Dissertations / Theses on the topic 'Kimberlite – South Africa – Kroonstad'

The Cretaceous (133Ma) Kroonstad Group II Kimberlite Cluster is located approximately 200km south west of Johannesburg on the Kaapvaal Craton. The cluster is made up of six kimberlite pipes and numerous other intrusive dike/sill bodies. Three of the pipes are analysed in this study, which includes the: Voorspoed, Lace (Crown) and Besterskraal North pipes. These pipes were emplaced at surface into the Karoo Supergroup, which is comprised of older sedimentary rocks (300-185Ma) overlain by flood basalts (185Ma). At depth the pipes have intruded the Transvaal (2100-2600Ma) and Ventersdorp (2700Ma) Supergroups, which are comprised dominantly of carbonates and various volcanic units respectively. The pipes have typical morphology of South African pipes with circular to sub-circular plan views and steep 82o pipe margins. The Voorspoed pipe is 12ha in size and is characterised by the presence of a large block of Karoo basalt approximately 6ha in size at the current land surface. This large basalt block extends to a maximum of 300m below the current land surface. The main Lace pipe is 2ha is size with a smaller (<0.5ha) satellite pipe approximately 50m to the west. No information is available on the morphology of the Besterskraal North pipe as it is sub-economic and no mining has occurred. Samples from the Besterskraal North pipe were collected from the De Beers archives. The Kroonstad Cluster has been subjected to approximately 1750m of erosion post-emplacement, which has been calculated by the analysis of the crustal xenoliths with the pipe infill. The hypabyssal kimberlite from the three pipes shows a gradational evolution in magma compositions, indicated by the mineralogy and geochemistry. The Lace pipe is the least evolved and has characteristics more similar to Group I kimberlites. The Voorspoed and Besterskraal North kimberlite are intermediately and highly evolved respectively. The gradational evolution is marked by an increase in SiO2 and Na2O contents. Furthermore the occurrence of abundant primary diopside, aegirine, sanidine, K-richterite and leucite indicates evolution of the magma. The root zones of the pipes are characterised by globular segregationary transitional kimberlite, which is interpreted to be hypabyssal and not the result of pyroclastic welding/agglutination. The hypabyssal transitional kimberlite (HKt) is characterised by incipient globular segregationary textures only and the typical tuffisitic transitional kimberlite (TKt) end member (Hetman et al. 2004) is not observed. The HKt contact with the overlying volcaniclastic kimberlite (VK) infill is sharp and not gradational. The presence of HKt in the satellite blind pipe at Lace further indicates that the distinct kimberlite rock type must be forming sub-volcanically. The HKt is distinctly different at the Voorspoed and Lace pipes, which is likely a result of differing compositions of the late stage magmatic liquid. Microlitic clinopyroxene is only observed at the Lace HKt and is interpreted to form as a result of both crustal xenolith contamination and CO2 degassing. Furthermore the HKt is intimately associated with contact breccias in the sidewall. The root zones of the Kroonstad pipes are interpreted to form through the development of a sub-volcanic embryonic pipe. The volcaniclastic kimberlite (VK) infill of the Kroonstad pipes is not typical of South African tuffisitic Class 1 kimberlite pipes. The VK at Voorspoed is characterised by numerous horizontally layered massive volcaniclastic kimberlite (MVK) units, which are interpreted to have formed in a deep open vent through primary pyroclastic deposition. MVK is the dominant rock type infilling the Voorspoed pipe, however numerous other minor units occur. Normally graded units are interpreted to form through gravitational collapse of the tuff ring. MVK units rich in Karoo basalt and/or Karoo sandstone are interpreted to form through gravitational sidewall failure deep within an open vent. Magmaclasts are interpreted to form in the HKt during the development of an embryonic pipe and therefore the term autolith or nucleated autolith may be applied. Debate on the validity of the term nucleated autolith is beyond this study and therefore the term nucleated magmaclast is used to refer to spherical magmaclasts in the VK. The emplacement of the Kroonstad pipes is particularly complex and is not similar to typical Class 1 tuffisitic kimberlites. However the initial stage of pipe emplacement is similar to typical South African kimberlites and is interpreted to be through the development of an embryonic pipe as described by Clement (1982). The vent clearing eruption is interpreted to be from the bottom up through the exsolution of juvenile volatiles and the pipe shape is controlled by the depth of the eruption (+/-2km) (Skinner, 2008). The initial embryonic pipe development and explosive eruption is similar to other South African kimberlites, however the vent is cleared and left open, which is typical of Class 2 Prairies type and Class 3 Lac de Gras type pipes. The latter vent infilling processes are similar to Class 3 kimberlites from Lac de Gras and are dominated at the current level by primary pyroclastic deposition.

