ETD Collection

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    Prospectivity mapping using stream sediment geochemistry along the Orange River Catchment for base metal, Prieska, Northern Cape, South Africa
    (2020) Mashale, Hilda Nthabiseng
    The Areachap Terrane which is part of the Namaqua Sector of the Namaqua-Natal Belt in the Northern Cape Province host volcanic-hosted Zn-Cu deposits at volcanic centres. Major deposits that were mined till early 1990’s include Copperton (at Prieska) and Areachap deposits. Currently, Orion mining/exploration Company is further exploring some of the best target areas including Copperton, Areachap and Kantienpan base metal occurrences. The primary objective was to map base metal mineralisation, determine the heavy metal contents of sediments, locate the source of anomalies and delineate targets for follow-up studies. A total of 9314 stream sediments samples were collected and analysed using XRF at the Council for Geoscience laboratory. Spatial joint analysis tool was used to calculate the element associated with their respective lithostratigraphy. Fuzzy OR Overlay operation wa sapplied to combine maps of relevant indicator elements associated with the geology. The results for elements associated with the known base metals occurring in Prieska area as well as relevant multi-element groups were plotted on distribution maps using ArcGIS. The mineralisation target M1, M2, and M3 are delineated as potential VMS mineralisation zone and considered for further follow-up study. The M13 and M14 anomalies are delineated for Co_Ni (±Cu) mineralisation. M13 and M14 anomalies are sourced from ultramafic debris transported from the Ghaap Group, however this potential target will require follow-up studiesforverification.ThecorrelationoftheCu-Pb-Znanomalywithalkalielements(Nb, Zr, Th, and U) and REEs (in Table 3.3) suggests there is a possibility that the M26–M29 anomaly are alkali-granitic genetic origin. The As, Ba, Ce, Cr, Cu, Hf, Nd, Ni, Rb, Sr, S, V, Zr and Zn contents showed a heterogeneous spatial distribution, reflected by high coefficient of variation and large standard deviation; these elements concentrations are extremely elevated in stream sediments. There is a very high Cu-Zn correlation coefficient calculated for samples near the Copperton deposit. Normal Q-Q plots for S, Zn, Pb, and Ba have similar trends with outliers of the high coefficient of variations which might be sourced from the mine wastes. The high Cu, Zn and Pb are derived from the ore minerals related VMS deposits. The Fe elevated concentration are derived from both primary minerals which are not directly related to the VMS or Co_Ni (±Cu) mineralisation
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    The sedimentology and mineralogy of the composite reef on Cooke Section, Randfontein Estates Gold Mine, Witwatersrand, South Africa
    (2019) Tucker, Rodney Frank
    The Composite reef at Cooke Section of Randfontein Estates Gold Mine is a Precambrian gold and uranium paleoplacer, comprising a con-glomeratic quartzite unit of the Turffontein Sup group (formerly Elsburg Series) of the Witwatersrand Supergroup. The reef zone appears to lie on an unconformity, and shows a distinct thickening toward the east, down the paleoslope. Internally, the reef is a multipulse unit, mainly comprising thin layers of gravel, which are interpreted as being longitudinal gravel-bars, and trough cross-bedded sands, which are believed to have been transverse sand-bars. Less frequently, clayey-matrix sands and debris flow type gravels were deposited. Vertical profiles indicate a series of generally fining-upward cycles, which usually start on scour surfaces, and grade upward from a layer of pebbles and heavy minerals, to a medium-grained sand, and rarely to a silt. Lateral profiles reveal the lenticular and channelled nature of the reef. Distinct scour channels may often be traced up to a few hundred metres. The paleocurrent discharge was highly fluctuating, and the dominant dispersal was in a south-easterly direction, away from the Panvlakte fault scarp. The water depth probably varied between 0,1 m and 0,5 m. The depositional environment was a braided alluvial outwash plain, corresponding closely to the Donjek mode1. Two major sub-environments have been recognized. The perennial braided alluvial outwash facies has a high mineralization potential as a result of its high degree of alluvial reworking while the more ephemeral debris-flow food-type environment has dumped clayey-matrix sand and gravel and has almost no economic placer mineralization potential. Gold and uraninite are the two primary ore minerals’ and occur together with a number of other mainly chalcophile minerals’. Four main periods of mineralization are evident. The allogenic detrital phase includes chromite sircon and fine-grained pyrite mineralization. These minerals’ were in hydraulic equilibrium with the sand fraction. During the second period coarse-grained colloform pyrite and magnesia-alumina-rich muds developed and accumulated in temporarily abandoned channels and interfluves areas. Gold and uraninite were concentrated during this period and show a strong association with colloform pyrite. Subsequent fluvial reactivation concentrated this