In the Middelplaats mine area of the Kalahari manganese field, two drill holes (MP53 and MP54) intersected anomalously high-grade manganese ore sitting stratigraphically just above an igneous body (likely a dike or sill). Manganese ore located within approximate 5 meters of the contact with the underlying igneous rocks has been substantially metasomatically upgraded from 25 percent manganese, to over 40 percent whilst the dominant manganese species within the ore has been altered to hausmannite. This report demonstrates the metasomatic alteration is related to devolatilization (removal and/or remobilization of H₂O, CO₂ and CaO) due to contact metamorphism caused by the underlying igneous rocks. The Middelplaats mine is situated in the southwest corner of the Kalahari manganese field where the paleo basin shallows out and ends. Within the mine area, several stratigraphic units pinch out or are truncated by the side of the basin. This pinching out of lithological formations has led to the underlying Ongeluk Formation being in contact with the much younger units of the Hotazel Formation. Therefore, geochemical investigation into the nature and source of the igneous rocks was also undertaken to see if the rocks from the two drill holes were related to one another and/or the underlying Ongeluk Formation. Results of these geochemical studies have demonstrated that the Middelplaats igneous rocks (dolerites) from the two drill holes (MP53 and MP54) share a co-genetic source region. There is also reasonable geochemical evidence that the source region of the Middelplaats igneous rocks was substantially similar to the source region of the Ongeluk Formation. This may indicate that the source region of the Ongeluk Formation was reactivated at some later stage resulting in the emplacement of doleritic dikes or sills in the Middelplaats mine area. The Middelplaats igneous rocks were also found to have undergone a slight but pervasive potassic alteration; with most of the original plagioclase feldspar showing some level of replacement by a potassium enriched feldspar. Although no source for this potassic fluid was found, the devolatilization reaction within the manganese ore appears to have released some potassium into the surrounding rocks. This additional potassium may be responsible for some localized potassic alteration.

MENVSC / Department of Mining and Environmental Gelogy / In the present study, the physico-chemical, applications, mineralogy, geochemistry and stable isotope of Lwamondo and Zebediela kaolin is documented, in order to understand the genesis, paleoenvironmental conditions and possible utilization. Mineral identification studies were conducted using X-ray diffractometer (XRD), Fourier transform infrared spectrophotometer (FTIR) and scanning electron microscope with energy dispersive X-ray micro analysis (SEM-EDX). Major oxides were identified by X-ray Florescence (XRF) whereas trace elements were identified by Laser Ablation Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Hydrogen and oxygen isotopic composition were determined by δ18O and δD isotopic measurements. Kaolinite was dominant mineral in all the kaolin samples whereas muscovite, quartz, goethite, hematite, smectite, anatase occurred in minor to trace quantities. The chemical data show that the kaolins are composed mainly of SiO2 and Al2O3 due to the presence of quartz and kaolinite, with minor to trace amounts of other elements such as Ca, Na, Cr, K, Fe, Mn, Mg, P and Ti which affected the kaolin application negatively. Lower concentration of Ca, Na, K, Fe, Mn, Mg, and Ti show the extent of the kaolinitisation. The samples were enriched in Ni and depleted in some other trace elements. The chondrite-normalised rare earth elements patterns show enrichmnent in Heavy Rare Earth Elements (HREE) than Light Rare Earth Elements (LREE) with slight positive Eu anomaly. The Rare Earth Elements (REE) pattern and the content of other trace elements show evidence of weathering processes related to kaolinitisatioon. Kaolin genesis is explained using kaolin mineralogy, particle morphology, structural order (functional group), major and trace elements geochemical data. The data suggest that kaolin is derived from the intensive chemical weathering of intermediate to mafic rocks deposited in non-marine environment. The stable isotopes were used to determine the paleoenvironmental conditions which influenced kaolinitisation of Lwamondo and Zebediela kaolins. Stable isotopes mean values for kaolinite from both Lwamondo and Zebediela were as follows: δ18O for Lwamondo= +18.57‰ and for Zebediela = +16.67 ‰ vii and δD for Lwamondo = -65‰ and for Zebediela = -64‰. The calculated mean temperatures were 26.94 ⁰C for Lwamondo kaolin and 36 ⁰C for Zebediela kaolin. Low temperatures were inferred from stable isotope values to have been involved in the kaolinitisation wherein hydrothermal processes were eliminated. The data suggests that kaolin was formed in a weathering environment. The kaolin is found to be suitable for brick making and based on the physico-chemical, mineralogical and chemical data it was suggested that the kaolin could also be used in producing low temperature ceramics, refractory materials, pottery and stoneware

The purpose of this study is to characterize the metasomatism that has taken place as a result of the chemical incompatibility between mafic and metaultramafic bulk compositions during high-grade regional metamorphism in the Tobacco Root Mountains, southwest Montana. Metasomatism of these rocks took place by both diffusionand infiltration-dominated processes. The result of these processes are characterized mineralogically and geochemically in the rocks.