The Du Toitspan kimberlite pipe located on the outskirts of Kimberley South Africa, is one four Cretaceous aged major kimberlite pipes from the well-known Kimberley cluster, the type locality for archetypal group I kimberlites. Twenty-seven samples representative of various kimberlite intrusions from the eastern lobe of the Du Toitspan kimberlite pipe have been analysed for their whole-rock geochemistry and mineral chemistry (olivine and phlogopite) with the aim of developing semi-quantitative models that constrain their petrogenesis and characterise their respective source region(s). Investigated intrusions include; D13-phlogopite kimberlite, D14-monticellite kimberlite, D17-serpentinized phlogopite kimberlite, and several narrow (<1m) calcite kimberlite dykes ranging in texture from aphanitic to macrocrystic. The aphanitic calcite dykes were further sub-divided into; a phlogopite-rich calcite kimberlite, a perovskite-rich calcite kimberlite, opaque-rich calcite kimberlites and serpentine calcit e kimberlites.

Includes bibliographical references.
The Outoitspan Group 1 kimberlite pipe forms part of the well-known cluster of pipes located in and around the city of Kimberley, South Africa. Eight macroscopically distinct intrusive phases, i.e. D2 Type 2, D2 Type 3, D2/D5, D5, D18, Type 5, D16 and the D16 dyke are present in the Northwest Corner area of the mine. Microscopically they range from macrocrystic to aphanitic hypabyssal (magmatic) kimberlites with varying amounts of opaque minerals, monticellite and phlogopite. Olivine is the dominant macrocryst phase and alteration varies from unaltered to highly serpentinised. These intrusive phases also contain variable amounts of crustal xenoliths.

Bibliography: leaves 139-146.
The Swartruggens (156 Ma) and Star (128 Ma) kimberlites are two Group II, diamondiferous, hypabyssal kimerlite dyke swarms, situated in the Northern Province and the Free State respectively, South Africa. Representative samples from all dykes exposed in the mining operations, the Main and Changhouse Dykes, South Fissure and the barren Muil Dyke at Swartruggens, and the Wynandsfontein, East Star, Clewer, Byrnes and Barren dykes at Star, have been analysed for their major and trace element contents and Sr, Nd and Hf isotope compositions. Primary kimberlite magma chemistry is subjected to considerable modification due to the incorporation of both mantle and crustal material during ascent to the surface, crystal fractionation, and post-emplacement alteration by deuteric fluids. This study aims to constrain the effects of these processes, and thus to identify least-modified, close-to-primary, parental magma compositions, with the view to understanding the source region characteristics of, and the petrogenetic processes giving rise to, these kimberlites.

