Application of 3D seismic analysis techniques to evaluate ore resources on Kloof, South Deeps and Driefontein gold mines, Witwatersrand Basin, South Africa.

This thesis presents the application of the state-of-the-art processing, interpretation and modeling to the 3D reflection seismic data that were acquired between 1988 and 2003 across the West Rand and West Wits line goldfields of the Archean Witwatersrand Basin. The re-processing of the old 3D seismic data using new imaging techniques, such as 3D Kirchhoff prestack time migration (KPSTM), has led to better imaging of the ore body, structures (faults and dikes), and steeply dipping stratigraphy. Detailed interpretations of the highly auriferous Ventersdorp Contact Reef (VCR) using advanced complex seismic trace and horizon - based seismic attributes, have led to discoveries of ore blocks (~ 1 km long and ~ 250 m wide) that are bound by multi-fault segments of the first-order scale Bank and West Rand faults, leading to an increase of the resource portfolio and potentially, the quantity of the reserves. In particular, the edge detection attributes have resolved faults with throws as small as 10 m and complex structural architectures such as intersecting and cross-cutting faults, and fault bifurcations which are difficult to detect using conventional techniques (e.g., amplitude, dip and azimuth). Potential conduits, such as faults and dikes for migration of water and methane into underground workings were also mapped using edge detection attributes. These results have the potential to play into safe mine planning. The interpretation of the merged 3D seismic datasets, integrated with underground maps, boreholes, absolute and relative geochronological data, has added to our understanding of the gross structural architecture and Neoarchaean tectonic evolution of the goldfields. On a first-order scale (400 m - 2.5 km) the data resolved: (1) the northerly-trending disharmonic Libanon Anticline with a wavelength of 8 km and amplitude of 2 km, which was formed during deformation in the Umzawami Event (ca 2.73 Ga); and (2) the north-northeast trending, west-dipping (65°–70°W) listric West Rand and Bank faults, which were formed during a major extensional event, herein termed the Hlukana- Platberg Event (2.70-2.64). On a second-order scale (25 m - 400 m) the datasets resolved: (1) the Tandeka and Jabulani thrusts 1.5 km below the West Rand and Bank faults in the depth interval of 6-8 km; and (2) a series of drag synclines and rollover anticlines in the immediate footwall and hangingwall of the West Rand and Bank faults. Further to this, the seismic sections across the goldfields provided evidence that the first- and second-order scale faults, thrust and folds were dissected, eroded and overlain by the Transvaal Supergroup above an angular unconformity. The oldest approximate age for the Transvaal Supergroup is given as 2.58 Ga, thus constraining the age of the faults, thrust and folds to the Neoarchaean or pre- 2.58 Ga

Application of seismic stratigraphy in reservoir characterisation: a case study of the passive margin deposits of the northern Orange Basin, South Africa

Abstract The Barremian-Cenozoic depositional sequences in the northern Orange Basin, SW, South Africa, were investigated using the principles of seismic stratigraphy to understand the interplay of tectonics and sedimentary processes in the distribution of potential hydrocarbon reservoirs. A seismic stratigraphic workflow (seismic sequence, seismic facies and lithofacies analysis) was completed by utilising three seismic lines (L1, L2 and L3) tied to Wireline data (gamma, checkshots and sonic) in two exploration wells (A1 and A2). Seven depositional sequences were mapped followed by the creation of lithofacies log interpreted from the gamma-ray log (GR) by setting maximum GR value at 60 API for Sandstone, 60–100 API for Siltstone and above 100 API for Shale. Six seismic facies units are recognised based on internal geometry and configurations of the seismic reflectors; Tangential-Oblique (SF1), Hummocky (SF2), Wavy-Parallel (SF3), Chaotic (SF4), Sub-parallel/parallel (SF5) and Divergent (SF6). SF4 is dominant within the Barremian-Aptian sequence and expressed in an incised valley fill, suggesting mass transport deposition accompanied by strong hydrodynamic conditions. Evidence of sedimentary basins progradation is seen within the Late-Albian-Turonian sequences, because of the occurrences of SF2, SF6 and SF 4 facies. SF5 facies is prominent in the Maastrichtian/Campanian sequence, indicating that the deposition of sediments may have been accompanied by uniform margin subsidence after the Late-Cretaceous uplift of the Africa margin. The occurrence of SF1 and SF4 facies within the Cenozoic sequence indicates terrigenous pro-deltaic deposits and mass transport deposits, respectively. Further results from seismic-lithofacies modelling reveal that sand deposits of Barremian-Aptian (SF4 facies unit) and Albian sequences (SF2 and SF6 facies units) are potential stratigraphic reservoirs in this part of the basin

