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

No description available.

This thesis explored, as its major aim, the crystallographic and compositional characteristics of a particular type of peridotitic garnet associated with kimberlite. This garnet has a highly sinusoidal rare-earth element (REE) pattern as its distinguishing feature. Before the main research question could be addressed, a technique had to be developed that enabled the rapid and straight-forward acquisition of a full profile digital X-ray diffractogram from a single sub-milligram crystal fragment. After extensive experimentation and testing, successful development and realization of a method that is capable of producing such data was achieved. The next step of this research project was to empirically investigate and assess the crystal lattice strain model (CLSM) of Blundy and Wood (1994). Careful analyses of the REE present in a suite of clinopyroxenes were compared to the crystal structure data given from the XRD technique outlined above. Clinopyroxene is particularly useful for such an assessment because the radius of the M2 site in this mineral is between the largest and smallest REE, making the distribution of REE particularly sensitive to variation of the M2 site, which in turn is a direct consequence of the overall pyroxene structure. Subsequent to illustrating that XRD data could be collected on such small material and the XRD data and structural data given from the CLSM correlate strongly, peridotitic garnets with sinusoidal REE patters were investigated. The conclusions drawn in the first two contributions – namely that it was possible to collect accurate and precise XRD data from sub-milligram specimens and that the crystal structure and REE distribution were directly related – were imperative for the deduction of conclusions in the final, major research question. The XRD analysis of many garnets with and without sinusoidal REE patterns showed the presence of a small amount of an additional phase in some of these garnets. While this phase (2 out of 3 peaks indexed as possibly orthorhombic perovskite) is not present in sufficient quantities to give rise to such a strong sinusoidal segment in the garnet REE pattern, it prompted the critical step forward in formulating a working hypothesis for the otherwise inexplicable REE patterns. Specifically, I posit that many of the sinusoidal garnets may originally have precipitated as a very high pressure phase (in the mantle transition zone or deeper) that subsequently underwent a subsolidus isochemical transformation to garnet. Possible original precursor mineralogy is a combination of two perovskites or a perovskite + iv garnet assemblage. Theoretical calculation using experimental partition coefficients demonstrated that a mixture of Ca-perovskite (CaPv) and Mg-perovskite (MgPv) REE patterns in the approximate proportions of 10% CaPv and 90% MgPv produce a REE diagram that is strikingly similar to those observed in sinusoidal single phase garnet. It has been shown experimentally that with increasing depth in the mantle, garnet plus a progressively increasing CaPv component is the stable mineral assemblage. Initial precipitation of two perovskites or CaPv + garnet as cumulates from a deep magma ocean would preserve the REE distribution of these minerals. Subsequent exhumation of such an assemblage would result in the retrogressive subsolidus phase transformation to a mineral stable at conditions of T and P of the shallow mantle environment, i.e. garnet, while retaining the REE pattern of the initial precipitate mineral assemblage. While this working hypothesis will require many more tests, its proposal may have significant implications for the mantle structure.

Vorgestellt wird ein Verfahren zum Betrieb von Hochverfügbaren Diensten. Das Verfahren basiert auf der OpenSource-Software kimberlite und wird im URZ zur Absicherung verschiedener Dienste eingesetzt.