Includes bibliography.
The Rietfontein kimberlite is an off-craton kimberlite pipe, located west of the Kaapvaal Craton at 26.75°, 20.04°E and hosts a range of xenocryst lithologies, including peridotite, eclogite and a suite of megacryst minerals. This study focuses on a suite of eclogite xenoliths, which were subject to a detailed petrographical and geochemical study, aimed at their characterisation and comparison to eclogites from on-craton and other off-craton localities. Garnet, clinopyroxene, accessory and secondary minerals were analysed for major element compositions using electron microprobe techniques and garnet and clinopyroxene trace element compositions were determined by Laser Ablation Inductively-Coupled-Plasma Mass Spectrometry (LA-ICP-MS) techniques. Oxygen isotopic compositions of five garnet samples were obtained using laser flourination techniques, followed by analysis by gas source mass spectrometry.

Bibliography: leaves 122-138.
The eclogites are essentially bimeneralic assemblages of garnet and clinopyroxene. Thirteen xenoliths contain accessory diamond with graphite on diamond surfaces. One has accessory ilmenite. The rocks are well equilibrated and are classified as Group 1 eclogites, based on their mineral textures and compositions. The calculated equilibrium temperatures for the eclogites range from 1157 °C to 1245 °C, assuming a pressure of 50 kbar. Two populations of eclogites are defined in terms of the calcium content of the garnet, equilibration temperatures and trace element abundances.

Thesis (MSc)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: The common presence of large volumes of coarse-grained olivine in kimberlite magmas has been proposed to attest to the volume of mantle xenolith material that has been disaggregated during the ascent of the magma. Orthopyroxene should constitute 10-50 vol% of mantle xenoliths in kimberlites, some of which must be disaggregated into the kimberlite, yet it is typically absent. This work tests the stability of orthopyroxene in ascending kimberlite magma by conducting experiments at pressures between 2.0 and 3.5 GPa and temperatures between 1100 and 1300°C. The starting material consisted of natural hypabyssal kimberlite that is close in composition to primary group I kimberlite magma with 5wt% orthopyroxene sourced from a natural peridotite added. At higher temperatures and pressures it is seen that orthopyroxene quantities exceed that of the starting material, but at lower temperatures and pressures it is absent. These results indicate that orthopyroxene is not stable in the magma composition investigated within the shallower part of the sub-continental lithospheric mantle. Based on increased olivine volumes in the experiments where orthopyroxene disappeared, as well as textural relationships between olivine and orthopyroxene, it is found that orthopyroxene dissolution is incongruent along the reaction Mg2Si2O6 (opx) = Mg2SiO4 (ol) + SiO2 (in the liquid). It is concluded that this reaction leads to a maximum addition of 5.5 vol% peritectic olivine to the kimberlite as it ascends through the depths equivalent to a pressure window of 2.0 to 3.5 GPa.
AFRIKAANSE OPSOMMING: The common presence of large volumes of coarse-grained olivine in kimberlite magmas has been proposed to attest to the volume of mantle xenolith material that has been disaggregated during the ascent of the magma. Orthopyroxene should constitute 10-50 vol% of mantle xenoliths in kimberlites, some of which must be disaggregated into the kimberlite, yet it is typically absent. This work tests the stability of orthopyroxene in ascending kimberlite magma by conducting experiments at pressures between 2.0 and 3.5 GPa and temperatures between 1100 and 1300°C. The starting material consisted of natural hypabyssal kimberlite that is close in composition to primary group I kimberlite magma with 5wt% orthopyroxene sourced from a natural peridotite added. At higher temperatures and pressures it is seen that orthopyroxene quantities exceed that of the starting material, but at lower temperatures and pressures it is absent. These results indicate that orthopyroxene is not stable in the magma composition investigated within the shallower part of the sub-continental lithospheric mantle. Based on increased olivine volumes in the experiments where orthopyroxene disappeared, as well as textural relationships between olivine and orthopyroxene, it is found that orthopyroxene dissolution is incongruent along the reaction Mg2Si2O6 (opx) = Mg2SiO4 (ol) + SiO2 (in the liquid). It is concluded that this reaction leads to a maximum addition of 5.5 vol% peritectic olivine to the kimberlite as it ascends through the depths equivalent to a pressure window of 2.0 to 3.5 GPa.

