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A crystal-chemical investigation of phases of relevance to lime-chromite roast reactions

Characterization and an investigation on ceramic properties of selected continental clay materials

Dissolution of minerals from geophagic clays from selected areas and their probiotics behaviours

  • Authors: Uchenna, Okereafor Godwin
  • Date: 2017
  • Subjects: Mineralogical chemistry , Probiotics - Therapeutic use , Clay minerals , Clay - Analysis
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/243004 , uj:25080
  • Description: M.Tech. (Extraction Metallurgy) , Abstract: Clay and its associated minerals are crucial materials with various applications ranging from industrial, health to traditional activities. Since time immemorial, the application of clays for traditional and health purposes have remained evident amongst Africans and rapidly gaining grounds in the world at large. Indigenous knowledge has constantly supported geophagia – the deliberate consumption of earthy material for several benefits such as mineral supplement to the body and treatment of diseases. In Southern Africa, geophagia is becoming a common practice irrespective of the social class, age and religion of the geophagists. Few reports on the characterisation of geophagic clays are available but none had considered probiotics and volatile fatty acids. Characterisation plays a vital role in the study of geophagic clays, as it provides useful information about the safety of its application by humans. The quality of such earthy material had been solely based on characterisation, which stirs issues of safety and environmental health. It was therefore imperative to consider other studies beside characterisation of geophagic clays to better appreciate the effects upon consumption by humans. Probiotics are known to be beneficial as they help maintain a healthy gut in humans. The effect of clays on these microorganisms and the possible impacts on humans is necessary. This current research study considered the application of Atomic absorption spectroscopy (AAS) together with Infrared fluorescence (XRF) and Infrared diffraction (XRD) as well as a front-line chromatographic and mass spectrometric analytical technique, i.e. two dimensional gas chromatography coupled with a time-of-flight mass spectrometry (GC×GC-TOFMS) for investigating the production of volatile fatty acids (VFAs) by the probiotics upon interaction with geophagic clays. The first phase of the study considered the physicochemical characterisation of geophagic clays sold in informal South African markets using 2g of the various samples moistened with 100mL of 0.5M, 1M and 2M HCl acid. The subsequent analysis of the filterate on AAS revealed the different clay samples containing several heavy metals such as copper (Cu), lead (Pb), zinc (Zn), iron (Fe), cobalt (Co), manganese (Mn), chromium (Cr). These heavy metals have been reported to have deleterious effects on humans when above the minimum permissible level. Further analysis using infrared fluorescence indicated average values of major elements such as SiO2 (54.02%), Al2O3...
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Mafic, ultramafic and anorthositic rocks of the Tete complex, Mozambique : petrology, age and significance