Diamonds have been discovered in a variety of potassic ultramafic rocks including group-I and group-II kimberlites, olivine lamproites and aillikites, all of which are macroscopically similar and can be difficult to differentiate when viewed under the microscope. However, group-I kimberlites, and to a much lesser extent group-II kimberlites and olivine lamproites, are known to contain economic concentrations of diamonds. This study addresses the problem of distinguishing among different types of kimberlitic and related rocks by developing a geochemically-based method for classifying them. / Geochemical methods have been largely ignored in the classification of kimberlites and related rock types due to high concentrations of xenoliths. However, this problem can be largely overcome by only selecting matrix material for analysis. An evolving kimberlitic magma will become enriched or improvished in Si due to the fractionation of olivine and phlogopite, depending on the initial Si concentration of the magma. As they have low Si concentrations, group-I kimberlites and aillikites can be separated from group-II kimberlites and meimechites, which have higher Si concentrations for any Mg content. Furthermore, since aillikites and meimechites are relatively rich in Fe compared to group-I and group-II kimberlites, these rock types form four separate fields on a Si vs. Fe discrimination diagram. Similar rock-type separation is observed when the ratio of La to Yb is plotted against the ratio of Sm to Yb. Kimberlite and other potassic ultramafic rocks were sampled from nine areas in Quebec: the Otish Mountains, Wemindji, Torngat Mountains, Desmaraisville, Temiscamingue, Ile Bizard, Lac Leclair, Baie James and Ayer's Cliff regions. Major and selected trace element concentrations were determined by XRF analysis for all samples, while a subset of representative samples was selected for trace element analysis by ICP-MS. Electron microprobe analyses of unaltered olivine and phlogopite were also conducted. / Of the 37 samples that were classified both mineralogically and chemically, 23 or 62% were correctly classified using Fe and Si. This number increases to 84%, if the REE are used in conjunction with Si and Fe. The Si vs. Fe discrimination diagram separates group-I kimberlite from most aillikite and meimechite rocks and group-II kimberlite/olivine lamproite rocks from most aillikite and meimechite rocks. Therefore, major and trace element geochemistry offers an important tool for the classification of kimberlitic rocks. / Vasilenko et al. (2002) and Francis (2003) both suggested that diamond grades can be correlated with the major element compositions of the kimberlites. The data collected in this study confirm the inverse relationship between TiO2 concentration and diamond grade. The lowest TiO 2 values were obtained on samples from the Otish Mountains and Renard samples in particular. Other areas of Quebec are characterized by higher TiO2 contents with most samples containing greater than 2 wt% TiO 2. Therefore, the kimberlitic rocks from the Renard locality have the greatest potential for an economic diamond deposit. The origin of this correlation needs to be explored, however, because it is unclear whether this is a feature of the mantle source, or reflects the survivability of diamonds within the kimberlites.

No description available.

Thesis (Ph. D.)--University of Chicago, Dept. of the Geophysical Sciences, August 1999. / Includes bibliographical references. Also available on the Internet.

The Kalahari Group sediments cover vast portions of the Archean Kaapvaal and Congo cratons that are considered highly prospective for economic kimberlites. In southern Africa, the term Kalahari refers to a structural basin, a group of Cretaceous to recent terrestrial continental sediments and an ill-defined desert, all of which have been grouped together as the Mega Kalahari by Thomas and Shaw (1993). The Mega Kalahari grouping includes sediments stretching from South Africa in the south to the Democratic Republic of Congo in the north, and from eastern Namibia to western Zimbabwe. This sand sea, at 2.5 million km², is the largest on earth and presents significant obstacles and challenges to the kimberlite explorationist attempting to locate bedrock-hosted diamondiferous kimberlite bodies. The Mega Kalahari sediments represent an ancient depositional environment with a complex history in which the stratigraphy and age of the deposits are not particularly well constrained or understood. Low fossil content, limited exposure, poor differentiation of the dominant surficial Kalahari Sand and a limited comprehension of an extensive duricrust suite has delayed the understanding of the sedimentological and environmental history of the basin. This sequence of sediments has accumulated and evolved through fluvio-deltaic, aeolian and groundwater processes, with characteristics due to primary deposition and subsequent modification being difficult to distinguish. Deposition in the Kalahari Basin has been subject to tectonic influences, changes in drainage directions and source areas of sediments, river capture and numerous large and small climatic fluctuations both in the basin and surrounding areas. It bears the imprint of recurring cycles during which the same sediments were reworked, sometimes by different agencies, all of which exacerbate attempts to correlate sedimentary units across the sequence. The Mega Kalahari is a series of contiguous Phanerozoic sedimentary basins situated within the African Superswell. The Superswell has dominated the gross geomorphology of southern Africa and contributed significantly to the present character of the Mega Kalahari and the evolution of the drainage systems. Overall, the tectonic framework established in southern Africa by the division of Gondwanaland led to the creation of a dual drainage system, with the hingeline acting as a watershed between a coastally-orientated exoreic system and an endoreic system draining into the interior. Deposition of sediments started in the late Cretaceous. Neo-tectonic activity expressed in the rifting in central Botswana, further influenced sedimentation rates and exerted a strong control over paleo-drainage directions. This revIew presents the complexities of the Kalahari cover sequence. The most Important geomorphological and sedimentary factors to be considered when designing and implementing kimberlite exploration programs within the Mega Kalahari environment are outlined and discussed. New data from exploration drilling programs are presented on the thickness of the Kalahari within portions of northern Namibia, western Zambia and Botswana. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

