Controls of magma emplacement and 3d modelling of cupriferous basic bodies of the Kuperberg suite at Narrap mine, Okiep copper district, Namaqualand

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dc.contributor.advisorKisters, Alexanderen_ZA
dc.contributor.authorBester, Andeonen_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Earth Sciences.en_ZA
dc.date.accessioned2023-11-21T08:59:49Z
dc.date.accessioned2024-01-08T16:10:52Z
dc.date.available2023-11-21T08:59:49Z
dc.date.available2024-01-08T16:10:52Z
dc.date.issued2023-12
dc.descriptionThesis (MSc)--Stellenbosch University, 2023. en_ZA
dc.description.abstractENGLISH ABSTRACT: The Okiep Copper District hosts more than 1800 copper-mineralised basic bodies that form part of the Koperberg Suite. These mafic magmas intruded the high-grade granite gneiss terrain of the Bushmanland Subprovince during a period of E-W extension (1060-1030 Ma) and peak, lower- granulite facies metamorphism. Basic bodies have different, commonly highly irregular geometries ranging from massive, steeply-plunging, carrot-shaped intrusions to thin stringers or foliation-parallel sills in the gneiss sequence. For the most part, however, basic bodies show subvertical E-W trending blade- or dyke-like geometries hosted by localised high-strain 'steep structures'. The close spatial relationship between basic bodies and steep structures highlights the importance of structural anisotropies as conduits facilitating mafic magma ascent through the stratified mid-crustal OCD. The 3D model of Narrap Mine's wall rocks and Koperberg Suite intrusions revealed three distinct structures: 1) a central cluster of vertical basic bodies cutting across various lithologies and emplacing along the vertical foliation of a prominent steep structure, 2) a subvertically orientated, laterally extensive collection of basic bodies emplaced along the upwarped lithological contact of the overlying Moddefontein Gneiss and underlying Wolfram Schist, and 3) subhorizontal penny-shaped sill-like bodies following the shallowly dipping regional gneissic layering. A commonality between all these structures is their discontinuous nature and small aspect ratios, indicative of buoyancy-driven, self- contained hydrofractures. Furthermore, these structures are congruent with mechanical anisotropies, be it lithological contacts or foliation, signifying the importance of anisotropies as magma propagation pathways. Additionally, the presence of multiple generations of Koperberg Suite magmas within a particular steep structure highlights the effectiveness of utilising steep structure fabrics as repeated pathways. This demonstrates that emplacement was independent of the regional stress field and occurred under low deviatoric stresses in the high-grade metamorphic, partially molten mid-crustal section of the OCD. In this case, structural anisotropies (foliations, lithological contacts, steep structure fabrics) determine the emplacement and orientation of basic bodies. The 3D model further indicates how the mechanically layered gneiss and interlayered metasediments impede the buoyancy-driven ascent of the Koperberg Suite magmas and modify their geometry. Basic bodies typically thicken and accumulate in schist and gneiss units as a result of the lower wall-rock rigidity. In contrast, the refractory Springbok Quartzite resists fracture dilation, yielding stringer-like geometries and the likely ponding of magmas below this unit. All these observations, including the three aforementioned structures, bear striking similarities to what is seen at the rest of the mines in the OCD, with the softer metasediment and gneisses above the Springbok Quartzite hosting the majority of the basic bodies mined historically. This stratigraphic position hosts the laterally branching structures, which have commonly emplaced along the underlying Wolfram Schist and overlying gneisses, and the subvertical clustered basic bodies that pinch and seemingly terminate against the upper contact of the Springbok Quartzite. Thus, future exploration should focus on the gneisses and schists hosting the branching structure and central cluster, in addition to following the down-plunge continuation of the central cluster below the quartzite as ponding is likely.