List of Titles

Analysis of saprolite-hosted Rutile-Graphite deposit: a case study of Malingunde saprolite-hosted Rutile-Graphite project in Central Malawi

- Zabula, Ansel Aliko

Authors: Zabula, Ansel Aliko
Date: 2024-10-11
Subjects: Uncatalogued
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/464970 , vital:76562
Description: The Malingunde graphite project, owned by Sovereign Metals Ltd (SML), has revealed significant potential for rutile and high-grade graphite in saprolite. This study addresses the complexity of mineral assemblages in the Malingunde area, emphasizing the coexistence of graphite and rutile. SML's exploration activities, including extensive drilling and soil sampling, have uncovered variations in associated minerals, such as muscovite, kyanite, garnets, and ilmenite. Rutile, initially discovered incidentally, has prompted further investigation, impacting the financial model of the project. This research aims to analyse the Malingunde deposit, focusing on understanding its mineralogy, formation, and potential for elements like vanadium. Geological surveys reveal the distribution of graphite in the Precambrian to lower Palaeozoic age basement complex, hosted in saprolite resulting from tropical weathering of graphitic gneisses. Exploration techniques, including remote sensing, and geophysics, are crucial in targeting graphite and rutile deposits. Ground electromagnetic surveys, airborne electromagnetic data, and GIS applications aid in identifying and quantifying mineralised areas. Geochemical analysis and metallurgical tests further contribute to understanding the ore body and processing methods. Results indicate an inverse relationship between graphite and rutile concentrations, influencing the economic viability of different regions within the project area. Correlation matrices and regression analyses reveal distinct geological conditions influencing the association of vanadium and graphite in Lifidzi and Malingunde. The study concludes with exploration potential outside the Malingunde project, highlighting regional prospects and potential byproducts like vanadium pentoxide. The ongoing metallurgical tests and pilot plant design signify the project's evolution toward production. Additionally, neighbouring licenses show potential, emphasizing the need for comprehensive research to define and quantify resources in the region. This research provides valuable insights for the mining industry, informing strategies for exploration, resource assessment, and potential byproduct utilization in similar geological settings. , Thesis (MSc) -- Faculty of Science, Geology, 2024
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Date Issued: 2024-10-11

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Gold mineralization at the Blue Rock Deposit, Gadzema Greenstone Belt: Implications on genesis and exploration for orogenic gold mineralization within Archaean Greenstone Belts of Zimbabwe

- Mavuwa, Tavashavira

Authors: Mavuwa, Tavashavira
Date: 2024-10-11
Subjects: Uncatalogued
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/464944 , vital:76559
Description: The Blue Rock gold deposit was re-discovered by African Consolidated Resources (ACR) in 2007, over a defunct historical gold mine at Blue Rock, during a regional geochemical soil sampling program, within the Gadzema Greenstone Belt (GGB), in Central Zimbabwe. Most significant orogenic gold deposits within this belt occur as BIF- and quartz vein hosted orebodies. But unlike them, gold mineralization at Blue Rock is associated with felsite and quartz porphyry rocks. The GGB is a northern extension of the Midlands Greenstone Belt (MGB), where the common occurrence of mineralized felsites, in close association with major gold reefs within numerous gold mines is well documented. But no significant effort was directed towards their understanding or exploration in the past. They were never considered viable exploration targets for significant economic gold deposits, until recently. More attention was instead focused on high-grade BIF and quartz vein hosted gold, that dominate most orebodies exploited by numerous mines within the belt. At Blue Rock, ACR defined a significant JORC compliant felsite-hosted gold resource of close to a million ounces, which represents a brand new attractive open-pit mining opportunity. But the successful exploration for such type of mineralization, whose footprint is so different from the common ones previously mined within the GGB, no doubt, calls for a good understanding of this type of mineralization. Which makes felsite-hosted gold mineralization a prime candidate for research, based on a deposit whose discovery and development, I was fortunate to be part of during the past few years. In this contribution, the genesis, localization and economic significance of felsite-hosted gold mineralization is investigated, using the gold deposit at Blue Rock as a case study. The deposit could be understood best through the Mineral Systems Approach, used in this study to interrogate alternative ideas about its genesis using published information and deposit-scale exploratory data. Results from the synthesis of published information on the evolution of Archaean Greenstone Belts and genesis of their host orogenic gold deposits, are consistent with models that view orogenic terrains as having formed through horizontal accretion in modern-day like subduction-accretion systems, at continental margins, where orogenic gold deposition occurred via processes that could be explained quite simply, through a universal orogenic gold mineral systems model. According to this model, orogenic gold deposits are believed to have formed from near neutral fluids containing dissolved gold, generated directly from the devolatilization of a subducted oceanic slab together with its overlying gold-bearing sulphide-rich sedimentary package, or indirectly through fluid released from a mantle lithosphere that was originally metasomatized and fertilized during an earlier subduction event. The fluid migrated up-dip from the mantle to crustal levels, through advection or seismic pumping along lithosphere- to crustal-scale fault zones, to form orogenic gold deposits within lower order structures. If these models are all accurate, then the GGB formed through subduction-related east-directed horizontal accretion at the continental margins of the Sebakwe Proto-Craton (SPC), and the genesis of felsite-hosted gold mineralization at Blue Rock could be explained eloquently through a universal orogenic gold model, in which mantle derived auriferous fluids were localised within lower order structures associated with felsites during the late stages of terrain accretion. Evidence from surface mapping and 3D modelling of exploratory drilling data, conducted during this research, strongly support the argument that the felsite hosted gold mineralization at Blue Rock, is neither unique nor accidental. It is just but, a simple product of the conjunction of favourable geological factors, no different to those that birthed typical GGB orogenic gold mineralization hosted within sheared sulphidic BIFs and quartz vein reefs. They all share the same geodynamic setting, fertility, preservation and regional architectural factors reminiscent of accretionary orogenic settings, albeit with differences in local architecture, variably controlled by geochemical and rheological properties of the different local host rocks. At deposit scale, the felsites occur as small dykes and sills emplaced along pre-existing structural zones of weakness. Gold mineralization is structurally controlled and associated mostly with brittle-ductile shears. During deformation, rheological contrast played a significant role in the selective failure of the more competent felsite rocks, resulting in the creation of permeability channels that allowed fluid migration. The more brittle and competent felsites acted as rigid bodies, that localised strain along their contacts with the surrounding less competent ductile mafic schists which acted as a relatively less permeable fluid cap rock. The irregular felsite contact zones with surrounding mafic schist caused a significant variation in the orientation of local principal maximum stress relative to the internally imposed regional stress, causing anomalously low minimum stress zones at deposit scale. Gold deposition occurred within low minimum stress structural traps dominated by sheared felsite contacts and their fractured interiors as well as triple junctions formed by complex structural geometries created by multiple felsite intrusions. The felsite hosted gold at Blue Rock can therefore be recognized as an orogenic gold mineral system archetype, for which an occurrence model is proposed. Understanding this type of mineralization is key for developing a robust exploration strategy - one that could be applied in a predictive capacity in exploration, to locate new economic gold deposits especially within well-endowed mature orogenic terrains, where exploration risk could be minimized by leveraging on new forward-thinking initiatives like Artificial Intelligence (AI) to re-analyze data from previous mining and exploration, allowing for a faster route to a return on investment. In a world of diminishing natural resources, the potential for previously ignored gold mineralization like the one at Blue Rock, becomes very significant. The prophetic words of Foster (1984), writing in Gold ‘82, therefore remain true and relevant to our time, that; “…. the way ahead for successful gold exploration is to search for new deposits not commonly recognized – in auriferous muds, disseminations in carbonate rocks, porphyries, and in felsic intrusive and extrusive volcanics…”. , Thesis (MSc) -- Faculty of Science, Geology, 2024
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Date Issued: 2024-10-11

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Controls of lateral and vertical variations in the geochemistry of the Hotazel Fe-Mn Formation at Nchwaning and Gloria mines, Kalahari Manganese Field, South Africa

