Browsing by Author "Philander, Carlo"
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- ItemDistribution, mineralogy and provenance of heavy minerals in cainozoic sediments of the Namaqua Mines area, West Coast of South Africa(Stellenbosch : Stellenbosch University, 1999-12) Philander, Carlo; Rozendaal, Abraham ; Stellenbosch University. Faculty of Sciences. Dept. of Earth Sciences.ENGLISH ABSTRACT: In view of the recent developments in heavy mineral exploration, a sampling programme was initiated to determine the economic potential of heavy mineral occurrences in the Kleinzee mining area. The primary objectives were to record the concentration and mineralogy of the heavy mineral population and also to determine their provenance. The heavy mineral occurrences are hosted by high maturity Miocene fluvial sediments and unconsolidated Plio-Pleistocene marine sediments overlying basement rocks of the Mjd-Proterozoic Namaqua Metamorphic Complex and Pan-African Gariep Supergroup. The development of the fluvial palaeochannels is linked to a major regression during the Late Oligocene whereas the marine deposits are genetically related to wave-cut, raised marine terraces between 0 and 90m amsl Quartz, followed by feldspar are the dominant light minerals. The total heavy fraction (>2.9 g/cm3 density) averages 6.4%, but concentrations are extremely variable and ranges from a few per cent in the fluvial sediments to as much as 60 per cent in particular marine successions. The mechanism anticipated for these anomalous accumulations is believed to be a powerful wave-regime with favourable burial conditions considered essential in preserving the mineralisation. Heavy mineral suites are diverse and consist of various proportions of ilmenite and its related alteration products, hematite, magnetite, rutile, zircon, garnet, amphibole, pyroxene, epidote, aluminosilicates, titanite, monazite, staurolite, collophane and glauconite. The economically valuable minerals, ilmenite, rutile and zircon constitute a very large portion of the total heavy mineral suite, often an order of magnitude greater than the gangue. Generally the total heavy mineral suite in the Kleinzee area is dominated by ilmenite (50-73 wt%), with zircon (6-12 wt%) and rutile (1 %) constituting the remainder of the economic fraction. The titanium-bearing minerals comprise in addition to pure ilmenite, a complex suite of Fe-Ti oxides often intimately intergrown. Single grain analyses indicate that ilmenites contain on average 51% Ti02 with only trace amounts of impurities. Only a small proportion (-8%) of the ilmenite fraction is altered and in most cases alteration was insufficient to enhance the titanium content of the ilmenite fraction. These results are remarkably consistent with previous studies conducted at other west coast localities, which indicates that climatic conditions during the Plio-Pleistocene were uniform along the entire west coast of South Africa. Zircon populations were found to be heterogeneous, displaying contrasting physical, geochemical, cathodoluminescent and radiometric properties. It is demonstrated that the heterogeneity of various zircon populations reflects the compositional maturity of their host sediments. As a result, zircon properties will allow conclusions about the evolutionary path of its host sediment. Similarly, zircon chemistry and radiometry can be useful to fingerprint and discriminate stratigraphic successions. Heavy mineral suites are qualitatively similar, _ indicating a uniform source area for the Kleinzee sediments. Heavy mineral assemblages indicate contributions from igneous and metamorphic as well as reworked sedimentary sources. Garnet, epidote, augite, hornblende, staurolite, titanite, rutile and aluminosilicates were demonstrated to be ultimately derived from metamorphic rocks. Other minerals such as the iron-titanium oxides, monazite and zircon were derived from igneous or metamorphic rocks. The striking similarity of mineral chemistry from Kleinzee sediments and lithologies from the NMC, unambiguously indicate the NMC as primary source terrain for the Kleinzee sediments. Mineralogical and textural evidence suggests that the majority of heavy minerals were eroded and transported from a nearby area, indicating a relative proximal source for the heavy minerals as -well as their host sediments. The present appraisal of the economic importance of heavy mineral occurrences in the study area indicates that it does not compare favourably with Quaternary megadeposits such as Richards Bay Minerals or Graauwduinen. The economic viability of the area is greatly impaired by the generally low heavy mineral content as well as the composition of the economic fraction which is dominated by less valuable ilmenite. Bulk chemistry as well as single grain analysis also indicate that the Ti02 content is low (<50%). However, a few target areas have been delineated which indicate limited economic potential and deserves a followup study in order to calculate their potential resources.