  • Authors: Evans, Richard John
  • Date: 2012-09-11
  • Subjects: Geology - Mozambique , Ultrabasic rocks - Mozambique , Petrology - Mozambique , Mineralogical chemistry , Mineralogy - Mozambique , Geochronometry - Mozambique , Geological time
  • Type: Thesis
  • Identifier: uj:10074 , http://hdl.handle.net/10210/7460
  • Description: M.Sc. , The ca. 800 km2 Tete Complex of NW Mozambique is located at the eastern end of the 830 ±30 Ma Zambezi Belt, near the transition zone into the Neoproterozoic Mozambique Belt. The Complex is located just south of the Sanangoe Shear Zone where Mesozoic and Late Palaeozoic cover rocks obscure much of the region. Country rocks immediately in contact with the Tete Complex include amphibolitic gneiss, graphite-bearing marble, calcsilicate gneiss, muscovite and biotite schist and quartzite of the Chidue Group. The Tete Complex may have been intrusive into the Chidue Group, although there is evidence inferring tectonic emplacement. Those few contact exposures that exist are equivocal. Some of the rocks within the Tete Complex have been affected by metamorphism up to amphibolite grade, although large proportions of the rocks retain pristine magmatic mineralogy and texture. The Tete Complex contains mafic, ultramafic and anorthositic rocks, dolerite dykes and minor Fe-Ti oxide-rich rocks that occur as rubble. Pyroxenite occurs as thin (<1-2 m), cumulate layers within gabbroic rocks. Most exposed anorthositic rocks occur in the Nyangoma area in the eastern part of the Tete Complex. The anorthosites and leucotroctolites are massive, coarse grained (2-3 cm), and contain plagioclase (An47-An57) megacrysts up to 10 cm in length, interstitial olivine (Fo59-Fobs) and orthopyroxene (En59- En75, mean A1203 = 1.84 wt.%) rimmed by clinopyroxene (mean = Wo 46En38Fs i6), pyrite and Fe-Ti oxides. Secondary biotite, iddingsite, epidote and green spinet are present. The stable coexistence of olivine and plagioclase limits the depth of emplacement to <7-8 kbar, or <20- 25 km; a relatively shallow level of emplacement is favored by the generally fine grain size of the gabbroic and doleritic rocks. Compositions of coexisting plagioclase and mafic silicates (orthopyroxene and olivine) are similar to those of massif-type anorthosites. Previously unmapped meta-anorthosite occurs along the western and northern margin (within the Sanangoe Shear Zone) of the Tete Complex and has been metamorphosed to amphibolite grade. The rock contains plagioclase (An38-An39), with the more Ab-rich compositions related to the formation of garnet (mean = A1m67GrotsPYI6Sp2). Metamorphic orthopyroxene (Enso-En53), clinopyroxene (mean = Wo37En38Fs25), mizzonitic scapolite (Me63), amphibole, biotite and apatite are present. High Cl contents in amphibole, scapolite and biotite (e.g., up to 4.7 wt. % in amphibole), suggest that a Cl-rich metamorphic fluid infiltrated the western margin of the Tete Complex. Olivine melagabbro from the north-central part of the Tete Complex contains plagioclase (An70-An26), olivine (Fo82-Fos4) and clinopyroxene (mean = WanEn1Fs0.2, mean A1203 = 2.56 wt. %), with primitive compositions compared to those in Nyangoma anorthositic rocks and pyroxenites. Pyroxenites are modally dominated by clinopyroxene (mean = Wo46-48En36-39Fsi3-18) with accessory interstitial plagioclases (Ano-An45) and discrete and exsolved orthopyroxenes (En 56-En75). Clinopyroxenes with high A1203 contents up to 9 wt. % are similar to high-Al pyroxene megacrysts. One sample of pyroxenite contains orthopyroxene (En56-En60) and plagioclase (An40-An45) with more evolved compositions compared to those in Nyangoma anorthositic rocks and olivine melagabbro. Normal Fe4- and Na-enrichment trends accompanying fractionation from magmas that may be common to the Nyangoma anorthositic rocks, pyroxenites and olivine melagabbro, are associated with an increase in Al relative to Cr along a line of nearly constant relative Ti content. Gabbro contains olivine and plagioclase crystals that are commonly zoned, thus ranging widely in composition (Fool -Fos°, Anss-Ans2)• Clinopyroxene (mean = Wo36En47Fsi6) constitutes ca. 34 modal % of gabbro. New whole-rock (Nyangoma anorthosite and leucotroctolite) and mineral (plagioclase, clinopyroxene and orthopyroxene) Sm-Nd isotopic data yields ages between 975 ±33 Ma and 1041 ±131 Ma. The igneous crystallization age of the anorthositic rocks is estimated at 1025 ±79 Ma (9-point whole-rock regression). Rb-Sr isotopic compositions for whole-rock samples reveal no meaningful age relationships. Initial Nd isotopic compositions (calculated at 1.0 Ga) correspond to E Nd values between +3.5 and +4.5 (mean = +4.1) with Is, = 0.70276 — 0.70288 (mean = 0.70282), both inferring magmatic derivation from a depleted mantle source, possibly with little or no contamination by Archaean crustal components. TDM model ages range between 1074 and 1280 Ma (mean = 1148 Ma). There is a striking similarity between the Tete Complex anorthosites and those of SW Madagascar in terms of Nd isotopic compositions and the nature of country rocks; in both regions the anorthosites were emplaced either magmatically or tectonically into shelf-type supracrustal metasediments (marbles, quartzites, graphitic schists, etc.). Anorthosites intruded similar country rocks in Draining Maud Land, eastern Antarctica. Although anorthosites from Mozambique and Madagascar share a common depleted mantle signature with little or no contamination by Archaean crustal components, a direct stratigraphic correlation between these two areas (and possibly eastern Antarctica), awaits further geological and geochronological data.
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Mineralogy, microbial characterisation and microwave processing of selected geophagic clays