The valorisation of platinum group metals from flotation tailings: A review of challenges and opportunities

Flotation tailings from South Africa’s platinum group minerals (PGM) represent complex polymetallic orebodies comprising a low-grade platinum group elements (PGE) content and complex mineralogical composition. Nevertheless, given the valuable mineral potential in the tailings, it is understandable that the substantial historic tailings deposits and sizeable annual production volume from primary processes represent a potential secondary resource. For several decades, valorising the PGM tailing materials received very little interest due to limitations associated with extractive metallurgical technology to achieve economically viable PGE extraction. The early 21st century saw the coming online of technologies, including but not limited to ultrafine grinding, suitable to meet challenges in primary metallurgical treatment processes to recover valuable minerals from ultrafine particle fractions, which could not otherwise be recovered. More so, such processes were critical in improving the liberation of partially liberated particles without compromising additional ultrafine generation. These technologies led to the development of re-treatment pilot tests and subsequent industrial re-treatment recovery processes. The current industrial re-treatment approach – via tertiary scavenging flotation circuits – renders profit in small increments up to 1 ∼ 2% additional recovery relative to the primary plant head grade. These small increments relate to about ∼12–30% PGE recovery of the feed grade to the re-treatment circuit, thereby enhancing the primary plant's overall economics as well as aiding the supply of critical metals to meet global demands. With a focus on South Africa, this review provides an overview of (a) the current and future drivers of the precious metals global demand; (b) proffers discussion on the PGM characteristic mineralogy and the metallurgical value chain; (c) relates the parent orebodies (“reefs”) mineral characteristics to the inherent processed tailings; (d) estimates the economic potential these massive processed waste materials contain, (e) provides an overview of existing technologies that are industrially used in tailing re-treatment plants; and (f) outlines a comprehensive understanding of the nature of value minerals rejection to tailings

Introduction to the special issue on “Cost-effective and innovative mineral exploration solutions”

Accepted Author ManuscriptApplied Geophysics and Petrophysic

Groundwater Circulation in the Shallow Crystalline Aquifer of Tharisa Mine, South Africa: Evidence from Environmental Isotopes and Near-Surface Geophysics

For underground mining, efficient groundwater management is one of the critical mining economics components. The region of interest, known as Tharisa Mine, is situated on the western limb of the Bushveld Igneous Complex, which is home to South Africa’s premier platinum-group metal resources. This work aimed to provide the findings from the investigation and imaging of the near-subsurface hydrogeological architecture in a shallow profile using stable isotopes of water (18O and 2H) and radioactive water isotopes (3H). Regarding isotope data, 18O varied from −3.5 to 1.5‰; 2H from −24 to 4.7‰; and 3H from 2.0 to 3.4 T.U. Utilizing combined geophysical techniques, the results were verified. Additionally, the geophysical methods, including seismic refraction tomography, multichannel analysis of surface waves, electrical resistivity tomography, and magnetics, helped identify the fluid’s pathways and lineaments during migration to verify the isotope results. The groundwater inflow volumes into the open pit were initially determined by integrating the following findings: the delineation of fracture systems/zones and fluid migration pathways; mining activities enhance the storage and transmission ability of the aquifer; and the main sources of water in the mine include mixing of surface and deep water sources, recycling of water possibly via lineaments, and tailings dam seepages

