Thesis (Ph.D.)--McGill University, 1962. / Written for the Dept. of Geological Sciences. Includes bibliographical references.

Thesis (Ph.D.)--University of Alberta, 2009. / Title from PDF file main screen (viewed on July 21, 2009). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Dept. of Earth and Atmospheric Sciences, University of Alberta. Includes bibliographical references.

The Abrahamskraal kimberlite pipe (group I) occurs approximately 5 km to the south-west of the geophysically defined margin of the Kaapvaal craton in the central Cape Province, and contains a variety of crustal and mantle xenoliths. This study focusses on xenoliths of deep-seated origin (mantle and lower-crustal), and in particular on garnet-orthopyroxene bearing assemblages which are amenable to thermobarometric techniques. Four major types of deep-seated xenolith have been identified, i.e. peridotites, dunites , eclogites, and garnet pyroxenites. The petrographic features and mineral compositions of these xenoliths are described . Pressures and temperatures of equilibration have been calculated primarily using the garnet-orthopyroxene thermometer of Harley (1984), and the Al-in-enstatite barometer of Nickel and Green (1985). The peridotites are coarse-textured (Harte, 1977), magnesium -rich rocks, and are typical examples of the common type I peridotites which generally dominate mantle xenolith suites in kimberlites. Garnet peridotite xenoliths define a geotherm which lies along a typical theoretical conductive geothermal gradient for shield areas (Pollack and Chapman, 1977), and which extends to a maximum pressure of 41 kb (~130 km). Comparison of the Abrahamskraal geotherm with that constructed for the northern Lesotho xenolith suite (calculated using the same thermobarometer couple), suggests that the lithosphere at the Namaqua /Kaapvaal boundary is not significantly thinner or hotter than that underlying the craton. Modelling of the craton boundary under the constraints provided by the Abrahamskraal geotherm, and by the distribution of diamond-bearing kimberlites in southern Africa, indicates that the Abrahamskraal kimberlite has sampled relatively thick, cool , Namaqua lithosphere. It is suggested that, in terms of diamond distribution, the age and magmatic history of the Namaqua lithosphere is of greater significance than its thickness. Two varieties of dunite occur at Abrahamskraal. Coarse-textured dunites with Mg-rich olivine compositions similar to those of the peridotitic olivines, probably originated by similar (but perhaps more extreme) processes to those which formed the peridotites. A finer-grained and relatively Fe-rich variety of dunite may represent ultramafic cumulates formed by fractionation of basic or ultrabasic magmas within the mantle. Two varieties of eclogite have been distinguished. Coarse-grained eclogites which yield relatively high temperature estimates, are believed to have originated from depths similar to those determined for the garnet peridotites, i.e. from the lower lithosphere. A distinctly finer grained variety of eclogite, yields significantly lower temperatures which may be based on frozen-in equilibria. A maximum depth of approximately 87 km (~ 27 kb) has been estimated for these xenoliths, but they may have originated from significantly shallower (possibly lower-crustal) levels. The garnet pyroxenite xenoliths are generally orthopyroxene-rich rocks which contain varying amounts of garnet (8 to 33 %) and clinopyroxene (0 to 64 %). Textural features indicate that the garnet and possibly some of the clinopyroxene has exsolved from an originally A l -rich orthopyroxene. The rocks are significantly more Fe-rich than the peridotite xenoliths, and their constituent minerals show a wide range of Mg/Mg+Fe ratios. The pressure-temperature array defined by the garnet pyroxenites is approximately isothermal, and spans a depth range from approximately 30 to 95 km. It deviates strongly (to higher temperatures) from the ambient geothermal gradient at the time of kimberlite emplacement, as inferred from the garnet peridotite xenoliths. The pressures and temperatures calculated for the garnet pyroxenites are based on mineral equilibria which are believed to have been frozen-in during cooling from an intial high­temperature (probably molten) state. Qualitative modelling of possible cooling paths in pressure-temperature-composition space, indicates that the apparent depth range displayed by the garnet pyroxenites, approximates the true depth range over which these rocks were emplaced. However, the apparent pressures calculated from core compositions are significantly lower than the true pressures at which the original rocks formed . The garnet pyroxenite xenoliths appear to represent a major, possibly Namaqua ­ age (~1000-1400 Ma), magmatic event involving the emplacement of large amounts of mafic magma over a significant depth range in the shallow upper mantle