PhD (Geology) / Department of Mining and Environmental Geology / Cretaceous-Tertiary Periods marked the break-up of Gondwana, a large landmass composed of most of the present-day southern continents. In understanding the events of the supercontinental break-up, paleoenvironmental studies need to be carried out. In such studies, kaolinites could be used as paleoenvironmental proxies due to their small particle sizes and large surface area. It is in this context that this research sought to reconstruct the paleoenvironments in which selected Cretaceous-Tertiary kaolin deposits in the Douala Sub-Basin in Cameroon formed. To achieve this objective, mineralogical and geochemical characterisations were carried out using x-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectrometry, thermal analyses and x-ray fluorescence spectroscopy. Trace elements and stable isotopes were analysed using mass spectrometries. Ages of zircons in the kaolins were determined using laser ablation magnetic sector-field inductively coupled plasma mass spectrometry (LA-SF-ICP-MS) U-Pb geochronology. Diagnostic evaluation for industrial applications of the kaolins were carried out using particle size distribution, texture, moisture content, pH, and electric conductivity. Six kaolin deposits from Cretaceous-tertiary Formations of the Douala Sub-Basin were studied; namely, Bomkoul (Tertiary), Dibamba (Tertiary), Ediki (Cretaceous), Logbaba (Cretaceous), Missole (Tertiary) and Yatchika (Cretaceous). The nature and occurrences of these kaolin deposits in Cameroon were determined through thorough mineralogical and geochemical characterisations of bulk (< 2 mm size fraction), silt (2-63 μm size fraction) and clay samples (< 2 μm size fraction). By quantifying the mineral phases present, the morphology and the functional groups in the kaolins are presented as the mineralogical characteristics of kaolins of each study site; whereas, the major oxides geochemistry and the micro-elemental composition constitute the geochemical characteristics of these kaolins. The minerals’ geneses were also determined and the prevailing paleoenvironmental and paleoclimatic conditions in which they were formed were reconstructed using trace elements and stable isotopes of oxygen and hydrogen in kaolinite. The maximum age of the kaolins were determined using U-Pb LA-SFICP-MS dating of zircons in the kaolin deposits. Diagnostic evaluation of the kaolins was carried out, and involved the determination of physical characteristics (particle size, texture, colour and moisture content) and physico-chemical characteristics (pH and electrical conductivity). Results showed that kaolinite and quartz (as major phases), smectite and/or illite (as minor phases), anatase and rutile (as minor or trace phases), goethite and hematite (as trace viii phases) were the mineral phases present in bulk and silt samples. Whereas, in the < 2 μm fractions, the mineral phases are made up of kaolinite and smectite (as major phases), smectite and/or illite (as minor phases), anatase and rutile (as minor or trace phases), goethite and hematite (as trace phases). The kaolins are mostly made up of thin platy or pseudo-hexagonal particles or flakes, books or stacks of kaolinite. The Dibamba, Logbaba and Missole II kaolins have well-ordered structures. Exothermic peak temperatures were generally between 943-988oC. The most abundant major oxides are silica and alumina, followed by iron oxide and titania; though Logbaba and Missole II had higher titania than iron oxide. 