Browse
Recent Submissions
Item Open Access A Sr-isotopic investigation of bifurcating chromitite layers of the UG1 at the Impala Platinum Mine, Rustenburg(University of the Free State, 2023) Nyakane, Tshepo Felix; Magson, Justine; Roelofse, FrederickChromitite bifurcations hosted within, but not limited to, the Upper Group 1 (UG1) chromitite layer in the Critical Zone of the Bushveld Complex are one of the most enigmatic geological features encountered. Several researchers have attempted to develop models explaining how these bifurcations could have been formed. Most of these studies were heavily based on field observation with little to no geochemical data to support their findings. In this study, samples of an exposure of chromitite bifurcations from the UG1 chromitite at Shaft No.11 of Impala Platinum Limited in the Western Limb of the Bushveld Complex were utilised to perform petrographic and geochemical work including Sr-isotopic determinations on plagioclase. The geochemical data collected, along with field observations, were used to develop a conceptual model explaining the development of the bifurcations. Four sample cuts (D, C, B, and A) across the anorthositic footwall of the UG1 chromitite, each with a width of 10 cm and varying lengths were sampled from the study area using a diamond saw. The sample cuts represent vertical transects across a set of bifurcating chromitite layers, taken approximately 1 m apart, on the northern side of the approximately 40 m section. Thirty-four polished thin sections were made representing all the sample cuts. The polished thin sections were studied petrographically with an Olympus BX51 microscope. Electron microprobe analyses were carried out to obtain the compositions of chromite and plagioclase crystals from the samples, and Laser Ablation Multi-Collector Inductively Coupled Mass Spectrometry was used to obtain in-situ isotopic compositions of the plagioclase crystals. Plagioclase in the anorthosite layers exhibits very little variation in An% with average values of 75.10 ± 3.27, 74.26 ± 1.93, 75.10 ± 3.27 and 73.85 ± 1.89 for sample cut D to A, respectively. Plagioclase in the chromitite layers reveals much more significant variation in An% with average values of 70.69 ± 14.15, 78.16 ± 15.26, 56.49 ± 33.13 and 55.50 ± 36.68 for sample cuts D to A, respectively. The in-situ plagioclase isotopic composition reveals that the initial ⁸⁷Sr/⁸⁶Sr ratios of plagioclase in anorthosite show very little variation both vertically and laterally through sample cuts A to D, with an average value of 0.7062 and individual layers that are generally within error compared to adjacent layers. Most chromitite layers also display ⁸⁷Sr/⁸⁶Sr ratios that are comparable to those observed in the anorthosite, although some of the thicker layers returned values that are more radiogenic, e.g., the bottom thick layer in sample cut A, which returned values on the order of 0.709 – 0.710. Taking into account the field relations along with the petrography and geochemistry of the study area, it is envisaged that the chromitite bifurcations in the study area were formed in the following stages: (1) Development of an irregular floor through the thermo-chemical erosion of the underlying anorthosite footwall. (2) The intrusion of chromite-rich slurry (mass balance requirement) as a basal flow resulted in thick chromitite layer deposition on an uneven surface. (3) Development of cyclic anorthosite and chromitite forming bifurcations. Pressure fluctuations (magma influxes, roof rupturing events, shock waves) permitted rapid transitions between the system's chromitite and plagioclase stability fields. A large reservoir of melt likely buffered compositional and isotopic changes. (4) The intrusion of a chromite-rich slurry led to renewed erosion and formation of the thick upper chromitite layer, with the thin chromitite layers now appearing as offshoots from the base of this layer. (5) Downward intrusion of slurry into rheologically weak zones led to the development of additional bifurcations.Item Open Access The allanite deposits on Vrede, Gordonia District, Cape Province(University of the Free State, 1961-11) Hugo, Petrus Jacobus; De Villiers, J. E.; Kent, LAllanite deposits of an unusual nature occur in two types of granulite on the farm. Vrede, portion of Cnydas West, Gordonia District, Cape Province. The granulites belong to the Archaean complex which is also represented by schists and gneisses. These rocks, which are described in detail, have been correlated with the Kaaien Series of the Kheis System. The ore bodies are characterised by their distinct banding and the close -connection between their distribution and the regional structure of the metamorphic rocks. Allanite occurs with tourmaline, apatite, zircon and monazite in bands ranging from one-sixteenth to two inches in thickness, parallel to the foliation of the granulites. The mineralisation, probably hydatopneumatolytic in nature, started with the introduction of zircon, monazite and tourmaline, after which apatite, allanite, magnetite and quartz followed in that order. The optic axial angle of the allanite is 2V=60° or more. A high magnesian variety, however, has a positive sign with 2V=40°. The range in refractive indices is: no~=1.732 - 1.757 n f3 = 1. 7 4 7 1. 7 68 n~ = 1.759 1.779 This variation is probably due to differences in chemical composition. The three analyses of allanite given have been recalculated on the basis of 13 (O, OH, F) atoms to the unit cell and the formulae obtained conform closely to the formula X₂ Y₃ Z₃ (O, OH, F) 13 developed by Machatschki. Chip sampling was done on all the deposits and the samples were radiometrically assayed against a standard uranium-thorium sample. The average values obtained are Allanite is, therefore, a prescribed material in terms of the Atomic Energy Act. The other ore minerals are all normal in their properties. A crystallising pegmatite is believed to have been the source of the mineralising, solutions giving rise to these deposits. This pegmatite and those of the surrounding area are related to a younger granitic intrusion, probably the acid granite intruded into parts of Bushmanland. The deposits opened up by 1960 occur intermittently over a total area of approximately 600 feet by 200 feet, but their extent in depth has still to be proved. Only the main deposit may perhaps be workable; if the allanite bands there extend to a depth of 200 feet, the ore reserve will be of the order of 1500 tons, assuming that the ore contains roughly 10 percent allanite.Item Open Access A stratigraphic-structural investigation of an area south of Pofadder, Namaqua Mobile Belt, South Africa(University of the Free State, 2021-12) Nel, Wayne Justin; Colliston, W. P.The area of the Namaqua Mobile Belt investigated is situated in the eastern part of the Aggeneys Terrane (2-1.06 Ga), south of Pofadder in the Northern Cape. The mapping campaign covered an area of 1,350 km², in the eastern Aggeneys Terrane which is juxtaposed against the Pofadder (2Ga) and Bladgrond Terranes. The terranes are separated by well-defined inter-terrane thrust boundaries, namely, the Groothoek Thrust that separates the Aggeneys and Pofadder Terranes in the north, and the Geelvloer Thrust separating the Bladgrond and Aggeneys Terranes in the south of the study area. The study area is defined by kilometre scale sheet intrusives hosting 23 stacked sequences of sheath fold nappes characterised by double vergence geometries, representing four well defined structural domains; the Witkoppies, Samoep, Lekdam and Houmoed Structural Domains. Three of the four domains contain supracrustal sequences, that can be divided into prominent structural successions and sequences. One structural domain however, the Samoep Structural Domain, is defined by a well foliated medium quartz-feldspar gneiss and contains