Controls of hydrothermal fluid flow and gold mineralization in the Sheba-Fairview Complex, Barberton Greenstone Belt, South Africa
| dc.contributor.advisor | Kisters, Alexander | en_ZA |
| dc.contributor.author | Jones, Caitlin | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. | en_ZA |
| dc.date.accessioned | 2021-11-27T16:39:44Z | |
| dc.date.accessioned | 2021-12-22T14:24:41Z | |
| dc.date.available | 2021-11-27T16:39:44Z | |
| dc.date.available | 2021-12-22T14:24:41Z | |
| dc.date.issued | 2021-12 | |
| dc.description | Thesis (MSc)--Stellenbosch University, 2021. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: The Barberton Greenstone Belt hosts high-grade gold-quartz-sulphide-carbonate orebodies where more than 350 ton of gold has been mined over 130 years. Some of the top gold-producing mines are located within the Sheba-Fairview Complex (SFC). On a deposit scale, the localized fluid conduits and subsequent sinks (reefs) are characteristically low-displacement faults or shear zones. Orebodies are located throughout the greenstone sequence, from the Weltevreden Formation in the Sheba Anticlinorium, into the well-bedded metasedimentary rocks of the Fig Tree and Moodies Groups on both the isoclinally folded northern limb of the Ulundi Syncline and southern, overturned limb of the Eureka Syncline. This study forms the link between the regional fluid flow and local fluid sinks underlain by the crescent-shaped Eureka and Ulundi synclines. This is accomplished by examining two bedding- discordant orebodies, namely the high-grade ‘flat structure’ hosted within the green fuchsite-quartz schist of the Weltevreden Formation, and the steeply-dipping Thomas fracture hosted in the subarkose of the Moodies Group. Structural, petrographic and geochemical analyses of the wall-rocks and auriferous reefs within the arcuate hinge zone of the SFC, reveal that the gold mineralization can be subdivided into three main structural associations. These include (1) reefs related to the central, regional-scale Sheba Fault characterized by quartz-carbonate stockworks, (2) orebodies associated with the anticlinal structures of Weltevreden rocks that are commonly shoot-like, particularly along the contacts of the anticlines with the overlying Fig Tree Group metaturbidites, and (3) smaller reefs within the arenaceous Moodies Group but also in the Fig Tree Group that crosscut bedding at high-angles. Mineralized fractures in the SFC are confined to certain lithological packages (greywacke, quartzite or green fuchsite-quartz schist) within the formations. The orebodies are better developed in competent lithologies with low tensile strengths that promote fracturing, especially in the presence of high fluid pressures. The competent gold-hosting units include the quartzitic units of the Moodies Group, the greywacke-dominated packages of the Fig Tree Group, but also the green fuchsite-quartz schist of the Weltevreden Formation. The competent horizons are related to either original compositions (e.g., greywacke and quartzite) or to an earlier alteration event during deformation that resulted in the increased competency (e.g., green schist). Bedding-parallel veins, sulphide mineralization and alteration are abundant within the well-bedded metasediments of the Ulundi and Eureka synclines and attest to the widespread bedding-parallel fluid flow during flexural-slip folding, where bedding planes acted as low-displacement slip surfaces. The concentration of orebodies in the hinge zone testifies to the regional fluid flow paths with fluid flow, following hydraulic gradients, from the fold limbs towards the hinge during the refolding of the synclines. Gold mineralization occurs in the later stages of the deformational history and is related to the refolding of the synclines during NW-SE directed shortening against the competent buttresses in the northwestern portion of the belt. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Die Barberton Groensteenstreek is gasheer vir hoërgraadse goud-kwarts-sulfied-karbonaat ertsliggame waar meer as 350 ton goud oor 130 jaar ontgin was. Van die mees goud produserende myne is in die Sheba-Fairview Distrik (SFD) geleë. Op ‘n afsettingskaal, is die gelokaliseerde migrasie van hidrotermiese vloeistof in waterleidings en daaropvolgende goud riwwe gekenmerk as skuifskeursones of verskuiwings met lae verplasing. Ertsliggame is regdeur die groensteen eenhede gevind, van die Weltevreden Formasie wat in die Sheba Antikliene voorkom, tot in die klippe van Fig Tree en Moodies Groepe wat goed gelaagd is, dié kom voor op beide die isoklinale geplooide noordelike flank van die Ulundi Sinklien en op die suidelike, omgekeerde flank van die Eureka Sinklien. Hierdie ondersoek vorm die skakel tussen die regionale vloeistofvloei en die gelokaliseerde vloeistof deponeer areas wat in die halfmaanvormige Eureka en Ulundi sinkliene voorkom. Hierdie word bereik deur twee rots-snydende ertsliggame te ondersoek, naamlik die hoërgraadse ‘flat structure’ wat in die groen skis van die Weltevreden Formasie deel vorm, en die Thomas struktuur wat in die subarkose van die Moodies Groep geleë is. Strukturele, petrografiese en geochemiese ontledings van die wandgesteentes en gouddraende riwwe binne die boogvormige skarniersone van die SFD het gewys dat die goudmineralisering in drie strukturele groepe onderverdeel kan word. Dit sluit die (1) riwwe wat geassosieer is met die sentrale, streekskaalse Sheba Verskuiwing wat gekenmerk word deur kwarts-karbonaat stokwerke, (2) langwerpige mineralisering wat verband hou met die antiklinale strukture van die Weltevreden gesteentes, en laastens (3) die klein riwwe wat binne die Moodies Groep, maar ook binne die Fig Tree Groep voorkom en wat die laagvlakke dwarsgang, in. Die gemineraliseerde verskuiwings in die SFD is beperk tot sekere litologiese eenhede (grouwak, kwartsiet of die groen skis) wat ‘n laer treksterkte het en wat breukvorming bevorder. Die bevoegde gouddraende lae sluit die kwartsitiese eenhede van die Moodies Groep in, die grouwak gedomineerde eenhede van die Fig Tree Groep, maar ook die groen skis van die Weltevreden Formasie. Die bevoegde horisonne is geassosieer met óf die oorspronklike samestelling (soos die grouwak en kwartsiet) óf met ‘n vroeëre verandering tydens deformasie, wat lei tot verhoogde bevoegdheid van die rotse (soos die groen skis). Are wat parallel aan die lae is, sulfiedmineralisering en verandering van die klippe is volop in die goed gelaagde metasedimente van die Ulundi en Eureka sinkliene en getuig van die deurdringende laag parallelle vloeistofvloei tydens die buigglipplooing waar laagvlakke soos glipvakke optree. Die konsentrasie van ertsliggame in die skarniersone getuig van die regionale vloeistofvloei kanale waar die vloei van die flanke van die plooi na die skarnier toe vloei tydens die herplooiing van die sinkliene. Goud mineralisering vorm laat gedurende die vervormings geskiedenis en hou verband met die plooiing van die sinkliene tydens NW-SO georiënteerde verkorting teen die bevoegde stutmure in die noordwestelike rand van die streek. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.format.extent | xi, 129 pages : illustrations (some color), maps | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/123844 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Gold mineralization -- South Africa -- Sheba-Fairview Complex | en_ZA |
| dc.subject | Geology, Structural -- South Africa | en_ZA |
| dc.subject | Barberton Greenstone Belt -- South Africa -- Sheba-Fairview Complex | en_ZA |
| dc.subject | Metasedimentary rocks | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Controls of hydrothermal fluid flow and gold mineralization in the Sheba-Fairview Complex, Barberton Greenstone Belt, South Africa | en_ZA |
| dc.type | Thesis | en_ZA |