Browsing by Author "Hicks, Nigel."

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A combined sedimentological-mineralogical study of sediment-hosted gold and uranium mineralization at Denny Dalton, Pongola Supergroup, South Africa.
(2009) Hicks, Nigel.; Hofmann, Axel.
The ~2.98 - 2.87 Ga Pongola Supergroup in South Africa is subdivided into the lower volcano-sedimentary Nsuze Group, and the upper sedimentary Mozaan Group, the latter comprising a several kilometres thick succession of fluvial to shallow marine sandstones and shales. Thin beds of gold and uranium-bearing conglomerates are locally present in the Mandeva Formation near the base of the Mozaan Group and have been mined at Denny Dalton in northern KwaZulu-Natal. The style of mineralization strongly resembles that of the Witwatersrand goldfields, however appears to be of low grade and limited tonnage. The ~1 m thick basal conglomerate, the “Mozaan Contact Reef” (MCR, herein referred to as CG 1), at Denny Dalton hosts erratic gold and uranium mineralization. The conglomerate is laterally discontinuous and occupies east-northeast trending scour channels. Polymict, matrix-supported conglomerates are common, while clast-supported conglomerates are rare. Well rounded, pebble to cobble-sized clasts of vein quartz and chert are hosted in a sandy matrix of quartz, pyrite and sericite. Where mineralized, the CG 1 hosts abundant rounded pyrite grains, interpreted as detrital in origin, with subordinate U-bearing minerals, such as brannerite and uraniferous leucoxene. Rounded detrital pyrite occurs in three phases, compact, porous and radial. Gold forms inclusions within massive pyrite grains, which are concentrated in shoots associated with the basal parts of the channel scours. SEM-EDX results, as well as the high reflectivity of the gold show a high Ag content, indicative of a primary origin for the gold within the pyrite grains. Uranium within CG 1 is hosted primarily as secondary inclusions of uranium within black chert pebbles within the basal cobble-sized regions of the conglomerate. Geochemical comparison of the chert pebbles at Denny Dalton with similar chert from the Nondweni Greenstone Belt indicates that the uranium is secondary in origin as no U anomalies occur in the Nondweni chert. Geochemical and SEM analysis of the uppermost conglomerate (CG 4) indicate the presence of uraninite and coffinite within the uppermost horizon as both fillings of voids within, and coatings on, detrital pyrite grains. Palaeocurrent data indicate a likely source terrain for the detrital material to the west of the inlier. This orientation, as well as differing mineralogical and sedimentological aspects between the Mandeva Formation and the correlative Sinqeni Formation within the main Pongola basin, indicate a separate and more proximal provenance for the auriferous conglomerates of the White Umfolozi Inlier. The Mandeva Formation is a fluvial to shallow marine sequence that has been affected by cyclic sea-level changes. The basal conglomerates of the Denny Dalton Member were deposited in a proximal braided alluvial plain environment. The conglomerates fine upwards into trough cross-bedded quartz arenites which appear to have been deposited as shallow marine sands in a shoreface environment. They are overlain with a sharp contact by a laterally extensive unit of polymictic conglomerate which represents a transgressive ravinement surface within the wave zone and marks the onset of a major marine transgression into the Pongola basin. The conglomerate is overlain by massive grits and coarse-grained quartz arenite. This unit is overlain with a sharp and locally sheared contact by shales and subordinate banded iron formation which can be traced into other parts of the Pongola basin and indicates continued rapid transgression onto large parts of the Kaapvaal Craton with deeper marine, sub-storm wave base sediments being deposited in quiet-water environments on a sediment-starved shelf. The heavy mineral assemblage as well as bulk geochemical data is consistent with a granitoid-greenstone source terrain for the conglomerates and sandstones. The geochemical composition of chert pebbles from the CG 1 is similar to the composition of cherts present in the Nondweni Greenstone Belt that is situated ~30 km west of the White Umfolozi Inlier. Multiple sulphur isotope (ä34S, ä33S) values for detrital pyrite from the MCR are consistent with an origin from mantle-like rocks, such as hydrothermal sulphide-quartz veins in a granitoid-greenstone setting. Palaeocurrent, mineralogical and geochemical data all point to a likely granitoid-greenstone provenance to the west of the White Umfolozi Inlier.
The seismic stratigraphy, geological evolution and CO2 storage potential of the offshore Durban Basin, South Africa.
(2017) Hicks, Nigel.; Green, Andrew Noel.
Abstract available in 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.