no isolated sheath fold structures. The structural domains are separated by intra-terrane thrust sheet boundaries that have been juxtaposed on top of one another. The stratigraphic sequences can be correlated with the upper succession of the Wortel Formation, defined in the west, together with a total new set of supracrustal rocks not yet identified in the Aggeneys Terrane. The stacked sequences of isolated double vergent isoclinal fold structures can be classified as sheath folds using listed criteria. Three prominent planar fabrics were identified within the study area namely: S0, S1 and S2. The S2 fabric is however only identified in the hinges pf macroscopic sheath folds as a sillimanite grade axial planar fabric and forms the regional fabric, defining the XY plane of the regional strain ellipse. The S2 fabric is also identified on a mesoscopic scale, by F2 Model 1 and 2 flow perturbation folds, seen in the YZ and XZ planes of the regional foliation, all planar fabrics are co-planar. The macroscopic sheath folds mapped during this study contain co-linear L fabrics defined by stretching lineations, fold axes of various fold phases and the long axes of the sheath folds and represents the X-direction of the regional strain ellipse. The co-linear linear fabrics have a mean east-northeasterly trend and plunge indicating the southwesterly directed tectonic transport overthrust direction. The planar fabrics have a mean dip toward the north-northeast across the study area. A progressive shear deformation model is proposed for the study area and is defined by six phases of deformation affecting all four structural domains, interpreted to take place under deep crustal conditions of upper amphibolite grade of metamorphism. The D1 phase is defined by the intrusion of kilometre scale sheet intrusives that define an S1 fabric, associated with inter- and intra-terrane thrusting. The D2 phase is defined by the development of macroscopic F2 sheath folds that fold an S0-1 foliation and define an S2 regional axial planar foliation. The D2 phase is also defined by F2 Model 1 and Model 2 folds. The D3 phase is defined by macroscopic F3 folds that refold D2 sheath fold traces and define localised S3 foliations that are also co-planar with S2. The D4 phase is defined by macroscopic F4 open folds that define a characteristic Z asymmetry that refolds all earlier structures, including kilometre scale sheet intrusives. The study area itself can be defined as a macroscopic D4 antiformal-synformal structure. The D5 phase is defined by east-west shears that are associated with the reactivated movements of thrust boundaries, and movements associated with flexural slip on the limbs of major D2, D3 and D4 structures. The D5 phase also rotates linear and planar fabrics in the north-western sector of the study area on the limbs of the major D4 synformal structure. The D6 phase is associated with northwest-southeast oblique trending shears that effect the eastern sector of the study area and deforms all earlier D2-D5 structures. It is concluded that the structures identified across the eastern Aggeneys Terrane formed progressively during a single long-lived event, formed by a process of sub-simple/general shear conditions, under deep crustal conditions.Item Open Access The Sr isotopic stratigraphy of the LCZ-UCZ transition in the Western Limb of the Bushveld Complex(University of the Free State, 2021) Malatji, Mafete; Roelofse, Frederick; Magson, JustineData on the modal mineralogy, whole-rock geochemistry, plagioclase mineral chemistry and Sr isotopic compositions in lithologies covering an interval of ~100 m across the Upper Critical Zone (UCZ) and Lower Critical Zone (LCZ) transition in the Western Limb of the Bushveld Complex are presented in this study. The aims of this study were to (1) investigate the presence or absence of isotopic disequilibrium in plagioclase (2) to investigate differences between the LCZ and UCZ from a geochemical, petrological and Sr isotopic perspective and (3) to refine chromitite formation models using the data obtained over the course of the study. Samples were obtained from the BH7929 drill core donated by Impala platinum to the University of the Free State. Samples were analysed using transmitted light microscopy, X-Ray Fluorescence Spectrometry (XRF), Inductively Coupled Plasma Mass Spectrometry (ICPMS), Electron Probe Micro-Analyzer (EPMA) and Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA MC-ICP-MS) to produce whole-rock major and trace element geochemistry and plagioclase elemental and isotopic compositional profiles across the UCZ-LCZ transition. Results reveal that the LCZ is composed of orthopyroxene-dominated lithologies that display cryptic layering, hosting two chromitite layers (MG1-2), with plagioclase predominantly existing as an intercumulus phase. Plagioclase is predominantly cumulus in the UCZ, dominating the UCZ lithologies that display modal layering. Two chromitite layers were investigated in the UCZ (MG3-4). Compositional breaks in whole-rock major and trace elements are detected at the UCZ-LCZ transition and at the level of the chromitite layers, reflecting variations in the dominant mineral phases. Fractionation indices including whole-rock Mg# and Cr/V ratio reveal little variation throughout the study interval in silicate-dominated lithologies, with variations mostly detected at the level of chromitite layers. Plagioclase An% averages 82.10 ± 1.90% in the UCZ, whereas it averages 73.58 ± 2.60% in the LCZ. Chromitite layers in the LCZ reveal lower An% values in comparison with adjacent silicate lithologies, whereas the UCZ reveals very little to no variations between chromitites and silicate lithologies. Sri values in the UCZ average 0.7059 ± 0.0003, whereas Sri in the LCZ averages 0.7054 ± 0.0004. Decreases in the Sri value of plagioclase are observed at the level of the chromitite layers in the LCZ, whereas the UCZ reveals a constant Sri up the stratigraphy. The data provide credence to the importance of magma mixing (i.e. Irvine, 1977) as a process operational in the formation of chromitite layers within the LCZ and UCZ and argue against models suggesting variations in intensive parameters or in-situ crystallization as dominant processes in the formation of chromitite layers. It is proposed that the UCZ-LCZ transition displays credible evidence for the repeated intrusion of batches of isotopically distinct magmas, with chromitite layers in the LCZ forming in response to the mixing of newly introduced and resident magma in a manner analogous to that envisaged by Irvine. The MG3 layer in the UCZ also appears to have formed as a direct consequence of mixing between newly intruded UCZ magma and the residual LCZ magma. The MG4 layer does not preserve Sr-isotopic evidence for magma mixing as it has similar Sri as that of adjacent silicate lithologies. In order to account for the mass balance of Cr, it is argued that at the level of chromitite layers, intruded magma pulses were chromite-laden, with additional chromite formation occurring in response to magma mixing. The MG1 chromitite layer provides potential evidence in support of such an argument in the form of multiple isotopically distinct populations of plagioclase that may have been intruded along with suspended chromite crystals.Item Open Access The parageneses of sulphide minerals in transgressive carbonatite of the Palabora Carbonatite Complex, South Africa(University of the Free State, 2019-03) Du Plessis, Pieter George; Roelofse, Frederick; Gauert, Christoph D. K.; Giebel, R. Johannes; Rentel, RaimundThe Palabora Complex, also known as the Palabora Carbonatite Complex, is situated in the Limpopo Province, next to the town of Phalaborwa. The complex intruded the Kaapvaal Craton in early Proterozoic times. The centre of the complex is known as the Loolekop pipe and hosts the youngest