Paleoproterozoic Mississippi Valley-Type Pb-Zn deposits of the Ghaap Group, Transvaal Supergroup in Griqualand West, South Africa

The Merensky Reef at Dwarsriver 372 KT with reference to the mineral chemistry and the platinum group minerals in the Merensky reef chromitite stringers

  • Authors: Rose, Derek Hugh
  • Date: 2012-06-06
  • Subjects: Merensky Reef Chromitite Stringers , Mineralogical chemistry , Platinum group minerals , Chromite , Bushveld Complex (South Africa)
  • Type: Thesis
  • Identifier: uj:2538 , http://hdl.handle.net/10210/4992
  • Description: M.Sc. , This study focuses on the Merensky Reef (MR) occurring within the Two Rivers Platinum mine property in the farm Dwarsriver 372 KT, on the Southern sector of the Eastern Limb of the Bushveld Complex. Five MR exploratory drill core intersections were obtained. Petrographic and mineral chemical characteristics of these drill core samples focused on the characterization of minerals like clinopyroxene, orthopyroxene, plagioclase, chromite and olivine. Data of the cryptic variation of orthopyroxene, plagioclase and chromite, from a 10 m interval (approximate thickness of the section studied); from footwall through the MR to the hangingwall lithologies at Dwarsriver are described in this study. Locally the vertical cryptic variation of these minerals is broadly consistent with regional trends of the RLS. The lateral variation (i.e. along strike) is less pronounced; however, locally these minerals appear to be chemically evolving moving to the south of the property. Footwall orthopyroxene compositions vary from a minimum of En66 and reach a maximum of En84. Those of the MR range from En71 to En85. Hangingwall orthopyroxene compositions range from En60 and reach a maximum of En80. Plagioclase compositions in the footwall units range from a minimum of An69 and reach a maximum of An85. Those of the MR range from a minimum of An35 to a maximum of An84. This wide range in plagioclase compositions is believed to be as a result of the increased presence of fluids within the MR interval. The hangingwall plagioclase compositions range from An64 to An84. By analogy of the Western Limb, where the lithologies of the Northwestern sector are believed to be proximal to the feeder of this limb; the local lateral variation in the present study suggests that the lithologies of either the Central or Western sectors are most probably proximal to the feeder for the Eastern Limb. PGM assemblages associated with and adjacent to the MR chromitite stringers were evaluated using an MLA. Data obtained from this technique is in broad agreement with regional studies of the MR. With the aid of wholerock PGE assays the MLA technique has proven to be a powerful tool in evaluating PGM assemblages relatively quickly, from a few carefully selected samples. The mineralogical associations of the PGM with the gangue and host minerals have shown three main associations. These are the associations of chromite, BMS and silicates with the PGM, of which the base metal sulfide (BMS) association is remarkable given that these have a relatively low modal abundance. The relatively high mineralogical association of the BMS with PGM has been explained by a model involving a base metal sulfide liquid which possibly scavenged chalcophile and siderophile elements. Chromite chemistry and modal analyses of MR secondary silicate phases, which peak adjacent to the chromitite stringers, suggests elevated fluid overprinting within and adjacent to the chromitite stringers. The upper chromitite stringers, however, have higher abundances of PGM phases that are believed to be secondary in origin relative to the basal chromitite stringers. Generally the PGM associated with the upper chromitite stringers are also bigger in size averaging 70 μm as opposed to 27 μm for those associated with the basal chromitite stringers. The increase in grain size of the PGM along with the higher modal abundance of secondary PGM phases associated with the upper stringers is believed to be as a result of fluids. These fluids although affecting both the upper and basal chromitite stringers, appear to have had a relatively higher influence on the upper chromitite stringers. The most common PGMs encountered in this study are isoferroplatinum, sperrylite, michenerite, maslovite, cooperite, laurite and braggite.
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