No description available.

M.Sc. / It is the focus of the study to qualitatively describe and then quantify the mineralogical and geochemical changes associated with the supergene alteration of carbonate-rich braunite lutite (Mamatwan-type ore) immediately below the Kalahari unconformity along the southeastern suboutcrop perimeter of the Hotazel Formation in the Kalahari deposit. It was also the objective of this study to determine the timing and duration of supergene alteration. Samples for polished thin sections were carefully selected from eight representative boreholes to be representative of all the lithostratigraphic zones and ore types. The thin sections were used to study mineralogy by means of reflected light microscopy and scanning electron microscopy. X-ray powder diffractometry on representative powder samples were used to study the mineralogy and geochemistry of the samples. Microprobe analyses were also performed on the representative samples. Finally the samples were submitted for 40Ar/39Ar geochronology. In this supergene enrichment zone carbonates are leached (associated with an increase in porosity) and Mn2+/Mn3+ -bearing minerals (kutnahorite, Mn-calcite an braunite) are altered to supergene Mn4+-bearing mineral phases (todorokite and manganomelane) and minor quartz. This process upgrades ore from 38 wt% Mn to ore with more than 40 wt% Mn. Element fluxes, enrichment and depletion of major and trace elements were quantified by mass balance calculations. Na2O, K2O, Sr, Ba, Zn and H2O were enriched, while Mn3O4, Fe2O3, CaO, MgO, P, B and CO2 were leached from the ore during supergene alteration. Results of this study suggest that the development of Post African I erosional surface may have taken place 45 Ma ago. The bottom of the weathering profile gives a well-defined peak at ca. 5 Ma that may possible coincide with the development of Post African II erosional surface. The major characteristics of the alteration process of the unaltered Mamatwan-type ore to supergene altered braunite lutite can be summarized as follow: • Leaching of Mn carbonates and Mn2+/Mn3+-oxides. • Formation of Mn4+-oxyhydroxides and quartz. • Decrease in relative density of the ore. • Increase in porosity of the ore. • Leaching of Mn3O4, Fe2O3, CaO, MgO, P, B, CO2. • Enrichment of Na2O, K2O, Sr, Ba, Zn, H2O. Chemical weathering processes along the Cenozoic Kalahari unconformity appear to have affected the manganiferous lithologies of the Hotazel Formation from 45 Ma onwards to 5 Ma. The weathering front processes very slowly through the Mn-rich braunite lutite (<10m in 40 Ma; <0.25m/Ma); producing a very uniform and microcrystalline supergene mineral assemblage with distinct characteristics.

M.Sc. / This study has served to expand the geological map of surroundings of the Venetia Mine (Limpopo Province, South Africa) incorporating the area lying south of the kimberlite deposit and bounded in the south by the Dowe-Tokwe fault. The most significant structural conclusion stemming from this mapping project is that the Venetia Synform seems to be tectonically separate from the surrounding area and actually forms a klippe (shallowly dipping thrust) against the Krone Metamorphic terrane and the Gotha Complex. Petrographic descriptions of quartzofeldspathic lithologies found in the Krone Metamorphic Terrane to the west of the Venetia klippe (Mellonig, 2004) are identical suggesting that they belong to the Gotha igneous complex. There are no differences in geochemical compositions of monzogranite to granodiorite, tonalite and quartz diorite from Farms Gotha and Venetia. The rocks are I-type granitoids that generally form in continental magmatic arcs. The amount of U and Th in the igneous rocks of the Farms Gotha and Venetia (contained in minerals found within quartz, plagioclase, amphibole and K-feldspar crystal boundaries and the magmatic zircons of the Farm Gotha samples) and the pattern produced by heat producing elements (Council for Geoscience Radiogenic Map), indicate that that the unexpectedly high concentration of these elements are not the result of regional metamorphism, but is the remnant of the final crystallisation phase of the magma of the area. REE plots of the Venetia Mine samples show negative Eu anomalies, indicating the presence of plagioclase and K-feldspar in the magma source of the Venetia mine samples. The assumption is, that most samples retained their original chemical compositions having experienced only weak deuteric alteration and no dynamic metamorphism.