rock types of the complex. These rock types are phoscorite (older), banded carbonatite (younger), and transgressive carbonatite (youngest). Transgressive carbonatite hosts one of the world’s largest copper deposits in the form of sulphide group minerals. The paragenesis of the various sulphide minerals is not well known, and a back and forth dispute exists of the formational processes (e.g. magmatic, hydrothermal, autometasomatic, etc.) which led to sulphide mineral crystallisation. This study shows that these sulphide minerals form part of different repetitive assemblages. These assemblages have distinguishable mineralogical, petrographical, geochemical, and paragenetic characteristics. Some assemblages that contain more than one generation of a certain sulphide mineral show differences in mineral chemistry (e.g. pentlandite group minerals, pyrrhotite, chalcopyrite, and sphalerite). The same assemblages that form part of transgressive carbonatite are also found in banded carbonatite. However, the sulphide mineral assemblage of phoscorite is completely different. This is indicative of different sulphide mineralisation events within the Loolekop pipe. The majority of transgressive carbonatite minerals show evidence of a magmatic origin, and most of them have been modified due to hydrothermal activity. Both processes are also responsible for sulphide mineral formation. This study also shows the discovery of sulphide minerals (e.g. heazlewoodite and shandite) and Cu-rich veinlets that have not been observed from this area in the past.Item Open Access Die geologie in die omgewing van Britstown(University of the Free State, 1977) Lemmer, William MurrayAfrikaans: 'n Stratigrafiese kolom is met behulp van geologiese kartering en profiele vir die gebied opgestel. Die twee eenhede van die Ventersdorpgroep kan gekorreleer word met die eenhede in die Bothaville-omgewing. Die nuwe standaard onderverdeling van die Karoosupergroep wat in die gebied gebruik is, verskil van die ou indeling. Paleogeomorfologiese gegewens en primêre strukture toon dat die Dwyka-ysplate in 'n suid-suidoostelike rigting beweeg het. Verskillende afsettingsomgewings soos diep mariene, onderste wegstrand, boonste wegstrand, strandfase, delta-top en kontinentale fluviale omgewings kan in die veld vir die Ecca- en Beaufortgroepe onderskei wrod. Primêre strukture, petrografiese en paleontologiese gegewens dui op 'n diep mariene, beperkte afsettingskom vir die Prins Albertformasie. Die Whitehill- en Tierbergformasies is onder soortgelyke toestande afgeset. Die water het vlakker geword en deltas wat die begin van die Beaufortsedimentasie aandui, het vanuit die suidweste gemigreer. Kontinentale fluviale sedimente is op die sikliese deltaïese sedimente afgeset. Die kontak tussen die Ecca- en Beaufortgroepe is graderend en vir praktiese doeleindes is die basis van die eerste deurlopende sandsteenlaag aan die bokant van die Eccagroep konsekwent as 'n herkenbare en karteerbare eenheid in die veld as kontak geneem. 'n Enkele kimberliet wat nie vantevore beskryf is nie, is gevind. Die verspreiding van kalkreet word beheer deur die topografie en kom net op ou Afrika-oppervlakke voor.Item Open Access Die sedimentologie van die Soutpansbergsteenkoolveld met spesiale verwysing na steenkoolvorming(University of the Free State, 1980) Van der Berg, Hendrik Jacobus; Visser, J. N. J.Afrikaans: Die Karoolae noord van die Soutpansberg is geleë in die Tshipise-kom wat tydens vorming deur oos-wesverskuiwings beheer is. 'n Hoë rug in die vloer verdeel die kom in die weste in 'n suidelike en 'n noordelike trog wat onderskeidelik deur kwartsiet en lawa van die Soutpansberggroep en ouer tuf onderlê word. Die kom is waarskynlik met die swak sone, geskep deur die Limpopo Mobiele Gordel, geassosieer. Na-Karooverskuiwings het 'n rol gespeel in die behoud van die Karoo-lae in die Tshipise-kom. Die Karoo-opeenvolging is litologies in 6 sones verdeel en die sedimentasie van die sones is deur middel van vertikale siklusse bestudeer. Sone 1, aan die basis, bestaan uit 'n onderse Sanderige en 'n boonste Kleiige Diamiktieteenheid. Die Sanderige Diamiktieteenheid word opgebou ui oorwegend diamiktietlae bestaande uit fragmente, enkeles geskraap en gefasetteer, van kwartsiet, lawa en tuf van wisselende grootte in 'n sanderige matriks. Dun warfagtige lae kom soms ook voor. Die eenheid word geïnterpreteer as 'n oorwegend fluvioglasiale afsetting, agtergelaat deur valleigletsers wat ooswaarts teruggetrek het. Fasiesveranderinge kom algemeen in 'n weswaartse rigting voor. Die Kleiige Diamiktieteenheid bestaan oorwegend uit koolstofryke, kleiige sedimente wat waarskynlik ook vanuit die ooste aangevoer is. Grofkorrelrige, sanderige materiaal was egter ook vanaf die sentrale rug in die weste afkomstig en is as kanaalafsettings tussen die kleiige lae afgeset is. Langs die steil afsettingshellings het moddervloeie ontstaan en 'n vermenging van grofkorrelrige en kleiige materiaal het tot die kleiige diamiktietlae aanleiding gegee. Sone 2 bestaan uit sandsteen, skalie-sliksteenassosiasie, moddersteen en steenkool, oorwegend in opwaarts fyner-wordende fluviale siklusse gerangskik. Die sedimente is hoofsaaklik deur meanderende rivieriere op die vloedvlakte as puntwal-, oewerwal- en deurbreekafsettings agtergelaat. Die sandsteen-skalieverhouding van die opeenvolging dui op 'n aanvoerrigting vanuit die noordooste. Tydens kort stabiele periodes het plantmateriaal in vloedkomme onder koel, redusereende toestande versamel en tot dun, afwisselende steenkoollae aanleiding gegee. Die baie wortelafdrukke, paleosols, tussengelaagde skalie en siklisiteit van die steenkoollae dui op 'n oorwegend in situ oorsprong vir die steenkool. Sone 3 volg diskordant op Sone 2 en bestaan uit 'n onderste grofkorrelrige Sandsteeneenheid, opgebou uit opwaarts fyner-wordende siklusse en is deur vlegstrome vanuit die suidooste afgeset. Dit gradeer in 'n Moddersteeneenheid bestaande uit dun opwaarts fynerwordende sandsteensiklusse en dik, grys tot koolstofryke, kleiige gedeeltes. Die afsettingshelling het platter geword en die eenheid is afgestet deur meanderende riviere met wye vloedvlaktes. Hoewel die litologie en sikliese ontwikkeling van Sone 4 presies met dié van Sone 2 ooreenstem, is die gesteentes van Sone 4 oorwegend rooi, pers en groen van kleur en plantmateriaal is afwesig, terwyl karbonaatryke knolle opwaarts in die sone meer algemeen word. Dit dui op afsetting deur meanderende strome vanuit die suide en suidooste tydens warm en droër klimaattoestande. Sone 5 bestaan uit 'n middelkorrelrige, goedgesorteerde sandsteen. Sone 5 bestaan uit 'n middelkorrelrige, goedgesorteerde sandsteen. Sedimentêre strukture aan die basis dui op afsetting deur water, maar hoër op kom uitsluitlik grootskaalse wig- en tafelvormige kruisgelaagdheid voor en word die lae as 'n windafsetting geïnterpreteer. Woestyntoestande het dus op daardie tydstip geheers en die heersende windrigting was vanuit die suidweste. Karoosedimentasie is deur die uitvloei van basiese lawa (Sone 6) en die indringing van dolerietplate en -gange afgesluit. Die Karoolae in die Tshipise-kom kan met dié in die hoof-Karookom gekorreleer word. (i) Die Sanderige Diamiktieteenheid word op grond van afsettingsomgewing en stratigrafiese posisie met die Dwykaformatsie gekorreleer. (ii) Die Kleiige Diamiktieteenheid verteenwoordig 'n oorgangsfase, maar word saam met Sone 2, waarin fossiele van Glossopteris en Vertebraria algemeen voorkom, met die Eccagroep gekorreleer. (iii) Sone 3 word op grond van litologie en die voorkoms van Dicroidium sp. met die Moltenoformasie gekorreleer. (iv) Sone 4 word met die Ellitoformasie gekorreleer. (v) Sone 5 word met die Clarensformasie gekorreleer. (vi) Sone 6 stem ooreen met die Drakensberggroep. Die Beaufortgroep is volgens hierdie indeling afwesig in die Tshipise-kom.Item Open Access Die sedimentologie