- Dorbor Jr., Stephen Baysah

Authors: Dorbor Jr., Stephen Baysah
Date: 2023-10-13
Subjects: Manganese ores Geology South Africa , Iron ores Geology South Africa , Geochemistry Geology South Africa , Kalahari manganese field , Banded iron formation , Hotazel mine
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/424621 , vital:72169
Description: The Paleoproterozoic Kalahari manganese field (KMF) in the Northern Cape Province, South Africa, hosts a large resource of manganese ores that has been of great interest over many decades. The Kalahari Manganese deposit (KMD), which is the largest of five erosional relics of the Hotazel Formation in the KMF, hosts three beds of Mn ores with alternating layers of banded iron formation (BIF) and hematite lutite. These three rock types are all evaluated for their mineralogy and geochemistry in this study, with emphasis on lateral and vertical distributions across the Gloria and Nchwaning Mines in the northernmost KMF, an area of high-grade, hydrothermally altered Mn mineralisation. The Mn ores of the Hotazel formation are traditionally categorised into two types. The carbonate-rich low Mn grade (Mn≤40 wt. %) ores (Mamatwan-type) domninates the largest part of the KMD, while carbonate-free, high Mn grade (Mn≥ 45 wt.%) ore (Wessels-type) occurs in the northernmost KMD. The Wessels-type ores are considered as the hydrothermally altered product of Mamatwan-type ores, and as indicated above, are the focus of this study. Five drill cores containing Wessels-type ores from the Nchwaning and Gloria area of the northern KMD were analysed to help understand the petrographic and particularly the geochemical variations in the Hotazel Fe-Mn Formation, both laterally for a given Mn layer of the three, and vertically across Mn layers as captured in specific drillcores. Petrographic and whole-rock geochemical results obtained from the three rock types of the Hotazel Formation show variations in their mineralogical and geochemical compositions, especially in the high-grade Mn ores themselves. Most of the samples of the BIFs layers are dominated by hematite and chert occurring in banded fashion, which is typical of a normal carbonate-free altered BIF discussed in this thesis. The BIFs can also be locally enriched in hematite (ferruginised), occurring as massive hematite ores usually at the top of the stratigraphic profiles. The presence of aegirine-rich assemblages is also noted occurring in some of the BIF and hematite lutite sections immediately above and below the Mn ore beds. The high-grade Mn ore beds vary greatly in mineralogy and texture of the ores laterally and even within a single drill core. In an extreme case, a single drillcore sampled from the Gloria mine (GL57) contains high-grade Wessels-type ore in the upper Mn bed and low-grade, Mamatwan-type ore in the lower Mn layer. Geochemically, the Mn ore bodies also show substantial geochemical variability, although a net increase in the Mn grade downward is usually characterised by a corresponding depletion in mainly bulk Ca, Si and carbonate. However, the Fe content appears to be consistently higher in the upper ore bodies of the drillcores than the lower ones, and the increase in the concentration of the Fe-oxide expectedly causes a relative decrease in the bulk Mn-oxide concentration, usually expressed as an antithetic relationship between the two elements. In terms of trace element distributions, this appears to be more significant in the Mn ores than the other two rock types affected by the same alteration process, probably due to the presence of Mn phases such as hausmannite and braunite serving as good hosts to several trace elements. Cu, Zn, Pb and to a lesser extent Mo are trace metals that appear to show elevated concentration levels (net enrichments) in high-grade Mn ore by comparison to the presumed Mamatwan-type protolith. Ba is an additional element of clear enrichment, manifested mainly as the mineral barite. The Northern KMD has a complex post-depositional history, which includes the intrusion of NE-SW-trending dykes, formation of the Mapedi/Gamagara erosional unconformity, normal faulting associated with the Wessels event and major thrust faults in the western part of the northern KMD. These structural events all have the potential to have contributed to the alteration and subsequent enrichment of the Mn ores in the Nchwaning and Gloria area. As such, the mineralogical, textural, and geochemical variations observed here can tentatively be attributed to the different structural features in the northern KMD. Classic interpretations suggest that normal N-S-trending fault structures have acted as fluid conduits for hydrothermal fluids, which led to the metasomatic alteration of the Mn ore body laterally. Drill cores proximal to and evidently affected by fault-controlled alteration in the SE and SW-portions of the Nchwaning area, have comparable mineralogical and geochemical characteristics for both ore bodies (upper and lower) with subdued alteration effects from the unconformed contact above. Fluids associated with the Mapedi/Gamagara unconformity, would have percolated down-stratigraphy causing oxidative ferruginisation, which led to the formation of massive hematite ores in the top BIF layers and ferruginised Mn ores in the Mn ore beds. This alteration effect appears more prominent in a drill core from the northern part of the study area where the unconformity contact appears more proximal to the upper Mn bed. Drill cores located in the western part of the Nchwaning area seem to also capture evidence of fluid alteration with enrichment in Na recorded in the local abundance of the mineral aegirine. Finally, the dyke structures appear to have acted as impermeable fluid barriers to both lateral and possibly down-dip fluid-flow. , Thesis (MSc) -- Faculty of Science, Geology, 2023
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Date Issued: 2023-10-13

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Origin and metallogenic significance of alkali metasomatism in the Paleoproterozoic Mapedi Formation, Kalahari Manganese Field, South Africa

- Ikwen, Emmanuella Biye

Authors: Ikwen, Emmanuella Biye
Date: 2023-10-13
Subjects: Metasomatism (Mineralogy) South Africa , Banded iron formations , Kalahari manganese field , Sugilite , Hydrothermal alteration , Quartzite
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/424632 , vital:72170
Description: The occurrence of alkali-rich metasomatic assemblages has been widely reported in various regions of the Kalahari Manganese Field (KMF). This alkali metasomatism has been characterized by the secondary introduction of elements such as K, Na, Li, Ba, P, V, Zn, As, amongst others. This study further explores the possibility of widespread alkali metasomatism in the KMF by reporting on and examining the occurrence of sugilite and other alkali-rich minerals at the contact between the Transvaal and Olifantshoek Supergroups in the Hotazel Mine area of the north-eastern KMF. The lithologies observed at the contact show macroscopic (such as cross cutting veins) and microscopic evidence of hydrothermal alteration. Using analytical methods such as X-ray diffraction, X-ray fluorescence, and scanning electron microscopy, results showed that in the north-eastern region of the KMF, the metasomatism observed at the Transvaal-Olifantshoek contact is mainly characterized by enrichment in sodium, and the occurrence of sodium minerals, predominantly in the form of aegirine. The aegirine forms exclusively in the quartzites of the Mapedi Formation along with minerals such as sugilite, baryte, banalsite, amongst others. Albite also occurs within the quartzites, but also within the Mapedi red shales. The secondary nature of these minerals is established by geochemical comparisons with pristine, as well as alkali-metasomatized samples of the same formation which were obtained from other parts of the KMF and Postmasburg. These comparisons showed that the Mapedi quartzites in the north-eastern KMF have undergone extensive oxidation compared to samples of the same formation which were obtained from Postmasburg. The north-eastern quartzites have an average hematite abundance of 17 wt.% compared to Postmasburg quartzite which have an average of 7 wt.% hematite. Furthermore, some quartzite samples contained up to 40 wt.% in hematite content. The comparisons also showed that Mapedi quartzites from the north-eastern KMF are substantially more sodium enriched compared to Mapedi quartzites from the Postmasburg region, which on average have sodium oxide content below detection limits. Geochemical comparisons were made between pristine Hotazel Formation samples from north-western KMF (Gloria Mine) and samples obtained from the north-eastern KMF (Hotazel Mine). Results showed that the samples obtained from the top of the Hotazel Formation (in the Hotazel mine area) are likely altered hematite lutite and not Banded Iron Formation, evident by their substantially high manganese oxide content (over 30 wt.% in some cases). When compared to pristine samples, the lutite also showed evidence of hydrothermal alteration, predominantly in the form of phosphate and barium enrichment, evident by the occurrence of baryte and apatite. The alkali metasomatism occurring at the contact between the Transvaal and Olifantshoek Supergroups was shown to be predominantly characterized by enrichment in Na, K, Li, Al, Ba, Sr, and P. The metasomatism characterized in this study was also proposed to possibly post-date an earlier metasomatic event which was characterized by leaching of silica and extensive oxidation of the rocks observed at the Transvaal-Olifantshoek contact in the north-eastern KMF. The occurrence of the alkali-rich minerals outlined above geochemically parallels other alkali-rich metasomatic assemblages reported in other parts of the KMF, as well as in the Postmasburg Manganese Field. Thus, based on the consistent occurrence of secondary, alkali-rich mineral assemblages across the KMF, characterized by the common occurrence of aegirine along with minerals such as sugilite and albite, there is evidence of a large-scale alkali metasomatism in the KMF. This study also explores the possible role that the Transvaal-Olifantshoek unconformity might have played in acting as a major conduit for fluid propagation because the observed mineral assemblages occur right at the contact between the Hotazel and Mapedi Formations. The occurrence of the alkali-rich minerals predominantly around the unconformity, as well as the relative depletion of phosphates in stratigraphically deeper parts of the Hotazel suggest that the fluid metasomatism was aided by the Olifantshoek-Transvaal unconformity surface. This study concludes that there is evidence for a strong link between the metasomatism occurring at the contact between the Hotazel and Mapedi formations (in the north-eastern KMF) and what is observed in the broader KMF region. , Thesis (MSc) -- Faculty of Science, Geology, 2023
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Date Issued: 2023-10-13

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Chemostratigraphy of the lowermost iron-manganese cycle of the Hotazel Formation, and implications for its primary depositional environment

