This research aims to better understand drainage systems during mid to late Large Igneous Province (LIP) formation. A multidisciplinary study was conducted on the Lewiston Basin in the Columbia River Flood Basalt Province and the Skye Lava Field in the North Atlantic Igneous Province. A general model for drainage systems in LIPs was developed with three stages. In the early-LIP stage, the volcanic and drainage systems are confined to small basins, but as the volumetric eruption rate increases the regional drainage system is forced to the edge of the lava field. During the mid-LIP stage, the eruption rate decreases and the drainage system moves into the lava field, depositing channel sediments in the lowest parts of province while finer sediments or palaeosols develop in topographically higher areas. In the Skye Lava Field the drainage system was dominated by the uplift of the Rum Central Igneous Complex and included the incision of shallow valleys, whereas in the Lewiston Basin the most important effect was the structural control on basin topography. During the lateLIP stage, topographically high areas experience significant incision into the lava field which are filled by intracanyon flows (thick canyon-filling lava flows). These intracanyon flows may compartmentalise potential reservoirs deposited between earlier lava flows. Siliciclastic sand bodies were observed up to 12 m thick and 850 m across with minor exposure gaps, and were correlated across up to 15 km. The palynofloras associated with a number of palaeoenvironments in each province were identified the effects of other controls on the palaeoecology such as moisture availability, ashfall and substrate were established. The changes in the paJaeoclimate of the Lewiston Basin were studied using palaeosol geochemistry and palynology.

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No description available.

No description available.

Anorogenic alkaline ring-type complexes form within continental plate settings. Alkaline magmatism is derived from the upper mantle, in which mantle metasomatism plays an important part, as well as from partial melting of the lower crust. Radial and concentric fractures develop during the ascent of alkaline magma. Extrusion of basic and felsic magma takes place along these fractures with felsic volcanics building-up central volcanoes. As a result of emptying of the magma chamber, the superstructure of the volcano collapses and a caldera is formed. During the caldera stage syenitic and granitic material are intruded into ring fractures. Alkaline ring-type complexes may be classified as (i) alkaline qranite and syenite-type and (ii) carbonatite and undersaturated-type. These ring-type complexes occur as distinct igneous provinces. Some major provinces occur in Brazil, Corsica, Namibia, Nigeria, Norway, Saudi-Arabia and Sudan. In Namibia the Damaraland igneous province is of Mesozoic aqe and it contains 15 alkaline ring-type complexes . These complexes are situated along north-eastern trends which correspond to transform directions of the South Atlantic. During the opening of the South Atlantic (Gondwana breakup) Pan-African age lineaments were reactivated which allowed emplacement of anorogenic alkaline magmatism. A zonation of alkaline granite and syenitetype in the west and carbonatite and undersaturated-type ring-complexes in the east correlates with down- and upwarp axes parallel to the line of Gondwana fragmentation. Alkali- and H⁺-metasomatism is related to the alkaline and syenite-type whereas alkali metasomatism (fenitization) is associated with carbonatite and undersaturated-type ring-complexes. Sn, W and Ta mineralization is associated with alkaline granites of some of the alkaline granite and syenite-type ring-complexes. Fe, F, PO₄ , Nb, Th, REE, Sr, Zn and Pb mineralization is associated with carbonatite complexes. Potential exists for: (i) porphyry Cu-Mo and epithermal-type (Au, Ag, Pt-metals, base metals) mineralization in the alkaline granite and syenite-type ring-complexes and (ii) disseminated Cu, Au, Aq and Pt-metals in carbonatite and undersaturated-type ring-complexes