van die Etage Holkranssandsteen, sisteem Karoo(University of the Free State, 1969) Beukes, Nicolas Johannes; Visser, J. N. J.Afrikaans: 'n Regionale, sedimentologiese studie van die Etage Holkranssandsteen is gedurende Maart 1968 tot Maart 1969, in Natal, Noordoos-Kaapland, die Vrystaat en Lesotho, voltooi. Die etage is in drie rotsstratigrafiese sones, gebaseer op 45 stratigrafiese profiele, ingedeel. Sone I bestaan uit dik- tot baie dikgelaagde, massiewe, baie fynkorrelrige sandsteen tot sanderige sliksteen. Die kontak met die Etage Rooilae is aan die basis van die deurlopende, massiewe sandsteen geneem. Dit is egter nie 'n vaste kontak nie, aangesien daar 'n geleidelike oorgang tussen die Rooilae en holkranssandsteen bestaan. Sone I bereik sy maksimum dikte in die noorde van die geboed en hier word dit veral deur 'n ligbruin of ligrooi kleur en volop kalsitiese konkresies gekenmerk. Holkranse kom algemeen in die sone voor. Hulle vorm deurdat die sandsteen wat 'n kalsitiese matriks bevat, makliker verweer. Klein, lensvormige afsettings met vlakwaterstrukture word dikwels aangetref. Sone II kan as 'n Kruisgelaagde Sone beskryf word. Dit bestaan uit kruisgelaagde en fynbelaagde, relatief growwer, skoon sandsteen tussengelaagd met massiewe, baie fynkorrelrige, vuil sandsteen. Lensvormige afsettings met kenmerkende vlakwaterstrukture is relatief skaars. Sone III bestaan hoofsaaklik uit massiewe, dik- tot baie dikgelaagde, vuil, baie fynkorrelrige sandsteen in die noorde en weste van die gebied. Na die ooste en suide gradeer die sandsteen lateraal in ligbruin en ligrooi, massiewe, dik- tot baie dikgelaagde, slikkerige sandsteen en sanderige sliksteen met volop klein kalsitiese konkresies. Lensvormige afsettings met kenmerkende vlakwaterstrukture kom algemeen voor, maar is veral opvallend op die kontak met die Drakensbergbasalt. Sandsteenlae kom tussengelaagd met die basalt voor en dui daarop dat die sedimentasie nie volledig met die eerste lawavloeiings beëindig is nie. Sedimentasie het in 'n vlak, binnelandse kom plaasgevind. Die afsetting van die Holkranssandsteen het waarskynlik vroeër in die noorde as in die suide van die gebied begin. Dit kan aan 'n geleidelike verskuiwing van klimaat (gekoppel aan Kontinentale Drywing of Poolverskuiwing) toegeskryf word. Die etage bereik sy maksimum dikte in die suidelike deel van die gebied. Die lokale veranderings in dikte is deur die uitvloei van lawas, wat sedimentasie beïnvloed het, en primêre duinstrukture veroorsaak. Die kruisgelaagde eenhede van Sone II kan aan die migrasie van duine toegeskryf word. Die brongebied van die sedimente was na die weste, noordweste en suidweste geleë en het hoofsaaklik uit sedimentêre materiaal van die Serie Beaufort bestaan. Die korrelgrootte van die kruisgelaagde sandsteen neem in die rigting van afsetting af. Die massiewe sandsteen dui op meer stabiele duine na afsetting, deurdat hulle nie herhaaldelik herwerk is nie. Strukture in die sandsteen word deur verwering of die uniformiteit in korrelgrootte verberg. Duine versadig met water het moontlik tot sandvloeiings en die vernietiging van strukture aanleiding gegee. Die korrelgrootteverspreidings van die sandstene stem met die van eoliese sedimente ooreen. Die kwartskorrels in die gesteentes is hoofsaaklik afgerond, maar die primêre afronding is deur diagenese verlaag. Die korrels besit gematte of pokdalige oppervlakke en dit word aan fisies-chemiese prosesse wat in woestyne teenwoordig is, toegskryf. Die sandstene is halfvolwasse en kan hoofsaaklik as sub-grouwakke geklassifiseer word. Die kruisgelaagde sandsteen is beter gesorteer en meer grofkorrelrig as die massiewe sandsteen. Die mineralogiese samestelling dui daarop dat die sedimente van die drie sones vanaf dieselfde brongebied afkomstig is. Seoliete kom in sommige van die sandstene voor en hulle is aan die vulkaniese aktiwiteite verwant. Die afsetting van die drie sones kan aan klimaatsveranderinge gekoppel word. Sones I en III is onder halfdroë woestyntoestande afgeset, terwyl 'n droë klimaat, soortgelyk aan die van 'n ware woestyn, tydens die afsetting van Sone II geheers het. Ten spyte van die droë klimaat het plante- en dierelewe, tot en met die uitvloei van die eerste lawas van die Etage Drakensberg, bly voortbestaan.Item Open Access A sedimentological study of the conglomerates in the Elsburg stage on the Welkom and Western holdings gold mines(University of the Free State, 1970-12) Kleynhans, Jacob Johannes; Botha, B. J. V.; Visser, J. N. J.; Antrobus, T.A sedimentological description of the layers of conglomerate in the Elsburg Stage of the Witwatersrand System, as disclosed by 23 boreholes and underground development on the Welkom and Western Holdings Gold Mines in the Orange Free State Goldfield, is given. The palaeocurrents in the Elsburg Stage as inferred from pebble-size distribution and preferred pebble orientation, were from two different directions. On Western Holdings Limited and the Welkom Mine area west of the Arrarat Fault, the layers of conglomerate were derived from the north-west. On the Welkom Mine area east of the Arrarat Fault, the direction of transport was from the south-west. These two different palaeocurrent directions can be explained by lateral movement along the Arrarat Fault. Thus, the eastern block of the lease area of the Welkom Gold Mining Company, which was formerly situated on the north-eastern flank of a delta fan, was displaced along the strike of the Arrarat Fault for a distance of approximately 6 000 m towards the south, while the western block (Welkom No.3 Shaft and Western Holdings Limited), was displaced towards the north. A detailed analysis regarding the composition, roundness, shape, orientation and sorting of the pebbles in the layers of conglomerate was undertaken. The sorting and roundness of the pebbles increase towards the centre of the basin, while the majority are orientated with their long axes parallel to the palaeocurrent direction. The percentage of non-durabIe pebble types also decreases in a down-current direction, while the durable types remain constant. The pebbles are mostly spheroidal, although certain types show a strong tendency to disc shaped. These features indicate that the layers of conglomerate were probably deposited on an alluvial fan bordering an inland lake or sea.Item Open Access Structural-stratigraphic investigation of an area near Kakamas and environs, Namaqua mobile belt, South Africa(University of the Free State, 2017-07) Mathee, Hendrik Lukas Marthinus; Colliston, W. P.The study area is near Kakamas in the Northwest Cape and is located in the tectonostratigraphic Grünau Terrane - an accreted crustal fragment associated with the Mesoproterozoic Namaqua Province. The mapping campaign covered an area of some 6,500 km2 comprising of highly deformed and metamorphosed pre-tectonic supracrustals and syntectonic sheet intrusives emplaced and tectonised during the 1.2 to 1 Ga Namaqua Orogeny. The granulite grade Grünau Terrane is juxtaposed against the amphibolite facies Bladgrond Terrane and transported south-westwards along the inter-terrane Hartbees River Thrust (HBRT). The study area incorporates the north-western section of the Riemvasmaak-Kenhardt Mega Sheath Fold (RK-MS) which contains a series of sheath fold complexes divided into five structural domains. Macroscopic sheath folds have been recognised and documented in the western Namaqua Province for both the ~2Ga Pofadder Terrane and the ~1.6Ma Aggeneys Terrane: this study reports for the first time, the details of large scale sheath fold complexes in the Eastern Namaqua sector. In the Aggeneys Terrane the Aggeneys Mountain consist of a series of stacked sheath folds and Gamsberg Mountain represents a single macroscopic sheath fold formed under a compressive simple shear regime associated with south-west accretion of terranes. The dominant stratigraphic