Includes bibliography. / Several physical characteristics, the carbon isotopic compositions, inclusion mineralogy, and distribution of the Dokolwayo diamonds were investigated. A representative suite of concentrate garnet megacrysts and macrocrysts were analyzed for their compositions. Concentrate macrocryst spinels and silicate inclusions recovered from these spinels were analyzed. The physical characteristics of the diamonds investigated were mass, size, morphology and colour. The relationship between mass and size in a population of diamonds recovered from a single hypabyssal intrusion and the general production as a whole, was found to be statistically the same. The most recognizable morphology is the dodecahedron. Octahedra decrease in significance with a decrease in size. Colourless stones predominate. Brown stones are more common than yellow stones, which is uncommon in primary southern Africa diamond populations. Diamonds characterized by "Tanganyika naats" have hitherto not been described from southern Africa. The relationship between the various physical characteristics investigated indicate that the general Dokolwayo diamond population consists of at least four sub-populations.

No description available.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / The northern sector of the Archaean Superior Craton has been a significant region for diamond exploration, hosting numerous alkaline intrusions of Proterozoic age. The focus of this study is on two kimberlite fields that are situated in eastern Canada, 400 km apart. These are the diamond-rich Renard pipes and dykes, and the Wemindji field, consisting of barren sheeted dykes. The nine diamondiferous Renard igneous bodies were emplaced between 655-630 Ma in the eastern sector of Laurentia into Archaean metamorphic rocks. Thin, subhorizontal Wemindji kimberlite sills were emplaced into granitic gneiss terrane of the Superior Province near Wemindji, Quebec, at 629 ± 29 Ma, along the inferred extension of the Kapuskasing Structural Zone. These kimberlite fields are grouped with the extensive Late Neoproterozoic magmatism of ultramafic and volatile-rich character, which is said to be associated with the breakup of Rodinia. Despite overall compositional similarity of the studied magmatic kimberlites, the material from Renard has higher concentrations of SiO2, Al2O3, MgO, and K2O, which reflects higher phlogopite abundances. The Wemindji sills show higher CaO concentrations due to high primary carbonate contents. Renard and Wemindji kimberlite incompatible trace element distributions are similar, with differences in Cs, Rb, and Sr corresponding to variable modal mineralogy. The initial 87Sr/86Sr ratios for the Renard kimberlites range between 0.70241 and 0.70765, while the Wemindji kimberlites have values between 0.70361 and 0.70442. Initial εNd values for the Renard kimberlites lie between +1.2 and +4.6, whereas the Wemindji kimberlite sills range between +0.2 and +4.8. Initial εHf values for the Renard kimberlites lie between +1.7 and +6.3, whereas the Wemindji kimberlite sills yielded values between +1.1 and +6.5. The overlapping Sr-Nd-Hf isotope compositions of these kimberlite suites indicate melt derivation from moderately depleted mantle sources. Osmium isotope compositions fall at the unradiogenic end for global kimberlites, with initial 187Os/188Os ratios ranging between 0.11539 and 0.12620 for Renard kimberlites, and between 0.11078 and 0.11729 for Wemindji kimberlites, with Os concentrations all below 1.3 ppb. These Os values suggest that an additional input from the CLM (i.e., ancient refractory cratonic peridotite), which is not reflected in the Hf and Nd radiogenic isotopes, is ii required. Both kimberlite suites depict mantle δ13C values (ca. -6 to –4 ‰), with evidence of hydrothermal alteration in the δ18O values (between 10 and 20 ‰ relative to SMOW). Production of an isotopically depleted melt occurred during the breakaway of Laurentia from Rodinia. Wemindji sits on the inferred extension of the Kapuskasing Structural Zone, which is suggested to have been a short-lived reactivated translithospheric rift-like feature, promoting CO2-rich melting conditions during the Late Neoproterozoic. The data from this study suggest that this ascending sublithospheric depleted melt component (more CO2-rich beneath Wemindji) interacted with a maximum input volume of 5% of the MARID-enriched CLM beneath the eastern Superior craton, and between 2% and 30% of ancient refractory cratonic peridotite. The lack of significant diamond in the Wemindji kimberlite dykes could be due to the resorption of the potential diamond in the CO2-rich kimberlite melt.