Part I consists of a detailied review of the available literature on the Fe- Ti oxides and their solid solution relationships. Particular attention is glven to the microstructures exhibited by these oxides and the hypotheses put forward to explain them. These data are synthesised and models are presented in which the microstructural developments in titaniferous magnetites amd ilmenites are explained in terms of current ideas on the influence of oxygen fugacity, exsolution mechanisms and crystal chemistry. These models have direct application to the microintergrowths observed in the naturally occurring Fe-Ti oxides from a wide range of igneous rocks. The available data on the minor and trace element chemistry of the Fe-Ti oxides are reviewed with particular reference to their variation in these minerals from different host rocks. The behaviour of the Fe-Ti oxides during secondary oxidation is discussed with particular reference to the oxidation of titaniferous magnetite and the weathering of ilmenite. The results of a mineralogical investigation into the co-existing Fe-Ti oxides from a range of igneous rocks including kimberlites, gabbros, dolerites, diabases, syenites, granophyres, granites and pegmatites are presented in Part 2 together with data on the ilmenites present in certain Eastern Cape beach sands. The kimberlite ilmenites are chemically distinct and can be readily distinguished on the basis of their relatively high MgO, Fe₂0₃ and Cr₂O₃ contents. They can also be distinguished from ilmenites from other igneous rocks on the basis of unit cell dimensions, d-spacings, reflectivities and micro-indentation hardness. The ilmenites from a wide range of basic to granitic igneous rocks exhibit a limited compositional range in which the MnO content appears to increase with increasing Si0₂ content. Relatively insensitive indirectly determined parameters such as unit cell dimensions, reflectivities and micro-indentation hardnesses cannot be used to distinguish between the ilmenites from the different rock types in these classes. The titaniferous magnetites exhibit progressively decreasing Ti0₂ contents from a maximum in the basic igneous rocks to a minimum in the granitic types. The titaniferous magnetite typically exhibits varying degrees of deuteric alteration, while the microstructures developed can be interpreted 1n terms of the models presented in Part 1. Part 3 represents an extension of Part 2 and deals with a mineralogical investigation of the titaniferous iron ores in five South African basic intrusions. The Bushveld and Kaffirskraal ores consist of multi-phase titaniferous magnetite grains containing crystallographically oriented ilmenite, ulvospinel and pleonaste microintergrowths. Minor coarser-grained ilmenite is also present. The Usushwana ores are texturally similar but contain abundant lamellar ilmenite in place of the ulvospinel. The primary features are well preserved in the unmetamorphosed Bushveld and Kaffirskraal ores. The Usushwana ores have been slightly metamorphosed resulting in the extensive replacement of the titaniferous magnetites by sphene and chlorite aggregates. The ores from these three complexes cannot be beneficiated by conventional ore-dressing techniques and require direct metallurgical treatment for the recovery of Fe, Ti0₂ and V₂O₅. The metamorphosed Mambula and Rooiwater ores have been recrystallised to a varying degrees and consist of multi-phase titaniferous magnetite grains containing modified ilmenite and pleonaste microintergrowths. These modified microstructures differ from those encountered in titaniferous magnetites from unmetnmorphosed basic rocks and their degree of modification can be related to the degree of met amorphism. Variable amounts of coarse granular ilmenite are also present and their development is related to the metamorphic grade and degree of recrystallisation. These ores can be partially beneficiated to yield ilmenite- and lower-Ti0₂ magnetite concentrates in which V₂O₅ contents of the magnetic fractions are higher than those of the original ores. The Trompsburg ores differ from those of the other complexes in that they are Mg-rich and are characterised by the presence of abundant olivine. The titaniferous magnetites typically exhibit well-defined ulvospinel cloth textures and are often surrounded by small amounts of graphite. They show evidence of a variety of extensive late-stage alteration features. The ores from the five investigated complexes are compared with similar ores from the Bushveld Complex. The ores from each complex can be readily distinguished on the basis of their chemical compositions and textural relationships. These features can be related to their crystallisation his tories and, in some cases, to post-crystallisation processes. The microstructural evolution of the ores from each complex is interpreted in terms of the models developed in Part I.

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No description available.

No description available.

A study was made of rocks outcropping along a road section in the vicinity of Hell's Gate, some 12 miles south of Boston Bar, British Columbia. Biotite schists belonging to the Hozameen group (Carboniferous or Permian in age), were the oldest rocks found. The Custer granodiorite, a heterogeneous igneous body having the average composition of a hornblende granodiorite, intrudes the biotite schists. The age of the Caster granodiorite is believed to be Upper Jurassic. Large numbers of pegmatite and aplite dykes intrude the Custer granodiorite. Two types of pegmatites, magmatic and metasomatic were distinguished. The Hell's date granodiorite, a uniform igneous body of trondjhemitic composition, intrudes the Custer granodiorite and also post dates the pegmatite and aplite dykes. The age of the Hell's Qate granodiorite is believed to be Upper Jurassic or possibly Lower Cretaceous. Sight plagioclase porphyry dykes, classified into one of three groups, (staple, multiple, and protoclastic types) were found. The plagioclase porphyry dykes are believed to be genetically related to the Hell's Gate granodiorite. Six dykes having an andesitic composition were found; the dykes have been classified into light colored and dark colored andesites. The rocks along the road section have been intensively fractured. Faulting has taken place close to the southern contact between the two granodiorites. The narrow N-S trending outcrop of Custer granodiorite in the area could possibly have been produced by faulting, and its shape suggests a horst structure, A study, using a method suggested by Gorai, was made of the plagioclase twins occurring in the Hell's Gate rocks. The conclusions drawn from this work largely confirms the conclusions drawn from the field evidence. / Arts, Faculty of / Geography, Department of / Graduate