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die Okiep Koper Distrik huisves meer as 1800 koper-gemineraliseerde basiese liggame wat deel uitmaak van die Koperberg Suite. Hierdie mafiese magmas het die hoë-graad granietgneis-terrein van die Bushmanland Subprovinsie binnegedring tydens 'n tydperk van O-W strekking (1060-1030 Ma). Die Koperberg Suite kom voor in verskeie vorms binne verskeie lithologieë in die OCD, van massiewe wortelvormige indringe in die Concordia Graniet tot dun draadagtige strukture in die Springbok- kwartsiet. Die mees algemene, egter, is subvertikale O-W neigende lemagtige strukture wat binne die gelokaliseerde hoë-spanning 'steil strukture' in die goed-gefolieerde Nababeep Gneis aangetref word. Die mede-bestaan tussen die basiese liggame en die steil strukture beklemtoon die belangrikheid van hierdie strukture as geleiers wat mafiese magma opgang deur die gelaagde middle kors OCD fasiliteer. Die 3D-model van Narrap-myn se muurrots en Koperberg Suite-indringings het drie onderskeidende strukture aan die lig gebring: 1) 'n sentrale groep vertikale basiese liggame wat verskeie litologieë deursny en langs die vertikale vouing van 'n prominente steil struktuur plaasvind, 2) 'n subvertikaal georiënteerde, lateraal uitgestrekte versameling basiese liggame wat geplaas word langs die opgewelde litologiese kontak van die oorliggende Moddefontein Gneiss en die onderliggende Wolfram Schist, en 3) subhorisontale muntvormige silliagtige liggame wat die oppervlakkig hellende regionale gneissiese laagligging volg. 'n Gemeenskaplikheid tussen al hierdie strukture is hul ononderbroke aard en klein aspekverhoudings, wat dui op drijfkrag-aangedrewe, selfbevatte hidrofrakture. Verder stem hierdie strukture ooreen met meganiese anisotropieë, hetsy litologiese kontakpunte of vouing, wat die belangrikheid van anisotropieë as magma-voortplantingsroetes aandui. Daarbenewens dui die teenwoordigheid van meervoudige generasies Koperberg Suite- magmas binne 'n bepaalde steil struktuur op die doeltreffendheid van die hergebruik van steil struktuure as herhaalde roetes. Dit toon aan dat die plasing onafhanklik van die streekspanningsveld was en onder lae deviatoriese spanning in die hoë-graad metamorfe, gedeeltelik gesmelte middelkors van die OCD plaasgevind het. In hierdie geval bepaal meganiese anisotropieë (vouings, litologiese kontakpunte, steil struktuurstowwe) die plasing en oriëntasie van basiese liggame. Die 3D-model dui verder aan hoe die meganies gelaagde gneiss en tussenlaag-metasedimente die drijfkrag-aangedrewe opstyging van die Koperberg Suite-magmas belemmer en hul geometrie verander. Basiese liggame verdik en akkumuleer tipies in skis- en gneiss-eenhede as gevolg van die laer wandrots-rigiditeit. In teenstelling hiermee weerstaan die weerstandige Springbok-kwartsiet die breukdilatasie, wat lei tot langer vorms en die waarskynlike opgaar van magmas onder hierdie eenheid. Al hierdie waarnemings, insluitend die drie genoemde strukture, vertoon treffende ooreenkomste met wat deur die res van die myne in die OCD waargeneem word, met die sagte metasedimente en gneisse bokant die Springbok-kwartsiet wat die meeste van die historiese basiese liggame herberg. Hierdie stratigrafiese posisie herberg die laterale vertakkingsstruktuur, wat gewoonlik langs die onderliggende Wolfram Skist en oorliggende gneisse geplaas word, en die subvertikale geklusterde basiese liggame wat knyp en oggendt blyk te eindig teen die boonste kontak van die Springbok-kwartsiet. Dus moet toekomstige eksplorasie fokus op die gneisse en skiste wat die vertakkingsstruktuur en sentrale groep herberg, asook die voortgesette daalbeweging van die sentrale groep onder die kwartsiet, aangesien opgaarwaarskynlik is.af_ZA
dc.description.versionMastersen_ZA
dc.format.extentix, 83 pages : illustrations (some color), mapsen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/128929
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshMagmas -- Namaqualand (South Africa) -- Compositionen_ZA
dc.subject.lcshIntrusions (Geology) -- Koperberg Suite (South Africa)en_ZA
dc.subject.lcshThree-dimensional modeling -- Mathematical modelsen_ZA
dc.subject.lcshGeology, Stratigraphic en_ZA
dc.subject.lcshCopper mines and mining -- South Africa -- Namaqualanden_ZA
dc.subject.lcshLower crustal environmenten_ZA
dc.subject.lcshOkiep Copper Districten_ZA
dc.subject.nameUCTDen_ZA
dc.titleControls of magma emplacement and 3d modelling of cupriferous basic bodies of the Kuperberg suite at Narrap mine, Okiep copper district, Namaqualanden_ZA
dc.typeThesisen_ZA
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