85% of the kaolins, portrayed extreme silicate weathering (chemical index of alteration > 80%) and are compositionally mature (index of compositional variability > 0.78). The geochemical composition of the kaolins showed that source rocks of these kaolins vary between rhyolite/granite and rhyolite/granite + basalt. The geochemistry also suggested that the kaolins formed in a marine environment (except Logbaba samples). Trace elements results revealed that Cretaceous-Tertiary kaolins in the Douala Sub-Basin are mainly enriched in rare earth elements compared to the upper continental crust, and have negative Eu anomaly. Large ion lithophiles (mainly Rb and U) were highly enriched in samples, high field strength elements (Y and Nb) were enriched in studied samples of all fractions; and transition trace elements generally had concentrations quite similar to upper continental crust values. Stable isotopes showed that the kaolins were formed in a supergene environment; and temperatures of kaolinitisation (assuming equilibrium with the global meteoric water line) were 26.58oC ± 9.65oC for Cretaceous kaolins and 29.40oC ± 7.22oC for Tertiary kaolins. Assuming equilibrium with the local (Douala) meteoric water line, the temperatures of kaolinitisation were 24.64oC ± 9.48oC for Cretaceous and 27.42oC ± 7.08oC for Tertiary kaolins. Four main zircon populations were identified from radiogenic dating: the 1st between 550 and 650 Ma, the 2nd between 950 and 1050 Ma, the 3rd around 1600 Ma and the 4th between 2800-3200 Ma. These four zircon populations belong to the Proterozoic (Neo-, Meso- and Paleoproterozoic) and the Archean. The maximum depositional ages of the kaolins, reflected by the youngest weighted averages of zircon populations varied between 588 ± 2 Ma and 612 ± 2 Ma, all belonging to the Ediacaran Period (Neoproterozoic). The diagnostic evaluation of the kaolins revealed that the kaolins are very sandy, with 50% of the samples having a sandy loamy clay or sandy loam texture. The colour of the samples varied considerably from white to darker colours (dark grey); with 15% of the kaolins being light reddish brown. The moisture content was generally very low (< 2 wt %) in all size fractions, except in Yatchika samples (moisture content > 2 wt %). The kaolins are generally acidic, with ix a pH(KCl) varying between 3.06 and 3.81, except in Missole I samples, which had a pH (KCl) < 2. The electrical conductivity (EC) generally varied between 20 to ~ 50 μS/cm, except Dibamba and MSL II 01 samples which had EC values in the interval 50 μS/cm < EC < 80 μS/cm; and Missole I samples having an EC > 7500 μS/cm. In conclusion, no great distinction was found between Cretaceous and Tertiary kaolins of the Douala Sub-Basin based on their mineralogy and geochemistry. The best kaolins in terms of these characteristics, and in comparison with the Georgia Kaolins (known for their high kaolinite quality), were the Dibamba (Tertiary), Logbaba (Cretaceous) and Missole II (Tertiary) kaolins. Based on their compositional maturity and mineralogical characteristics, these three kaolins are considered to be second cycle sediments; unlike Bomkoul, Yatchika and Ediki kaolins, which are believed to be first cycle sediments. Based on the trace elements and stable isotopes composition, Cretaceous and Tertiary kaolins of the Douala Sub-Basin were derived from felsic rocks. However, Cretaceous kaolins were formed in a cooler anoxic reducing environment; whereas the Tertiary kaolins were formed in a warmer oxidising environment, with higher precipitation. Ages of zircons in Cretaceous-Tertiary kaolins suggested that the zircon formed during two main tectonic events: the Eburnean orogeny, during which older zircons crystallised and the Pan-African orogeny, during which younger zircons crystallised. The maximum depositional ages of the kaolins varied between 588 ± 2 Ma and 612 ± 2 Ma. The main identified sources of these zircons are the Archean Ntem Complex, the Paleoproterozoic Nyong Group and the Neoproterozoic Yaounde Group. The diagnostic evaluation indicated that the particle size greatly influences the mineralogy and geochemistry of the kaolins because the finer particles (< 2 μm) have higher amounts of kaolinite and Al2O3. The moisture content of the kaolins makes them suitable as paint fillers and in soap production. Paper coating, paper filler, ceramics, pharmaceutics and cosmetics are potential applications for the kaolins, though particle size reduction and beneficiation will give them a higher quality. However, because these kaolin deposits are not big and extensive, they cannot be recommended for large scale industrial applications; but they can be used for bricks, pottery and stoneware manufacturing.

