We have re-processed high-resolution 3D reflection seismic data from the West Wits Line and West ... more We have re-processed high-resolution 3D reflection seismic data from the West Wits Line and West Rand goldfields (South Africa) and combined it with underground mapping observations. First-, second-and-third-order-scale fault and dyke structures offset the Black Reef Formation (BRF), a distinct seismic reflector that acts as a marker horizon for the gold-bearing conglomerates that are found at the base of the NeoArchaean-Palaeoroterozoic Transvaal Supergroup. The BRF is of considerable economic and academic interest since it contains payable concentrations of gold, especially in areas where it lies adjacent to the Witwatersrand Supergroup’s gold-bearing conglomerates.
First-order scale structures in the West Wits Line and West Rand goldfields of the Witwatersrand ... more First-order scale structures in the West Wits Line and West Rand goldfields of the Witwatersrand Basin (South Africa) were mapped using the high-resolution 3D reflection seismic method. Structural models constrain the magnitude of displacement of thrusts and faults, the gross structural architecture and Neoarchaean tectonic evolution of the West Rand and Bank fault zones, which offset the gold-bearing reefs of the basin. The merging of several 3D seismic surveys made clear the gross strato-structural architecture of the goldfields; a macroscopic fold-thrust belt is crosscut by a macroscopic extensional fault array. These are dissected, eroded and overlain by the Transvaal Supergroup above an angular unconformity. The seismic sections confirm that the West Rand Group (ca. 2985-2902 Ma) is unconformably overlain by the Central Rand Group (ca. 2902-2849 Ma), with tilting of the West Rand Group syn-to post-erosion at ca. 2.9 Ga. The seismic sections also confirm that an unconformable relationship exists between the Central Rand Group and the auriferous Ventersdorp Contact Reef (VCR), with an easterly-verging fold-thrust belt being initiated concomitant to deposition of the VCR at approximately 2.72 Ga. Fold-thrust formation included development of the (1) newly identified first-order scale Libanon Anticline, (2) Tandeka and Jabulani thrusts which displace the West Rand Group, and (3) parasite folds. The fold-thrust belt is crosscut by a macroscopic extensional fault array (or rift-like system of faults) which incepted towards the end of extrusion of the Ventersdorp lavas, and certainly during deposition of the Platberg Group (2709-2643 Ma) when a mantle plume may have heated the lithosphere. The West Rand and Bank fault zones formed at this time and include (1) the West Rand and Bank faults which are scissors faults; (2) second and third-order scale normal faults in the immediate footwall and hanging wall of the faults; (3) drag synclines, and (4) rollover anticlines.
International Journal of Rock Mechanics and Mining Sciences, 2014
A model of the Ventersdorp Contact Reef (VCR) orebody at Kloof Gold Mine was derived by integrati... more A model of the Ventersdorp Contact Reef (VCR) orebody at Kloof Gold Mine was derived by integrating 3D reflection seismic data with information derived from underground mine mapping and exploration drilling. The study incorporated the depth-converted prestack time migrated (PSTM) seismic cube, the mine geomodel, faults and dikes mapped in excavations, mine development infrastructure, and intersections of the VCR by surface and underground exploration drilling. The 3D seismic data provide an accurate geometric model of the VCR orebody and its offsets. The underground mapping datasets help to define minor faults and dikes that are below seismic resolution limits. The integration of the these datasets allowed (1) for better mapping of fault architectures and distributions within the lease area, (2) definition of the likely zones of difficult ground conditions around seismically imaged dikes and faults, and (3) better predictions of the number and spacing of faults that offset the VCR within minable blocks. The model is useful in mitigating both economic and safety risks of deep mining.
As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imagi... more As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imaging of certain ore horizons in some of the Witwatersrand basin gold mines. The merged historical 3D seismic reflection data acquired for Kloof and South Deep mines forms an integral part of their Ventersdorp Contact Reef mine planning and development programme. The recent advances in 3D seismic technology have motivated the reprocessing and reinterpretation of the old data sets using the latest algorithms, therefore significantly increasing the signal-to-noise ratio of the data. In particular, the prestack time migration technique has provided better stratigraphic and structural imaging in complex faulted areas, such as the Witwatersrand basin, relative to older poststack migration methods. Interpretation tools such as seismic attributes have been used to identify a number of subtle geologic structures that have direct impact on ore resource evaluation. Other improvements include more acc...
