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Typescript (photocopy). / Digitized by Kansas Correctional Industries

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Chemical sediments in a variety of geomorphic environments (pedogenic, fluvial, palustrine, lacustrine and pan) were investigated from seven regions (SW Kalahari, Kgalagadi, Kalkweissrand, Etosha, Linyanti, Okavango and Ngami) in the Kalahari of southern Africa. These primary and multi-phase sediments were characterised by a range of pure and intergrade silcrete, calcrete and dolocrete fabrics which contained an array of structures indicative of the crystalline and biogenic processes responsible for their precipitation, epigenesis and paragenesis. Petrography, mineralogy and isotope geochemistry provided significant insight regarding the environmental and geochemical conditions at the time of precipitation. Petrography indicated that the majority of chemical sediments were undergoing epigenetic modification as a consequence of the desiccation induced transition from phreatic to vadose diagenetic and geochemical conditions. The role of rapidly infiltrating meteoric water, associated with unstable wetting fronts, is believed to be instrumental in vadose diagenesis and the precipitation of crystalline/alpha fabric carbonate. Salinisation within the capillary fringe and deeper vadose zone is believed to be responsible for the sequence dolomitisation of crystalline calcite within mature sequences. Highly saline pan conditions instigate the precipitation of authigenic dolomite, calcite and K-feldspar within the surface sediments and authigenic silica at depth. Phreatic water beneath the islands, floodplains and fluvial systems of the Okavango, which undergoes evapotranspirational and transmission salinisation and ultimately terminal desiccation, are similarly precipitating silcrete. Pedogenic processes principally associated with C₄ vegetation are responsible for the gratification of carbonate mud within desiccating lacustrine, palustrine and pan sediments. Within the thin sandy Kalahari soils, pedogenesis is limited, but biogenic/beta fabric precipitation linked to mycorrihizae and tree/shrub savanna vegetation is instrumental in the formation of hardpans and the modification of upper calcrete horizons. The dominance of a distinct assemblage (smectite/kaolinite or sepiolite/palygorskite) of authigenic clay minerals present within all the environments provides evidence of semi-arid precipitation within Mg and Ca enriched saline/rapidly evaporating water or brackish/reduced permeability environments.

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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / This thesis describes techniques proposed for analysing images of borehole cores. We address two problems: firstly, the automated stratigraphic classification of cores based on texture and secondly, the location of thin chromitite layers hidden in pyroxenite cores. Texture features of different rock types are extracted using wavelets, the theory of which provides an intuitive and powerful tool for this purpose. A Bayesian classifier is trained and used to discriminate between different samples. Thin, planar chromitite layers are located using a shortest path algorithm. In order to estimate the physical orientation of any layer found, a sinusoidal curve is fitted. The proposed algorithms were implemented and tested on samples taken from photographed cores. A high success rate was obtained in rock classification, and thin planar layers were located and characterised.

A Thesis presented to the Department of Geophysics of the University of the Witwatersrand, Johannesburg / Violent failure of the rock surrounding under ground excavations forms a major hazard and obstacle in deep-level mining. (Abbreviation abstract) / AC 2018

Foram realizadas medidas de espectroscopia gama simples, de espectroscopia gama-gama em anti-coincidência e coincidência em dezessete amostras de rochas vulcânicas irradiadas com nêutrons térmicos. Foram determinadas, utilizando cálculo covariante, 33 elementos químicos (Al, As, Ba, Ca, Ce, Cl, Co, Cr, Cs, Dy, Eu, Fe, Hf, K, La, Lu, Mg, Mn, Na, Nd, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, Ti, U, Yb, Zn e Zr), dos quais 21 elementos traço. Foi determinado o limite máximo de detecção para o irídio em 11 amostras. Foi obtido um valor máximo de 0,7 ppb. Os resultados foram comparados com o processo astrofísico de formação da Terra. A concentração de urânio e tório variou entre 3 ppm e 9 ppm, com exceção das amostras de Kilimanjaro, que variou entre 40 ppm e 45 ppm. Abaixo da concentração de 12 ppm presentes na crosta terrestre. Espera-se concentrações menores devido a estimativas de tório e urânio através do calor emitido pela Terra. Foram determinados 10/17 lantanídeos, com destaque para a abundância de Ce em Kilimanjaro, cujos valores obtidos foram de 272 (6) ppm e 319 (11) ppm. / Single gamma ray spectroscopy, gama-gama coincidence and anticoincidence spectroscopy have been performed to study 17 volcanic rocks irradiated with neutrons. We have determined, using covariant calculations, 33 chemical elements including 21 trace elements: Al, As, Ba, Ca, Ce, Cl, Co, Cr, Cs, Dy, Eu, Fe, Hf, K, La, Lu, Mg, Mn, Na, Nd, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, Ti, U, Yb, Zn e Zr. We set a maximum limit of detection for iridium in 11 samples. We have determined a maximum value of 0,7 ppb. The results were associated to the astrophysical process that led to the Earth formation. Thorium and uranium abundance ranged between 3 ppm e 9 ppm, except for the samples of Kilimanjaro, which ranged from 40 ppm to 45 ppm. Less than 12 ppm, the Earth\'s Crust abundance of thorium and uranium. Using the heat emitted by Earth to estimate the abundance of them led to significant lower values. We have also determined 10/17 lanthanides, like Ce that has an abundance of 272 (6) ppm and 319 (11) ppm, in the case of Kilimanjaro\'s samples.

Includes bibliographical references (leaves 153-157). Petrographic image analysis proved particularly useful in determining the parameters for statistical analysis for the simple mineralogies displayed in the samples from the Hutton Sandstone. Concentrates on establishing techniques for statistical study of data collected by PIA to subdivide the framework grains from the porosity or cement.