A reappraisal of legacy reflection seismic data from the western margin of the Kaapvaal craton, South Africa, with implications for Mesozoic-Cenozoic regional tectonics

The 150 km long, 6 s TWT, 2D seismic profile KBF03A, which was acquired in 1994 and lies near the western edge of the Kaapvaal craton in South Africa, has been reprocessed using standard reflection seismic processing methods. The results exhibit a significant improvement in the imaging quality of the subsurface features and an evident boost in the signal-to-noise ratio. The improved seismic data, combined with application of seismic attributes, integration with surficial geological and geophysical maps, and computation of velocity tomograms, has revealed previously undetected structural features within the supracrustal sequences underlying the profile. In particular, the Phanerozoic sediments found along the profile, comprising exclusively Kalahari Group and Dwyka Group deposits, are disrupted by multiple folds of varying wavelengths (~1–10 km) and variably oriented normal and thrust faults. Additionally, the effect of the Moshaweng fault, previously characterised as a listric fault extending to depths of >10 km, on the Phanerozoic sediments has been further constrained to suggest repeated extensional reactivations and a more recent (<1 Ma) inversion. Considerations of the eastern end of the profile have suggested links between some of the observed structural features and the nearby ~146 Ma Morokweng impact structure, the lateral expanse of which is poorly constrained in the literature. The collection of these newly imaged features is interpreted as evidence for multiple Late Mesozoic to Cenozoic tectonic events, including polyphasic reactivation of basement structures, under both extensional and compressional stress regimes. By analysing these newly detected features, our study not only provides new insight into the neotectonic evolution of the Phanerozoic sediments along the western margin of the Kaapvaal craton, but also demonstrates the utility in reprocessing legacy data and reveals its untapped potential.DATA AVAILABILITY STATEMENT : Seismic research data are not shared. Geological outcrop and magnetic map data can be found on the website of The Council for Geoscience South Africa (http://www.geoscience.org.za/index.php/2019-03-13-12-40-41).https://www.elsevier.com/locate/tecto2023-05-26hj2022Geolog

Constraints on the Geometry and Gold Distribution in the Black Reef Formation of South Africa Using 3D Reflection Seismic Data and Micro-X-ray Computed Tomography

Geological and geophysical models are essential for developing reliable mine designs and mineral processing flowsheets. For mineral resource assessment, mine planning, and mineral processing, a deeper understanding of the orebody's features, geology, mineralogy, and variability is required. We investigated the gold-bearing Black Reef Formation in the West Rand and Carletonville goldfields of South Africa using approaches that are components of a transitional framework toward fully digitized mining: (1) high-resolution 3D reflection seismic data to model the orebody; (2) petrography to characterize Au and associated ore constituents (e.g., pyrite); and (3) 3D micro-X-ray computed tomography (µCT) and machine learning to determine mineral association and composition. Reflection seismic reveals that the Black Reef Formation is a planar horizon that dips &lt; 10° and has a well-preserved and uneven paleotopography. Several large-scale faults and dikes (most dipping between 65° and 90°) crosscut the Black Reef Formation. Petrography reveals that gold is commonly associated with pyrite, implying that µCT can be used to assess gold grades using pyrite as a proxy. Moreover, we demonstrate that machine learning can be used to discriminate between pyrite and gold based on physical characteristics. The approaches in this study are intended to supplement rather than replace traditional methodologies. In this study, we demonstrated that they permit novel integration of micro-scale observations into macro-scale modeling, thus permitting better orebody assessment for exploration, resource estimation, mining, and metallurgical purposes. We envision that such integrated approaches will become a key component of future geometallurgical frameworks.Funder: Department of Science and Innovation (DSI)-National Research Foundation (NRF) Thuthuka (grant no. 121973); DSI-NRF CIMERA</p