Browsing by Author "Hoyer, Lauren."

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Local-to micro-scale structural controls on shear-zone-hosted gold mineralisation, Ngubevu area, Natal Thrust Front, Tugela Terrane, South Africa.
(2021) Chagi, Onele.; Carranza, Emmanuel John Muico.; Hoyer, Lauren.
The research described in this dissertation focused on shear-zone-hosted precious and base metal mineralisation in the Ngubevu area, in the Natal Thrust Front of the Tugela Terrane in the Natal Metamorphic Province of South Africa. This province forms part of a 400-km-wide metamorphic belt referred to as the Namaqua-Natal Metamorphic Province, which stretches from the Northern Cape on the west coast to KwaZulu-Natal on the east coast of the country. Unlike the western Namaqualand Metamorphic Province, which is well-explored and well-exploited for several mineral deposits, the Natal Metamorphic Province is relatively poorly explored. One reason for this is that the nature of structural controls on mineralisation in the Natal Metamorphic Province is poorly understood. In the research described in this dissertation, known occurrences of shear-zonehosted precious and base metal deposits in the Golden Eagle and Champion Mines in the Ngubevu area, which have been described in the literature, were studied in the micro-scale, and the findings obtained were integrated with existing knowledge of regional- to local-scale deformation in the Tugela Terrane, in order to deduce the structural controls of such mineralisation in the area. The micro-scale data, studied by spatial analytical methods (i.e., point pattern analysis, Fry analysis, fractal analysis and shape analysis) show that the mineralisation in the area operated in at least two spatial scales, within each thin section sample, of at most 0.005 μm and at least 0.002 μm and that, within each thin section sample, the occurrence of shear-zone-hosted precious and base metal deposits is non-random as they exhibit clustered and/or regular spatial distributions. Microfractures in the area generally show major northerly trends in their alignments. Likewise, microscale mineral distributions show NNE–SSW and NNW–SSE trends in their orientations. These findings suggest that N–NE-directed compression controlled the occurrence and distribution of shear-zone-hosted precious and base metal mineralisation in the Ngubevu area. This N–NEdirected compression and thrusting during deformation (D1) controlled the circulation and concentration of mineralising hydrothermal fluids in the Natal Thrust Front. These hydrothermal fluids formed quartz veins along nearly E–W-trending foliations resulting in mineralisation in the clustered and regular spatial patterns observed in the micro-scale.
Rock fabric study of Karoo dolerite sills along the KwaZulu-Natal North Coast, South Africa : implications for the magma source.
(2015) Hoyer, Lauren.; Watkeys, Michael Keith.
Abstract available from the pdf file.
The structural evolution of the Bumbeni Complex and Bumbeni Ridge and its relationship with Gondwana break-up: insights from high resolution aeromagnetic data and field mapping.
(2021) Ncume, Mawande.; Hoyer, Lauren.; Hicks, Nigel.
The Bumbeni Complex is the remnant of a Cretaceous volcanic centre (~133 Ma) that is now exposed along the southern end of the Lebombo Mountain Range, adjacent to the cover sequences that infill the Zululand Basin in northern KwaZulu-Natal, South Africa. The Bumbeni Complex forms the western limit of the north-east trending Bumbeni Ridge and postdates the rocks of the Karoo Large Igneous Province. The comparison of field relationships, structural data, high-resolution aeromagnetic data and borehole logs are used to determine the formation and structural evolution of the Bumbeni Complex and Bumbeni Ridge by understanding the tectonic regimes responsible for the development of the brittle deformation structures in the study area. These events are then correlated with the regional tectonic events related to Gondwana break-up, thus further constraining the timing of deformation and possible formation mechanisms of the Bumbeni volcanism. The rhyolites of the Jozini Formation (Lebombo Group) provide a basement to the rocks of the Bumbeni Complex. These rhyolites are characterised by a N-S oriented eastward dipping normal and dextral strike-slip faults and associated planar systematic joint sets. These fractures are representative of a dextral strike-slip regime, interpretable on a dextral Riedel shear system. The presence of these dextral strike-slip faults suggests that a rotation in the paleo-stress regime from a vertical 1 to a horizontal NE-SW oriented 1 have occurred during deformation, which may be related to the second deformation event (175–155 Ma) attributed here to stage two of Gondwana break-up. These structural deformation patterns developed in the Jozini Formation are absent in the rocks of the Bumbeni Complex, suggesting the deformation in the Lebombo Group occurred prior and/or during the eruption and intrusion of the Bumbeni Complex. The aeromagnetic data defines four distinct magnetic domains (Domains 1–4), which are separated by distinct regional magnetic discontinuities and are defined by their structural framework. Domain 1 occurs in the SW of the study area and is characterised by N-S oriented wide lineaments (low frequency, deep seated), and correlate with the Lebombo Group and are likely related to the N-S oriented faults occurring in the Jozini Formation rhyolites. The formation of these structures is here associated with the E-W orientated spreading attributed to the initial stages of Gondwana break-up (~180–175 Ma). Domains 2, 3 and 4 mainly display E-W and NE-SW oriented high frequency shallow structures, which cross-cut each other suggesting that the shallow structures occurred at different times and post-date the occurrence of the deep structures. These structures are related to the second deformation event which is constrained between stages 2 and 3 (175–135 Ma). The field evidence reveals that the Bumbeni Complex comprises basaltic and rhyolitic rocks of the Mpilo and Fenda Formations, respectively, indicating bimodal volcanism typical of rift related extension. The bimodal volcanism is most likely related to local extension associated with the upwelling of the continental lithospheric mantle. The position of the Zululand Basin boreholes (ZD and ZG) in relation to the aeromagnetic anomalies and the geomagnetic timescale, reveal that the Bumbeni Complex comprise NE-striking remanent and non-remanently magnetised plutonic bodies. These NE-striking plutonic bodies, which are a result of ascended magma occur in the southeast and northeast of the study area, delineated from the aeromagnetic data, and are indicative of emplacement during positive and negative polarity periods which prevailed during the Cretaceous. The position of the Bumbeni Complex and extension of the volcanism along the Bumbeni Ridge is correlated with a once-active E-W trending spreading centre located in the Northern Natal Valley at ~133–125.3 Ma, based on its paleo-position. Thus, the Bumbeni event is attributed to a combination of these processes. This event is likely a volcanic centre that formed along a failed rift system.