- Masoabi, Ntseka Thomas

Authors: Masoabi, Ntseka Thomas
Date: 2022-10-14
Subjects: Chemostratigraphy , Great Oxygenation Event , Manganese ores Geology South Africa Northern Cape , Banded iron formation
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/362938 , vital:65376
Description: The giant Kalahari Manganese Field (KMF), located in the Northern Cape Province, South Africa, comprises approximately half of the world’s manganese resources, estimated at about eight billion tons at grades ranging from 20-48 wt%. The KMF is linked to a period in geological time when the Earth’s atmospheric and oceanic conditions underwent a major transition from oxygen-deficient to oxygen-enriched conditions – an event famously referred to as the Great Oxidation Event (GOE) that occurred around 2.4 Ga. The KMF deposits are hosted in Banded Iron Formation (BIF) of the Paleoproterozoic Hotazel Formation in the uppermost Transvaal Supergroup. The sedimentary Mn ores are interbedded with Hotazel BIF in the form of three alternating depositional cycles of BIF, transitional hematite lutite and laminated, carbonate-rich manganese ore. The lowermost and thickest of the three cycles is the most economically significant and has been mined for several decades on a large scale from the southernmost KMF. In this study, two drill cores from the southern KMF were inspected, logged and sampled at a high resolution of approximately half-meter interval per sample. The selected cores, namely G774, capturing the lower portion of the Hotazel Formation from the Mamatwan locality, and MP-56, capturing the corresponding portion from the Middleplaats locality, are geographically proximal to each other, with a horizontal distance of roughly 3 km separating the two of them. The G774 drill core is characterized by a conspicuously thick manganese layer covering a thickness of 50 m, with the overlying BIF reaching a total thickness of 11 m. The MP-56 drill core, on the other hand, has a relatively thinner corresponding manganese layer of 30 m in thickness, while the overlying BIF layer exhibits a thickness of 24 m. The extent of sampling up-section was constrained by an apparently coeval black shale layer which represents the chosen upper stratigraphic marker for the lower part of the Hotazel section in the broader area that is under investigation in this thesis. That way, a high resolution chemostratigraphic approach was employed to elucidate the potential factors contributing to the relative sedimentary lateral thickness variations seen across the southernmost KMF. High-resolution geochemical data were used to explore relationships and signals that might constrain relative precipitation rates for iron and manganese against detrital species, fluctuating redox conditions in the original environment of deposition, and chemostratigraphic correlation. All geochemical data (i.e., major oxides, minor and trace elements and carbonate carbon isotopes) were obtained respectively through employing X-ray Fluorescence (XRF), Laser Ablation Inductively Coupled Mass Spectrometry (ICP-MS), and Gas-source mass spectrometry. Comparative considerations made between the bulk geochemistry of the two sequences (i.e., Mamatwan and Middleplaats sections) reveal that periods of high-Mn deposition in the Hotazel Formation appear to be very Ca-carbonate rich (as indicated by high CaO, LOI and Sr concentrations). This, in turn, suggests that the Mn abundance is in the Hotazel ores is controlled mainly by the silicate phase braunite and is diluted by the deposition of Ca-carbonate through time. Bulk-rock concentration results for trace elements of the High Field Strength Element (HFSE) group (namely Zr, Hf, Y, Nb and Sc) were utilized to constrain the rates of either clastic and/or volcanic detrital inputs, as they traditionally represent refractory mineral particles of a common detrital/volcanic origin. The two chemosedimentary sequences preserve these elements in very low and thus quantitatively negligible concentrations – suggesting that the Hotazel depositional environment received very low and insignificant influx of a terrigeneous detrital component. A selection of these elements was therefore used to deduce, with caution, the relative as opposed to absolute precipitation rate of the major chemical constituents (i.e., Fe + Si vs Mn + carbonate), assuming a constant detrital flux through time. It was found that the relative abundances of Zr, Y and Nb is roughly 1.5 – 2 times as high in the BIF lithofacies relative to the Mn ones at both localities. This led to the inference that the Mn-enriched portion of the sediment must have been deposited at approximately twice the rate that the Fe-rich (BIF) portion was originally deposited. In terms of redox-sensitive elements, the elements Co and Mo seem to reveal the most valuable insights into the redox environment of primary chemical deposition. Cobalt displays a unique pattern in that its highest concentration is attained at the hematite lutite transitions (similarly with the REE in this regard), while very low and seemingly invariant concentration is exhibited within the core of the main orebodies. The same pattern seems to be reproduced to a degree by the corresponding bulk MgO component, whereby MgO abundance maxima are associated with the basal hematite lutite and the hematitic flanks of the Mn-ore zone, while the core of the Mn-rich layer attains relatively low and essentially invariant MgO concentrations. This implicates a close and direct association of Co with the hematite fraction of the rocks and a concurrent enrichment in Mn-rich carbonate (dolomite). On the other hand, Mo seems to have a direct and clear association with peak MnO2 content of the rocks, which in turn presents a high possibility of Mo having adsorbed onto primary Mn-oxyhydroxides in the water column, thus providing evidence that Mn-oxide must have acted as an important Mo sink, at least locally. Finally, the carbonate-carbon isotope results provide a useful tool that brings the two stratigraphic sections “together“, in conjunction with other correlatable chemostratigraphic parameters (e.g. Co, Mg). The results demonstrate that bulk carbon fluxes and isotopic signals in the sediments must reflect primary processes of deposition, and that correlation across two apparently disparate lithostratigraphic sections can be effected. The key finding is that, at times, manganese deposition in one part of a vii stratified basin was evidently accompanied by simultaneous BIF deposition at another, thus painting a very complex picture of massive primary chemical precipitation of Fe and Mn at the dawn of the GOE. , Thesis (MSc) -- Faculty of Science, Geology, 2022
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Date Issued: 2022-10-14

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Constraints on Cr-PGE Mineralisation Models: Geochemical and petrological studies in the Middle Group 1 and 3 Chromitites, Western Limb, Bushveld Complex, South Africa

- Arunachellan, Yogendran

Authors: Arunachellan, Yogendran
Date: 2022-10-14
Subjects: Chromite South Africa Bushveld Complex , Mineralogy South Africa Bushveld Complex , Geochemical surveys South Africa Bushveld Complex
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/362730 , vital:65357
Description: The Bushveld Complex in South Africa has been of interest in various research groups for decades, along with diverse theories regarding its origin, formation, and emplacement. These theories include magma mixing, contamination, and changes in the chamber's ephemeral parameters. Of interest for our current study is the formation of the middle group chromitite layers in the Western Limb. In this research, we aimed to determine the emplacement mechanism of the MG group chromitites by scrutinising the MG 1 and MG 3 layers. In core KD 151, the focus was placed on the MG 3 and MG 1 chromitite layers and their associated silicate rocks; on these regions of the core, time was spent for detailed observations. The differences and similarities of these layers were explored as the study advanced. The objectives were to determine the in-situ or proximal crystallisation of the chromitite by evaluating mineral textures and compositions. This required that we determine the characteristics of the immediate HW (hanging wall) and FW (footwall) to these chromitites, with insights into the relationship that anorthositic zones may offer and examine the PGE profiles of the chromitites in contrasting lithological settings. The sampled borehole was in the Western Limb of the Bushveld Complex; the immediate HW, chromitite layers and FW were divided into sections (2.5 x 5 cm) along selected horizons for a microscale study. The preliminary results of a study on the sub-economic Middle Group (MG) layers within the Critical Zone (CZ), contrasting the MG 1 (Lower CZ) and MG 3 (Upper CZ) chromitite layers of the Rustenburg Layered Suite of the Bushveld Complex, South Africa were analysed. The MG 3 and 1 suites of silicate rocks show disequilibrium textures between the pyroxenes and plagioclase, forming discontinuous olivine rims. These reaction rims are interpreted as products of magmatic aqueous fluid-facilitated reactions with minerals in a sub-solidus state. Deformation of the plagioclase was also noted in MG 1; this fracturing indicates either the transportation of these minerals or compaction by an overlying crystal mush. The MG 3 package of plagioclase, pyroxene and chromite compositions range from An67-78, En71-86 and Cr# of 68-84, respectively. The MG 1 package of plagioclase, pyroxene and chromite compositions are An64-91, En79-88 and Cr# of 70-80, respectively. The Cu/Pd ratio decreases from the base of the FW as it approaches the base of the chromitite, then remains low within the chromitite layer and finally increases upwards in the HW. These trends are observed in both the MG 3 and 1 package, therefore not influenced by the sulphide control. There is a decrease in both IPGE and PPGE upwards as the HW progresses into the chromitite. The FW levels of Ir and Ru increase upwards immediately adjacent to the FW contact, while Pd and Rh concentrations decrease. The whole-rock Mg# indicates a decrease in the MG 3 with a uniform increase in the HW and an erratic upward increase observed in the FW. The chondrite normalised PGE plots show a bell-shaped curve which is evident for the En content of the pyroxenes and the content of plagioclase with the highest values in the chromitite layer itself. The Cr# of the chromite decreases upwards with the highest values along the FW. The Cu/Pd ratio for MG 1 indicates chromitite control rather than sulphide control of the PGE. The whole-rock Mg# decreases in MG 1 with higher uniform values observed in the HW and FW. The geochemical and petrological data from the MG group study revealed that in situ fractional crystallisation seems unlikely as the sole mechanism for their formation in the CZ. A model is suggested in which the migration and transport of a magmatic slurry type suspension with accompanying hydrous fluids would likely have resulted in the emplacement of these chromitite packages along with the PGE mineralisation of the chromitites. , Thesis (MSc) -- Faculty of Science, Geology, 2022
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Date Issued: 2022-10-14

