The Triassic Molteno Formation is a clastic sedimentary sequence consisting of a series of cycles, dominated lithologically by coarse grained sandstones. Aspects of the petrography have been examined using the conventional petrographic microscope as well as the scanning electron microscope. Both solution and overgrowth features are present not only on the quartz grains but also on certain of the heavy mineral species present. Intrastratal solution of garnet would appear to be a significant feature in the Molteno Formation. Mineralogical examination of the laterally persistent Indwe Sandstone Member indicates no significant variation in heavy mineral content. Evidence from a study of zircon elongation ratios shows the presence of two distinct zircon populations indicating two provenance areas. X-ray diffraction and electron microprobe analysis has identified mineral species characteristic of granites, pegmatitic granite and metamorphic rocks, especially amphibolites. Palaeocurrent data indicates that this source area lay to the south-east; to the south the source area consisted mainly of the Cape Supergroup sediments. Analysis for Nb, Zr, Y, Sr, Rb, Zn, Mn, Ba, Cu, Ni, Co, Cr, V and Ti for 22 samples from the Molteno Formation, indicates, as expected for a highly arenaceous sequence, a substantial depletion in these trace elements. No consistent variation of trace element concentration occurs with height in the sequence so trace element content may not be used for purposes of stratigraphic correlation. There are indications of trace element variation with geographical position, no doubt a reflection of the contribution of 2 source areas of different compositions. Factor analysis of the interelement correlations has identified 3 factors which influence the trace element content of the Molteno Formation these are a "heavy mineral" factor, a "pH-Eh" factor and a "clay mineral" factor. These trace factors are ultimately an expression of the source rock composition, the prevailing climate and a combination of the two. Comparison with the more argillaceous overlying Elliot Formation, indicates that factors influencing geochemical variation in this sequence were far more complex than for the Molteno Formation

The Birds River Gabbro Complex is intruded into sediments of the Karroo Stormberg Group in the area SW of Dordrecht in the northeastern Cape. A geochemical investigation, restricted to the igneous rock suite, gabbro-ferrogabbro-ferrotholeiite, presents new major-element data as well as data for twelve trace elements - Ba, Sr, Rb, Zr, Y, Nb , Zn, Cu, Ni, Co, V and Cr. The strong degree of differentiation of Kokstad-type tholeiitic magma in the Birds River intrusion, as noted by previous investigators, is revealed in variation diagrams in which data are plotted against a simple index of fractionation. Later differentiates are strongly enriched in Si, Ti, Fe, Na, K, P, Ba, Rb, Zr, Y, Nb, Zn and Cu but depleted in Mg, Ca, AI, Ni, Co and Cr. Extreme differentiation resulted in a strong depletion of Ti, Fe, P, Cu and V in the most highly evolved ferrotholeiites. Field evidence suggests the initial emplacement of strongly fractionated magmatic residua derived from fractional crystallization processes in a magma chamber at depth during cauldron subsidence of a mass of sediments within an annular fracture. These porphyritic, in part glassy, ferrotholeiites are enriched in Si, Na, K, Ba, Zr, Rb, Y, Nb and Zn and were engulfed by a later episode of renewed hypabyssal intrusive activity from the original source area. The younger gabbro was emplaced in a series of closely-spaced heaves or pulses of relatively undifferentiated Kokstad-type magma. The gabbro differentiated in place to form ferrogabbros which chemically closely approximate ferrotholeiite compositions. toidal facies. Residual liquids crystallized as a pegmatoidal facies. A simple fractional crystallization path, modelled on the assumption that the gabbro and ferrotholeiite form a continuous series, indicates that the least evolved ferrotholeiite can be derived from the initial gabbro composition by the fractionation of major amounts of plagioclase and pyroxene but lesser amounts of olivine. Crystallization and removal of magnetite and other Fe-oxides were relatively more important during the later stages of differentiation. The variation of major- and trace-elements in tholeiitic Karroo magma under conditions of strong differentiation at Birds River serves as a framework for the regional study of the geochemistry of other Karroo dolerites and volcanics of the north-eastern Cape. New geochemical data are presented for a sample of thirty chilled and coarse-grained Karroo dolerites collected throughout the north eastern Cape. For the most part, the chilled dolerites are relatively undifferentiated and the average composition differs only slightly from that determined by Walker and Poldervaart (1949). Variation diagrams reveal the steady increase in Si, Al, Ca, Na, K and P and the residual trace elements