Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources.
| dc.contributor.author | Frimmel, H | |
| dc.contributor.author | Hallbauer, D | |
| dc.date.accessioned | 2016-08-01T13:07:25Z | |
| dc.date.available | 2016-08-01T13:07:25Z | |
| dc.date.issued | 1999 | |
| dc.date.updated | 2016-08-01T11:31:40Z | |
| dc.description.abstract | Crush-leach data were obtained, using High Performance Gradient Ion-Chromatography and Capillary Electrophoresis, on individual generations of aqueous fluid inclusions in hydrothermal quartz from three different auriferous conglomerate horizons (reefs) in the late Archaean Witwatersrand Basin, South Africa. These data, supplemented by oxygen isotope analyses of hydrothermal quartz and in combination with microthermometric analyses, help to constrain the chemical composition, pH, temperature of formation and the possible source of the mineralizing fluid which, in places, was capable of mobilizing some of the primarily detrital gold in the fluvial Witwatersrand sediments. The dominant cations in the aqueous fluid inclusions are Na + and Ca 2+, with C1- or HCOj being the dominant anion, whereas K รท, Mg 2+, and SOlare subordinate. Most fluid inclusions have elevated NH~- concentrations which are directly correlated with those of NO 3. In a number of samples small amounts of organic acids (formate, propionate, and acetate) were also detected. A largely meteoric source is inferred for the gold-mobilizing fluids in the Witwatersrand reefs because of a lack of Br- in the fluid, a composition distinctly different from that of seawater, the presence of organic acids, and ~18Ofluid values around 0%0. The fluids are ascribed to hydrothermal infiltration triggered by the 2020 Ma Vredefort impact which also created a secondary permeability in the form of a dense network of micro-fractures preferentially in the conglomerate beds of the already metamorphosed Witwatersrand rock sequence. This fluid differs from the regional metamorphic fluid in the basin by having a considerably higher pH (5.7-7.2). The difference in pH might explain why the older, fairly acidic metamorphic fluid was apparently less capable of mobilizing the gold as gold solubility reaches its peak at the pH calculated for the fluid ascribed to the impact. | en_ZA |
| dc.identifier | http://dx.doi.org/10.1007/BF01161722 | |
| dc.identifier.apacitation | Frimmel, H., & Hallbauer, D. (1999). Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources. <i>Mineralogy and Petrology</i>, http://hdl.handle.net/11427/21090 | en_ZA |
| dc.identifier.chicagocitation | Frimmel, H, and D Hallbauer "Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources." <i>Mineralogy and Petrology</i> (1999) http://hdl.handle.net/11427/21090 | en_ZA |
| dc.identifier.citation | Frimmel, H. E., & Hallbauer, D. K. (1999). Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources. Mineralogy and Petrology, 66(1-3), 55-81. | en_ZA |
| dc.identifier.issn | 0930-0708 | en_ZA |
| dc.identifier.ris | TY - Journal Article AU - Frimmel, H AU - Hallbauer, D AB - Crush-leach data were obtained, using High Performance Gradient Ion-Chromatography and Capillary Electrophoresis, on individual generations of aqueous fluid inclusions in hydrothermal quartz from three different auriferous conglomerate horizons (reefs) in the late Archaean Witwatersrand Basin, South Africa. These data, supplemented by oxygen isotope analyses of hydrothermal quartz and in combination with microthermometric analyses, help to constrain the chemical composition, pH, temperature of formation and the possible source of the mineralizing fluid which, in places, was capable of mobilizing some of the primarily detrital gold in the fluvial Witwatersrand sediments. The dominant cations in the aqueous fluid inclusions are Na + and Ca 2+, with C1- or HCOj being the dominant anion, whereas K รท, Mg 2+, and SOlare subordinate. Most fluid inclusions have elevated NH~- concentrations which are directly correlated with those of NO 3. In a number of samples small amounts of organic acids (formate, propionate, and acetate) were also detected. A largely meteoric source is inferred for the gold-mobilizing fluids in the Witwatersrand reefs because of a lack of Br- in the fluid, a composition distinctly different from that of seawater, the presence of organic acids, and ~18Ofluid values around 0%0. The fluids are ascribed to hydrothermal infiltration triggered by the 2020 Ma Vredefort impact which also created a secondary permeability in the form of a dense network of micro-fractures preferentially in the conglomerate beds of the already metamorphosed Witwatersrand rock sequence. This fluid differs from the regional metamorphic fluid in the basin by having a considerably higher pH (5.7-7.2). The difference in pH might explain why the older, fairly acidic metamorphic fluid was apparently less capable of mobilizing the gold as gold solubility reaches its peak at the pH calculated for the fluid ascribed to the impact. DA - 1999 DB - OpenUCT DP - University of Cape Town J1 - Mineralogy and Petrology LK - https://open.uct.ac.za PB - University of Cape Town PY - 1999 SM - 0930-0708 T1 - Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources TI - Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources UR - http://hdl.handle.net/11427/21090 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/21090 | |
| dc.identifier.vancouvercitation | Frimmel H, Hallbauer D. Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources. Mineralogy and Petrology. 1999; http://hdl.handle.net/11427/21090. | en_ZA |
| dc.language | eng | en_ZA |
| dc.publisher | Springer | en_ZA |
| dc.publisher.institution | University of Cape Town | |
| dc.source | Mineralogy and Petrology | en_ZA |
| dc.source.uri | http://link.springer.com/journal/710 | |
| dc.title | Gold mobilizing fluids in the Witwatersrand Basin: composition and possible sources. | en_ZA |
| dc.type | Journal Article | en_ZA |
| uct.type.filetype | Text | |
| uct.type.filetype | Image | |
| uct.type.publication | Research | en_ZA |
| uct.type.resource | Article | en_ZA |