The dissertation reviews the present knowledge regarding diamonds, from its formation in the lithospheric upper mantle at depths between 150 and 300 km, to its final valuation in terms of US$/carat by diamantaires in London, Antwerp, Tel Aviv and New York. The dissertation is divided into two complimentary sections. Section one focuses on the formation, emplacement, occurrence and characteristics of kimberlites and, when present, their associated trace amounts of diamonds. The section follows a logical sequence from the regional tectonic-, local structrual- and geodynamic controls on kimberlite formation and emplacement to the characteristics of individual kimberlite morphology, mineralogy, petrography and geochemistry. Finally, the environment or diamond formation, resorption and the characteristics that have led to the marketability of diamonds are discussed. Section two reviews the current exploration techniques used in locating diamondiferous kimberliies and the subsequent economic evaluation of these kimberlites. A brief history of known Southern African kimberlite occurrences, grades, tonnages, tectonic settings, ages and regional structural controls is given. The prospective countries mentioned are Angola, Botswana, Lesotho, South Africa, Swaziland, Tanzania and Zimbabwe. Exploration techniques considered are ; the application of a landscape analysis and investigation of the surface processes active in a given area, indicator mineral sampling (with reference to their mineralogy and exploration significance), remote sensing techniques (subdivided into satellite imagery and aerial photography), geophysical techniques (including the magnetic-, gravity-, electrical-, radiometric- and seismic methods as well as heat flow models), geochemical techniques, petrographic- and electron beam techniques as well as geobotanical- and geobiological techniques. Finally, a brief summary of current evaluation techniques employed on diamondiferous kimberlite deposits is presented. The review covers kimberlite sampling methods, sample processing, diamond grade distributions (with reference to the experimental variogram model, statistical methods used in grade distribution calculations as well as block definition and local grade estimation). Stone size distributions, including microdiamond counts and value estimation, are also discussed.
KMBT_363
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Bibliography: pages 188-203.
The Jagersfontein kimberlite contains an abundance of both deformed high-temperature peridotites and Cr-poor megacrysts. The Cr-poor megacryst suite is represented by olivine, orthopyroxene, clinopyroxene and garnet. The megacrysts show features which are unique to Jagersfontein, a particularly notable feature being the absence of ilmenite and ilmenite-silicate intergrowths. Major element and REE compositions of the Cr-poor megacryst suite are consistent with a magmatic fractionation sequence. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of the Cr-poor clinopyroxene megacrysts indicate a source similar to that of non-DUPAL ocean island basalts. Deformed peridotites at Jagersfontein have high calculated temperatures of equilibration (1132-1361°C), which are slightly lower but which overlap with those of the Cr-poor megacryst suite. Both the high-temperature peridotites and the Cr-poor megacrysts yield similar pressures of equilibration (51±2 kbar), indicating their association with a thermal perturbation and supporting a close spatial association between them. Olivine and pyroxenes in the high-temperature peridotites appear homogeneous, but compositional gradients were observed in several garnet porphyroclasts. These garnets show rim enrichments in TiO₂ and Na₂O. This zonation in the garnets is evidence for enrichment of the deformed peridotites shortly before kimberlite eruption. This enrichment is likely to be due to interaction with the megacryst magma. In addition, the high-temperature peridotites show a general enrichment in Fe, Ti, Na and Al with decreasing Ca/(Ca+Mg). Such features support a magmatic aureole model, in that temperature and degree of enrichment might be expected to increase with proximity to the megacryst magma body. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of clinopyroxene separates from the high-temperature peridotites are similar to those from oceanic peridotites. Modal abundances and olivine forsterite contents of the high-temperature peridotites are consistent with an origin as residues of partial melting events involving basalt formation. It is suggested that partial melting events, in the upper mantle beneath Jagersfontein, resulted in the formation of a depleted protolith which underplated the base of the Archaean lithosphere. This depleted protolith was subsequently enriched by interaction with the Cr-poor megacryst magma just prior to kimberlite eruption. The high-temperature peridotites therefore represent samples from the base of the lithosphere rather than from the convecting asthenosphere.