Ba, Zr, Rb, Y, Nb and Zn with increasing differentiation of the dolerites from more basic types. The concentrations of K, Ba and Rb are highly variable in some Karroo dolerites while new data suggest that Nb levels in the dolerites are low, being generally less than 10 ppm. The strong variation of the K-related elements (K, Ba and Rb) as well as the large ranges determined for certain inter-element ratios, such as K/Rb, Zr/Nb and K/Zr in the chilled Karroo dolerites, suggest that factors other than fractional crystallization processes need to be considered to account for individual variations. Little correlation exists between petrographic type as defined by Walker and Poldervaart (1949) and geochemical character. New geochemical data are also presented for ten Karroo basaltic lavas from the lowermost horizons of the lava sequence exposed in the Barkly East area. Major- and trace-element data indicate that these earliest Karroo extrusives are on average enriched in Si and Rb but depleted in Co and Ni when compared with the averaged chilled Karroo dolerite. Compared with basalts from Lesotho, the Barkly East basalts are enriched in Si but depleted in Ni and possibly Nb, Cu and V. The andesite is markedly enriched in Si, Na, K, Ba, Sr, Rb, Zr and Nb but depleted in Mg, Ca, V, Ni , Cu, Co and Cr. The subdued rate of Ni depletion and the absence of olivine as a major phenocryst phase in the series basalt to andesite, in the Barkly East area, suggests that differentiation trends may be controlled by the fractional crystallization of orthopyroxene and plagioclase, the two common phenocrysts present in these volcanics. The strong depletion of V and Cu in the andesite may indicate some magnetite removal during fractional crystallization.

This study of the lower part of the Rustenburg Layered Suite in the Western Bushveld Complex is based mainly on drill core samples from three localities, which are approximately 130 km apart. The NG-sequence, situated in the northwestern sector of the complex (Union Section, R.P.M.) extends from the floor of the complex to the base of the upper Critical Zone. The sequence is ca. 1800 m thick and it comprises mainly ultramafic cumulates, namely pyroxenites, olivine pyroxenites, harzburgites and dunites. Norites and anorthos ites are present only in minor proportion. Within the upper half of the NG-sequence ten prominent chromitite layers are correlated with the LGI MG4-interval. Correlation is also established between published sequences and the two other sequences studied, located 8 km and 55 km, respectively, east of Rustenburg. Whole-rock chemical data (major and trace elements), microprobe and Sr isotope data are presented. Petrographic studies provide modal analyses and measurements of grain size. All petrographic, mineralogical and other geochemical data point to an origin of the cumulates of the NG-sequence by crystallization from liquids of the U-type lineage and derivatives thereof. No evidence is found for the involvement of parental liquids with a distinctly different composition or crystallization order (A-liquids). However, subtle compositional variations of the parental liquids are evident in slight changes of the Cr content in orthopyroxene or in variations of Sr isotope ratio. The NG-sequence is characterized by intervals with reversed fractionation trends caused by repeated influxes of pristine magma (during periods of high magmatic activity) resulting in a high degree of rejuvenation. These intervals are overlain by others with a normal fractionation trend, interpreted as cumulates formed in periods with low or no magmatic activity, in which fractional crystallization controlled bulk composition of the evolving liquid. The Lower Zone in the NG-sequence is dominated by a progressive shift towards more primitive compositions, while in the Critical Zone fractionation was the major operating process in the magma chamber. However, during deposition of the pyroxenitic lower Critical Zone several replenishment events occurred, during which fresh Cr-rich magma was emplaced. Massive chromitite layers were deposited after mixing between the newly emplaced magma and the resident residual liquid shifted bulk compositions into the primary field of chrome-spinel. Cumulus plagioclase crystallized after bulk composition of the residual liquid was driven to the orthopyroxene plagioclase cotectic by continued fractional crystallization; this occurred once in the Lower Zone, yielding a single, thin norite layer, and again in the upper Critical Zone of the NG-sequence. A facies model is proposed based on the stratigraphic and compositional variations along strike in the Western Bushveld Complex. This model explains the variations by means of the position of the sequence with regard to a feeder system. The olivine- and orthopyroxene-rich, but plagioclase-poor NG-sequence represents the proximal facies, while the SF-sequence (poor in ferromagnesian phases, but plagioclase-rich) is developed as a distal facies, close to the Brits graben.

