The Significance of Erosion Channels on Gold Metallogeny in the Witwatersrand Basin (South Africa): Evidence from the Carbon Leader Reef in the Carletonville Gold Field

2020 ◽  
Author(s):  
G. T. Nwaila ◽  
J. E. Bourdeau ◽  
Z. Jinnah ◽  
H. E. Frimmel ◽  
G. M. Bybee ◽  
...  
Keyword(s):  
South Africa ◽  
High Resolution ◽  
Mass Balance ◽  
Closed System ◽  
Seismic Data ◽  
Crucial Role ◽  
Sediment Load ◽  
Witwatersrand Basin ◽  
Petrographic Analyses ◽  
Group A

Abstract Within the eastern portion of the Carletonville gold field, the gold- and uranium-rich Carbon Leader reef of the Central Rand Group (Witwatersrand Supergroup) is truncated by an erosion channel. This channel is asymmetrical and lenticular in shape, measuring 150 to 180 m in width and up to 100 m in depth. High-resolution seismic data show that the erosion channel cuts from the Carbon Leader reef into all older units of the Central Rand Group down to the Roodepoort Formation of the underlying West Rand Group. A total of seven bore-holes were drilled into the channel, revealing that it is composed of quartzite at its base (9 m thick), overlain by deformed (lower) and laminated (upper) chloritoid-bearing shale (21 m thick) and quartzite (18 m thick). The Carbon Leader reef is highly enriched in gold (5–40 g/t Au), whereas the gold tenor of the erosion channel fill is in general much lower (<1 g/t Au), although locally grades of as much as 3.8 g/t Au are reached. Detailed seismic, sedimentological, and petrographic analyses revealed that the channel was filled with locally sourced sediments from the Main Formation. A closed-system mass balance further demonstrates that gold in the erosion channel could have been entirely sourced from the Carbon Leader reef. Sediment load played a crucial role in the distribution of gold in the channel, thus supporting a stratigraphically controlled modified placer model for the origin of gold in the Carbon Leader reef.

PROSPECTIVITY OF THE OTWAY SUPERGROUP IN THE CENTRAL AND WESTERN OTWAY BASIN

1990 ◽  
Vol 30 (1) ◽  
pp. 263 ◽  
Author(s):  
E. Kopsen ◽  
T. Scholefield
Keyword(s):  
High Resolution ◽  
Success Rate ◽  
Seismic Data ◽  
Reservoir Quality ◽  
Critical Elements ◽  
The Future ◽  
Group A ◽  
Coal Measures ◽  
Migration Pathways ◽  
Depth Of Burial

Recent hydrocarbon discoveries in the non-marine rift fill sequence of the Otway Basin at Windermere, Katnook and Ladbroke Grove have upgraded the importance of this relatively poorly known interval of the sedimentary column and provide hydrocarbon trapping models for future exploration. Using a seismic stratigraphic approach based on high resolution seismic data and the geological re-evaluation of many key early wells, a clearer pattern has emerged for the distribution of major reservoir and seal units.The best reservoirs occur in the Crayfish Group 'A', 'B' and 'D' units and the Windermere Member of the Lower Eumeralla Formation. One of the most critical elements in controlling the more prospective areas is the diagenetic characteristics of the main hydrocarbon objective units. Reservoir quality is significantly affected by the abundance or absence of volcanic detritus and depth of burial, and as a result, the most attractive reservoir is the Crayfish 'A' lying at depths shallower than 3000 m. Lateral fault seals and good vertical seals are present at various stratigraphic levels through the sequence for the development of effective traps in fault blocks and anticlines.The Casterton Group and the basal coal measures zone of the Lower Eumeralla Formation overlying the Windermere Member are identified as the most prospective oil sourcing units in the sequence. Secondary oil sourcing intervals occur within the Crayfish 'C' unit and at the top of the Lower Eumeralla Formation. A higher drilling success rate is now expected in the future with hydrocarbon fairways in the supergroup expected to comprise:Fault blocks and anticlines in the more basinal areas, e.g. the Katnook and Ladbroke Grove gas fields.The 'shoulders' of the main rift depocentres where fault traps will be most prevalent, e.g. the Kalangadoo CO2 discovery.Portions of the northern platform lying on migration pathways extending from the main graben (hydrocarbon kitchen) areas.

La Traviata Affair

2018 ◽  
Author(s):  
Hilde Roos
Keyword(s):  
South Africa ◽  
Racial Boundaries ◽  
Cultural Organization ◽  
Colored People ◽  
Art Forms ◽  
Group A ◽  
La Traviata ◽  
Apartheid Regime ◽  
Opera Production ◽  
The Way

Opera, race, and politics during apartheid South Africa form the foundation of this historiographic work on the Eoan Group, a so-called colored cultural organization that performed opera in the Cape. The La Traviata Affair: Opera in the Time of Apartheid charts Eoan’s opera activities from its inception in 1933 until the cessation of its work by 1980. By accepting funding from the apartheid government and adhering to apartheid conditions, the group, in time, became politically compromised, resulting in the rejection of the group by their own community and the cessation of opera production. However, their unquestioned acceptance of and commitment to the art of opera lead to the most extraordinary of performance trajectories. During apartheid, the Eoan Group provided a space for colored people to perform Western classical art forms in an environment that potentially transgressed racial boundaries and challenged perceptions of racial exclusivity in the genre of opera. This highly significant endeavor and the way it was thwarted at the hands of the apartheid regime is the story that unfolds in this book.

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