Includes bibliographical references.
While a clear and unequivocal model for the formation of diamonds is still lacking, the past few decades have seen a 'revolution' in the scientist's perception of mantle processes, particularly that regarding diamond formation. Kramers (1977) fIrst clearly recognised the ancient origin of diamonds from his studies of composited sulphide inclusions. However, it was not until mid-Archean ages were obtained from syngenetic garnet inclusions in diamond by Richardson et al. (1984), that it became generally accepted that most diamonds were in fact very much older than their kimberlitic hosts, and could therefore not have been precipitated from the kimberlite magma.

Thesis (M. Ed.) - Central University of Technology, Free State, 2008
The purpose of this study is to investigate the perceptions of secondary school educators towards inclusive education in Maokeng.”Inclusive education defined as schools, centres of learning and educational systems that ensure that all children learn and participate” (Van Rooyen & De Beer, 2006). Two secondary schools were chosen for this study, with eight respondents who are mainstream educators. There were four male educators and four female educators in the sample. The qualitative methodology, in particular Textual Orientation Discourse Analysis (TODA), was used as the tool to obtain information from the respondents. The respondents, as educators at secondary schools, were selected according to their level of education, experience at work, their age and the way that they perceive inclusive education in secondary schools. The main finding shows that there are educators who favour inclusive education and there are those who are not in favour of inclusive education. Some contributing factors for not being in favour were reported as, lack of information regarding inclusive education, the time factor, lack of resources, inadequate knowledge and skills of educators, need for training, lack of teacher support, efficiency of the support teacher, disruptive and unchallenged learners and their impact on schools. Given the above findings and conclusion, the study recommends that educators should be sufficiently supported by well informed para-professionals, in order to make inclusive education a success. Resources should be well distributed to various institutions where inclusive education is going to be instituted. Government experts should work in collaboration with experts from the university with regard to the attainment of skills, in order to improve the work of educators at schools, particularly those who work with disabled learners. At school level, specialized educators and those who are able to identify learners with problems should be hired. The number of educators needs to increase, in order to reduce large numbers of learners in each class, which will enable educators to reach each learner.

A research project submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science.
Rb-Sr emplacement ages of nineteen kimberlites from the Prieska Province vary from 74 to 174 Ma, Their isotopic, whole-rock geochemical signatures and perovskite REE distributions were also determined. Non-micaceous and micaceous kimberlites from the area show similar petrographic, geochemical and isotopic compositions relative to cratonic kimberlites, indicating similar sub-continental mantle source compositions in the two tectonic environments. Transitional varieties of kimberlite, which can be defined petrographically, geochemically and isotopically are also recognised from the area, but are not prevalent in the cratonic environment. The Prieska Province kimberlites are possibly derived by partial melting processes within a subcontinental reservoir characterised by a spectrum of compositions from time-averaged depleted (HllMU) to enriched (Group II). The occurrence of these components in both on- and off-craton settings indicates that the kimberlite source area is not strictly linked to the suberatonic lithosphere. Mantle' plume sources are not favoured because of the variable source compositions and distribution of emplacement ages within the Province. Transitional kimberlites were derived from a source component with mixed character, not yet noted from within the Kaapvaal Craton. This is the first documented example of isotopically transitional kimberlites from southern Africa.
AC2017

