Browsing by Author "Reid, Dave"
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- ItemOpen AccessGeochemistry and petrogenesis of the Tsirub nephelinite-basanite intrusions, Aus, southern Namibia(2007) Nakashole, Albertina; Reid, DaveNephelinite-basanite intrusions found on the Tsurib farm near Aus in southern Namibia are described for the first time. The petrography is very similar to each other wih texture ranging from porphyritic to microporphyritic where olivine is dominant, and sometimes the only, phenocryst/microphenochryst phase, and less commonly clinopyroxen; the groundmass consists of clinopyroxine, olivine, Fe-Ti oxides and secondary generation amphibole. Rare felsic xenoliths comprising alkali feldspar (orthoclase) and clinopyroxene (diopside and aegerine-augite) occur in the two major intrusive bodies.
- ItemOpen AccessThe geochemistry, kinematics and geodynamics of the Gannakouriep dyke swarm(1992) Ransome, Ian G D; Erlank, A J; Reid, DaveThe Gannakouriep dyke swarm comprises a linear swarm of north to northeast striking mafic dykes emplaced during late Proterozoic rifting in the Gariep belt. The swarm has a strike length of over 300 km crossing terrane boundaries of the Gordonia sub-province, Richtersveld igneous sub-province and 8 ushmanland sub-province of the Namaqua Mobile Province. The main axis of dyke intrusion is centred within the 2.0 Ga Richtersveld igneous sub-province where the density of dyking increases westwards across strike towards the Gariep belt, prior to disappearing within the sediment/basement contact of the para-autochthonous Port Nolloth Assemblage. An internal Rb-Sr mineral isochron, together with pyroxene K-Ar plateau and whole rock model TCHUR ages, indicate that the dyke swarm was intruded around 720 Ma. The majority of the dykes comprise subophitic relict gabbros and dolerites of alkali affinities replaced by metamorphic minerals of both greenschist and amphibolite facies. The greenstones are encountered within the NE striking eastern sector of the dyke swarm which records the original tensile stress field, whilst amphibolites are encountered in the northerly striking western sector of the swarm which has been rotated 26° anticlockwise during Pan-African (500-550 Ma) deformation in the Gariep belt. The latter age of regional metamorphism and deformation is supported by available K-Ar age data on whole rock samples and amphibole mineral separates. Integrated field relationships, continuum mechanics modelling and geochemical studies suggest that the swarm was initiated as a series of low level crustal magma chambers which subsequently gave rise to a series of dyke complexes that comprise the Gannakouriep dyke swarm. The geochemical variability between individual dyke complexes across the entire swarm is negligible; only slight differences being recorded by their high-field-strength element concentrations. The latter suggests that all dykes are genetically linked to a single mantle diapir, with only slight source characteristic heterogeneities. All dykes are ferro-tholeiites with no primitive (picritic) member being present. Geochemical trends recorded by the swarm are easily reconcilable in terms of fractionation of the phenocryst assemblage olivine, plagioclase, clinopyroxene, (ilmenite and Ti-magnetite). However an earlier phase of fractionation of essentially olivine and plagioclase at the base of the crust is suggested since constraints on the degree of partial melting (3-6%) imposed by REE patterns would derive an alkali basalt parental melt. The geodynamic relationship between the Gannakouriep dyke swarm and rifting in the Gariep belt is accounted for by a lithospheric plate model containing non-coincidental crustal and mantle weaknesses represented by late Namaquan D4n extensional faults and a mantle weakness possibly resulting from crustal thickening within the Richtersveld igneous sub-province during Namaquan tectonics.
- ItemOpen AccessAn investigation into the dissolution of pyroxene : a precursor to mineral carbonation of PGM tailings in South Africa(2014) Meyer, Nicole Anne; Becker, Megan; Broadhurst, Jennifer Lee; Reid, DaveCarbon sequestration through mineral carbonation is becoming an increasingly attractive alternative for mitigating excess CO₂ in the atmosphere. Mineral carbonation is a natural process whereby CO₂ is fixed to CaFeMg-silicates to form Ca-, Fe-, and Mg-carbonates. This process is thermodynamically favourable and the products are benign and stable over millions of years. Pyroxene-rich tailings generated from the processing of PGM ores in South Africa have the potential to sequester significant amounts of CO₂ (~14 Mt per annum). In the indirect pH swing method, silicate minerals are initially leached at low pH and then carbonated at high pH. A previous study on these tailings highlighted the slow extraction of cations from orthopyroxene, the major Mg-host. The low reactivity of the orthopyroxene resulted in an overall low conversion of tailings to carbonates with only 30 % for Ca, 3 % for Mg and 9 % for Fe. Under similar experimental leach conditions, ~100 % dissolution of olivine and serpentine can be achieved.
- ItemOpen AccessProterozoic crustal evolution of the Awasib Mountain terrain, southern Namibia, with speical reference to the volcanic Haiber flats formation(1989) Hoal, Brian Garner; Reid, Dave; Erlank, A JThe middle to late Proterozoic Awasib Mountain terrain (AMT) straddles the boundary between the Rehoboth and Gordonia subprovinces in southern Namibia. The AMT is made up of two major crustal components, the older of which is correlated with the Namaqualand Metamorphic Complex (NMC), and the younger with the Sinclair Sequence.