This study is an account of the stratigraphic sequence, the petrography, mineralogy (microprobe investigations of orthopyroxene, clinopyroxene, olivine and plagioclase feldspar), and whole-rock major- and traceelement geochemistry of the silicate cumulates of the Upper Critical Zone in the western Bushveld Complex. Two parts of the study - an investigation of a 350m column incorporating the MG3 and UGI Footwall Units, and a comparison of two additional Upper Critical Zone profiles with a previously compiled profile between the UGI and Bastard Units - are focused on RPM Union Section in the northwestern sector of the Complex. The third part is a detailed vertical and lateral investigation of the Bastard Unit at the top of the Critical Zone, which draws on sampling and data compilation from seventeen profiles in the western limb of the Complex. The MG3 Unit (45m) is made up of a lower chromitite layer overlain by a norite-pyroxenite-anorthosite sequence while the UGlFW Unit (295m) is composed of a related series of lower chromitite layers (MG4) overlain by a pyroxenite-norite-anorthosite sequence capped by the UGI chromitite layer. These mafic cumulates display a distinctive pattern of oscillating cryptic variation in whole-rock Mg/(Mg+Fe), FeO/Ti0₂, Cr/Co and Ni/V ratios through the sequence. Sympathetic oscillations are recorded for compositions of orthopyroxene and plagioclase feldspar and eight subcycles are recognised through the UGlFW Unit. The entire sequence is characterised by the presence of small, spheroidal, embayed and irregularly shaped plagioclase grains which are poikilitically enclosed in cumulus orthopyroxene grains of both pyroxenites and norites. This texture is indicative of partial resorption of pre-existing feldspar primocrysts within the melt prior to their being incorporated into the host orthopyroxene grains. Textural, geochemical and isotopic data suggest that this sequence was built up by periodic additions of fresh, relatively primitive liquid into fractionated resident liquid, and subsequent mixing within the magma chamber. The Bastard Unit sequence, described in Chapter 4, is the last and most complete cyclic unit (c. 60m) of the Critical Zone, and its upper contact defines the boundary between the Critical and Main Zones of the Complex. This Unit can conveniently be sub-divided into a lower part, where orthopyroxene occurs as a cumulus phase, and the upper part which is composed entirely of anorthosite (Giant Mottled Anorthosite). The basal part of the Unit (≤ 18m) comprises a thin chromitite layer < O.5cm) overlain by a pyroxenite-melanorite-norite-leuconorite sequence. The basal pyroxenite is orthocumulate in character and rapidly gives way to norites and leuconorites. A distinct threefold subdivision emerges within the Giant Mottled Anorthosite which is predominantly an adcumulate which becomes orthocumulate in character at its top. Apart from minor deviations in thicknesses these lithologies are recorded over the entire strike-length covered in this study. Profiles of cryptic variation are compiled for orthopyroxene, plagioclase and whole-rock data and show that the Bastard Unit displays a characteristic pattern which is maintained throughout the western Bushveld Complex. A minor yet distinctive reversal in cryptic variation is revealed at a level which is stratigraphically variable within the lower Giant Mottled Anorthosite, and results in a double cuspate pattern. A remarkable feature of the basal Bastard pyroxenites is that although the modal proportion of mafic to felsic constituents varies systematically away from the northwestern sector, the Mg/(Mg+Fe) ratio of orthopyroxenes remains constant at 0.804 over a lateral strike distance of 171km. Within the upper part of the Unit the orthopyroxene is markedly Fe-rich and it is here that inverted primary pigeonite appears for the first time as a cumulus phase. In addition, K-feldspar, oscillatory zoned plagioclase grains and high levels of incompatible trace elements are noted at this level. On the basis of the data presented it is concluded that the Bastard Unit represents the crystallisation of a final, relatively large influx of hotter primitive liquid, with upper Critical Zone affinities, and subsequent mixing with a column of cooler (less dense) supernatant liquid which had in part hybridized with the overlying Main Zone magma. It is hypothesised that this new liquid was emplaced as a basal flow beneath supernatant liquid and that it initiated the deposition of mafic cumulates at its base. The supernatant liquid is interpreted as representing the fractionated residuum produced by crystallisation of earlier cyclic units, with plagioclase on the liquidus, and that it contained an abundance of small plagioclase primocrysts in suspension. Development of the Unit can be viewed as a two-stage process. In the lower half of the unit, chemical and physical parameters typical of the new magma dominated the crystallisation process, and resulted in cumulates very similar to other relatively complete Upper Critical Zone units. In the upper, leucocratic sequence, above a minor reversal, crystallisation was from a liquid which was the product of mixing of a minor pulse of primitive liquid with the reservoir of hybridized supernatant liquid. Although the Bastard Unit is not continuous around the entire Western limb of the Complex, it is concluded that it developed in a single, or connected, magma chamber and that its irruptive feeder zone was located in the proximal northwestern facies of the Complex.

Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Foreland basins commonly fill with sediment derived from the adjacent fold/thrust belt, providing a relatively simple source-to-basin configuration. However, that is not true for the early southwestern Karoo Basin, since the composition of the Ecca Group sedimentary rocks do not match the composition of the adjacent fold/thrust belt. The southwestern Karoo Basin is bordered to the west and south by the Cape Fold Belt (CFB) and provides the opportunity to study the linkage between its early structural evolution and deposition in the two spatially and temporally distinct Tanqua and Laingsburg depocentres. The CFB was formed when the early Palaeozoic passive continental margin, which formed a large section of the southern edge of Gondwana, evolved into an active convergent margin during the late Palaeozoic. Orogenesis resulted in a northwest-trending Cedarberg branch and an eastwest-trending Swartberg branch. The oroclinal bend between the two branches includes large-scale northeast-trending syntaxis structures, such as the Hex River and Baviaanshoek anticlinoria, which influenced the sedimentation path into the basin. Spectral gamma ray (SGR), mineralogical and geochemical studies of exposed rocks from the Tanqua and Laingsburg depocentres indicate a near uniform provenance for both, dominated by granitic and metamorphic material derived from a provenance seemingly far beyond the CFB. SGR data, combined with lithology, show that regional stratigraphic correlation is possible in the Skoorsteenberg, Kookfontein and Waterford Formations in the Tanqua depocentre. The same is true for the Laingsburg and Fort Brown Formations in the Laingsburg depocentre. There are no major changes in the SGR data set between the successive sandstone or shale units that could imply different origin, and no distinct signals in the SGR pattern of the shale intervals that could potentially correspond to maximum flooding surfaces. The Tanqua and Laingsburg depocentre sandstones are very fine- to lower mediumgrained, tightly packed, poorly to well sorted, and have undergone mechanical compaction and pressure solution. The mineralogical composition and texture of these sandstones suggest that they have undergone high-grade diagenesis to low-grade regional burial metamorphism to the lower greenschist facies (250 ± 50ºC; ~2 kbars). They are mineralogically and geochemically classified as lithic arenites and greywackes, and the Tanqua depocentre sandstones are slightly more mature than the Laingsburg depocentresandstones. REE patterns for the Tanqua and Laingsburg depocentre sandstones are similar, suggesting that both form part of the same evolutionary pattern and that the sediments have one common origin, i.e. a provenance predominantly composed of granitic material. Homogenous εNd-values for all sandstone samples of around –5 at the time of deposition indicate that there is little or no variation in provenance between the Tanqua and Laingsburg depocentre sediments. TCHUR model ages of 0.70 to 0.95 Ga, and TDM model ages of 1.19 to 1.49 Ga, resulted from a mixture of Archaean and Proterozoic material in unknown proportions. The most likely source terrane is thought to be the North Patagonian Massif. The latter show Nd isotopic compositions corresponding to an average εNd-value of -5 at 265 Ma. / AFRIKAANSE OPSOMMING: Voorlandkomme word oor die algemeen gevul met sediment afkomstig van die aanliggende plooigordel, wat lei tot ‘n redelik eenvoudige brongebied-tot-afsettingskom konfigurasie. Dit is egter nie van toepassing vir die vroeë suidwestelike Karookom nie, aangesien die samestelling van die Ecca Groep sedimentêre gesteentes nie ooreenstem met die samestelling van die aanliggende plooigordel nie. Die suidwestelike Karookom word aan die weste en suide begrens deur die Kaapse Plooigordel en bied die geleentheid om die verwantskap tussen die vroeë strukturele evolusie en afsetting in die twee ruimtelik en temporeel afsonderlike Tankwa en Laingsburg subkomme te bestudeer. Die Kaapse Plooigordel het gevorm toe die vroeë Palaeosoïkum kontinentale grens, wat ‘n groot deel van die suidelike grens van Gondwana was, ontwikkel het tot ‘n aktiewe konvergerende grens gedurende die laat Palaeosoïkum. Orogenese het gelei tot die vorming van ‘n noordwes-strekkende Sederberg tak en ‘n ooswes-strekkende Swartberg tak. Die oroklinale buig tussen die twee takke