L’origine des suites de mégacristaux des kimberlites est sujette à d’intenses débats depuis de nombreuses années. La suite complexe de mégacristaux (grenat, clinopyroxène, zircon, baddeleyite, ilménite, rutile et nodules d’intercroissances rutile-silicates) des kimberlites diamantifères de Mbuji-Mayi (Kasaï Oriental), mises en place au Crétacé dans le craton archéen du Congo-Kasaï, a été étudiée en détails dans le but d’établir les relations entre les différents minéraux de la suite, leur relation au magma kimberlitique-hôte et au manteau lithosphérique cratonique archéen. L’étude des mégacristaux de grenat des kimberlites pauvres en diamants du Kundelungu (Katanga) a permis en outre d’établir la comparaison entre les mégacristaux de deux provinces kimberlitiques en République Démocratique du Congo, qui diffèrent notamment par leur âge de mise en place et par la composition et l’âge du socle traversé. <p>L’ensemble des données minéralogiques et géochimiques acquises (éléments majeurs et en traces, géochimie isotopique de l’oxygène, du Nd et de l’Hf) est intégré dans le but de déterminer la nature du (ou des) processus qui a (ont) donné naissance à ces suites de mégacristaux. <p>En parallèle, l’origine d’un xénolite rare de clinopyroxénite à kyanite exceptionnellement riche en Cr des kimberlites de Mbuji-Mayi a été explorée.<p>Bien qu’ils partagent de nombreuses caractéristiques avec d’autres suites de mégacristaux kimberlitiques, les mégacristaux de RDC sont généralement enrichis en Cr et appauvris en Fe et Ti, et ne présentent pas de preuve d’une origine par cristallisation fractionnée à partir d’un magma, ce qui permet de suggérer une origine différente, en l’occurrence une liaison plus directe avec le manteau lithosphérique réfractaire local lors de leur formation. Une origine métasomatique par interaction entre un liquide/fluide précurseur de la kimberlite et les péridotites du manteau lithosphérique est donc favorisée. L’ensemble des espèces minérales qui forme la suite de mégacristaux peut en effet trouver un équivalent compositionnel dans les lithologies métasomatisées de la lithosphère mantélique. <p>Les mégacristaux de grenat des deux provinces partagent des similarités frappantes qui sont interprétées en termes de processus de formation similaires. En revanche, ils ont systématiquement montré un comportement géochimique singulier, suggérant un processus de formation différent des autres mégacristaux. Ils semblent en effet avoir retenu l’héritage des compositions variables d’anciens protolites de grenat affectés récemment par un métasomatisme de type kimberlitique. Ces grenats résultent de la recristallisation de grenats initialement présents dans les péridotites cratoniques de la lithosphère archéenne. Par contre, les mégacristaux de clinopyroxène, zircon, baddeleyite, ilménite, rutile et les nodules d’intercroissances rutile-silicates se sont effectivement formés récemment par l’interaction métasomatique entre le liquide/fluide proto-kimberlitique et les péridotites cratoniques. Des variations locales du rapport (fluide et/ou liquide)/roche et de l’activité en SiO2 lors de la percolation du magma proto-kimberlitique asthénosphérique dans le manteau lithosphérique cratonique, couplées à la nature propre à la kimberlite de la région, permettent d’intégrer l’ensemble des mégacristaux dans un modèle pétrogénétique commun, avec des processus de formation parfois contrastés. <p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished