Convection in magma chambers, driven by compositional density differences, is thought to be a major process in fractionation of liquid from crystals in the differentiation of magmas. Compositional convection has been tested for by undertaking two sets of experiments in silicate melts, and by re-examining the vertically differentiated gabbro-granophyre Glen More ring dyke on the Isle of Mull. Crystal growth quenching experiments have been carried out in a synthetic basalt in which iron is replaced by cobalt. Co-Mg olivine was overgrown on olivine seeds cemented in alumina crucibles and the glasses produced on quenching were analysed by EPMA for compositional variation at and above the overgrowth-glass interface. Boundary layers up to 50?m wide, and depleted in Co and Mg by upto 25 %, have been found at crystal-glass interfaces, and plumes of the same melt have been detected above the apexes of growing olivine crystals. The computed density difference which causes the convection of this boundary layer, melt is in the region of 1 %. This phenomenon, known as compositional convection, has been seen associated with dissolving crystals in silicate melts, and around growing crystals in aqueous salt solutions, but this is the first time it has been reported accompanying crystal growth in silicate melts. Other experiments in which hematite underwent dissolution in a natural basalt melt show that dense, Fe-enriched melt can be lifted above its origin by the buoyant rise of bubbles. In both sets of experiments a zone of buoyant boundary layer melt has been produced by side-wall crystallization of hercynite. This zone of melt has convected up and has ponded beneath the meniscus by a process that can be likened to side-wall crystallization in magma chambers. Petrological, mineralogical, textural, and new geochemical evidence from the re-examination of the Glen More ring dyke strongly suggests that the petrological variation is the result of a magma mixing mechanism. It is proposed that this was produced by the injection of a basic magma which underwent partial consolidation. This was then followed by a second injection of a silicic magma which underwent partial mixing with the dioritic residual magma remaining after crystallization of gabbros from the initial magma.

Caradocian phosphorite nodules sampled from the Powys county of N. Wales, U.K. have been investigated in order to characterize the deposit geochemically, mineralogically and petrographically and to evaluate their mode of formation. Nodules are the main form of phosphorite although phosphatized organic fragments and oolitic grains are also present. On the basis of petrographio characteristics, nodules are grouped into two types; Type I nodules (with abundant organic material) and Type II nodules (with abundant clay minerals). Mineralogical compositions of the phosphorite nodules reflect varying degrees of dilution of the phosphate material, francolite, by authigenic and detrital minerals. Examination with the scanning electron microscope of freshly fractured surfaces of nodules suggests that the apatite formed authigenically as a direct chemical precipitate. Surfaces of abundant siliceous spicules and other organic fragments as well as some minerals appear to be favoured sites for apatite nucleation. Geochemical studies showed significant impoverishment of lattice elements and enrichment of non-lattice elements in both types of nodules. Chemically the phosphorite nodules may be described in terms of four major components: SiO2, CaO, P2O5 and F. The average concentrations of trace elements present in these nodular phosphorites were compared with an average concentration in marine shales. The enrichment and/or depletion largely suggested precipitation from sea water. The proposed model of phosphorite formation involves inorganic (or biochemical) precipitation of apatite within pore waters of anoxic sediments and subsequent concentration of the apatite by physical processes. Oxidation of organic material during sulphate reduction is the main source of phosphate. This is supported by the very light delta13c isotopic composition of structural carbonate present in the francolites. These studies have also shown that these phosphorites have undergone differential leaching during weathering processes with the development of secondary phosphate: minerals, decarbonation of francolite and removal of many major and minor elements.

The Mars Science Laboratory rover, Curiosity, is using a comprehensive scientific payload to explore rocks and soils in Gale crater, Mars. Recent investigations of the Bagnold Dune Field provided the first in situ assessment of an active dune on Mars. The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on Curiosity performed quantitative mineralogical analyses of the <150m size fraction of the Namib dune at a location called Gobabeb. Gobabeb is dominated by basaltic minerals. Plagioclase, Fo56 olivine, and two Ca-Mg-Fe pyroxenes account for the majority of crystalline phases along with minor magnetite, quartz, hematite, and anhydrite. In addition to the crystalline phases, a minimum similar to 42wt % of the Gobabeb sample is X-ray amorphous. Mineralogical analysis of the Gobabeb data set provides insights into the origin(s) and geologic history of the dune material and offers an important opportunity for ground truth of orbital observations. CheMin's analysis of the mineralogy and phase chemistry of modern and ancient Gale crater dune fields, together with other measurements by Curiosity's science payload, provides new insights into present and past eolian processes on Mars.