sluit grootskaalse noordoosstrekkende sintaksis strukture in, soos die Hex Rivier en Baviaanshoek antiklinoria, wat die sedimentasie rigtings na die kom beïnvloed het. Spektrale gammastraal (SGR), mineralogiese en geochemiese studies op die dagsome van die Tankwa en Laingsburg subkomme dui ‘n byna identiese brongebied aan vir beide, oorheers deur granitiese en metamorfe materiaal vanaf ‘n brongebied oënskynlik vêr vanaf die Kaapse Plooigordel. SGR data, gekombineer met litologie, dui aan dat dit moontlik is om regionale stratigrafiese korrelasies in the Skoorsteenberg, Kookfontein en Waterford Formasies in die Tankwa subkom te maak. Dieselfde geld vir die Laingsburg en Fort Brown Formasies in die Laingsburg subkom. Daar is geen groot veranderinge, wat ‘n verskil in oorsprong kan aandui, in the SGR datastel tussen die opeenvolgende sandsteen of skalie eenhede nie, en ook geenuitstaande tekens in the SGR patroon van die skalie-intervalle wat moontlik kan ooreenstem met ‘n maksimum vloedingsvlak nie. Die Tankwa en Laingsburg subkom sandsteenlae is baie fyn- tot laervlak mediumkorrelrig, dig gekompakteer, swak tot goed gesorteer, en het meganiese kompaksie en drukoplossing ondergaan. Die mineralogiese samestelling en tekstuur van hierdie sandsteenlae dui daarop dat hulle hoë-graadse diagenese tot lae-graadse regionale begrawingsmetamorfose tot laervlak groenskis fasies (250 ± 50ºC; ~2 kbars) ondergaan het. Hulle word mineralogies en geochemies geklassifiseer as litiese areniete en grouwakke. Die Tankwa subkom sandsteenlae is effens meer volwasse as die Laingsburg subkom sandsteenlae. Die lantanietgroep patroon vir die Tanqua en Laingsburg sandsteenlae is eenders, wat aandui dat beide deel gevorm het van dieselfde evolusionêre ontwikkeling en dat die sedimente een gesamentlike oorsprong gehad het, naamlik ‘n brongebied bestaande hoofsaaklik uit granitiese materiaal. Homogene εNd-waardes van ongeveer –5 by tye van afsetting vir al die sandsteen monsters dui daarop dat daar min of geen verandering in brongebied vir die Tankwa en Laingsburg subkom sedimente was nie. TCHUR model ouderdomme van 0.70 tot 0.95 Ga, en TDM model ouderdomme van 1.19 tot 1.49 Ga, is afkomstig van ‘n mengsel van Argeïese en Proterosoïese materiaal in onbekende hoeveelhede. Die mees waarskynlike brongebied is die Noord Patagoniese Gebergtes. Dit wys Nd isotopiese samestellings wat ooreenstem met ‘n gemiddelde εNd-waarde van –5 by 265 Ma.

Thesis (MSc) -- Stellenbosch University , 1995. / ENGLISH ABSTRACT: A number of small greenstone bodies of the Bridgetown Formation are exposed as elongated lenses and dykes within metasediments of the Malmesbury Group in the Western Cape Province, South Africa. The Malmesbury Group is part of the Neoproterozoic to Cambrian (Namibian) Saldania Subprovince which is the southern continuation of a Pan-African mobile belt system. A detailed geological and geochemical study was conducted on the largest outcrop of the Bridgetown Formation, situated 20km east of the town Moorreesburg. The Bridgetown Formation consists of a meta-volcano-sedimentary sequence that experienced polyphase deformation and metamorphism up to the lower greenschist facies. Tectonically, the Bridgetown Formation is included in the Boland tectonic domain, east of the Piketberg-Wel lington fault zone that is suggested to run Skm west of Heuningberg and subparallel to the Berg River. This agrees with Rabie's (1974) original subdivision of the tectonic domains. The Bridgetown Formation consists of: i) A basal unit of poorly differentiated alkaline metabasalt with a within-plate tectonomagmatic fingerprint. ii) An intermediate unit of poorly differentiated tholeiitic metabasalt, intruded by a younger tholeiitic metabasite with a low degree of differentiation. Both members of the intermediate unit have ocean-floor basalt (P-type MORB) and island arc basalt fingerprints. iii) An upper unit of poorly differentiated as well as more evolved alkaline metabasalts, interlayered with metatuff with an alkaline basaltic composition, metasedimentary rocks with a marine origin, and graphitic schists and muscovitequartz schists, both with a continental crust provenance. iv) An overlying metasedimentary sequence including dolomite, massive and oolitic chert, jasper and jaspilite. The Bridgetown Formation probably also comprises a lower metamorphosed ultramafic unit, indicated by the association of Ni- and Cr-rich talc