features are suites of sheeted granitoids interdigitating pre-tectonic supracrustals that consist of metasedimentary and volcaniclastic rocks. The oldest of the supracrustals is the Blouputs Formation with a provenance age of c.1800 Ma. The intrusives are a combination of leucocratic to granodioritic granites and the product of kilometre scale anatexis. Both the supracrustal and intrusive rocks are confined to the five structural domains. The Vaaldrift sheath fold is the only structure (Domain 4) that does not have an inter-sheeted granite associated with the supracrustals. The intrusive rocks has an intrusive age distribution ranging from the oldest, Eendoorn gneiss (1200 Ma) to the youngest, Friersdale charnockite (1080 ±13 Ma). The sheath fold complexes are bounded by intra-terrane thrusts along which thrust sheets (both supracrustals and granites) are cut out. The boundary of the RK-MS is defined by the Waterval thrust which is the sole thrust to the intra-terrane thrust system. The macroscopic sheath folds which are mapped during this study contains co-linear L-fabrics consisting of meso- and macroscopic fold axes of various fold phases and mineral stretching lineations plunging towards the north-north-east, which indicates a south-south-westerly tectonic transport direction. Three main fabrics are defined during this study, namely: S0 (compositional banding), S1 and the regional S2; both foliations are caused by shear processes and are also recognisable in the sheeted intrusives (e.g. Rooipad, Eendoorn and Harpersputs). The foliation and axial planes of the macroscopic sheath folds have a co-planar relationship and trend north-west. On a mesoscopic scale, two types of folds have been defined as model 1 and model 2 folds, which formed simultaneously during a flow perturbation process. North-west trending shear zones are mapped as the last stage of deformation during which the intra-terrane thrust was reactivated as sub-vertical shear zones. A progressive shear deformation model is proposed for the structures in the study area. Four deformation phases were recognised with the first of them having two separate sub-phases (D1a and D1b). The initial phase of the first event (D1a) resulted in the mesoscopic model 1 and model 2 folds during terrane assembly. The main deformation event was the second D1 event (D1b), characterised by macroscopic scale sheath folds (F1) formed during flow perturbation under general shear. The D1(b) event consisted of two phases of sheath folds (F1 and F2), the F2 being localised refolding of the F1 structures during a similar process. The D1(b)F1 structures are characterised by folded S0/S1 with S2 as an axial planar cleavage. Two metamorphic events are recorded by previous authors for the area: the first event was during terrane amalgamation at ~1200Ma and the second event during the last stages of deformation (1018±11 to 1024±14Ma; D4 north-west shear event). The second deformation phase (D2) is characterised by the intrusion of the Oranjekom Complex (~1100Ma) which is simultaneously deformed into a sheath fold; it defined the end of a progressive shear model which initiated at D1a. The Grünau Terrane underwent two phases of kilometre scale anatectic melting producing two of the most prominent lithological units, namely: Eendoorn gneiss (~1200Ma) and Witwater gneiss (~1123±6). The third deformation phase (D3) resulted in the intrusion of the Friersdale Charnockite into pre-existing macroscopic D1(b)F1 and F2 sheath fold hinge zones. This emplacement resulted in the D3 folds which are associated with D4 shearing. The D4 shear event caused reactivation of intra-terrane thrusts as sub-vertical shear zones and shears such as the Cnydas, Neusberg and Duiwelsnek shear zones along the limbs of the macroscopic sheath folds. The D4 shear zones trend north-westerly with an associated oblique movement resulting in both a lateral and vertical displacement of strata and structures. The dominant lateral displacement is predominantly sinistral with East-up; the sigmoidal rotation (on km-scale) of F1 axial traces of the macroscopic sheath folds are prominent features of this late shear event. It is concluded that a dynamic model combining progressive shear deformation during flow perturbation (layer-normal differential and layer-parallel shear) from a mesoscopic to a macroscopic scale resulted in the intricate structures mentioned above.Item Open Access Syn- to post-intrusive deformation in the chromitiferous harzburgite unit of the Uitkomst Complex, Nkomati Mine, Mpumalanga Province(University of the Free State, 2013-06) Joubert, Pieter Lourens; Gauert, C. D. K.The mafic to ultra-mafic, intrusive Uitkomst Complex, situated some 20km northeast from the town of Badplaas in the Mpumalanga province of South Africa, contains a Chromitiferous Harzburgite unit that host a layer of massive chromitites at the top. The massive chromitites crop out, as three hills on the farm Uitkomst 541 JT and is exploited by South Africa’s only primary Nickel mine, the Nkomati Mine. The main research criteria of this project are the involvement of syn- and post-magmatic deformation in the petrogenesis of the Massive Chromitite Layer of the Uitkomst Complex. On chromitite hill no.1 (open pit no.3) the layer of massive chromitites consist of five smaller chromitite sub-layers with an average, individual thickness of between 1 to 3 meters. These sub-layers and lenses are stacked on top of each other and separated by layers of talc-carbonate schist, to form a massive chromitite zone with a combined thickness of up to 30m. The project consists of four interlinked investigations: 1. A geological mapping exercise in open pit three of the Nkomati Mine. This investigation forms the basis of the project and focuses on the general geological and geometrical properties of the chromitite layers. The investigation suggests that chromitite lenses MC4 and MC5 that occurs at the base of the Massive Chromitite Layer, in the study area, were deposited as a result of continuous crystallization as they are inter grown through a large gradational contact. The fractured nature and movement indicators along the bottom contacts of chromitite lenses MC1, MC2 and MC3 higher up in the layer suggest post-intrusive duplication through thrust faulting. 2. An investigation of the geological structures in the study area once again emphasized the similarities and continuity in chromitite lenses MC4 to MC5 and supports a continuous depositional event. The jointing in chromitite lenses MC1, MC2 and MC3 are not affected by the movement along the bottom contacts of the chromitite layers but get terminated at the gradational top contacts. This suggests that the fracturing along the bottom contacts might represent syn-intrusive deformation and that these three chromitite layers were rather deposited individually through magmatic processes and rules out the possibility of structural duplication. 3. A petrographic investigation revealed that each chromitite lens experienced a unique degree of crystal deformation, this syn-intrusive deformation suggests that the chromitite was already in the solid phase during transportation. Furthermore each chromitite lens has a unique chromite to matrix ratio that suggests unique physical conditions during the crystallization phase of each chromitite lens. This indicates that the chromitite lenses were deposited as rafts of semi-solid chromitite and further suggests that the rafts were initiated by various pulses of magma replenishment into the primary magma chamber, supplying the conduit system. 