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Lateral and vertical mineral-chemical variation in high-grade ores of the Kalahari Manganese Field, and implications for ore genesis and geometallurgy

- Motilaodi, Donald

Authors: Motilaodi, Donald
Date: 2022-10-14
Subjects: Manganese ores , Geometallurgy , Hydrothermal alteration , Petrology , Mineralogy , Geochemistry
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/362972 , vital:65379
Description: The Kalahari Manganese Field (KMF) is a world-class resource of manganese ore hosted by the Paleoproterozoic Hotazel banded iron formation. KMF ores are categorised into two main types, i.e., low-grade, carbonate rich, braunitic ore (Mn≤40wt%) and carbonate-free, high-grade, Ca-braunite+hausmannite ore (Mn≥44wt%). High-grade ores, also known as Wessels type from the homonymous mine in the northernmost KMF, are thought to have formed from variable degrees of hydrothermal carbonate and silica leaching from a low-grade ore precursor, termed Mamatwan-type after the homonymous mine in the southernmost KMF. This project aims to conduct a mineralogical and mineral-chemical study of representative manganese ore samples from a suite of drillcores intersecting both the upper and the lower layers in the northern KMF, covering the areas of Wessels, N’chwaning and Gloria mines. Petrographically, the high-grade Mn ore displays great variability in three-dimensional space. Texturally, the ores exhibit a great variety of textures which may or may not show preservation of the laminated and ovoidal textures that typify the postulated low-grade protore. There is also significant variation in the mineralogical and geochemical characteristics of the high-grade Mn ores both vertically and laterally. Vertical variation includes, probably for the first time, variability between the upper and lower ore layers within individual drillcores of the Hotazel sequence. Mineralogically, the ores contain variable modal abundances of the ore-forming minerals braunite (I, II, “new”) and hausmannite, and much less so of bixbyite, marokite and manganite. Common accessories include andradite, barite and low-Mn carbonate minerals. Chemically, the dominant ore minerals braunite and hausmannite, contain Fe up to 22 and 15wt% respectively, which accounts for the bulk of the iron contained in the ores. Braunite compositions also exhibit a large range with respect to their ratio of Ca/Si. Mineral-specific trace element concentrations for the same minerals measured by LA-ICP-MS, reveal generally large variations from one element to the other. When normalized against the trace element composition of bulk low-grade precursor ore, strong enrichments are recorded for both hausmannite and braunite in selected alkali/alkali earth elements, transition metals and lanthanides, such as Sc, Co, Zn, Cu, Pb, La, and Ce. These are akin to enrichments recorded in average high-grade ore. Although there is also no obvious relationship between Fe content in both hausmannite and braunite and their trace element abundances, the drillcore that captures high-grade ore with the highest trace element concentrations appears to be located most proximal to a major fault. Results collectively suggest that high-grade Mn ores of the KMF have undergone a complex hydrothermal history with a clear and significant metasomatic addition of trace elements into ore-forming minerals. First order trends in the mineralogical and mineral-chemical distribution of the ores in space, suggest hausmannite-dominated ores near the Hotazel suboutcrop, and an apparent decline in ore quality with braunite II-andradite-barite-calcite ores as the major graben fault is approached in a southwesterly direction. The latter trend appears to be at odds with prevailing fault-controlled alteration models. Elucidating that hydrothermal history of the Wessels-type high grade Mn ores of the KMF, will be crucial to understanding the compositional controls of these ores in space, and the potential impact thereof in terms of geometallurgy. , Thesis (MSc) -- Faculty of Science, Geology, 2022
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Date Issued: 2022-10-14

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The geology, mineralogy, structure and economic aspects of the pegmatite-hosted Swanson Tantalum Deposit, Tantalite Valley area, southern Namibia

- Pepler, Laubser

Authors: Pepler, Laubser
Date: 2022-04-06
Subjects: Pegmatites South Africa Pofadder (Region) , Tantalum South Africa Pofadder (Region) , Geology South Africa Pofadder (Region) , Mineralogy South Africa Pofadder (Region) , Pegmatites South Africa Pofadder (Region) Structure , Pegmatites Economic aspects South Africa Pofadder (Region) , Pofadder Shear Zone‎ , Tantalite Valley Complex‎ , Orange River Pegmatite Belt‎ , Lower Fish River/Onseepkans Thrust Zone‎
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/291303 , vital:56843
Description: This study presents the geology, mineralogy, structure, and economic aspects of the recently explored Swanson Tantalum Deposit occurring within the Namaqua Sector of the Namaqua Natal Metamorphic Province, Tantalite Valley area, southern Namibia. It is an LCT-type pegmatite hosted (microlitetantalite- tapiolite ± spodumene – lepidolite - zinnwaldite) tantalum deposit forming part of a highly localised sill-and-dyke swarm comprised of 15 shallow dipping and significantly mineralised pegmatites. This deposit forms part of the western portions of the regionally developed∼ 1040 – 950 Ma Orange River Pegmatite Belt (ORPB) which was locally emplaced syn-tectonically into competent host rocks in the core zone of the late-stage crustal scale transcurrent dextral, ductile to brittle-ductile D4 Marshall Rocks – Pofadder Shear Zone (MRPSZ), where it crosscuts the rocks of the D2 Lower Fish River - Onseepkans Thrust Zone (LFROTZ). A JORC Maiden Mineral Resource of 1.2 Mt @ 412 ppm Ta2O5 + 76 ppm Nb2O5 + 0.29 wt. % Li2O (with an applied cut-off grade of 236 ppm Ta2O5 and a minimum thickness of 1 m) has recently been estimated for the deposit. The deposit is currently being advanced to feasibility stage with the aim of outlining economic Mineral Reserves. It currently hosts a globally significant and market-relevant “high grade – low tonnage” tantalum Mineral Resource. Recent litho-structural mapping of this deposit has shown that its structural setting encompasses a locally developed lower strain extensional quadrant associated with the mega-scale shear zone bound competent mantle porphyroclast: the mafic-ultramafic Tantalite Valley Complex (TVC), or TVC megaclast. A succession of syn-D4 MRPSZ-hosted granitic melts comprising earlier leucogranite intrusions and later mineralised pegmatites of the Swanson Tantalum Deposit have variably utilised this extensional structure. The earlier leucogranites have clearly exploited mylonitic foliations associated with the development of core zone of the MRPSZ, while the mineralised pegmatites have utilised later-stage shallow-dipping Riedel fractures developed within more competent host rock. The tantalum tenor of pegmatites comprising the Swanson Tantalum Deposit is clearly structurally controlled, with tantalum tenor increasing from NW towards the SE over relatively short distances, toward the TVC megaclast. Although highly speculative without robust geochronological and petrographic investigation, field observations from this study highlights that the host rocks to the Swanson Tantalum Deposit, namely the mottled hybrid metagabbro (HMG), usually described as being syn-D2 in age (∼ 1200 – 1100 Ma), may possibly be syn-D4 in age (∼ 1040 – 950 Ma). If this is proven to be true, it may represent the earliest syn-D4 melt known for the MRPSZ. The Swanson Tantalum Deposit area therefore represents a prime area for studying and potentially constraining the upper and lower age limits of the MRPSZ. , Thesis (MSc) -- Faculty of Science, Geology, 2022
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Date Issued: 2022-04-06

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Trace element and sulphur isotope variations of sulphides in the Koperberg Suite, O’okiep Copper District, Namaqualand, South Africa: implications for formation of sulphides and the role of crustal sulphur assimilation