M.Sc. (Geology)
This treatise presents the first comprehensive investigation in petrography and geochemistry of a mantle-derived eclogite xenolith suite from the Balmoral kimberlite. Eclogites form a minor component of the Earth’s mantle however they play a vital role in our understanding of geodynamic processes, i.e. the subduction of oceanic crust (Jacob, 2004) and the crystallization of diamond within the sub-cratonic lithosphere. A large portion of eclogites from the Balmoral kimberlite pipe is comprised of bimineralic (garnet and clinopyroxene) rocks with the rest being corundum-bearing. Mica with average modal abundances ≤10 vol% is observed as an accessory phase in bimineralic xenoliths. Modal abundances of corundum in corundum-bearing samples range between 1 and 6 vol%. Textures are ambiguous in Balmoral eclogites and thus chemical criteria of McCandless and Gurney (1989) places all Balmoral eclogites into Group II. As typically observed in garnets from eclogites (Hills and Haggerty, 1989; Jacob, 2004), garnets from Balmoral eclogites are chromium- and manganese-poor. They have a general trend from pyrope-rich towards grossular-rich compositions, with some almandine. Garnets from the bimineralic eclogites have disparate suites of low- and high-MgO samples. High-MgO bimineralic garnets are pyropic in composition with averages at Pyr63Gros22Alm15, whereas garnets from the low-MgO suite are widespread from relatively less pyropic towards grossular-rich compositions with average compositions of Pyr49Gros40Alm11. Garnets from the corundum-bearing eclogites are homogeneous and characterised by the highest grossular component (averaging at Gros47Pyr28Alm25). The clinopyroxenes for Balmoral eclogites are omphacitic in composition. Jadeite content is highly variable (ranging between 8 and 58 wt%) in these clinopyroxenes. The clinopyroxenes in bimineralic eclogites are characterised by a wide variation from diopside-rich towards jadeite-rich compositions. Clinopyroxenes in corundum-bearing eclogites have the highest jadeite levels.

Water quality and space constraints have become major concerns regarding the No. 7 waste water dam at Petra Diamonds’ Cullinan mine. The unique location of the dam constrains further development, while unsustainable accumulation of waste water inside the dam increases the risk of potential environmental contamination from seepages and spillages. The dam retains a significant amount of very poor quality water. Its excessively high pH, dissolved salt content, density and extreme turbidity result from the concentration of natural weathering products of the diamond bearing kimberlite ore. The turbidity results from the dispersion of colloidal chlorite, saponite and nontronite clay. Along with the chemistry of the solution, their colloidal shape contributes equally significantly to the non-settlement of these suspended clays. Flocculation of the dispersed clay particles will provide (a) for easy and effective separation of the clay material from the waste water and (b) more convenient options for water treatment (and subsequent redistribution) This study was aimed at contributing to a better understanding of the dynamic interactions in the No 7 Dam system to contribute towards identifying a suitable means/method for chemical flocculation of the clay particles. The individual components of the system (clays, water quality) and influx contributors (kimberlite and its leachate) were systematically characterized by means of X-Ray Diffraction, X-Ray Fluorescence, petrographic microscopy, electron microscopy, electrophoretic mobility and standard water- and soil quality analyses. The baseline quality of the Cullinan kimberlite leachate was obtained based on ASTM D5744 principles. It was found that adjusting the pH-level and ionic strength of the waste water to the critical coagulation point (cK) (as determined by electrophoretic mobility and batch jar experiments) automatically induced coagulation. Higher valence cations were displaced from pH dependent surface charge sites by proton adsorption. The resultant increased ionic strength, in combination with decreased thickness of the ionic double layer, was sufficient for the automatic initiation of high strength disordered face-face and edge-face bonds. During batch Jar tests, flocculation initiated within 4 minutes after the addition of HCl (0.5 M) and total sedimentation completed within 3 hours. The use of commercial flocculants might decrease the sedimentation time. As expected a significant increase in dissolved salt content of the clear supernatant was observed. No re-dispersion of the dried clay occurred. Throughout the study geochemical modeling was performed with PHREEQC software to identify/determine possible effective experimental conditions, minimizing experimental time and expenses. The program was also used to model outcomes of the possible water treatment options, indicated in literature as viable options for similar situations. These options can be tested to extend upon the current research.
MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015