Browsing by Author "Lawless, Patrick Joseph"

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    Some aspects of the geochemistry of Kimberlite xenocrysts [Microfiche]
    (1974) Lawless, Patrick Joseph; Ahrens, L H; Gurney, J J
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    Some aspects of the mineral chemistry of the peridotite xenolith suite from the Bultfontein Diamond Mine, Kimberley, South Africa
    (1978) Lawless, Patrick Joseph; Gurney, John J
    The xenolith suite from the Bultfontein Mine, Kimberley, South Africa, comprises lherzolites, harzburgites, and wehrlites with and without garnet; garnet olivine websterites and polymict peridotites. Many of the peridotites contain phlogopite and/or potassic-richterite which are interpreted as metasomatic minerals together with ilmenite, rutile, sulphides, and rare zircon. The variations in texture, mineral chemistry, equilibration conditions and bulk chemistry are described. No diamond-bearing assemblages have been found. The textures vary from coarse to porphyroclastic and to fluidal mosaic and laminated and disrupted. The deformed xenoliths have textures which may vary over distances of centimetres in individual specimens. The range of textures is greater than that reported for the xenoliths from Thaba Putsoa and Matsoku kimberlite pipes of northern Lesotho. There is no clear correlation between texture, mineral chemistry, or bulk chemistry in the Bultfontein xenoliths. Temperatures and pressures of equilibration have been calculated using three different geothermometers and three geobarometers, and the uncertainties involved in their application have been discussed. Some of the deformed xenoliths appear to have equilibrated at marginally higher temperatures and pressures than the undeformed xenoliths. The four-phase garnet lherzolites do not define a "perturbed geotherm" similar to that found in several other kimberlite localities in southern Africa and elsewhere.