- Marima, Edmore

Authors: Marima, Edmore
Date: 2022-04-06
Subjects: Sulfur Isotopes , Magmatism South Africa Namaqualand , Sulfides , Koperberg Suite (South Africa) , Copper sulfide , Sulfur Absorption and adsorption
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/291117 , vital:56820
Description: The major economic copper sulphide deposits hosted in the late Mesoproterozoic intrusions of the Koperberg Suite in the O’okiep Copper District immediately overlie sulphur-bearing paragneisses of the Khurisberg Subgroup in an otherwise low-sulphur granitic basement. The dominant sulphide assemblage (chalcopyrite and bornite) hosted in the Koperberg Suite is also atypical of the intermediate solid solution (iss) assemblage (chalcopyrite and pyrrhotite) observed in most Cu-Ni magmatic sulphide deposits. This study presents sulphur isotope and in-situ trace element analysis of sulphides from the Koperberg Suite and the Khurisberg Subgroup with the view of placing constraints on the role of sulphide-bearing supracrustal metasedimentary of the Khurisberg Subgroup as a source of additional sulphur in the genesis of these deposits, and ore-forming (sulphide formation) processes which result in trace element variations registered by sulphides hosted in the Koperberg Suite. The high concentrations (up to 2100 ppm) of monosulphide solid solution (mss)-incompatible trace elements (e.g., Te, Se, Bi, Ag, Pb), and the depletion in Ni and Co (<40 ppm) of sulphides hosted in the Koperberg Suite are instead consistent with the derivation of such sulphides from a Cu-rich sulphide melt which segregated from a Ni-rich sulphide melt prior to magma emplacement in the middle crust, in agreement with one of the petrogenetic models for the Koperberg Suite proposed in the existing literature. The low S/Se ratios ( ̴650-10300) of sulphides hosted in the Koperberg Suite and the high S/Se ratios ( ̴18800-56000) registered by the main sulphide phase (pyrite) in the Khurisberg Subgroup argues against crustal contamination of the Koperberg Suite magmas by the Khurisberg Subgroup. The S/Se and Cu/S ratios of coexisting bornite and chalcopyrite hosted in the Koperberg Suite are positively correlated with the bornite modal abundance in the Koperberg Suite. Such trends are interpreted to be consistent with progressive oxidation of sulphide melt, a process which results in the crystallisation of iss-bornite assemblage and/or replacement of iss with bornite due to the enrichment of Cu and depletion in S of the sulphide melt. The oxidation of sulphide melt is likely to have been effectuated by the fractional crystallisation of mss in a prior sulphide melt segregation event and/or the fractional crystallisation of Fe2+-dominated silicate phases. Fractionation of the Cu-rich melt sulphide melt (segregated from mss) also tends to enrich the residual sulphide melts in Se. Thus, the chalcopyrite-dominated assemblage with S/Se ratios of ̴1300-10200 observed in the less basic rocks in the Koperberg Suite (leucodiorites and leuconorites) is interpreted to have formed from the least evolved sulphide melt, whereas the bornite-dominated assemblage with S/Se ratios of ̴650-5500 observed in the more mafic members of the Koperberg Suite (orthopyroxenites and norites) is interpreted to have formed from the most evolved sulphide melt. The ẟ34S isotopic signatures in sulphides of the Koperberg Suite (-1.4 to +1.91‰) and the proposed contaminant, the Khurisberg Subgroup (-1.2 to +3.5‰), overlap with the those of the Koperberg Suite below the Khurisberg Subgroup (+0.74‰) and typical mantle-derived magmatic rocks (0 ± iv 2‰). Hence, the sulphur isotope variations are inconclusive as an indicator of possible crustal sulphur assimilation into the intruding mantle magma. However, considering the trace element systematics and the sulphur isotope data, the Koperberg magmas likely attained sulphur saturation at deeper crustal levels. , Thesis (MSc) -- Faculty of Science, Geology, 2022
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Date Issued: 2022-04-06

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Characterisation of the ultramafic and carbonatite components of the Schiel Alkaline Complex in the Limpopo Province of South Africa

- Mahomed, Uzayr

Authors: Mahomed, Uzayr
Date: 2021-10-29
Subjects: Ultrabasic rocks South Africa Limpopo , Carbonatites South Africa Limpopo , Geology South Africa Limpopo , Mica South Africa Limpopo , Biotite South Africa Limpopo , Magmatism , ‎Schiel Alkaline Complex , ‎Phoscorite , ‎Glimmerite
Language: English
Type: Academic theses , Master's theses , text
Identifier: http://hdl.handle.net/10962/294768 , vital:57253
Description: Owing to the poor documentation of the phoscorite-carbonatite association present in the Schiel Complex and the associated economic potential of other known phoscorite-bearing complexes, the Schiel Complex is widely thought to have similar economic potential. This complex is often compared to the lucrative Phalaborwa Complex, as it is thought to have crystallised from a common parental melt, with a similar age of emplacement. This study aims to provide clarity on the physical and chemical characterisation of the various rock types present in the Schiel Complex, with this study being the first petrological investigation based on fresh in-situ samples gathered from 3 borehole cores which were drilled by FOSKOR in the 1960s. The sampled sections of the ultramafics from the Schiel Complex are comprised of end-member rock compositions of either magmatic phoscorites or pyroxenites or metasomatic glimmerites, where gradational contacts between these various end-members produce rock varieties that contain characteristics of one or more end-member types. Carbonatite rocks are present as medium-grained, coarse-grained and banded calcio-carbonatite varieties where the carbonatite rocks are proposed as being the metasomatic medium for glimmerite production. Contrary to previous research, the structure of the ultramafic and carbonatite bodies are present as vein and veinlet structures which seem to originate from a single pipe-like body, from which these rock types intruded into the surrounding syenitic country-rock. Metasomatic alteration of the ultramafic sections of the Schiel Complex also show that the carbonatite rocks must have intruded after some ultramafic magmatism. The presence of the same minerals, with similar chemistries, in both the ultramafic and carbonatite rocks as well as similar REE chondrite-normalised plots show that the various rock types may have originated from a common parental magma, where the accumulation and crystallisation of minerals is the most likely factor in producing the various Schiel Complex rock varieties, causing silicate minerals to be present in the carbonate fraction of the magma, and carbonate minerals in the silicate fraction of the magma. Apatite is the expected rare earth element (REE) mineralising mineral in phoscorites, but is shown to be depleted in REE content in the Schiel Complex due to metasomatic fluid infiltration causing the scavenging and dissipation of REEs. These rocks have also crystallised containing no significant copper-bearing mineralisation, contrary to that which is seen in the Phalaborwa Complex. A comparison of mica minerals between the Schiel Complex rocks and the Phalaborwa Complex rocks show that the two complexes have undergone unique emplacement processes and should not be considered as sister complexes. Efforts to date the glimmerite and carbonatite rocks based on zircon grain U/Pb geochronology proved unsuccessful in constraining the current ages of emplacement provided by previous researchers, but rock relationships show that the current accepted sequence of events cannot be correct, providing scope for further research. This study provides an update on the chemical and physical characteristics, based on the only available sample suite of the ultramafic and carbonatite components, of the Schiel Complex, increasing the depth of documentation of these rare rock types and aiding in refuting some conclusions on the genesis, emplacement and evolution of the Schiel Complex proposed by previous research. , Thesis (MSc) -- Faculty of Science, Geology, 2021
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Date Issued: 2021-10-29

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Genetic connectivity of the roundjaw bonefish (Albula glossodonta) in the Southwest Indian Ocean

- Talma, Sheena Claudia Aisa Lydie

Authors: Talma, Sheena Claudia Aisa Lydie
Date: 2021-10-29
Subjects: Bonefish Mauritius , Bonefish Seychelles , Bonefish Genetics , Bonefish Habitat , Bonefish Geographical distribution , Bonefish Larvae Dispersal , Genetic markers , Cytochrome b , Fish populations Mauritius , Fish populations Seychelles , Marine ecotourism , Saltwater fly fishing , Bonefish fisheries Catch effort
Language: English
Type: Master's theses , text
Identifier: http://hdl.handle.net/10962/192174 , vital:45202
Description: The Southwest Indian Ocean (SWIO) islands of Mauritius and Seychelles are both highly dependent on tourism and fisheries for their economies. One of the growing ecotourism sectors is saltwater fly fishing, an industry based on catch-and-release fishing for a host of species, including bonefishes. Bonefishes (Albula spp.) have received significant research attention in the Pacific and Atlantic Oceans, with only sporadic research conducted in the Indian Ocean. My project aimed to investigate the genetic connectivity of the roundjaw bonefish (Albula glossodonta) in two island states (Seychelles and Mauritius) within the SWIO using a mitochondrial genetic marker (cyt-b) and next generation sequencing (ddRADseq). Samples collected were grouped based on their spatial distribution. The Seychelles consisted of four island groups (Inner Island Group, Aldabra Group, Amirantes and Alphonse Group, and Farquhar Group) whereas Mauritius was represented by one island group (Saint Brandon). Genetic analyses were undertaken between and within each of these groups. Mitochondrial cytochrome-b identified two species of bonefish: Albula glossodonta and Albula oligolepis; the latter was only genetically identified from the Inner Island Group. I hypothesise that this is due to habitat partitioning, with A. oligolepis being a deeper dwelling bonefish species compared to A. glossodonta, which occupies shallow water habitats such as sand flats, atoll lagoons and reef flats. Neutral SNP loci revealed a panmictic pattern of distribution for A. glossodonta throughout the Seychelles Island groups but showed a pattern of weak structure between Seychelles and Mauritius. Genetic diversity indices such as allelic richness, showed low diversity across the sampling sites (AR range: 1.761-1.889). Population structure tests such as pairwise FST showed low but significant population structure. The highest FST indices were recorded between the Aldabra and Farquhar Groups, as well as the Aldabra and Saint Brandon Groups (0.044 ± 0.000 and 0.040 ± 0.000, respectively). Descriptive tests such as PCA and DAPC showed similar trends, whereby Saint Brandon clustered separately from the other samples from the Seychelles Island groups. However, these trends were Abstract seen at very low variations (PCA axes 1 and 2 accounted for only 2.0 and 1.9 % of the total variation, respectively). A population assignment test grouped the individuals as one ancestral population. A spatial principal component analysis showed that Saint Brandon was dissimilar to the Seychelles Island groups. Like other Elopomorph species, bonefishes have leptocephalus larvae capable of long-distance dispersal which may explain the well-mixed genetic population observed within the Seychelles islands. Although currents within the Indian Ocean, especially on a mesoscale, are not well understood, the South Equatorial Current likely facilitates connectivity between the Seychelles islands while also limiting gene flow between Seychelles and Mauritius. Understanding population structure is important for informing the appropriate management and conservation strategies, especially in oceanic nations where data informing important industries like tourism and fisheries are often limited. The bonefish fly fishing industry is well-known to be a lucrative sector, generating, for example US$ 1.4 million a year in the Bahamas. This study recognised that there are numerous knowledge gaps relevant to the bonefish industry that need to be addressed, including: 1) understanding the socio-economic importance of fly fishing to island states like Seychelles, 2) estimating the abundance and species distribution of bonefishes within Seychelles, 3) understanding effectiveness of MPAs for recreational fishery species like bonefish and, lastly, 4) generating more fishery-relevant biological information on the heavily targeted fly fishing species within Seychelles. These needs must be met to inform management plans and to better manage the fly fishing ventures that target species like bonefish. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
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Date Issued: 2021-10-29