The petrogenetic relationships of the different varieties of kimberlite in the De Beers Mine and Letseng-Ia-terai composite diatremes have been investigated using petrographic and chemical methods. Kimberlites in the Letseng-Ia-terai diatreme were found to be strongly contaminated by crustal material, mainly basalt. A method to correct for the effects of the contamination has been developed and applied to these kimberlites. Using the corrected data, the four kimberlite types in each group appear to be related to each other by crystal/liquid fractionation models. However the two groups cannot be related to each other. The De Beer Mine has two varieties of kimberlite, a monticellite apatite and calcite rich variety which intruded first, and a phlogopite rich type forming a discrete cylindrical body within the earlier kimberlite. These two kimberlites do not appear to be related by any of the fractionation models discussed. An examination of the data from this work and published sources, suggests that kimberlites are derived from below the low velocity zone by small degrees of partial melting involving garnet lherzolite with subordinate phlogopite and carbonate. Diamonds are probably incorporated as xenocrysts in the magma. Upward movement and emplacement of kimberlite appears to have been very rapid. The diatremes were probably eroded and shaped by gas, derived from the kimberlite magma, escaping to surface along weak zones in the earth's crust. Xenoliths of crustal material incorporated in the kimberlite on intrusion have also been studied and various features due to alteration by the magma are described, including the formation of natrolite and cebollite. The latter is a rare mineral that has not been described from kimberlite before. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

Master of Science / Department of Geology / Saugata Datta / Pamela Kempton / The Critical Zone is the realm where rocks meet life. This study examines the physicochemical interactions that occur when interbedded limestone-shale systems and kimberlitic rocks weather to form soils. Fast weathering processes with extensive soil loss have been a major environmental concern in the Flint Hills for decades. Knowledge of soil formation processes, rates of formation and subsequent loss, and understanding how these processes differ in different systems are critical for managing soil as a resource. Kimberlites are CO₂-rich igneous rocks that are high in Mg and Fe; they are compositionally distinct from the Paleozoic limestones and shales found throughout the rest of the region. This study will compare the geochemistry and mineralogy of the Stockdale Kimberlite in Riley county to that of interbedded limestone-shale system typical of the Flint Hills as sampled from Konza Prairie LTER. Bulk composition and mineralogy of the soils overlying these different bedrock types have been analyzed using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), bulk elemental extractions, and particle size analyses. Results show that the kimberlitic soils have higher concentrations of Fe, Mg, Ca, K and some trace elements in greater proportions (e.g. Ti, Ni, Cu). The weathering products differ mineralogically as well, e.g. lizardite is abundant in kimberlitic soils and absent from the limestone terranes. Kimberlite derived soils also contain minerals as well such as kleberite (an alteration product of illminite), phlogopite, and magnetite. Kimberlite-sourced soils have different physical properties than the thin limestone-sourced soils surrounding them. Particle size analysis shows that the limestone-shale soils have different proportions of the clay size fraction in different core locations (~47% in highlands, ~51% at watershed base, ~41% in lowlands) whereas kimberlitic soils have a larger sand fraction than Konza (~19% vs. 10%). Clay minerals from the limestone-shale system reveals clay micas, kaolinite, and some expandable 2:1 layer silicates. Clay minerals from kimberlite-sourced soils are identified as primarily smectites with clay micas and kaolinites. Similarities between the kimberlite and limestone-shale soils are primarily seen in the shallower portions of the soil profile, suggesting that loess/wind-blown dust make a significant contribution to the soils in both areas. It could be concluded that kimberlite-sourced and limestone-shale-sourced soils produce weathering products that differ both chemically and mineralogically and could potentially have agricultural significance in terms of water retention as well as ionic and nutrient mobilities in these soils.