Inrushes of ground water and the ignition of flammable gases pose risks to workers in deep South ... more Inrushes of ground water and the ignition of flammable gases pose risks to workers in deep South African gold mines. Large volumes of water may be stored in solution cavities in dolomitic rocks that overlie the Black Reef (BLR) Formation, while there are several possible sources for methane, namely, coal seams, kerogen found in some gold ore bodies, or methane introduced by igneous intrusions. Potential conduits that may transport water and methane to underground workings were mapped using 3D reflection seismic data. Edge detection attributes successfully identified many faults, some with displacements as small as 10 m. Faults that displace the Ventersdorp Contact Reef (VCR) and the BLR horizons were of special interest, as known occurrences of fissure water and methane in underground workings show a good correlation with faults that were imaged on the VCR and BLR horizons. Because there are uncertainties in determining the linkage of faults with aquifers and methane sources, it is ...
Effective exploration for mineral deposits depends on a sound understanding of the processes and ... more Effective exploration for mineral deposits depends on a sound understanding of the processes and geological structures that contributed to their formation. The reflection seismic method has proven to be a powerful tool that provides a high-resolution image of the subsurface and information about structural and lithological relationships that control mineral deposits. The method has also become an attractive geophysical tool for deep exploration and mine planning. In this paper, we review the use of reflection seismic methods to obtain a better understanding of the architecture and ore-forming processes of three diverse mineral regions: the Kevitsa Ni-Cu-PGE district in Finland, the goldfields of the Witwatersrand Basin South Africa, and the Bathurst Mining Camp, Canada. Seismic data, both 2D and 3D, from the Kevitsa deposit clearly image the 3D geometry of the ore-bearing intrusion and provide information about its relationship to the host rock units and nearby intrusions within a larger tectonic framework. 3D seismic data from the Witwatersrand Basin not only provide clear images of major structures, including a distinct reflection that acts as a marker horizon for the gold-bearing reef, but also provide information that may be useful in resolving a longstanding controversy regarding the origin of the gold in the Basin. For example, it might be possible to show that dykes formed impermeable barriers, thereby falsifying the epigenetic hydrothermal models. 2D and 3D seismic data from the Brunswick No. 6 area in the Bathurst Mining Camp suggest that the Brunswick horizon (which contains the bulk of the massive sulfide and associated iron deposits) occurs within a reflective package that extends down to at least 6-7 km depth.
We have re-processed high-resolution 3D reflection seismic data from the West Wits Line and West ... more We have re-processed high-resolution 3D reflection seismic data from the West Wits Line and West Rand goldfields (South Africa) and combined it with underground mapping observations. First-, second-and-third-order-scale fault and dyke structures offset the Black Reef Formation (BRF), a distinct seismic reflector that acts as a marker horizon for the gold-bearing conglomerates that are found at the base of the NeoArchaean-Palaeoroterozoic Transvaal Supergroup. The BRF is of considerable economic and academic interest since it contains payable concentrations of gold, especially in areas where it lies adjacent to the Witwatersrand Supergroup’s gold-bearing conglomerates.
First-order scale structures in the West Wits Line and West Rand goldfields of the Witwatersrand ... more First-order scale structures in the West Wits Line and West Rand goldfields of the Witwatersrand Basin (South Africa) were mapped using the high-resolution 3D reflection seismic method. Structural models constrain the magnitude of displacement of thrusts and faults, the gross structural architecture and Neoarchaean tectonic evolution of the West Rand and Bank fault zones, which offset the gold-bearing reefs of the basin. The merging of several 3D seismic surveys made clear the gross strato-structural architecture of the goldfields; a macroscopic fold-thrust belt is crosscut by a macroscopic extensional fault array. These are dissected, eroded and overlain by the Transvaal Supergroup above an angular unconformity. The seismic sections confirm that the West Rand Group (ca. 2985-2902 Ma) is unconformably overlain by the Central Rand Group (ca. 2902-2849 Ma), with tilting of the West Rand Group syn-to post-erosion at ca. 2.9 Ga. The seismic sections also confirm that an unconformable relationship exists between the Central Rand Group and the auriferous Ventersdorp Contact Reef (VCR), with an easterly-verging fold-thrust belt being initiated concomitant to deposition of the VCR at approximately 2.72 Ga. Fold-thrust formation included development of the (1) newly identified first-order scale Libanon Anticline, (2) Tandeka and Jabulani thrusts which displace the West Rand Group, and (3) parasite folds. The fold-thrust belt is crosscut by a macroscopic extensional fault array (or rift-like system of faults) which incepted towards the end of extrusion of the Ventersdorp lavas, and certainly during deposition of the Platberg Group (2709-2643 Ma) when a mantle plume may have heated the lithosphere. The West Rand and Bank fault zones formed at this time and include (1) the West Rand and Bank faults which are scissors faults; (2) second and third-order scale normal faults in the immediate footwall and hanging wall of the faults; (3) drag synclines, and (4) rollover anticlines.