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Genetic relationships between migmatites and the Swartoup Pluton in the Swartoup Hills (central Namaqua Belt)

- Schmeldt, Graeme Alvin

Authors: Schmeldt, Graeme Alvin
Date: 2021-10-29
Subjects: Migmatite South Africa Northern Cape , Intrusions (Geology) South Africa , Metamorphic rocks South Africa Northern Cape , Metamorphism (Geology) South Africa Northern Cape , Onseepkans (South Africa) , Namaqualand (South Africa) , Anatexis , Swartoup , Koenap
Language: English
Type: Master's theses , text
Identifier: http://hdl.handle.net/10962/192162 , vital:45201
Description: The central Namaqua Metamorphic Complex can be characterised by long-standing high-temperature (up to granulite/amphibolite facies) conditions between _ 1300 and 1100Ma, inevitably resulting in widespread metamorphism and plutonism. Hosted within a NW–SE striking antiformal structure about 40 km east of Onseepkans, Northen Cape, South Africa, in the Swartoup Hills, lies the Swartoup Pluton. The Swartoup Pluton was sampled and described in hand specimen and thin section. The study area was photographed, with all data presented in this study. The various rock types are readily discerned in the field due to their characteristic weathering colours and overall fabrics. The Swartoup granodioritic body is hosted within metasediments of the Bysteek and Koenap Formations, of the Arribees Group. The package was later intruded by another later granitoid, the Polisiehoek Granite-gneiss. The Bysteek Formation, a wall rock to the S-type Swartoup Pluton, reacted at the contact with the igneous body resulting in localised feldspathic granites and granodiorites with prominent, often euhedral, garnet, pryoxene and titanite. The Swartoup Pluton is divided into two subgroups. The first is characterised by higher P2O5 contents, _ 0.3 – 0.4 wt.%, shown with a narrower constraint on its Rb contents, _ 80 – 160 ppm, than the second, with _ 0.14 – 0.4 wt.% P2O5 and 20 – 310 ppm Rb. Meanwhile the Polisiehoek Granite-gneiss shows _ 50 – 420 ppm Rb and _ 0.04 – 0:1 wt% P2O5. As a whole, the Swartoup Pluton is characterised by somewhat elevated CaO concentrations (_ 1.5 – 6.0 wt.%), relative to calculated averages of granites (1.8 wt.% CaO, Le Maitre, 1976) and granodiorites (3.9 wt.% CaO, Le Maitre, 1976). Whilst most of the Swartoup specimens were classified as granodiorites, some orthopyroxene-bearing monzodiorite and orthopyroxenebearing monzonite were locally found and sampled. However, much of the body appears to be granodioritic to granitic in composition. The Polisiehoek Granite-gneiss is characterised by its orange-brown weathering colour in the field, sheared texture, lower P2O5 and higher total alkali content than the Swartoup Pluton. The Polisiehoek Granite-gneiss is a highly fractionated S-type granite, as shown by plots of (a) (Na2O + K2O)/CaO and (b) FeOT/MgO versus Zr + Nb + Ce + Y (Whalen et al., 1987; Zhang et al., 2019) and also of (c) (Al2O3 + CaO)/(FeOT + Na2O + K2O) versus 100 × (MgO + FeOT + TiO2)/SiO2 (after Sylvester, 1989). Classification schemes identify the Polisiehoek Granite-gneiss as either a granite (TAS diagram, after Middlemost, 1994) or alkali granite (R1R2 diagram, after De la Roche et al., 1980). , Thesis (MSc) -- Faculty of Science, Geology, 2021
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Date Issued: 2021-10-29

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Ilmenite megacryst-hosted melt inclusions from the Monastery kimberlite: implications for kimberlite origins

- Van Huyssteen, Aiden

Authors: Van Huyssteen, Aiden
Date: 2021-04
Subjects: To be added
Language: English
Type: Masters theses , text
Identifier: http://hdl.handle.net/10962/178387 , vital:42935
Description: Polymineralic inclusions encapsulating a daughter assemblage of crystalline phases (including silicates, oxides, and carbonates) and an amorphous glass phase, hosted in ilmenite megacrysts from the Monastery kimberlite, were investigated texturally and geochemically in order to constrain their melt origin, modeof formation, and evolution prior to quenching. The isolated nature of the melt inclusions within the ilmenite megacrysts provides an opportunity to study components of primary kimberlitic magma captured within the SCLM (4.5–6 GPa) that has been isolated from pervasive modifying processes that are common in kimberlites. The common daughter phase assemblage within the melt inclusions comprises serpentine, phlogopite, calcite, spinel, kassite, perovskite, ilmenite, and glass. The glass is Si-Mg-Fe-rich, with low Al2O3 contents. It is also K2O- and TiO2-free, with variably depleted REE. In composition, serpentine forms a crystalline equivalent to the glass. However, these phases are optically distinct. Serpentine represents two modes of formation: (i) discrete euhedral grains set within a glass matrix that represent a primary phase, crystallising directly from the entrapped melts, and (ii) as patches of partially crystallised glass that represent a secondary phase formed by the devitrification of the glass. Spinel and phlogopite form along early kimberlitic evolutionary trends and record the depletion of the melt in TiO2, Al2O3, and K2O, which typically decreases from the core to the rim of the crystals. Volatile and alkali-bearing minerals (calcite, apatite, phlogopite) crystallised within the melt inclusions from the captured alkali-rich carbonated-silicate kimberlite melt. The daughter mineral assemblage initially crystallised as euhedral and subhedral grains with a uniform composition under equilibrium conditions. Subsequent crystallisation formed grains that exhibit magmatic zoning due to their crystallisation in a progressively depleted melt. Lastly, the crystallisation of skeletal oxide grains occurred under disequilibrium conditions, at a stage of magma ascent with rapidly changing variables including temperature, melt viscosity, and diffusivity. Prior to complete crystallisation, the residual Si-Mg-Fe melt of this crystallisation process was quenched to form the observed glass. The phases that constitute the common daughter assemblage show large variations in modal proportions, forming a continuum from silicate-rich to carbonate-rich endmember inclusions, with certain daughter phases absent in some inclusions. This suggests that the melt was heterogenous at the time of capture and comprised immiscible silicic/oxidic and carbonate melts. Phase separation, therefore, may have started prior to capturing of magma batches as inclusions in ilmenite, but further segregation and crystallisation continued after these batches had become isolated from the megacryst matrix as melt inclusions. The immiscibility and co-existence of the silicic/oxidic and carbonate melts is preserved by textural features between calcite and glass, such as rounded globules of calcite grains set within a silicate glass matrix, calcite forming the matrix for euhedral silicate and oxide minerals, and calcite occupying the interior void of skeletal oxide grains set within a silicate glass matrix. Furthermore, spherulitic globular domains of Ca- and Ti-rich glasses set within a matrix of the Si-Mg-Fe glass suggest that the silicic/oxidic melt underwent further segregation into oxide-rich (Ca-Ti) and silicate-rich (Si-Mg-Fe-Al-K-Ti) melts, potentially crystallising the oxide and silicate minerals of the daughter assemblage, respectively. The abundance of incompatible trace elements and the Cr-poor composition of secondary low-Mg ilmenite as a daughter mineral within the melt inclusions (~1400 ppm Nb; <0.1 wt% Cr2O3; <0.1 wt% MgO), in addition to the Cr-poor composition of the other daughter phases within the inclusions (i.e. <0.1 wt% Cr2O3 for phlogopite and spinel), indicate that they crystallised from a similar melt as the Cr-poor, but high Mg-ilmenite megacrysts (~1400 ppm Nb; <0.1 wt% Cr2O3; ~10 wt% MgO). Furthermore, the melt inclusions are randomly distributed and no textural and/or geochemical evidence for melt infiltration of the ilmenite megacrysts was associated with the melt inclusions. These features are consistent with a primary origin for the melt inclusions which implies a cognate relationship between the megacrysts and the captured kimberlite melt. , Thesis (MSc) -- Faculty of Science, Geology, 2021
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Date Issued: 2021-04

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High-resolution geological, petrological and geochemical investigation of the mid mid-lower c. 3.3 Ga Kromberg type type-section, Barberton greenstone belt, South Africa Africa