mineralization only a short distance from the site of its origin. Pebble’s and heavy minerals’ became winnowed down to the base of transverse sand bars or else became entrapped in openwork gravels. The third phase of mineralization took place during diagenesis and is represented by local reconstitution of pyrite in the form of diagenetic concretion modules. The final phase resulted from a low-grade metamorphic event which is shown by indicator minerals’ to be lower green schist facies. A partial reconstitution of ore minerals’ and chalcophile elements notably copper, lead and zinc took place during this phase. The mineralogy of the reef was quantitatively investigated by a geochemical analysis of twenty-five elements. An R-mode factor analysis produced five factors~ which have been interpreted as a chalcophile element and colloform-pyrite factor an allogenic detrital oxide factor, a remobilized chalcophile-element factor and a sericite-clay factor. Soda loads onto a fifth factor which is unexplained. A multiple regression analysis of the geochemical data has produced a predictive equation for gold and uranium. This equation relates to the sediment logical and mineralogical observations made and therefore is regarded as realistic. Gold is proportional to colloform pyrite which is estimated by sulphur or iron. This is improved by the inverse proportionality of chrome or zirconium3 which in effect eliminates the effect of the allogenic phase 1 pyrite. The inverse, proportionality of potash reflects the degree of placer reworking3 as it is present as sericite the predominant clay mineral. Grade prediction has been reviewed in the light of sedimentological mineralogical and geostatistical analyses. Optimum prediction can only result from an integration of all these aspects3 in a multi-disciplinary approach. The most pertinent sedimentological aspects in this regard are paleocurrent dispersal and lithofacies analysis. The mineralogical aspect must be quantitative3 and this is best achieved by a multiple regression of geochemical data. An initial geostatistical (kriging) exercise has demonstrated the necessity of carefully considering the sedimentology before dividing the area into sub-areas. The minor (ore-shoot) axis of semivariogram analyses in areas where a unimodal paleocurrent exists corresponds very closely with the mean paleocurrent trend but misleading semivariogram results are obtained when the sub-areas have a divergent paleocurrent pattern.
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    Structure of the fada-gourma shear zone Eastern Burkina Faso
    (2018) Sehloho, Pulane Relebohile
    The Baoulé-Mossi Domain in eastern Burkina Faso is a greenstone belt-granitoid terrane, formed in a volcanic arc tectonic environment. Volcanism and magmatism were coeval at around 2239 Ma, and this formed the basement rocks of the Fada-Gourma Shear Zone (FGSZ) region. Crosscutting relations observed in the field, aided by zircon U-Pb age data reveal that pluton emplacement continued to post-2167±12 Ma. The youngest units are NW-trending dolerite dykes, dated at 1814±26 Ma in eastern Burkina Faso. The study area has five defined deformation events. D1 is responsible for the remnant NW-trending S1 foliation in some of the granite gneisses and the foliated and gneissic granodiorites outside of the shear zones. The σ1 principal compressive stress orientation was NE-SW. The metamorphic grade associated with D1 is amphibolite facies. D2 had a NW-SE oriented compressive stress direction, and this resulted in thrust faulting and the NE-trending dominant structural grain in the study area. The associated metamorphic grade for D2 is lower amphibolite facies. D3 involved a dextral-reverse slip along faults with a NE trend, with southeast-block-up displacement. The principal compressive stress axis was ENE-WSW to ESE-WNW directed. Metamorphic grade associated with D3 is greenschist facies to lower amphibolite facies. D4 caused the sinistral reactivation of the NE-trending D3 structures. The sinistral shear overprint the dextral displacement and a sigmoidal foliation related to D4 is discernible on the aeromagnetic imagery data. The principal compressive stress axis during D4 was NNE-SSW to N-S oriented. The metamorphic grade during D4 was greenschist facies. D5 is a late-stage brittle deformation that led the formation of NW-trending extensional fracture cleavage planes. The imagery data was integrated with field data to aid in establishing the orientation of foliations, and the kinematic and geometric information at map scale and at outcrop scale. Petrographic descriptions provided information at a micro-scale where available. The study area is host to gold mineralization, and there is a network of active artisanal mines in the northern domains of the study area. Tambiga Hill is one of the larger actively mined quartz stockwork vein deposits in the Gourma region. Gold mineralization is concomitant with quartz veins, and is hosted either adjacent to the quartz veins, or within the veins. Gold is either invisible, or occurs as nuggets. Pyrite, tourmaline, ankerite and minor malachite are also present as accessory minerals within the quartz veins. Gold mineralization is associated with the late stages of D2, and D3.