International Journal of Rock Mechanics and Mining Sciences, 2014
A model of the Ventersdorp Contact Reef (VCR) orebody at Kloof Gold Mine was derived by integrati... more A model of the Ventersdorp Contact Reef (VCR) orebody at Kloof Gold Mine was derived by integrating 3D reflection seismic data with information derived from underground mine mapping and exploration drilling. The study incorporated the depth-converted prestack time migrated (PSTM) seismic cube, the mine geomodel, faults and dikes mapped in excavations, mine development infrastructure, and intersections of the VCR by surface and underground exploration drilling. The 3D seismic data provide an accurate geometric model of the VCR orebody and its offsets. The underground mapping datasets help to define minor faults and dikes that are below seismic resolution limits. The integration of the these datasets allowed (1) for better mapping of fault architectures and distributions within the lease area, (2) definition of the likely zones of difficult ground conditions around seismically imaged dikes and faults, and (3) better predictions of the number and spacing of faults that offset the VCR within minable blocks. The model is useful in mitigating both economic and safety risks of deep mining.
As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imagi... more As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imaging of certain ore horizons in some of the Witwatersrand basin gold mines. The merged historical 3D seismic reflection data acquired for Kloof and South Deep mines forms an integral part of their Ventersdorp Contact Reef mine planning and development programme. The recent advances in 3D seismic technology have motivated the reprocessing and reinterpretation of the old data sets using the latest algorithms, therefore significantly increasing the signal-to-noise ratio of the data. In particular, the prestack time migration technique has provided better stratigraphic and structural imaging in complex faulted areas, such as the Witwatersrand basin, relative to older poststack migration methods. Interpretation tools such as seismic attributes have been used to identify a number of subtle geologic structures that have direct impact on ore resource evaluation. Other improvements include more acc...
Inrushes of ground water and the ignition of flammable gases pose risks to workers in deep South ... more Inrushes of ground water and the ignition of flammable gases pose risks to workers in deep South African gold mines. Large volumes of water may be stored in solution cavities in dolomitic rocks that overlie the Black Reef (BLR) Formation, while there are several possible sources for methane, namely, coal seams, kerogen found in some gold ore bodies, or methane introduced by igneous intrusions. Potential conduits that may transport water and methane to underground workings were mapped using 3D reflection seismic data. Edge detection attributes successfully identified many faults, some with displacements as small as 10 m. Faults that displace the Ventersdorp Contact Reef (VCR) and the BLR horizons were of special interest, as known occurrences of fissure water and methane in underground workings show a good correlation with faults that were imaged on the VCR and BLR horizons. Because there are uncertainties in determining the linkage of faults with aquifers and methane sources, it is ...
Effective exploration for mineral deposits depends on a sound understanding of the processes and ... more Effective exploration for mineral deposits depends on a sound understanding of the processes and geological structures that contributed to their formation. The reflection seismic method has proven to be a powerful tool that provides a high-resolution image of the subsurface and information about structural and lithological relationships that control mineral deposits. The method has also become an attractive geophysical tool for deep exploration and mine planning. In this paper, we review the use of reflection seismic methods to obtain a better understanding of the architecture and ore-forming processes of three diverse mineral regions: the Kevitsa Ni-Cu-PGE district in Finland, the goldfields of the Witwatersrand Basin South Africa, and the Bathurst Mining Camp, Canada. Seismic data, both 2D and 3D, from the Kevitsa deposit clearly image the 3D geometry of the ore-bearing intrusion and provide information about its relationship to the host rock units and nearby intrusions within a larger tectonic framework. 3D seismic data from the Witwatersrand Basin not only provide clear images of major structures, including a distinct reflection that acts as a marker horizon for the gold-bearing reef, but also provide information that may be useful in resolving a longstanding controversy regarding the origin of the gold in the Basin. For example, it might be possible to show that dykes formed impermeable barriers, thereby falsifying the epigenetic hydrothermal models. 2D and 3D seismic data from the Brunswick No. 6 area in the Bathurst Mining Camp suggest that the Brunswick horizon (which contains the bulk of the massive sulfide and associated iron deposits) occurs within a reflective package that extends down to at least 6-7 km depth.
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