- ItemGeological setting and a geometallurgical evaluation of the Namakwa Sands heavy minerals deposit, West Coast of South Africa(Stellenbosch : Stellenbosch University, 2015-12) Philander, Carlo; Rozendaal, Abraham; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.ENGLISH ABSTRACT: The Namakwa Sands deposit, which is situated along the west coast of South Africa features world-class titanium and zircon resources with a challenging processing character. This study employs geometallurgical principles to define and quantify key mineralogical properties of the deposit that could affect throughput, recovery and quality. In addition to geotechnical investigations, a representative suite of ore and process samples were systematically studied with light microscopy, XRF, XRD, QEMSCAN, LA-ICP-MS and EMPA. The siliciclastic, arenaceous Namakwa Sands deposit developed during the Early Pliocene (~5 Ma ago) to the Late Pleistocene and the deposit stratigraphy assimilates well into the regional West Coast Group. The mineralisation is hosted by two adjacent ore bodies, which are strikingly different in various aspects. Graauwduinen West (GD West) consists of three strandline-dune couplets set in a transitional shallow marine-aeolian environment, whereas Graauwduinen East (GD East) comprises a dune deposit sans marine influence. Multiple, superimposed duricrust horizons effectively cemented the medium-grained ore bearing sands of both ore bodies. GD West is characterised by greater oversize (+1 mm fraction) and slimes (-45 μm fraction) percentages as well as poorer levels of mineral liberation and mineral surface exposure, unfavourable processing attributes that are all related to the duricrust. Mineralised trends are conspicuously distinct for the two ore bodies, i.e. southwest-northeast for GD West and southeast-northwest for GD East. The degree of mineralisation is significantly better for GD West than GD East, but heavy mineral assemblages from GD East are marked by higher proportions of the valuable minerals zircon, rutile, ilmenite and its alteration product leucoxene. Ilmenite (FeTiO₃) is the chief valuable mineral present and about 20% of the ilmenite population is affected by various stages of alteration. Optically, two coloured varieties of rutile (TiO₂), namely yellow and the more common red type are recognised. Their major element chemistry is similar, but red rutile contains greater levels of V and Cr, but lesser quantities of Fe and Nb than the yellow variety. About 72% of the zircon (ZrSiO₄) population are optically clear, and hosts lesser quantities of the penalty elements U, Th, REE and Fe than the coloured varieties. Statistical differences in the bulk geochemistry and mineralogy of the two ore bodies indicate contrasting sediment routing dynamics. Proximal source terranes utilising fluvial-marine courses supplied the required heavy minerals budget for GD West. By contrast, the source of GD East is considered to originate mainly via an interior, fluvial-aeolian corridor. Overall, however, quantitatively the medium to high-grade facies Namaqualand Metamorphic Province is considered the key contributor to the heavy mineral population of the Namakwa Sands deposit. The complexity of the ore characteristics observed, translates into a challenging and variable processing response. Only mineral grade, liberation, magnetic deportment, particle size and particle chemistry were established as meaningful mineral recovery drivers. The recovery of valuable minerals during primary concentration, which entails wet spiral separation, is mainly an inverse function of gangue grade. This study confirms that duricrust cementing agents are the key contributor to poor mineral liberation, which result in significant tailings losses during spiral separation. Variations in the magnetic susceptibility of the heavy mineral fraction, subtract significantly from mineral recoveries during wet magnetic secondary concentration. Particle chemistry becomes an important recovery driver during final mineral separation due to the sensitive trade-off between stringent product quality specifications and mineral recovery. Ilmenite recovery for instance is mainly controlled by the intricate deportment of SiO₂, a key product quality penalty that is intimately locked with the ilmenite host as surface coatings and silicate inclusions. Similarly, the deportment of the penalty elements Fe, Ti, U and Th, which reach high concentrations in coloured zircon varieties, are complex and present major constraints to the recovery of the current zircon population. The total recovery potential is better for zircon than for the titanium minerals, which is consistent with actual mineral recovery trends. Overall, the mineral liberation and the abundance of gangue minerals, particularly garnet and pyroxene, represent the most detrimental constraints to the recovery of the valuable mineral fraction. The mineral recovery potential is markedly different for the two ore bodies. GD East demonstrates a better mineral recovery potential compared to GD West. Particle chemistry and magnetic susceptibility are the key penalties that constrain ilmenite recovery for GD East ore, whereas zircon recovery is mostly impacted by particle chemistry. Mineral liberation, particle chemistry and gangue grades are the key penalties that limit mineral recovery for GD West ore. The gains in mineral resource intelligence materialised into a tangible improvement in mineral resource utilisation over the duration of the study. Enticing opportunities to further improve mineral resource utilisation revolves around creating a better fit between ore characteristics and related metallurgical behaviour, processing technology and market requirements.