This study focuses on exocontact mineral assemblages to determine composition, thermal signatures, and the extent of exomorphism that occurred between the Mt. Mica pegmatite and the migmatite host rock at the contact. Biotite-garnet thermometry of country rock samples resulted in an average temperature estimate of 630 °C. Measured biotite Fe/(Fe+Mg) ratios were used to calculate an fO2 of -18. The results indicate that the country rock and pegmatite formed under similar oxidizing conditions near the quartz-fayalite-magnetite (QFM) equilibria buffer. Whole rock (REE) analysis indicates an interaction trend between the country rock and pegmatite. Exomorphism does not appear to have been significant at Mt. Mica, likely due to the moderately evolved nature of the pegmatite. Minor B leakage into the surrounding country rock is constrained to within 15 cm from the contact. Results indicate no enrichment of alkali elements (Li, Rb, Cs), As, U, or F occurred in minerals analyzed.

No description available.

A thesis submitted in fulfilment of the requirements for the degree of PhD in Geology< University of the Witwatersrand. / Numerous small base-metal deposits occur in the acidic rocks of the Bushveld Complex, and modern exploration programs are currently re-examining this metallotect in an attempt to refine the current working hypothesis for mineralisation in these granites. The hypothesis proposed for the origin of mineralisation is multifaceted, encompassing both spatial and temporal relationships between at least three episodes of ore formation. The first episode of mineralisation (typified by the Zaaiplaats tin deposit) occurred at relatively high temperatures (>600'C to 4000' C), and resulted in the formation of orthomagmatic cassiterite, scheelite and an early generation of fluorite. At lower temperatures (200°C<T<400°C), where processes were essentially fluid dominated, a mesothermal Cu-Pb-Zn-As-Ag-Au assemblage was deposited (exemplified by the Spoedwel, Boschhoek and Albert copper and silver deposits). A third episode of mineralisation resulted in the formation of an Fe-U-F assemblage and is recognised at several, but not necessanly all, of the deposits examined (for example, the Albert silver deposit). The extended nature of this three-stage paragenetic sequence is considered to reflect widespread mixing between an early fluid derived by H20-saturation of the granitic magma and an external meteoric/connate fluid, circulation of which was stimulated by the long-lived high heat-productive capacity of the Bushveld granites, as well as exhumation of the metallotect; The early high-temperature Sn/W assemblage was precipitated while magmatic fluids dominated the system. With time, the pluton cooled and was subject to regional uplift. Fractures developed, acting as conduits for external fluids of meteoric and/or connate origin. The late magmatic fluids, enriched in incompatible metals (and volatiles), interacted with the latter fluid, resulting in the localised precipitation of a secondary, lower-temperature mineral assemblage (Cu-Pb-Zn) in the zone of fluid mixing. As the external fluid component became progressively more dominant, the paragenesis changed, forming the :final Fe-U-F assemblage. The formation of these three different, temporally separate assemblages is adequately explained in terms of a fluid mixing model, wherein the concentration ofmetaIs and localisation of ore deposits are controlled by lithology and structure. / Andrew Chakane 2018

A thesis submitted to the Faculty of Science in fulfilment of the requirements for the degree of Doctor of Philosophy at the School of Geosciences University of the Witwatersrand, Johannesburg, 2017 / Namibia, the 6th largest producer of uranium globally, has produced uranium from Pan African granite-hosted (primary) deposits since 1976, and from palaeochannel deposits since 2007; exporting 3 472 tonnes U in 2016. The large granite-hosted deposits at the Husab Mine are expected to add over 5 700 tonnes U/year at peak, while three large primary-hosted deposits remain in various stages of development at Goanikontes, the Ida Dome, and Valencia. This study presents a comprehensive geological, geochemical and uranium mineralogical appraisal of four of the major primary-hosted uranium deposits, all situated within the southern Central Zone (sCZ) of the polydeformational (D1-D3) Damara Belt. The sCZ comprises highly deformed Neoproterozoic sediments, unconformably draped over rheologically competent granite-gneiss domes and inliers of a Palaeoproterozoic basement. A suite of fractionated sheeted leucogranites (SLGs) are a characteristic of the final stages of Orogenic deformation; while most SLGs appear to precede D3 deformation and metamorphism (ca. 510 Ma); most of the mineralised SLGs across the region invade reduced-facies sediments in pressure shadows formed in the hinges and limbs of upright D3 antiforms, proximal to basement inliers. A pre-existing, six-fold, alphabetised SLG classification scheme is revised and extended to categorise distinctive and consistent field and petrographic characteristics of the SLGs across the region. Discriminating SLG sub-types is less consistent in standard geochemical diagrams, except where high field-strength (HFS) and rare-earth elements (REE) are concerned. REE profiles in pre-D3 SLGs reflect abundances, or paucities, of characteristic accessory mineral assemblages; while REE profiles show relative REE enrichment, prominent REEfractionation and -ve Eu anomalies in the uraniferous SLGs, reflecting lower-percentage partial melts in the more uraniferous samples. The overwhelming majority of primary uranium mineralisation is in magmatic uraninite, followed by coffinite which predominate as a replacement phase of uraninite, and more rarely as solid solution with thorite. The refractory minerals betafite and brannerite are rare, but are locally abundant in discrete, magmatic textures within uraniferous SLGs of some deposits. Hydrated uranyl silicates predominate in the supergene portions of the orebodies across the region. An electron microprobe study presents the first comprehensive assessment of uraninite compositions in the region, while Husab deposit betafite and brannerite compositions allow for a well-rounded comparison with refractory minerals from the Rössing deposits. Key Words Primary Uranium, Granite, Orogenic, Damara, Namibia, Rare Earth Elements, Mineralisation, Fractionation, High-grade Metamorphism, Economic Geology, Mining, Processing, Uraninite, Coffinite, Etango, Goanikontes, Husab, Ida Dome, Rössing, Valencia / XL2018