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    Palaeoenvironmental successions and sequence stratigraphy of the early to Middle Devonian Bokkeveld Group in the Clanwilliam Sub-basin, Western Cape Province, South Africa
    (2017) Penn-Clarke, Cameron Roy
    Reassessment of the sedimentology of the Bokkeveld Group in the Clanwilliam Sub-basin has allowed for the recognition of twelve lithofacies (1-12) comprising eight lthofacies association (A-H). Comparison of these lithofacies and lithofacies associations, as well as their palaeontological and ichnological content, with both ancient and modern analogues and applied experimental sedimentology suggests that sedimentation of the Bokkeveld Group in Clanwilliam Sub-basin occurred within three board siliciclastic depositional systems in a marginal-and-shallow marine setting. These are namely 1) A storm-and-wave-dominated shallow marine depositionl system comprising system offshore (Os) , offshore transition zone-to-distal Lower shoreface (OTZ-dLSF), proximal Lower shoreface (pLSF) and Upper shoreface-beach complex (USF-Beach) palaoenvironments. This is the most common depositional system in the field study area and persisted during sedimentationof the Gydo, Gamka, Voorstehoek, Hex River, Waboomberg, Wupperthal, Osberg and Karoopoort Formations. [Abbreviated Abstract. Open document to view full version]
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    Modelling the Witwatersrand basin: a window into neoarchaean-palaeoproterozoic crustal-scale tectonics
    (2017) Molezzi, Marcello
    The aim of this study was to investigate and evaluate the 3D structural architecture around the Vredefort dome in the Witwatersrand basin, in particular the unexposed southern portion. This was done in order to establish strato-tectonic relationships, first order deformation structures, and basement architecture. The outcomes provide a more detailed architecture around the central uplift that may be used in future work aimed at examining the nature of giant terrestrial impacts. In summary, the integration of borehole, surface mapping, and 2D reflection seismic data provides a well constrained 3D geological model of the dome, central uplift, and adjacent areas (covering approximately 11600 km2). Seven structural features are discussed from the 3D modelling results. These include, (1) a normal fault in the lower West Rand Group, (2) an undulate, normal faulted truncation plane, constrained as post-West Rand Group and pre or early-Central Rand Group, (3) a truncation plane and local enhanced uplift constrained as pre to syn-VCF, (4) a listric fault system, constrained as post-Klipriviersberg Group and syn-Platberg Group, (5) a truncation plane, constrained as syn-Black Reef Formation, (6) folds, including a large asymmetric, gentle anticline here named the Vaal Dam Anticline, constrained as post-Magaliesberg Formation and pre-Vredefort impact, and (7) a listric fault across the southeastern margin of the Vredefort dome, constrained as late to post-central uplift formation. The findings support previous work by Tinker et al. (2002), Ivanov (2005), Alexandre et al. (2006), Dankert and Hein (2010), Manzi et al. (2013), Jahn and Riller (2015), and Reimold and Hoffmann (2016). However the findings oppose various parts of previous work by Friese et al. (1995), Henkel and Reimold (1998), and Reimold and Koeberl (2014). A new term is also proposed for the periclinal folds located around the central uplift, i.e., impact-type curvature-accommodation folds. This study demonstrates the importance of integrating multiple sources of data into a single 3D spatial environment in order to better refine and distinguish impact-related deformation from the pre-existing basement architecture.