4. The mineral chemical investigations of the chromite crystals reveal a normal fractionating trend for chromitite lenses MC4 and MC5. This further supports that they were deposited during a continuous crystallization event. An irregular variation pattern in the Cr number and Mg number in relation to the depositional sequence of the three upper chromitite lenses support that their crystallization were initiated by various pulses of magma replenishment. The former two investigations mainly suggest the involvement of post-magmatic deformational processes, whereas the latter two investigations reveal that the geomorphology of the Massive Chromitite Layer is mostly influenced by syn-magmatic processes that occurred in both the primary magma chamber further down from the study area and the conduit system in the vicinity of the study area.Item Open Access The geology of an area west of Welkom, O.F.S.: (degree blocks 2825 A and B and 2826 A)(University of the Free State, 1980-10) Behounek, Norbert Josef; Grobler, N. J.Rocks present in the mapped area range from Early Precambrian (Easement granite) to the most recent deposits of aeolian sands, alluvium, gravel and calcrete. Outcrops of Ventersdorp rocks are scarce and widely scattered. Nevertheless, agglomerates and felsic lavas of the Makwas'sie Quartz Porphyry Formation, fanglomerates, .quartzites, volcanic breccias, tuff, mafic massive la.vas and pillow lavas of the Rietgat Formation, quartzites of the Bothaville Formation and plateau lavas of the Allanridge Formation could be distinguished and studied. The latter were all grouped together in accordance with the lithostratigraphic classification of Winter (1976), because of the proximity to his type area. Overlying the Ventersdorp Supergroup are shales and/or tillite of the Karoo Sequence. Bore holes drilled to the east (outside) of the mapped area proved that Dwyka glacial deposits are preserved in pre-Karoo valleys and/or valleys excavated through ice movement. Here, the Dwyka Formation consists of tillite, varved shales and a glacio-fluvial unit, viz. the sandstone-siltstone-shale unito In the western sector of the mapped area. Ventersdorp rocks are directly overlain by black, micaceous shales of the Ecca Group (Prince Albert Formation). The V/hitehill .Formation is probably not present as one continuous layer over the whole of the mapped area, and only occurs in a few isolated pockets. As a result the Prince Albert Formation is in most cases overlain by grey shales of the Tierberg Formation which grades from shales and mudstones (marine deposits) upwards into rhythmic layers of grey shales and sandstones (deltaic deposits). The transitional zone between the Ecca Group (Tierberg Formation) and the overlying Beaufort Group is exposed on the farm Basberg 416. The Beaufort Group in this area shows the typical features of a fluvial deposit, viz. coarse-grained channel-axis facies which laterally grade into finer-grained and thin-bedded hannelmarginal facies and levee mudstone deposits. The latter sediments were most probably deposited on the flood plain of a braided rivero Intrusive rocks consist of post-Karoo dolerites (sills and dykes) and the kimberiite intrusions at Rovic Diamond Mines. Nodular and laminated calcrete deposits are the most abundant calcrete deposits in the area under investigation, Aeolian sands cover large tracts of this area and occurmaiicly as aeolian sheet deposits but also as dunes of variable magnitude. The Vaal River Gravels and the alluvial sands and silts of the Yet and Sand Rivers are the most significant alluvial deposits present in the mapped area. Pans of variable shaper, and sizes have originated through the erosion of paleo river channels by subsequent wind action.Item Open Access Die geologie van die serie Stormberg in die sisteem Karoo, suid van Bethlehem, O.V.S.(University of the Free State, 1964-08) Kingsley, Charles Seymour; Van Biljon, W. J.Afrikaans: 'n Gebied tussen Bethlehem en Fouriesburg, waarin alle etages van die Etage Bo-Beaufort tot die Etage Drakensberg verteenwoordig is, is gekarteer asook die veldgegewens opgeteken. Oor geskikte roetes in die gebied is monsters geneem waarop verskillende petrografiese ondersoeke gedoen is. Vanaf swaarmineraalstudies kon gevolgtrekkings gemaak word omtrent oorspronggebied en afsettingstoestande van die Serie Stormberg. Korrelgrootte en -verspreiding is in die sandstene deur sifanalise bepaal. 'n Vergelykende studie is met behulp van die mikroskoop op die sandstene sowel as op die dolerietindringings en lawavloeiings uitgevoer. Uit die resultate kon in hooftrekke die volgende afleidings gemaak word: Die oorsprongrotse van die sedimente moes hoofsaaklik vanaf granitiese stollingsgesteentes wat êrens na die suidooste geleë was afkomstig gewees het. Die afsetting van die sedimente moes in landelike meergebiede geskied het. Die Moltenolae se afsetting moes relatief vinnig onder nat toestande plaasgevind het, terwyl die Eooilae en Holkranssandsteen onder 'n geleidelike droeër-wordende klimaat gevorm is. Die laaste stadiums van afsetting van die Holkranssandsteen het gelyktydig met die eerste lawavloeiings plaasgevind. Laastens was die dolerietgange in hierdie gebied moontlik ook die toevoerkanale vir die basaltiese Drakensberglawa.Item Open Access Quantitative evaluation of minerals in coal deposits in the Witbank and Highveld Coalfields, and the potential impact on acid mine drainage(University of the Free State, 2003-05) Pinetown, Kaydy Lavern; Van der Westhuizen, W. A.A mineralogical and geochemical study on the coal and coal-bearing successions of the Witbank and Highveld Coalfields in the Mpumalanga Province of South Africa was proposed in order to, firstly, investigate the quantitative distribution of minerals in the lithological units, and secondly, to correlate this data with the potential of the units to contribute to acid mine drainage conditions in the region. X-ray diffraction and X-ray fluorescence techniques were used to analyse the samples from the study area. Samples from the No.1, No.2, No.4 and No.5coal seams were collected from several mines in the Witbank Coalfield, while samples from the No.4 and No.5coal seams were collected from borehole material obtained from the Highveld Coalfield. The inorganic components make up approximately 8.00 to 35.00 wt% of a coal sample. Si02 concentrations varied between 0.00 and 35.00 wt% of a sample, AI203 between 0.50 and 16.00 wt%, Fe203 between 0.03 and 10.00 wt%, and S between 0.15 and 8.00 wt%. Minor concentrations of CaO (0.00 to 8.00 wt%) and MgO (0.00 to 1.00 wt%) were present. P205 occurred in concentrations of 0.00 to 3.50 wt% and K20 was in the order of 0.00 to 1.30 wt%. Na20 values were the lowest varying between 0.00 and 0.45 wt%. The only difference in chemistry between Witbank and Highveld coals was a slight increase in Na20 (0.00 to 0.51 wt%) in the Highveld coals. These results were confirmed by the XRD investigations. The mineral components in the XRD patterns were semi-quantitatively evaluated in terms of dominant (>40% of the mineral fraction), major (10-40%), minor (2-10%), accessory (1-2%) and rare « 1%) constituents. The mineral fraction in the coals was dominated by quartz and kaolinite, with major to minor and trace amounts of calcite, dolomite and pyrite, as well as accessory phosphates phases. XRF and XRD results for the coal-bearing units were also in good agreement. Higher K20 and Na20 concentrations were obtained in the sandstones in comparison to the siltstone and carbonaceous shale samples, and were supported by the presence of feldspars and clays such as illite in XRD interpretations. A normative program designed for Australian coals and sedimentary rocks, called Sednorm, was used to calculate normative mineralogical compositions from the geochemical results. Good \ correlations were obtained for comparisons made between the chemical composition, mineralogical interpretations and normative results for the coal and sediment samples. Acid-base accounting was used to investigate the potential of the coal and coalbearing units to produce acid mine drainage conditions. The acid and neutralising