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Carbon-gold systematics in the Barberton Greenstone Belt
Thesis (MSc)--Stellenbosch University, 2023.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2023
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| _version_ | 1867614115686514688 |
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| access_status_str | Open Access |
| author | La Cock, Rutger Alexander |
| author2 | Von der Heyden, Bjorn |
| author_browse | La Cock, Rutger Alexander Von der Heyden, Bjorn |
| author_facet | Von der Heyden, Bjorn La Cock, Rutger Alexander |
| author_sort | La Cock, Rutger Alexander |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2023.
|
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/129379 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:46:55.034Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/129379 Carbon-gold systematics in the Barberton Greenstone Belt La Cock, Rutger Alexander Von der Heyden, Bjorn Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. Gold ores -- South Africa -- Barberton Greenstone Belt Geochemistry -- South Africa -- Barberton Ore deposits -- South Africa -- Barberton Greenstone Belt Carbonates -- Analysis Scanning electron microscopy -- Technique UCTD Thesis (MSc)--Stellenbosch University, 2023. La Cock, R. A. 2023. Carbon-gold systematics in the Barberton Greenstone Belt. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/ec854a2b-8900-4223-816a-ba4b125bb087 ENGLISH ABSTRACT: The relationship between carbon and gold has been a subject of interest to scientists and geologists for over half a century. The deposits of Fairview mine lie within the Barberton Greenstone Belt (BGB) and provide a unique opportunity to study the relationship between carbon and gold in some of Earth’s oldest, well-preserved continental crust. Previous research has shown that mineralised shear zones at Fairview contain carbon in the form of carbonates and graphite. Scanning electron microscopy (SEM) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are used in conjunction to reveal how ore fluids evolved over time. Major and minor element changes are best seen in variations in carbonate chemistry whilst changes in trace metal concentrations are captured by detailed mapping of zoned pyrite. A dominance of the dolomite-ankerite series of carbonates appear favourable when seeking higher gold grades as they form sites of replacement for auriferous pyrite. Based on analyses using Raman spectroscopy (RS), the graphite in shear zones is of nanocrystalline size and has a high degree of structural disorder. Graphite Raman geothermometry indicate that this graphite has been exposed to maximum temperatures averaging around 400 ⁰C, although the use of graphite from shear zones for thermometry has been shown to be problematic. Carbon isotope analyses suggest that ore fluids were derived from carbonaceous shales of the Fig Tree Group, or from a similar lithology beyond the BGB. X-ray computed tomography (XCT) highlights the close spatial association between Au-bearing sulphides and graphite within the Fairview ore. Most of the graphite is interpreted as being deposited from fluids, with the graphite then later acting as a chemical trap during subsequent fluid flow events, where gold deposition took place via carbon reduction. A Re-Os isochron age of 2652 ± 64.3 Ma for pyrite is the result of resetting of Re-Os isotopes during cratonic extension which initiated the Transvaal Supergroup sedimentation process. Based on existing geochronology data, it is theorized that melting of a shallowly subducting slab beneath the continental crust of the Barberton terrane helped transport auriferous fluids to upper crustal levels, where gold was deposited in shear zones. This research highlights the important role of carbon in forming large, high-grade gold deposits in Archaean greenstone belts. AFRIKAANSE OPSOMMING: Die verwantskap tussen koolstof en goud is al meer as ‘n halfeeu lank ‘n onderwerp van belangstelling vir wetenskaplikes en geologoë. Die afsettings van Fairview-myn lê binne die Barberton Groensteen Gordel (BGG) en bied ‘n unieke geleentheid om die verwantskap tussen koolstof en goud in sommige van die Aarde se oudste, goed bewarde kontinentale kors te bestudeer. Vorige navorsing verwys dat mineraliseerde skeursones by Fairview bevat koolfstof in die vorm van karbonate en grafiet. Skandeerelektronmikroskopie en laser ablasie induktief gekoppelde plasma massaspektrometrie word saam gebruik om te openbaar hoe erts draende vloeistowwe met verloor van tyd ontwikket het. Majeur en mineur element veranderinge word die beste gesien in variasies in karbonate chemie terwyl veranderinge in spoorelemente word die beste waargeneem deur gedetailleerd kartering van gesoneerde piriet. ‘n Oorheersing van die dolomiet-ankeriet reeks van karbonate lyk gunstig wanneer iemand hoër goudgrade soek want die vorm plekke vir vervanging deur pyriet. Gebaseer op ontledings gebruiking Raman spektroskopie, die grafiet in skeursones is van nanokristallyne grootte en het ‘n hoë graad van strukturele versteuring. Grafiet Raman geotermometrie dui aan dat hierdie grafiet was blootgestel aan maksimum temperature van gemiddeld ongeveer 400 ⁰C, hoewel die gebruik van grafiet uit skuifsones vir termometrie problematies getoon is. Koolstofisotooponteldings dui daarop dat ertsvloeistowwe afkomstig van koolstofhoudende skalies van die Fig Tree Groep, of van ‘n soortgelyke litologie buite die BGG. X-straal rekenaartomografie bekoemtoon die noue ruimtelike assosiasie tussen gouddraende sulfiede en grafiet binne die Fairview erts. Die meeste van die grafiet word geïnterpreteer dat dit uit vloeistowwe neergelê is, met die grafiet wat later as 'n chemiese lokval optree tydens daaropvolgende vloeistofvloeigebeure, waar goudafsetting deur koolstofreduksie plaasgevind het. ‘n Re-Os isochron ouderdom van 2652 ± 64.3 Ma vir piriet is ‘n gevolg van die terugstel van Re-Os isotope in piriet tydens kratoniese uitbreiding wat die Transvaalse Supergroep sedimentasieproses begin het. Gebaseer op bestaande geochronologie data, daar word teoretiseer dat die smelting van 'n vlak subdukterende plaat onder die kontinentale kors van die Barberton-terreen gehelp het om goud-draende vloeistowwe na boonste korsvlakke te vervoer, waar goud in skeursones neergelê is. Hierdie navorsing beklemtoon die belangrike rol van koolstof in die vorming van groot, hoëgraadse goudafsettings in Argeiese groensteen gordels. Masters 2023-11-29T06:59:03Z 2024-02-20T09:29:07Z 2023-11-29T06:59:03Z 2024-02-20T09:29:07Z 2023-11-29 Thesis https://scholar.sun.ac.za/handle/10019.1/129379 en Stellenbosch University xi, 128 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Gold ores -- South Africa -- Barberton Greenstone Belt Geochemistry -- South Africa -- Barberton Ore deposits -- South Africa -- Barberton Greenstone Belt Carbonates -- Analysis Scanning electron microscopy -- Technique UCTD La Cock, Rutger Alexander Carbon-gold systematics in the Barberton Greenstone Belt |
| title | Carbon-gold systematics in the Barberton Greenstone Belt |
| title_full | Carbon-gold systematics in the Barberton Greenstone Belt |
| title_fullStr | Carbon-gold systematics in the Barberton Greenstone Belt |
| title_full_unstemmed | Carbon-gold systematics in the Barberton Greenstone Belt |
| title_short | Carbon-gold systematics in the Barberton Greenstone Belt |
| title_sort | carbon gold systematics in the barberton greenstone belt |
| topic | Gold ores -- South Africa -- Barberton Greenstone Belt Geochemistry -- South Africa -- Barberton Ore deposits -- South Africa -- Barberton Greenstone Belt Carbonates -- Analysis Scanning electron microscopy -- Technique UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/129379 |
| work_keys_str_mv | AT lacockrutgeralexander carbongoldsystematicsinthebarbertongreenstonebelt |