Fifty-four kimberlite pipes and dykes cut Precambrian granite in the Singida region of Tanganyika. The pipes range from 60 to 2500 feet in diameter, and occur in clusters and lines. The lines follow fracture zones. In addition to intrusive kimberlite, the pipes contain massive to stratified kimberlite tuff and sedimentary-tuffaceous beds. Some pipes have jackets of explosion breccia. The Singida pipes represent the upper parts of kimberlite volcanoes. The kimberlite consists mostly of serpentine which has replaced olivine. Magnesium ilmenite, pyrope, dark green diopside and perovskite are characteristic accessory minerals. After consolidation, the kimberlite was entirely serpentinized, and partly carbonatized and silicified. The absolute age of the pipes is not known. Indirect evidence suggests an early Tertiary age. The Singida kimberlites may have been emplaced during an early ultrabasic phase of Tertiary-Recent alkaline volcanism of the Eastern Rift Valley.

Fifty-four kimberlite pipes and dykes cut Precambrian granite in the Singida region of Tanganyika. The pipes range from 60 to 2500 feet in diameter, and occur in clusters and lines. The lines follow fracture zones. In addition to intrusive kimberlite, the pipes contain massive to stratified kimberlite tuff and sedimentary-tuffaceous beds. Some pipes have jackets of explosion breccia. The Singida pipes represent the upper parts of kimberlite volcanoes. The kimberlite consists mostly of serpentine which has replaced olivine. Magnesium ilmenite, pyrope, dark green diopside and perovskite are characteristic accessory minerals. After consolidation, the kimberlite was entirely serpentinized, and partly carbonatized and silicified. The absolute age of the pipes is not known. Indirect evidence suggests an early Tertiary age. The Singida kimberlites may have been emplaced during an early ultrabasic phase of Tertiary-Recent alkaline volcanism of the Eastern Rift Valley.

Secondary structures (e.g., fractures, sand lenses, kimberlite intrusions) can compromise the ability of clay-rich bedrock aquitards to protect underlying aquifers from near-surface contamination. To date, the effects of secondary structures on water migration and solute transport in these deposits have been poorly characterized. This study characterized the water migration and solute transport mechanisms at both a geologically simple and a geologically complex late-Cretaceous shale aquitard, with the field sites located 5 km apart in central Saskatchewan, Canada. The geotechnical properties and hydrogeologic properties of the complex aquitard were altered by kimberlite volcanism and subsequent hydrothermal alteration during its deposition (99 to 112 Ma BP). High-resolution, 1-D vertical profiles of conservative δ2H and Cl were collected from both sites (203 and 353 m deep, respectively) to define the vertical solute transport mechanisms. The shape of the 1-D tracer profiles and associated solute transport modeling from the geologically simple site suggest diffusion is the dominant transport mechanism through the entire thickness of the Lower Colorado shale aquitard (330 to 246 m above sea level, asl). Similarly, profiles through the complex, fractured, Cretaceous shale and associated modeling suggest diffusion is the dominant transport mechanism through the entire profile despite the presence of fractures; however, hydrothermal alteration during cooling of the kimberlite volcaniclastic material reduce the effective porosity (ne) of the kimberlite material from 40% to 1-5%. Results also suggest that, despite kimberlite emplacement in the study area, water migration and solute transport in the overlying and underlying Cretaceous shale may be unaffected by kimberlite volcanism and associated fracturing and alteration.