Masters Degrees (Geology)
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Browsing Masters Degrees (Geology) by Advisor "Grobler, N. J."
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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 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.