South Africa remains the 5th largest producer and 4th largest exporter of coal in the world. It is also the largest supplier of coal to the European Union. This fact is significant as the European Union has recently supported the environmental lobby that threatens the combined full scale use of coal in Europe and other first world countries. This promotes the development of clean coal technologies in order to counter the ever increasing number of environmental constraints threatening the export market. One critical development in clean coal technologies is coal beneficiation, which allows the reduction of ash and inert content. Permian coals from South Africa have characteristically high ash and inertinite contents and therefore require further beneficiation. The Witbank coalfield No. 4 seam is no exception. It can be described as being more inert and having a higher mineral content compared to the No. 2 seam in the same coalfield also mined for export purposes. With the increase in environmental legislation and the push towards “clean coal” this raises a concern in terms of the performance and marketability of export coal produced from the No. 4 seam. This seam will in the future be economically significant and is still a great source for export steam coal. Due to the nature and composition of the No. 4 seam, coal beneficiation is essential to reduce the mineral and inert content to be in line with export quality specification levels. Washability characteristics of the No. 4 seam coal indicate that the No. 4 seam is difficult to beneficiate. Until recently the main clean-ability parameters evaluated in South African export coals as per customer specification included mainly heating value, moisture and ash reduction with little to no work being done on trace element concentration reduction. This paper focuses on the partitioning of the trace elements within the seam in relation to the organic and inorganic affinity of the trace elements and possible methods of trace element reduction by removal using coal beneficiation techniques. The techniques investigated include reduction by washing using dense medium beneficiation and flotation. In each evaluation the focus was on trace-element-tomineral and trace-element-to-organic matter relationship and hence setting the basis for liberation analysis to evaluate reducibility. By the evaluation of the coal mineralogy, petrography and trace element relationships, methods of optimum trace element reduction can be established. With the focus on marketing it was shown that carbon loss need not be sacrificed in the reduction of specific trace elements in the No. 4 seam and that the trace element distribution itself allows for beneficiation whilst maintaining acceptable yields. Processes and possible beneficiation techniques for optimum trace element reduction and marketability in the case of the No.4 seam are proposed.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2014. / The Central African Copperbelt is located in the Lufilian Arc which straddles the border between Zambia and the Democratic Republic of Congo (DRC). Mineralisation of the cupriferous Arc is found in basal Neoproterozoic Katangan Supergroup sedimentary rocks, which in DRC are termed the Mines Series Subgroup. The Mines Series is divided into the dolomitic and carbonaceous GRAT, DStrat RSF, RSC, SD and CMN units. The composition of the units is homogeneous across the Lubumbashi district and potentially across the Katangan basin. This study focussed on the Kinsevere and Ruashi deposits in the Lubumbashi district, which are approximately 50 km apart. The study confirmed that relative eustatic sea level changes resulted in the non-deposition of the RSF and RSC stratigraphic units at Kinsevere. Sedimentation was followed by early pervasive potassic alteration and silicification at the diagenetic stage whilst a magnesian dolomitisation event resulted in alteration of potassic feldspars and recrystallisation of carbonates. Albitisation was veincontrolled and late-stage scapolitisation altered evaporitic nodules. Finally, haematisation by late iron-rich fluids circulating through the Roan Group strata resulted in oxidation of sulphides. The structural analysis of Kinsevere Central pit indicates E-W and N-S shortening whereas the Ruashi pit 1 deposit underwent NE-SW and N-S shortening. Initial shortening, associated with Kolwezian deformation (D1), resulted in the formation of NE-thrust folds and a primary set of joints. The Kolwezian deformation event (D2), reoriented the shortening direction from E-W to N-S, creating interference folds and possibly a second set of joints. The final phase in the structural evolution of the Kinsevere and Ruashi deposits was late-stage brittle deformation (faulting). Mineralisation was a multi-stage process. Disseminated chalcopyrite and carrollite were deposited from formation waters during diagenesis in a stable basin environment. Chalcopyrite, carrollite, chalcocite and bornite are predominantly located at the base of the DStrat, whereas chalcopyrite and pyrite dominate the stratigraphically higher portions of the deposits. Hypogene vein mineralisation began at the syn- to late- orogenic stage with carrollite and chalcopyrite in beddingparallel veins. Possible changes in the compression direction created the perpendicularly oriented veins that host chalcopyrite, carrollite, bornite, covellite, digenite and chalcocite. Finally a late stage of chalcopyrite and pyrite deposition occurred in and around the evaporites, indicating a strong correlation between mineralisation, evaporites and scapolitisation. iii Near-surface supergene alteration of hypogene sulphide ores, resulted in Cu-Co carbonates and oxides, such as malachite, azurite, cobaltiferous malachite, chrysocolla, kolwezite and sphaerocobaltite being deposited in vugs and pore spaces above the meteoric water line. Faulted and brecciated zones tend to have deeper supergene alteration. Between the sulphide facies at depth and the supergene oxide facies at surface is a transition zone which marks the depth to which oxidation has penetrated. Sulphur isotope analysis from the Kinsevere and Ruashi deposits suggests a sulphur contribution from a continental Red-Bed sedimentary source and from an evaporitic source.

