Browsing by Author "Hartnady, Chris"

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    A study of epigenetic mineralisation in the Central Zone of the Damara Orogen, Namibia with special reference to gold, tungsten, tin and rare earth elements
    (1992) Steven, Nicholas Macrae; Moore, John M; Hartnady, Chris
    Epigenetic, rare earth element, gold, tin and tungsten, mineralisation in the NE-trending, intracratonic branch of the deeply eroded, Late Proterozoic/Early Palaeozoic, Pan-African Damara Orogen is hosted by meta-arkoses, marbles and metaturbidites in the magmatic arc (Central Zone; CZ) of the orogen, a tectonostratigraphic entity that is characterised by multiple deformation, greenschist/amphibolite-facies, low-pressure/high-temperature metamorphism and numerous granitic and pegmatitic intrusions. This thesis integrates regional and detailed geological mapping with petrographic studies, whole rock geochemistry (obtained by X-ray fluorescence spectrometry, atomic absorption spectrometry, fire assay and infra-red spectroscopy), mineral chemistry studies (electron microprobe and X-ray diffraction) and geochronological work (Rb-Sr whole-rock and mineral age determinations and Pb-Pb model ages) to examine epigenetic mineralisation in the Usakos-Karibib-Omaruru district, central Namibia. The investigated area straddles the magnetically defined Omaruru Lineament, which divides the CZ into southern (SCZ) and northern (NCZ) portions. Mapping and lithostratigraphic work support the geophysical evidence for this subdivision: in the SCZ, predominantly continental and shallow marine Damaran metasediments are floored by a 1.7-2.0 Ga granite gneiss basement inlier, that is transected by numerous ENE-trending aurif erous megashears. These structures controlled late Proterozoic mafic dyke emplacement, Damaran rifting and sedimentation, alkaline volcanism and the localisation of hydrothermal fluids in the overlying cover rocks. In the NCZ, where basement inliers are not exposed, the metamorphosed equivalents of Damaran shallow marine carbonates are overlain by deeper water sediments and turbidites. Sedimentation was controlled by rifting, facies belts being oriented parallel to the axis of the orogen. Felsic and mafic volcanic rocks comprise only a fraction (< 5 % ) of the Damara Sequence.
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    The structural and engineering geology of the Country Rock at Finsch Mine
    (1998) Barnett, Wayne Peter; Barnett, Wayne Peter; Stowe, C; Preece, C; Hartnady, C; Stowe, Clive W; Preece, C; Hartnady, Chris
    This project was undertaken at Finsch Mine, De Beers Consolidated Mines Ltd., in order to collect the relevant information to build a database for the country rock. The country rock is comprised of the ~2.5 Ga sediments of the Griqualand West Basin: the banded ironstones and carbonates of the Ghaap Group. A stratigraphic column has been produced that correlates the country rock at Finsch Mine with the corresponding strata in the accepted stratigraphy of the Griqualand West Sequence. Periods of regression and transgression in the Early Proterozoic basin may have controlled the Ca/Mg ratio and the percentage of limestone deposition. Later hydrothermal dolomitization had a significant affect on the amount of secondary dolomite present in the country rock. The rock structures (faults, dykes ad fractures) in the country rock were mapped in detail. The data was placed into MicroStation (a CAD package), which now acts as a limited three dimensional GIS database for the mapped structures. The structural data was analyzed and a complete three dimensional structural model was produced. The faulting belongs to a strike-slip system formed by crustal shear late during the Namaqua-Natal orogeny (ca. l.l Ga). A complex structural/tectonic history is suggested whereby transtension is followed by a rotation of the tectonic stress vectors with resultant transpression. During transpression the fault-parallel jointing/cleavage is fanned by fault-parallel folds and a conjugate set of joints form as a result of WSW directed crustal shortening. Extensive line sampling of the rock discontinuities (joints) was undertaken. The characteristics of the joints were qualitatively described/mapped across the mine. The data from the line sampling was analyzed and used to quantify the qualitative descriptions. The mapped joint's characteristics are graphically presented on plans, described by the author as 'joint-nets'. Up to six joint sets have been observed and genetically linked to the structural history. Distinct homogeneous structural domains do not exist at Finsch mine, but the joints were used to crudely define some domains. The rock types in the carbonate succession were studied in detail and distinct different types were sampled and tested to obtain UCS, point-load strengths and Young's moduli. This project describes the process of Rock Mass Classification so that the reasons for the data collection and analyses are apparent to the reader. The data collected during this project suggests that the kimberlite pipe had a significant affect on the smrnunding country rock, maybe as far 20 to 30 metres from the pipe contact. It is suggested that the intrusion of the precursor kimberlite bodies and the main pipe caused some deformation of the country rock mass. Such a suggestion is contrary to the classical understanding of kirnberlite emplacement.
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    Three applications of satellite borne repeat pass SAR interferometry in Southern Africa
    (2000) Doyle, Gavin S; Wilkinson, Andrew John; Hartnady, Chris; Inggs, Michael
    Synthetic Aperture Rada Interferometry (InSAR) is a relatively new remote sensing technique, which can be used to derive precise topographic height change information over large areas. It is a technique which has been used in a great variety of situations, from the topographic mapping of Venus to the detection of subtle ground deformations due to earthquakes and mining subsidence. The InSAR technique involves using the phase information inherent in radar images to extract elevation and elevation change information. The process requires very careful co-registration of a pair of complex images of the same scene, followed by the multiplication of the one image by the complex conjugate of the other. In this manner, a phase difference image, or interferogram is generated, in which subtle differences in the distances from the two imaging sensors to the ground are mapped, thereby making it possible to generate a height model of the ground surface. An extension to the InSAR technique, is that of difference image, or interferogram is generated, in which subtle differences in the distances from the two imaging sensors to the ground are mapped, thereby making it possible to generate a height model of the ground surface.