- Ndlela, Sibusisiwe

Authors: Ndlela, Sibusisiwe
Date: 2021
Subjects: Petrology -- Eswatini and South Africa -- Barberton Greenstone Belt , Geology -- Eswatini and South Africa -- Barberton Greenstone Belt , Geochemistry -- Eswatini and South Africa -- Barberton Greenstone Belt , Onverwacht Group (South Africa) , Barberton Greenstone Belt (Eswatini and South Africa) , Groups (Stratigraph) -- South Africa
Language: English
Type: Thesis , Masters , MSc
Identifier: http://hdl.handle.net/10962/172241 , vital:42179
Description: The geology of the SE limb of the Kromberg type-section, its origin and its evolution has remained controversial for more than five decades since its discovery by Viljoen and Viljoen (1969). Different lithostratigraphy and geodynamic models have been proposed that were centred around two end-member models, a continuous layer-cake stratigraphy model (Viljoen and Viljoen, 1969c, Lowe et al., 1999) or a tectono-stratigraphic model (de Wit et al., 2011, Furnes et al., 2012). Additionally, the Kromberg type-section mafic-ultramafic sequence represents a relatively thin, dismembered sequence compared to other formations or ‘complexes’ in the Onverwacht Group. Previous geology workers relied on the field interpretations for the construction of the geological architecture of the Kromberg type-section; but no petrographic analyses were conducted for accurate, integrated geological characterization of different rock compositions. To address controversies centred around the Kromberg type-section geology and geodynamic setting, this study is aimed at testing previously proposed stratigraphic and geodynamic models by integrating high-resolution geological mapping, petrography, mineral chemistry and whole-rock geochemistry to verify rock characterization. The aim is to accurately reconstruct the volcano-sedimentary architecture of the Kromberg type-section and to compare this to the results of previous fieldwork. Moreover, the manner in which the Kromberg sequence may relate to current Archean geodynamic models is evaluated, and a new model explaining the origin and evolution of the Kromberg type sequence is proposed. The integration of high-resolution field mapping, petrography and geochemistry has allowed for a high precision study and that has resulted in the construction of a new geological architecture for the SE limb of the Kromberg type-section. The stratigraphic thickness of the SE limb of the Kromberg sequence comprises dominant c. 80% volcanic rocks and minor c. 15% intrusive rocks, intercalated by 7 volcano-sedimentary chert horizons (c. 5%). Four main rock types (groups) are present in the Kromberg type-section with two sub-types of komatiitic basalts (the Badplaas-type and Geluk-types), Fe-rich tholeiitic basalt, cumulate peridotite, and a metadunite. Although the Kromberg type-section records sub-greenschist to lower greenschist facies, more than 50% of the rock samples classify as altered with parts of the stratigraphy recording extensive chloritization and severe ocean-floor silicification. Geochemical data revealed an enrichment in SiO2, K2O, Ba, Rb and variation in HREE for highly silicified samples whereas, chloritized samples are enriched in FeO and have concave upward LREE patterns. Partially chloritized tholeiites and komatiitic basalts have overlapping SiO2 signatures, relatively flat REE patterns and a small negative Nb anomaly in the primitive mantle-normalized spider diagrams. This thesis provides the first Lu-Hf isotope data on whole rock samples from the Kromberg type-section. The εHf values at t=3.33 Ga range between -0.62 to +4.18 and Hf model ages range between 3.43 - 4.27 Ga. The rock compositions are compared to the geochemistry of other greenstone belt rocks, which are considered to provide insight onto the geodynamic setting under which the Kromberg mafic-ultramafic sequence formed. The rock compositions reveal plume-related processes where a primitive mantle melt interacts with recycled mafic crust or mafic lower crust of older units of the Onverwacht Group. Only a small Nb anomaly is found in some samples and the data plots outside the subduction zone (forearc and back-arc) field. Rare-Earth element profiles are flat and not consistent with a subduction zone signature, as proposed in previous studies. Rifting of an oceanic floor in a juvenile basin is proposed for the formation of the Kromberg type-section rocks, prior to being tectonically accreted during regional transpressional deformation at c. 3.23 Ga.
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Date Issued: 2021

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A comparative mineralogical and geochemical study of manganese deposits in the Postmasburg Manganese Field, South Africa

- Thokoa, Mamello

Authors: Thokoa, Mamello
Date: 2020
Subjects: Manganese ores -- South Africa -- Postmasburg , Geology -- South Africa -- Postmasburg
Language: English
Type: Thesis , Masters , MSc
Identifier: http://hdl.handle.net/10962/167609 , vital:41496
Description: The Postmasburg Manganese Field (PMF), located in the Northern Cape Province of South Africa, is host to some of the largest deposits of iron and manganese metal in the world. These deposits are restricted to a geographical area known as the Maremane Dome, an anticlinal structure defined by folded dolostones of the Campbellrand Subgroup and overlying ironformations of the Asbestos Hills Subgroup of the Neoarchaean-Palaeproterozoic Transvaal Supergroup. Manganese ores associated with the Maremane Dome have been divided into two major classes in the literature: the Wolhaarkop breccia-hosted massive ores of the Eastern Belt, as well as the shale-associated ores of the Western Belt. The Eastern Belt ores have been classed as siliceous in nature, while the Western Belt deposits are reported to be typically ferruginous. These divisions were made based on their varying bulk chemical and mineralogical compositions in conjunction with their different stratigraphic sub-settings. Presently, both deposit types are explained as variants of supergene mineralisation that would have formed through a combination of intense ancient lateritic weathering in the presence of oxygen, extreme residual enrichments in Mn (and Fe), and accumulations in karstic depressions at the expense of underlying manganiferous dolostones. This study revisits these deposits and their origins by sampling representative end-member examples of both Eastern Belt and Western Belt manganese ores in both drillcore (localities Khumani, McCarthy and Leeuwfontein), and outcrop sections (locality Bishop). In an attempt to provide new insights into the processes responsible for the genesis of these deposits, the possibility of hydrothermal influences and associated metasomatic replacement processes is explored in this thesis. This was achieved using standard petrographic and mineralogical techniques (transmitted and reflected light microscopy, XRD , SEM-EDS and EMPA), coupled with bulk-rock geochemical analysis of the same samples using a combination of XRF and LAICP- MS analyses. Combination of field observations, petrographic and mineralogical results, and geochemical data allowed for the re-assessment of the different ore types encountered in the field. Comparative considerations made between the bulk geochemistry of the different end-member ore types revealed no clear-cut compositional distinctions and therefore do not support existing classifications between siliceous (Eastern Belt) and ferruginous (Western Belt) ores. This is supported by trace and REE element data as well, when normalised against average shale. The geochemistry reflects the bulk mineralogy of the ores which is broadly comparable, whereby braunite and hematite appear to be dominant co-existing minerals in both Eastern Belt (Khumani) and Western Belt (Bishop) ore. In the case of the McCarthy locality, manganese ore is cryptomelane-rich and appears to have involved recent supergene overprint over Eastern Belt type ore, whereas the Leeuwfontein ores are far more ferruginous than at any other locality studied and therefore represent a more complex, hybrid type of oxide-rich Mn mineralisation (mainly bixbyitic) within massive hematite iron ore. In terms of gangue mineralogy, the ores share some close similarities through the omnipresence of barite, and the abundance of alkalirich silicate minerals. Eastern Belt ores contain abundant albite and serandite whereas the main alkali-rich phase in Western Belt ores is the mineral ephesite. In both cases, Na contents are therefore high at several wt% levels registered in selected samples. The afore-mentioned alkali enrichments have been variously reported for both these deposit types. The occurrence of high alkalis cannot be explained through classic residual or aqueous supergene systems of ore formation, as proposed in prevailing genetic models in the literature. Together with the detection of halogens such as F and Br through SEM-EDS analyses of ore from both belts, the alkali enrichments suggest possible hydrothermal processes of ore formation involving circulation of metalliferous sodic brines. Selected textural evidence from samples from both ore belts lends support to fluid-related models and allow the proposal for a common hydrothermal-replacement model to have been responsible for ore formation across the broader Maremane Dome region.
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Date Issued: 2020

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A reappraisal of the origin of the Hotazel Fe-Mn Formation in an evolving early Earth system through the application of mineral-specific geochemistry, speciation techniques and stable isotope systematics