potentials are largely dependant on the abundance and availability of minerals such as pyrite and calcite respectively. According to the screening criteria proposed by Usher et al. (2001), averages for Neutralising Potential Ratio (NPR) suggest that all the coal and coal-bearing units, excluding the unit between No. 1 and No. 2 coal seams, are potentially acid generating. The latter lithological unit is considered to be inconclusive. The average Net Neutralising Potential (NNP) values suggest that the NO.5 coal seam, NO.4 Upper coal seam, and between NO.4 and NO.2 coal seams are potentially acid generating. This is a result of the weathering of carbonates in these lithological units. The other units could become either acidic or neutral. In theory it is possible to calculate the AP from the analysed S by multiplying the S value by 31.25. Assuming that all sulphide-S is available for oxidation, then the total S analysed could be used to predict the AP for samples on which no acid-base determinations has been carried out. Similarly, the excellent correlation between the NP and CaO, and between the NP and combined CaO and MgO, confirms that these chemical components are largely responsible for NP values. It is then also possible to predict the NP by using the CaO and MgO concentrations for samples for which no AP or NP data is available. The application of ABA in this study offered a major contribution to understanding the complexities governing water-rock interactions. Results provided a preview of situations that might arise regarding groundwater quality in a certain area, but also offers ample time to decide on appropriate prevention or remediation programs. The potential for these lithological units to contribute to the deterioration of groundwater is evident.Item Open Access Die geologie van die gebied Poortjie 3022B in die distrikte Britstown, Carnarvon, Prieska en Victoria-Wes, Noord-Kaapland(University of the Free State, 1977) Van der Westhuizen, Willem AndriesDie geologiese geskiedenis van die gebied was kompleks en word gekenmerk deur verskeie diskordansies en klinodiskondansies asook vulkanisme, vervorming, metamorfose en vergletsering. Die oudste gesteentetipe is die Welgevondengraniet, 'n horst, wat as vloer beskou word. In die noordoostelike hoek van die gebied dagsoom dolomiet; kalksteen en gestreepte ysterformasie van die Sisteem Transvaal. Wes van die Doornberglineament dagsoom gesteentes bestaande uit arkoose, lawa, kalksteen en gestreepte ysterformasie wat vroeër as 'n gedeelte van die Serie Marydale beskou was, maar wat nou die Soetvleiformasie genoem word, en wat 'n ouderdom vergelykbaar met die Transvaalgesteentes het. Die geochemie van die Soetvleilawas dui 'n tholeiïetiese basaltiese samestelling aan. Die lae van die Sisteem Transvaal knyp uit teen die Welgevondengraniet en gevolglik kan die Welgevondengraniet as ‘n gedeelt e van die westelike grens van die Transvaalkom beskou word, of dit kan in hoog in die. Transvaalkom wees met 'n laterale variasie in die litologie wes van die hoog af. Wes van die Welgevondengraniet is daar 'n dik opeenvolging van metapelitiese gesteentes bestaande uit kwartsiete, gneise en amfiboliete wat met die Matsap/Kheis gekorreleer word. Die graad van metamorfose is egter eerder vergelykbaar met dié van die Namakwalandse Mobiele Gordel as met die Kheis- of Matsapdomein verder noord. Die gesteentes het drie hoofperiodes van vervorming ondergaan waarvan die eerste twee isoklinaal ko-aksiaal was, met ‘n noord-noordwestelike strekking, gevolg deur 'n periode van oopplooiing loodreg op die b-plooias van die eerste twee periodes van vervorming. Hierdie laaste periode van plooiing het koepel-en-kom strukture tot gevolg gehad. Die gesteentes wes van die Doornberglineament was aan verskeie temperatuur- en druktoestande blootgestel en gevolglik kan twee isograde deur die gebied getrek word. Daar is 'n toename in graad van metamorfose van oos na wes en die metamorfe gebiede bestaan uit baie laegraadse-, laegraadse- en 'n medium- tot hoëgraadse area. Na die tydperke waartydens vervorming en metamorfose plaasgevind het, het 'n glasiale periode begin waartydens die Serie Dwyka afgeset is. Uit die voorkoms van halietkristalle in die Étage Bo-Dwykaskalies kan afgelei word dat die afsetting van dié Serie onder vlakwatertoestande plaasgevind het en nie in 'n relatief diep see soos aanvanklik vermoed is nie. Na die afsetting van die Karoosuksessie het doleriet, en nog later, kimberliet die Karoogesteentes binnegedring. Die Karoogesteentes word grootliks deur resente materiaal soos kalkreet, sand en grond bedek. Ondergrondse water is geassosieer met verskuiwings en lineêre strukture en goeie lewerings kom voor. Geormorfologies bestaan die gebied uit groot vlaktes met inselberge. Die vernaamste erosiesiklusse was die Afrika- en na—Afrikasiklusse.Item Open Access An evaluation of the coal bed methane potential of the Mid-Zambezi and North Eastern Kalahari Karoo basins(University of the Free State, 2017) Potgieter, Johannes Hermanus Jacobus; Van der Westhuizen, W. A.; Nel, L.With the growing energy demand worldwide it is very important to identify any new fossil fuel resources for future use. Coal remains the most widely used fossil fuel for electricity generation in Southern Africa but over the past two decades gas has been seen as a possible supplement and ultimate replacement for the coal. A lack of world class conventional gas accumulations in Southern Africa, unconventional gas deposits, hosted in the Karoo Supergroup, have been investigated as an alternative gas source. The primary unconventional resource focused on in north-eastern Botswana and north-western Zimbabwe to date has been coal bed methane (CBM), a natural gas generated during the coalification process and stored within internal coal structures. A major limiting factor for a regional investigation into the CBM resource potential is the lack of exploration information specifically focused on gas rather than coal. The gas saturation state of coal has a notable impact on the measureable gas content value as well as the production potential within an area. One of the assumptions of previous semi-regional assessments was that the coal is fully saturated, which has not been the case from dedicated gas exploration campaigns in the region. As part of this evaluation the coal ranks, obtained from historic borehole data over the study area, were compared to the laboratory measured maximum sorptive capacities to determine the theoretical gas content of the coal. Investigations of two regional analogous coal fields showed that the coals are unlikely to be fully saturated and for a resource evaluation based on coal rank it is imperative to use a range of saturations for the final data inputs. Schlumberger’s GeoX software was used for a probabilistic resource calculation using Monte Carlo simulations with ten thousand iterations. The resource estimation results showed a wide distribution of probable values. Even with a resource value of 22Tcf, the major basins in Canada and the US have significantly higher resource densities than that of the Study Area indicating a lower prospectivity for CBM.Item Open Access The development and application of key profit drivers in mineral resource management(University of the Free State, 2002-02) Van Niekerk, Gerhardus Johannes; Van der Westhuizen, W. A.; Boer, R. H.Every mining operation is constantly seeking for new ways to manage a broad range of business variables. Managers across the production chain find themselves torn between the initiatives to reduce costs, balancing throughput and asset utilisation improvements, maintaining product quality, and other similar performance indicators. This they do in their respective areas of responsibility, measuring against their set targets. Herein lies the dilemma: Which operational factors will maximise the profit