The Emeishan Large Igneous Province is one of the largest igneous provinces in the world. It is marked by basaltic extrusives that vary in Ti amount, classified as high Ti and low Ti. Several mafic to ultramafic intrusions occur in the province as well as granitic intrusions. The mafic-ultramafic intrusions are associated with mineralization; large layered utlramafic intrusions bearing Fe-Ti-V mineralization, while small dyke like or sill like intrusions contain Cu-Ni-PGE mineralization. The Zhongchang and Yantiangou mafic- ultramafic intrusions are small such intrusions bearing Ni-Cu-PGE mineralization. The deposits show a lot of similarities in source magma, evolution and mineralization. Parental magma for both deposits show alkaline tendencies, and a high Mg # indicative of primitive magma that underwent little crustal contamination. Mantle range Cu/Pd ratios show parental magma fertile in chalcophile elements and both deposits proceed to show depleted mantle normalized values as a result of sulphide saturation and subsequent mineralization. Mineralization in Zhongchang is hosted at the contact between peridotite and pyroxenite, interstitial to olivine and clinopyroxene. Alteration minerals include epidote and chlorite. High Cu/Pd ratios suggest earlier sulphide saturation and removal of a PGE sulphide, and a second sulphide saturation phase resulted in Ni-Cu mineralization. Mineralization in Yantiangou is hosted in biotite effectively following fractionation of olivine and clinopyroxene after which sulphide saturation occurred, precipitating sulphide minerals in biotite. Pyrite and millerite occur as a result of late stage hydrothermal alteration. Cu/Pd ratios are high indicating prior sulphide saturation occurred where PGE partitioned into sulphides. Ni/MgO ratios observed for both deposits indicate a state of sulphide under saturation where PGE partitioned into tellurides and bismurthinides and Ni into olivine. Average tenors for mineralized units are; Zhongchang at 5%Ni, 9% Cu, 4300ppb Pt and 2000ppb Pd, and Yantiangou having relatively lower tenors at 3.2%Ni, 6.5% Cu, 3000ppb Pt and 1300 ppb Pd.

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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.

The sinter quality is dependent on sinter mineralogy, which in turn depends on the chemical compositions of the sinter mix. Although many research works have been conducted, further investigation on the effect of chemical compositions (MgO, A2O3, Basicity) on the sinter quality is still required for further improvement of the sinter and more alternative additives are still being tested. In this project, a sinter pot has been used to manufacture sinters, which were characterized using point-counting to quantify the different phases and X-Ray diffraction to identify the polymorphic forms of Ca2SiO4 of the silicate phases. The produced sinters were evaluated with respect to reducibility index (RI), reduction degradation index (RDI), physical breakdown (TI and AI), and production properties (yield, coke breeze rate and production rate). The influence of ignition temperature, magnesium oxide, alumina addition and basicity on the mineralogy as well as physical and chemical properties of iron ore sinters were investigated. Results were obtained as follows: <ol><li>For the Base case with a basicity of 2, 2.8 mass% MgO content, 1.7 mass % Al2O3 and 10 mass% CaO, the effect of ignition temperature, which ranged between 864oC and 1100oC, on the sinter quality was investigated. Results showed that the ignition temperature had an effect on the sinter properties: reducibility (RI), physical strength (TI and AI), production properties (yield, coke breeze rate and production rate). The temperature 1053oC was the best ignition temperature for an economically acceptable sinter. A further increase in ignition temperature was found to form melt on the surface of the sinter produced, leading to a sinter of low quality. Also, X-rays diffraction pattern showed that the allotropic transformation of the Ca2SiO4did not take place.</li> <li>The Low SiO2– Low Al2O3 sinter had the highest reducibility index and had the highest Abrasion index and the lowest coke breeze rate at 2.8 mass% MgO content compared to all the sinters produced in this project.</li> <li>For the High SiO2 – Low Al2O3 sinter MgO was added through dolomite and fused magnesia. A comparative study on the effect of dolomite and fused magnesia was conducted. The sinter to which fused magnesia was added had lower reducibility, higher reduction degradation, higher tumble index, lower abrasion index and lower coke breeze rate than the sinter to which dolomite was added.</li> <li>High SiO2 – High Al2O3 sinter had the lowest reducibility index, the lowest reduction degradation, the lowest tumbler index and the highest coke breeze rate.</li> <li>The increase in MgO content in all the sinters produced increased the coke breeze rate.</li></ol> / Dissertation (MSc)--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted

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The Yreka copper property is situated on the west side of Neroutsos Inlet about nine miles northwest of Port Alice In the northern part of Vaneouver Island, British Columbia. The property is underlain by rooks of the Vancouver Group, including greenstones, limestones, breccias and tuffs striking approximately northwest and dipping southwest into the mountainside at about 35 degrees. They, are intruded by dykes and sills of quartz-feldspar porphyry, quarts diorite and basalt. The mineral deposits are located in large bodies of skarn which have been formed in the tuffaceous rocks of the middle part of the sequence. The skarn zones consist roughly of three subparallel units which appear to conform approximately with the bedding. The largest of these skarn zones is about 1500 feet long and more than 100 feet wide, and contains sulphide bodies of economic interest. Other sulphide showings have been found on the property but do not appear to be of economic significance. The skarn zones are of pyrometasomatic origin of the type not related to an igneous contact. Development work in the early part of the century included stripping and trenching, driving a number of adits in various places in the skarn zones, and mining of a small tonnage of ore. Recent work, consisting of mapping, sampling and diamond drilling, has shown the property to be a prospect of considerable merit. / Arts, Faculty of / Geography, Department of / Graduate