A thesis submitted in fulfilment of the requirements for the degree of PhD in Geology University of the Witwatersrand / Numerous small base-metal deposits occur in the acidic rocks of the Bushveld Complex, and modern exploration programs are currently re-examining this metallotect in an attempt to refine the current working hypothesis for mineralisation in these granites. The hypothesis proposed for the origin of mineralisation is multifaceted, encompassing both spatial and temporal relationships between at least three episodes of ore formation. The first episode of mineralisation (typified by the Zaaiplaats tin deposit) occurred at relatively high temperatures (>600'C to 4000' C), and resulted in the formation of orthomagmatic cassiterite, scheelite and an early generation of fluorite. At lower temperatures (200°C<T<400°C), where processes were essentially fluid dominated, a mesothermal Cu-Pb-Zn-As-Ag-Au assemblage was deposited (exemplified by the Spoedwel, Boschhoek and Albert copper and silver deposits). A third episode of mineralisation resulted in the formation of an Fe-U-F assemblage and is recognised at several, but not necessanly all, of the deposits examined (for example, the Albert silver deposit). The extended nature of this three-stage paragenetic sequence is considered to reflect widespread mixing between an early fluid derived by H20-saturation of the granitic magma and an external meteoric/connate fluid, circulation of which was stimulated by the long-lived high heat-productive capacity of the Bushveld granites, as well as exhumation of the metallotect; The early high-temperature Sn/W assemblage was precipitated while magmatic fluids dominated the system. With time, the pluton cooled and was subject to regional uplift. Fractures developed, acting as conduits for external fluids of meteoric and/or connate origin. The late magmatic fluids, enriched in incompatible metals (and volatiles), interacted with the latter fluid, resulting in the localised precipitation of a secondary, lower-temperature mineral assemblage (Cu-Pb-Zn) in the zone of fluid mixing. As the external fluid component became progressively more dominant, the paragenesis changed, forming the :final Fe-U-F assemblage. The formation of these three different, temporally separate assemblages is adequately explained in terms of a fluid mixing model, wherein the concentration ofmetaIs and localisation of ore deposits are controlled by lithology and structure. / Andrew Chakane 2018