- Mhlanga, Xolane Reginald

Authors: Mhlanga, Xolane Reginald
Date: 2020
Subjects: Manganese ores -- South Africa -- Hotazel , Manganese ores -- Geology , Iron ores -- South Africa -- Hotazel , Iron ores -- Geology , Geochemistry -- South Africa -- Hotazel , Isotope geology -- South Africa -- Hotazel , Geology, Stratigraphic -- Archaean , Geology, Stratigraphic -- Proterozoic , Transvaal Supergroup (South Africa) , Great Oxidation Event
Language: English
Type: Thesis , Doctoral , PhD
Identifier: http://hdl.handle.net/10962/146123 , vital:38497
Description: Marine chemical sediments such as Banded Iron Formations deposited during the Archean-Palaeoproterozoic are studied extensively because they represent a period in the development of the Earth’s early history where the atmospheric O₂ content was below the present levels (PAL) of 21%. Prior to the Great Oxidation Event (GOE) at ca. 2.4 Ga, highly ferruginous and anoxic marine environments were dominated by extensive BIF deposition such as that of the Griqualand West Basin of the Transvaal Supergroup in South Africa. This basin is also thought to record the transition into the first rise of atmospheric O₂ in our planet, from the Koegas Subgroup to the Hotazel Formation dated at ca. 2.43 Ga (Gumsley et al., 2017). Two drill cores from the north eastern part of the Kalahari Manganese Field characterized by a well-preserved and complete intersection of the cyclic Mn-Fe Hotazel Formation were studied at a high resolution (sampled at approximately one-meter interval). Such high-resolution approach is being employed for the first time in this project, capturing in detail the three manganese rich layers intercalated with BIF and the transitions between these lithofacies. The micro-banded BIF is made up of three major phases, namely Fe-Ca-Mg carbonates (ankerite, siderite and calcite), magnetite, and silicates (chert and minor Fe-silicates); laminated transitional lutite consist of mainly hematite, chert and Mn-carbonates, whereas the manganese ore layers are made up of mostly calcic carbonates (Mn-calcite and Ca-kutnahorite) in the form of laminations and ovoids, while Mn-silicates include dominant braunite and lesser friedelite. All three lithofacies are very fine grained (sub-mm scale) and so petrographic and mineralogical observations were obtained mostly through scanning electron microscope analysis for detailed textural relationships with focus on the carbonate fraction. Bulk geochemical studies of the entire stratigraphy of the Hotazel Formation have previously provided great insights into the cyclic nature of the deposit but have not adequately considered the potential of the carbonate fraction of the rocks as a valuable proxy for understanding the chemistry of the primary depositional environment and insights into the redox processes that were at play. This is because these carbonates have always been attributed to diagenetic processes below the sediment-water interface such as microbially-mediated dissimilatory iron/manganese reduction (DIR/DMR) where the precursor/primary Fe-Mn oxyhydroxides have been reduced to result in the minerals observed today. The carbonate fraction of the BIF is made up of ankerite and siderite which co-exist in a chert matrix as anhedral to subhedral grains with no apparent replacement textures. This suggests co-precipitation of the two species which is at apparent odds with classic diagenetic models. Similarly, Mn-carbonates in the hematite lutite and manganese ore (Mn-calcite, kutnahorite, and minor rhodocrosite) co-exist in laminae and ovoids with no textures observed that would suggest an obvious sequential mode of formation during diagenesis. In this light, a carbonate-specific geochemical analysis based on the sequential Fe extraction technique of Poulton and Canfield (2005) was employed to decipher further the cyclic nature of the Hotazel Formation and its primary versus diagenetic controls. Results from the carbonate fraction analysis of the three lithofacies show a clear fractionation of iron and manganese during primary – rather than diagenetic - carbonate precipitation, suggesting a decoupling between DIR and DMR which is ultimately interpreted to have taken place in the water column. Bulk-rock concentration results for minor and trace elements such as Zr, Ti, Sc and Al have been used for the determination of either siliciclastic or volcanic detrital inputs as they are generally immobile in most natural aqueous solutions. These elements are in very low concentrations in all three lithofacies suggesting that the depositional environment had vanishingly small contributions from terrigenous or volcanic detritus. In terms of redox-sensitive transition metals, only Mo and Co appear to show an affinity for high Mn facies in the Hotazel sequence. Cobalt in particular attains a very low abundance in the Hotazel BIF layers at an average of ~ 4 ppm. This is similar to average pre-GOE BIF in South Africa and worldwide. Maxima in Co abundance are associated with transitional hematite lutite and Mn ore layers, but maxima over 100ppm are seen in within the hematite lutite and not within the Mn ore proper where maxima in Mn are recorded. This suggests a clear and direct association with the hematite fraction in the rocks, which is modally much higher in the lutites but drops substantially in the Mn layers themselves. The similarities of bulk-rock BIF and modern-day seawater REE patterns has been used as a key argument for primary controls in REE behaviour and minimal diagenetic modification. Likewise, the three lithofacies of the Hotazel Formation analysed in this study all share similar characteristics with a clear seawater signal through gentle positive slopes in the normalised abundance of LREE versus HREE. Negative Ce anomalies prevail in the entire sample set analysed, which has been interpreted before as a proxy for oxic seawater conditions. However, positive Ce anomalies that are traditionally linked to scavenging and deposition of primary tetravalent Mn oxyhydroxides (e.g., as observed in modern day ferromanganese nodules) are completely absent from the current dataset. The lack of a positive Ce anomaly in the manganese ore and peak Co association with ferric oxides and not with peak Mn, suggests that primary deposition must have occurred within an environment that was not fully oxidizing with respect to manganese. The use of stable isotopes (i.e., C and Fe) was employed to gain insights into redox processes, whether these are thought to have happened below the sediment-water interface or in contemporaneous seawater. At a small scale, all lithofacies of the Hotazel Formation record bulk-rock δ¹³C values that are low and essentially invariant about the average value of -9.5 per mil. This is independent of sharp variations in overall modal mineralogy, relative carbonate abundance and carbonate chemistry, which is clearly difficult to reconcile with in-situ diagenetic processes that predict highly variable δ¹³C signals in response to complex combinations of precursor sediment mineralogy, pore-fluid chemistry, organic carbon supply and open vs closed system diagenesis. At a stratigraphic scale, the carbonate δ¹³C (-5 to -13‰) variations between the different lithologies could instead represent temporal changes in water-column chemistry against well-developed physico-chemical gradients, depth of deposition and biological processes. The low iron isotope values recorded in the hematite lutite and manganese ore samples can be attributed to fractionation effects of initial oxidation of ferrous iron to form Fe-oxyhydroxides in the shallow parts of the basin, from an already isotopically highly depleted aqueous Fe-pool as proposed previously. The slightly higher but still negative bulk-rock δ⁵⁶Fe values of the host BIF can be attributed to water-column Fe isotopic effects at deeper levels between primary Fe oxyhydroxides and an isotopically heavier Fe(II) pool, which was subsequently preserved during diagenetic recrystallization. All above findings were combined into a conceptual model of deposition for the three different lithologies of the Hotazel Formation. The model predicts that free molecular oxygen must have been present within the shallow oceanic environment and implicates both Mn and Fe as active redox “players” compared to classic models that apply to the origin of worldwide BIF prior to the GOE. The deposition of the Hotazel strata is interpreted to have occurred through the following three stages: (1) BIF deposition occurred in a relatively deep oceanic environment above the Ongeluk lavas during marine transgression, where a redoxcline and seawater stratification separated hydrothermally sourced iron and manganese, in response to an active Mn-shuttle mechanism linked to Mn redox cycling. Abundant ferrous iron must have been oxidized by available oxygen but also by oxidised Mn species (MnOOH) and possibly even some soluble Mn(III) complexes. Through this process, Mn(III) was being effectively reduced back into solution along with cobalt(III), as Mn(II) and Co(II) respectively, thus creating maxima in their concentrations. A drawdown of Fe(OH)₃ particles was therefore the only net precipitation mechanism at this stage. Carbonate species of Fe and the abundant magnetite would possibly have formed by reaction between the ferric hydroxides and the deeper Fe(II) pool, while organic matter would also have reacted in the water-column via DIR, accounting for the low δ¹³C signature of Fe carbonate minerals. (2) Hematite lutite formation would have occurred at a relatively shallower environment during marine regression. At this stage, reductive cycling of Fe was minimal in the absence of a deeper Fe(II) reservoir reacting with the ferric primary precipitates. Therefore, DIR progressively gave way to manganese reduction and organic carbon oxidation (DMR), which reduced MnOOH to form Mn(II)-rich carbonates in the form of kutnahorite and Mn-calcite. Co-bearing Fe(OH)₃ would have precipitated and was ultimately preserved as Co-bearing hematite during diagenesis. (3) Deposition of manganese-rich sediment occurred at even shallower oceanic depths (maximum regression) where aerobic organic carbon oxidation replaced DMR, resulting in Ca-rich carbonates such as Mn-bearing calcite and Ca-kutnahorite, yet with a low carbon isotope signature recording aerobic conditions of organic carbon cycling. Mn(III) reduction at this stage was curtailed, leading to massive precipitation of MnOOH which was diagenetically transformed into braunite and friedelite. Simultaneous precipitation of Co-bearing Fe(OH)₃ would have continued but at much more subdued rates. Repeated transgressive-regressive cycles resulted in the cyclic BIF-hematite lutite- manganese ore nature of the Hotazel Formation in an oxidized oceanic environment at the onset of the Great Oxidation Event, which was nonetheless never oxic enough to drive Mn(II) oxidation fully to its tetravalent state. The mineralogy and species-specific geochemistry of the Hotazel strata, and more specifically the carbonate fraction thereof, appear to faithfully capture the chemistry of the primary depositional environment in a progressively evolving Earth System. This project opens the door for more studies focusing on better constraining primary versus diagenetic depositional 2020 Hotazel Fe and Mn deposition mechanisms of iron and manganese during the period leading up to the GOE, and possibly re-defining the significance of Fe and Mn as invaluable redox proxies in a rapidly changing planet.
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Date Issued: 2020

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