bodies, Ni-and errich banded chert, chlorite schist and small dolomite-talc-chlorite bodies at Spitskop, situated directly northwest of the main greenstone body. The sequence of eruptive stages and the geochemistry of the metavolcanics resemble Hawaiian volcanism , indicated by an initial deep water stage of alkaline magmatism, followed by main tholeiitic edifice and post-caldera alkaline magmatism. Post-caldera alkaline magmatism occurred contemporaneously with deposition . of sediments and chemical precipitates (carbonates and cherts). The Bridgetown metavolcanics have no magmatic association with either the Bloubergstrand volcanics or mafic and intermediate plutonic rocks in the Malmesbury Group. However, some physical and geochemical similarities exist between the Bridgetown Formation and the age related Grootderm Formation of the Marmora Terrane (Gariep Supergroup) which is considered to represent ophiolitic material. The Bridgetown Formation probably represents segments of oceanic crust, including seamounts of oceanic islands, which were tectonically emplaced in an accretionary prism zone during subduction of oceanic crust underneath the Kalahari Craton, 600 to 700 Ma ago. This resulted in the present spatial configuration of various small greenstone bodies in the Malmesbury Group. To date no exploitable mineral deposits have been found 1n the Bridgetown Formation. However, Au and As anomalies in stream sediment and soil samples, taken in the Spitskop area, require further attention. lt is suggested that the gold and arsenic is hosted in brittle deformed clear to milky quartz veins which developed at zones of competency contrasts in all the li tholog ies in the Spitskop area. / AFRIKAANSE OPSOMMING: 'n Aantal klein groenskisliggame van die Bridgetown Formasie is blootgestel as verlengde lense en gange binne metasedimente van die Malmesbury Groep in die Wes-Kaap Provinsie, Suid-Afrika. Die Malmesbury Groep is deel van die Neoproterozo·iese tot Kambriese (Namibiese) Saldania Subprovinsie wat die suidelike voortsetting is van 'n Pan-Afrikaanse mobiele gordel sisteem. 'n Gedetaileerde geologiese en geochemiese studie is gedoen op die grootste dagsoom van die Bridgetown Formasie, gelee 20km oos van die dorp Moorreesburg. Die Bridgetown Formasie bestaan uit 'n metavulkanies-sedimentere opeenvolging wat pol ifase vervorming en metamorfisme tot en met die laer groenskis fasies ondergaan het. Die Bridgetown Formasie word hier in die Boland tektoniese domein ingedeel deur die Piketberg-Wellington verskuiwingsone 5km wes van Heuningberg, subparallel a an die Bergrivier, te plaas. Dit stem ooreen met Rabie ( 197 4) se oorspronkl ike verdeling van die tektoniese domeine. Die Bridgetown Formasie bestaan uit: i) 'n Basale eenheid wat hoofsaaklik bestaan uit min gedifferens ieerde alkali-metabasalte met binneplaat tektonomagmatiese eienskappe. ii) 'n lntermediere eenheid wat bestaan uit min gedifferensieerde tholeiitiese metabasalt en 'n jonger intrusiewe tholeiitiese metabasiet wat 'n lae graad van differensias ie ondergaan het. Beide intermediere eenhede het oseaanvloer-basalt (P-t ipe MORB) en eilandboog basaltiese eienskappe. iii) 'n Boonste eenheid wat bestaan uit min gedifferensieerde asook meer gedifferensieerde alkal i-metabasalte, tussengelaagd met metatuf met 'n alka libasaltiese samestelling; metasedimentere gesteentes met 'n mariene oorsprong, en grafitiese ski ste en kwarts-muskoviet skiste, beide met 'n kontinentale kors oorsprong . iv) 'n Oorliggende metasedimentere opeenvolging wat dolomiet, massiewe en ooli tiese chert, jaspis en jaspiliet insluit. Die Bridgetown Formasie slu it moontlik ook 'n onderliggende gemetamorfiseerde ultramafiese eenheid in; aangedui deur die assosiasie van Ni- en Cr-ryke ta lkl iggame, Ni- en Cr-ryke gebande chert, chlorietskis en klein dolomiet-talk-chloriet liggame by Spitskop, gelee direk noordwes van die hoof groensteenliggaam. Die opeenvolg ing van magmatisme en die geochemie van die metavulkaniese gesteentes stem ooreen met Hawaiiese vulkanisme, naamlik 'n diepwater stadium, gekarakteriseer deur alkaliese magmatisme, gevolg deur 'n hoof tholeiitiese opbouing en post-kaldera alkaliese magmatisme. Die post-kaldera alkaliese magmatisme het gelyktydig plaasgevind met afsetting van sedimente en chemiese presipitate (karbonate en cherte ). Die Bridgetown metavulkaniese gesteentes het geen magmatiese assosiasie met 6f die Bloubergstrand