probe microanalysis, accompanied by more recent advancements in hyperspectral infrared imaging and X-ray computed tomography. Integrated use of these techniques allows mineral abundance, textural relationships and mineral chemistry to be addressed over the range of particle and agglomerate sizes. Additionally, diagnostic leach results can be better interpreted when calibrated against robust mineralogical data. The linkage of ore attributes, metallurgical behaviour and their distribution in the orebody forms an integral part of a geometallurgical approach to predicting, and addressing, changes during the heap leaching process. Further investigation should address the fundamentals of gangue reaction with strong acid, and concomitant structural breakdown during curing and agglomeration processes, and how this differs from gangue-acid reactivity under weaker acid conditions, combined with temperature and fluid flow effects of heap leaching. Pre-and post- characterisation is necessary to understand and quantify the effects of variables for gangue-acid reactivity in these various operations. The characterisation outcomes should lead to a refinement of the hierarchy of gangue mineral reactivity under different conditions of comminution and leaching, and how these in turn relate to identified ore types that are mined

Mineralogical Factors Affecting the Dense Medium Separation of Nickel Sulfide Ores

Dense medium separation (DMS) is often used to reject a large portion of gangue material upfront to create cost and energy savings during processing. As lower-grade ores with complex mineralogy are being increasingly exploited, the properties of the gangue minerals begin to play a more important role in the upgrading of the ore. It is therefore important to understand these mineralogical factors to be able to select suitable processing routes for specific ore types. Two nickel sulfide deposits in southern Africa were chosen as case studies to understand differences in DMS efficiency when applied to different ores: Ore A and Ore B. Both ores showed nickel upgrades using DMS and the products were then characterized using QEMSCAN, with the aid of X-ray diffraction and electron probe microanalysis. Overall, particle density remains the main control on the separation, followed by sulfide texture, with massive and net-textured sulfides having larger grain sizes and therefore better liberation than disseminated sulfides. In addition to the concentration of sulfides, primary and secondary silicate minerals are separated by their density differences, which can affect the recovery of finely disseminated sulfides associated with them. Particle size is also important in DMS, with material near the cut-point density separating on size rather than density. The understanding of the mineralogical properties affecting DMS can aid in the prediction of the suitability of DMS for different ore types

Mineralogical Factors Affecting the Dense Medium Separation of Nickel Sulfide Ores

Dense medium separation (DMS) is often used to reject a large portion of gangue material upfront to create cost and energy savings during processing. As lower-grade ores with complex mineralogy are being increasingly exploited, the properties of the gangue minerals begin to play a more important role in the upgrading of the ore. It is therefore important to understand these mineralogical factors to be able to select suitable processing routes for specific ore types. Two nickel sulfide deposits in southern Africa were chosen as case studies to understand differences in DMS efficiency when applied to different ores: Ore A and Ore B. Both ores showed nickel upgrades using DMS and the products were then characterized using QEMSCAN, with the aid of X-ray diffraction and electron probe microanalysis. Overall, particle density remains the main control on the separation, followed by sulfide texture, with massive and net-textured sulfides having larger grain sizes and therefore better liberation than disseminated sulfides. In addition to the concentration of sulfides, primary and secondary silicate minerals are separated by their density differences, which can affect the recovery of finely disseminated sulfides associated with them. Particle size is also important in DMS, with material near the cut-point density separating on size rather than density. The understanding of the mineralogical properties affecting DMS can aid in the prediction of the suitability of DMS for different ore types

THE USE OF 3D X-RAY COMPUTED TOMOGRAPHY FOR GOLD LOCATION IN EXPLORATION DRILL CORES

Abstract Three-dimensional computed tomography (3DCT) is a non-destructive characterisation technique that was applied to the study of gold-bearing ore from the Witwatersrand Deposit, South Africa. The ability to pinpoint gold occurrence prior to downstream comminution and leaching would potentially reduce processing costs. The aim of the study was therefore to determine to what extent gold, typically fine-grained in occurrence, could be identified in situ. Two gold-bearing drill core pieces were investigated using 1-mm focal spot X-ray tomography and micro-focus X-ray tomography (µXCT). Using the derived data, the cores were physically cut and polished for examination by conventional automated scanning electron microscopy (SEM) to detect gold grains. The SEM results were then compared against the µXCT data. Gold was, to an extent, located by µXCT and validated against SEM data. These first findings suggest that areas rich in gold can be pinpointed by 3DCT prior to conventional assessment, hence potentially reducing processing costs. Keywords: 3D computed tomography, micro-focus X-ray tomography, gold INTRODUCTION The use of 3D computed tomography (3DCT) is well known in the medical industry, where CATScan (computed axial tomography) technology is routinely used. Some other applications for 3DCT may be found in the fields of anatomy, palaeontology, archaeology and automated manufacturing. The technique has only recently gained more attention in the field of minerals processing, however. With the exception of a steady stream of publications from the University of Utah [1], the literature is otherwise sparse in contributions on 3DCT applied to minerals processing. Since 3DCT is a non-destructive method, it shows potential benefits in reduced sample preparation costs, analytical time and data quality compared with conventional 2D microscopy (e.g., optical and SEM-based techniques). The method uses, usually, X-rays that penetrate a sample. In the interaction with the components of the sample the radiation changes its nature -a shift in the energy spectrum due to absorption and scattering interactions with the components in the sample. This change is referred to as attenuation. Less commonly, neutrons and γ-rays may be also used to pass through the sample, and are thus also attenuated by the components through which they pass. The detected attenuated signals (commonly referred to as radiographs) are then processed and related to the components in the sample, thus allowing identification. Cone beam * Correspondence to: [email protected]