of the organisation as a whole as opposed to the individual areas. And what is the impact of parameters outside their domains on their performance areas? Phalaborwa Mining Company has been no exception in this scenario. With time the same issues and operational challenges were presenting itself to the management team. The question had to be asked: Would a fundamentally new approach to viewing the business unearth anything new and useful to take this remarkable company to new heights? This study was launched to challenge the views of business and to offer answers to the above dilemma. The study has shown a remarkable degree of interlinkedness between production variables across the production chain. For instance, the mineralogy and petrology of the rock mined had strong effects in the milling, flotation and even smelting processes, and the status of the metal market price conditions offered exciting options to operational managers, provided the relationships are understood. Using an integrated model the magnitude and nature of interrelationships between the drivers of performance are explained. As a result it could provide the capability to "play off' costs against benefits for operating decisions. For example: How long should one keep the open pit mine operational and should it be decommissioned at the same or at a different time as the downstream units? The integrated nature of the business model clearly showed that to reach optimal performance for the whole company, decision-makers across the production chain need to plan collaboratively. It was evident that the powerful modelling approach will loose its effectiveness if the organisational thinking is not changed to a collective one. The model therefore, could only be effective if it is embedded into the planning and monitoring business cycles.Item Open Access The source material of the Big Pebble Marker and Rosedale reefs in the Welkom Goldfield(University of the Free State, 1990-06) Steenekamp, Johannes Marthinus Andries; Grobler, N. J.English: In this study the clasts of the Big Pebble Marker (BPM) in the Aandenk Formation and the basal conglomerate of the Rosedale Member (ROM) in the Eldorado Formation, in the Welkom Goldfield, were investigated. The aim of this study was to employ a different approach to acquire an insight into the nature of the provenance of the gold-bearing conglomerates in the Welkom Goldfield. To achieve this, the quantitative and qualitative compositions of two coarse and polymictic reefs were studied. Observations were made at six underground IocaIities per reef. At each locality a clean, reasonably flat surface, of three to four square metres, with sufficient conglomerate exposure, was investigated. A modal count of the different types of clasts present was done at one thousand points per exposure with the aid of two grid frames. The long axes of at least two hundred clasts, falling on preselected lines, were measured. The long axes of the ten largest clasts in the selected area were also measured. Representative samples of the various clast types present were taken for laboratory study. Every exposure studied, was photographed. All samples were cleaned meticulously to prevent any contamination with matrix material. A total of 126 samples were analyzed for gold, major and trace elements. A selection of samples were also analyzed by means of XRD and microprobe for mineral composition. Petrographic studies were carried out on thin sections of all the samples. A few samples were investigated by means of electron microscope. Fluid inclusion studies were carried out on four quartz samples. All the field data and analytical results were processed statistically plotted on concentrations on computer. Petrographic information were standard ternary diagrams. Average gold in the different clast types were compared with world wide averages for comparable rock types. Field data indicate different transport mechanisms for the BPM and RDM. Composite or multiple provenances are also indicated for both reefs. Quartz and chert dominate the clast assemblages of both reefs, but more so in the case of the BPM. Results from the clast assemblage plots on the ternary diagrams indicate thrust belt and recycled orogenic provenances for the BPM and RDM. Clasts, derived from greenstone-type source rocks, occur predominantly in both reefs. Silica dominates the chemical composition of the majority of the clasts. On average, chert clasts from the BPM contained the highest gold concentrations (143 ppb) of all the clast types. Based on modal composition, the total c last assemblage of the BPM is approximately 6X more auriferous than that of the RDM (76 ppb vs 12 ppb). Respectively, these figures are approximately 30X and 5X higher than the figure of 2,4 ppb, which is generally accepted for a Barberton-type granite-greenstone crust.Item Open Access An investigation of the trace element compositions of gold from Zimbabwe and South Africa: implications for tracing the source of archeological gold artefacts(University of the Free State, 2011-03) Netshitungulwana, Robert; Tredoux, Marian; Jacobson, LeonThe early black farmers who settled in southern Africa were involved in trading and metal technology. The history of mining for metals like iron, copper, tin and gold in southern Africa spans at least the past 2000 years. The main aim of the research was to test the viability of using gold chemistry to compare the composition of gold ores in South Africa and Zimbabwe with those of the archaeological gold artefacts from Thulamela, Mapungubwe and Great Zimbabwe. Samples from the Archaean greenstone belts in South Africa and Zimbabwe, as well as samples from ores associated with the Witwatersrand Supergroup, were used in the study. Trace element signatures were determined by laser ablation inductively coupled plasma mass speetrometry (LA-ICP-MS), a technique whereby low concentrations (down to low ppb levels) can be detected. In addition, Ag concentrations (wt %) were determined using a scanning electron microprobe, so that Ag could be used as an internal standard during the LA-ICP-MS runs to give semi-quantitative data. The most commonly occurring isotopes in gold, namely, 56Fe, 59Co, 60Ni 63CU, 66zn, 75As, 1880S, 105pd, 195pt, 202Hg, 107.109Ag, and 204, 206,207,208Pb and 209Bi, were used to construct the signatures, using their intensities in the mass spectra in counts per second (cps). Isotopic ratios were used to compare the gold ores with each other. The results show some variations in the signatures of gold from the greenstone belts and the Witwatersrand Basin. The 107Ag and 202Hg concentrations in gold from the Witwatersrand Basin are high compared to the greenstone belts. These differences have implications for the various models of gold deposition in these environments, pointing to different geochemical histories. Multivariate correspondence analysis plots for the major gold deposits show the wide group of the Barberton samples with little or no distinctive characteristics, compared to the Zimbabwean gold samples. The Witwatersrand gold plotted differently to the Barberton Greenstone Belt but closely related to the Zimbabwean greenstone belts. The ratio plot of 56Fe/107 Ag versus 202HglI07 Ag shows that archaelogical gold artefacts differ completely from the natural gold, indicating that the gold could not merely have been cold-worked, as has been suggested. This suggests that gold from anyone archaeological site could not be related to any particular or even regional source. This could be associated with the possibility of mixing of gold from multiple sources, recycling, contamination in melting and trade in items.Item Open Access Structural-rock mechanics study of failed tunnels, Harmony Gold, Masimong Mine, Welkom(University of the Free State, 2016-01) Victor, Gerhard; Colliston, W. P.
- «
- 1 (current)
- 2
- 3
- »