vulkaniese gesteentes 6f mafiese en intermediere plutoniese gesteentes in die Malmesbury Groep nie. Fisiese en geochemiese ooreenkomste bestaan egter tussen die Bridgetown Formasie en die Grootderm Formasie van die Marmora Terrein (Gariep Supergroep) wat beskou word as ofiolitiese materiaal. Die Bridgetown Formasie verteenwoordig moontlik segmente van oseaankors, insluitende oseaan-eilande, wat tektonies in 'n melange sone ingeplaas is tydens subduksie van oseaankors onder die Kalahari Kraton in (600 tot 700 Mj gelede). Dit verklaar die huidige ruimte like verspreiding van verske ie klein groensteenliggame in die Malmesbury Groep. Tot en met hede is geen ontginbare mineraalafsettings in die Bridgetown Formasie ontdek nie. Au en As anomalie in stroomsediment- en grondmonsters, geneem in die Spitskop area, behoort egter verdere aandag te geniet. Daar is voorgestel dat die goud en arseen voorkom in brosvervormde helder tot melkerige kwartsare wat ontwikkel het in swak sones in al die litologie in die Spitskop area.

Thesis (MSc.)--Stellenbosch University, 1994. / ENGLISH ABSTRACT: The NAD deposit forms part of the A-Mine Complex in the Rooiberg tin field in the north-western Transvaal. Mining started in 1986 and the mine was closed recently following a decline of tin prices and metallurgical problems with ore recovery. The deposit is hosted by the Boschoffsberg Quartzite Member of the Pretoria Group sediments and is structurally controlled within the so-called Tin Zone. Extensive alteration of the original host rocks occurred during the mineralisation event. Potassic remobilisation and redistribution appear to have taken place pervasively. The nature of the original host rock was altered to such an extent that it cannot be classified correctly. Previous workers refer to the host rock as an arkose because of its feldspathic nature. Wall rock alteration in the hanging- and foot wall of the different ore lodes (fractures) is generally similar. Very little change is observed in whole rock chemistry away from the lodes. The mineral chemistry of the ore lode minerals is indicative of fluid composition and mineralising conditions in the NAD deposit. The FeO/(FeO + MgO) ratio of tourmalines indicates deposition at a distance from the source of the mineralising fluids. Pyrite trace element chemistry differs from that of the Leeuwpoort deposit, indicating changing fluid chemistry. Contrary to previous assumptions that the carbonate present is ankerite, abundant siderite occurrences were found. Pyrite may co-precipitate with siderite under specific physico-chemical conditions. Cassiterite is generally trace element poor and relatively enriched in Fe. Hydraulic brecciation of the fractures as well as the tourmaline chemistry are strong indicators of a hydrothermal origin for the NAD deposit. However, the origin of the hydrothermal fluids is still uncertain. / AFRIKAANSE OPSOMMING: Die NAD- tinafsetting vorm dee/ van die A-Myn-kompleks in die Rooiberg tinveld in die noord-wes Transvaal. Die myn is in 1986 geopen en is onlangs gesluit weens swak tinpryse en metallurgiese ertsherwinningsprobleme. Die tinafsetting kom voor in die Boschoffsberg Kwartsiet lid van die Pretoria Groep sedimente. Dit is strukturee/ gekontroleer binne die sogenaamde Tin Sone. Vorige navorsers het na die waardgesteente as 'n arkose verwys op grand van die hoe veldspaat-inhoud. lntensiewe en uitgebreide verandering van die oorspronklike waardgesteentes het plaasgevind tydens mineralisasie. Deurdringende kalium-hermobilisering en -herverspreiding het plaasgevind. Die aard van die oorspronklike waardgesteente is egter tot so 'n mate verander, dat dit chemies nie korrek gek/assifiseer kan word nie. Wandrotsverandering van die verskil/ende ertsskeute in beide die voet- en dakgesteentes is baie soortge/yk. Die heelrotsgeochemie van die wandgesteentes verskil baie min weg van die ertsskeute af. Die mineraalchemie van die ertsskeut-minerale is aanduidend van die v/oeistofsamestelling en mineralisasietoestande van die NAD-tinafsetting. Die FeO/(FeO + MgO) verhouding van toermalyne dui daarop dat afsetting op 'n afstand vanaf die bron van die mineralisasie-vloeistowwe plaasgevind het. Die spoor-elementchemie van die NAD-piriete verskil van die piriete van die Leeuwpoort tinafsetting, wat verandering in vloeistofsamestelling aandui. In teenstelling met vorige aannames dat die karbonate in die Rooiberg tinafsettings as ankeriet bekend staan, is daar volop sideriet gevind. Piriet kristalliseer dikwels saam met sideriet onder spesifieke fisiese en chemiese toestande. Kassiteriet is meestal arm aan spoor-elemente, maar is relatief verryk in Fe. Hidroliese breksiering van die skeute en die toermalyn-chemie dui sterk op 'n hidrotermale oorsprong vir die NAD afsetting. Die bron van die vloeistowwe is nog nie definitief vasgestel nie. / Digitized at 300 dpi Colour PDF format (OCR), using ,KODAK i 1220 PLUS scanner. Digitised, Ricardo Davids on request from IBL 10 September 2013

<p>The Morokweng impact structure which is located in the North West province of South Africa, has attracted attention as a potential host for Ni-PGE mineralization. Geochemical exploration techniques using hydroxylamine partial extraction were used to determine the nature and source of surface geochemical anomalies known to occur in the overlying aeolian sang regolith. About 40 aeolian samples were taken from an area of about 35 square kilometer, located in the north eastern sector of the Morokweng impact structure. The samples were sieved to various grain size fractions and partially extracted using varying concentration of hydroxylamine hydrochloride at 50&deg / C.</p>

<p>The Morokweng impact structure which is located in the North West province of South Africa, has attracted attention as a potential host for Ni-PGE mineralization. Geochemical exploration techniques using hydroxylamine partial extraction were used to determine the nature and source of surface geochemical anomalies known to occur in the overlying aeolian sang regolith. About 40 aeolian samples were taken from an area of about 35 square kilometer, located in the north eastern sector of the Morokweng impact structure. The samples were sieved to various grain size fractions and partially extracted using varying concentration of hydroxylamine hydrochloride at 50&deg / C.</p>

PUMPS mimics natural geothermal vents as a conceptual model designed for the remediation of acid mine water (AMW) in voids of abandoned gold mines of the Witwatersrand Basin in South Africa. In this system, a reaction chamber containing Desulfotomaculum kuznetsovii sulfate reducing bacteria will be set at the bottom of a 3-4 km deep mine that will be flooded. A geothermal system with at least one (1) doublet will be drilled from the bottom of the mine to the depth of 8km, where the temperatures are sufficient for geothermal energy harvesting. AMW, used as a geothermal fluid, will be pumped down the injection well and circulate through hot rock. The hot water is then used to generate electricity and then channelled into the reaction chamber to undergo bio-remediation. Following treatment, the water flows back into the mine voids where it will improve the quality of untreated AMW through dilution. Eventually, the mine will be flooded with clean water that can be stored underground and/or pumped up to surface for social and ecosystem services. Following an introduction and proof of concept for the PUMPS, the research builds further on the technical and economic evaluation of the PUMPS in order to assert its viability and sustainability. The technical viability includes testing the ability for Desulfotomaculum kuznetsovii to survive in high pressure condition; quantifying the amount of energy that can be drawn from the geothermal reservoir; determining the placement and scheme of the geothermal wells; and, finally, developing a robust economic model of the system. Experiments show that Desulfotomaculum Kuznetsovii can tolerate high pressure conditions in of at least 100bar at their ideal sulfate reducing temperature of 63°C. Geochemical modelling shows that AMW can be used effectively as a geothermal fluid for PUMPS. To achieve highest efficiency and minimal fluid loss, the geothermal wells should be placed along the SSE-NNW direction, based on the known stress field across the Witwatersrand Basin. With a flow rate of 30l/s the energy drawn from the geothermal reservoir is sufficient to drive PUMPS and the surplus energy is determined by the volume of AMW treated per day. All results indicate that the PUMPS is technically and economically viable. The economic model shows that the value and viability of the PUMPS is best reflected with a comprehensive inclusion of potential revenue (for example from chemical solution mining of deep seated gold) and financial/environmental incentives.