Les oscillations en composition et taille des grains peuvent parfois être générées dans les intrusions magmatiques, produisant des motifs caractéristiques à l’échelle du centimètre au mètre sous forme de couches cycliques. Il est essentiel de comprendre l’origine de ces motifs afin d’établir les circonstances géologiques de formation de ces corps. Nous travaillons avec l’hypothèse que ces motifs sont le résultat d’un processus d’auto- organisation non linéaire selon lequel l’interaction entre la dynamique de cristallisation et la diffusion cause la ségrégation des minéraux selon leur nature et leur taille. Ce mécanisme est semblable à celui à l’origine des bandes de Liesegang et mène à des caractéristiques comparables, telles qu’une progression géométrique de la position des bandes. Dans le but d’obtenir une description plus complète du processus de formation des motifs périodiques dans le contexte d’un système magmatique eutectique binaire en contact avec une roche- mère plus froide, nous présentons un modèle numérique en une dimension de nucléation et croissance qui généralise les modèles précédents. Notre modèle inclut une correction tenant compte de l’effet de la porosité sur la tortuosité, ainsi que le mûrissement d’Ostwald, facul- tativement. La solidification est contrôlée par des paramètres clés déterminant l’émergence du motif. De plus, en utilisant une géométrie sphériquement symétrique, notre modèle peut être appliqué à la formation de granites orbiculaires.

>Magister Scientiae - MSc / The 535 Ma post-orogenic Yzerfontein Pluton is a composite pluton that comprises rocks of mafic, intermediate and felsic compositions belonging to the shoshonitic series. The Yzerfontein Pluton forms part of the Cape Granite Suite of the Late-Proterozoic to Early-Cambrian Pan-African Saldania Belt. In this study, major- and trace-element data for the various rocks of the pluton, which act as hosts to extensive hydrothermal veining, are presented and integrated with the petrographic examination of the host rocks in order to constrain their petrogenesis.

The Peña del Seo tungsten deposit in northwestern Spain is situated in the tin (Sn)-tungsten (W) metallogenic province of Europe − one of the richest tin-tungsten (tantalum-lithium) mineral provinces in the world. The European Union’s current goal is to become self-sufficient of these commodities in the near future and the iTARG3T project was launched in order to improve the understanding and provide innovative exploration methods of these types of deposits. This master thesis will contribute to the iTARG3T project. The aim was to determine which physico-chemical conditions (temperature, pressure, salinity) that prevailed during the emplacement of the Peña del Seo deposit. A geochemical study was done consisting of a fluid inclusion study on the quartz veins from the deposit, and a whole-rock geochemistry analyse of the granitic rock. Homogenisation temperatures ranged between 97,6° C to 325,6° C and salinities (NaCl % equiv.) between 0,2% to 21,3%. The fluid was determined to consist of a two-component system of H2O and NaCl based on eutectic temperature. Based on its geochemical classification the granitic rock was considered to be an alkali granite, strongly peraluminous with S-type characteristics. At least two different types of fluids were present during the emplacement of the Peña del Seo deposit, one that was hot and with a moderate salinity, and one that had a lower temperature than the other fluid and a lower salinity, possibly meteoric water. The depositional mechanism of tungsten is thought to be caused by a combination between mixing between two fluids and cooling of the fluids, with the main depositional mechanism being cooling since the change in salinity was not of such magnitude that it would change the fluid chemical composition, while the decrease in temperature was. It is uncertain whether the granitic rock found at Peña del Seo is part of the granitic cupola of the greisen system. The granitic rock has similar characteristics as the leucogranites of the West Asturian-Leonese Zone and based on quartz vein morphology, which cut the D2 foliation, time of emplacement of the deposit could be linked to the syntectonic event at 320-310 Ma. If the relation between the granitic rock and the greisen system can be determined the time of emplacement would be possible.

>Magister Scientiae - MSc / The Sea Point contact, Cape Town, South Africa, exposes the contact between the Neoproterozoic Malmesbury Group metasedimentary rocks of the Pan-African Saldania belt and the intrusive S-type Peninsula Granite of the Neoproterozoic-Paleozoic Cape Granite Suite (CGS). The exposure outcrops over an area of approximately 170 m × 60 m with the northern end of the exposure being characterized by the country rock–microgranite intrusive contact. Heading further south, the outcrop transitions to the main contact zone, which is a predominantly gradational zone marked by sheets of compositionally variable granitic injections (collectively referred to as hybrid granite phases) concordant to the country rock structure, before reaching the main pluton area comprising the voluminous coarse-grained porphyritic granite. Using a combined study incorporating field, structural, geochemical, isotopic and U-Pb geochronological data, the intrusive contact is investigated to determine the construction history of the pluton and delineate possible emplacement mechanisms.

The specific surface area, determined by the BET method, is a parameter often used to scale results of mineral studies of surface reactions in terms of rate and capacity to the field scale. Such extrapolations of results from small-scale laboratory experiments to the field-scale are important within many environmental applications. An example of this is for the prediction of radionuclide retention in the bedrock surrounding a deep repository for radioactive waste, following failure of the engineered barriers, where radionuclides may sorb onto minerals constituting the geological environment. As a first step, the approach used in this work is to study the relationship between specific surface area and the particle size (0.075-8 mm) and to approach the field scale via measurements on large, centimetre-sized pieces, for seven natural minerals commonly found in granite: apatite, biotite, chlorite, K-feldspar, hornblende, labradorite and magnetite. The underlying assumption is that sorption of radionuclides can be related to specific surface area of a particular mineral in a continuation of this project.The results show that the phyllosilicates biotite and chlorite have a specific surface area that is about 10 times larger than the other minerals. Over the range of particle size fractions studied, the specific surface area varies between 0.1 and 1.2 m2g-1 for biotite and chlorite. The other studied minerals have specific surface areas varying between 0.01 m2g-1 for the largest fraction and up to 0.06 - 0.12 m2g-1 for the smallest. Results show linear relationships between the specific surface area and the inverse of the particle size for all studied minerals for small particle sizes, as expected. For some minerals, however, the data seemingly can be divided in two linear trends, where a change in internal surface area, surface roughness and/or particle geometry as the particle size decreases may explain this behaviour. Interestingly, for larger particles, there is a deviation from the linearity observed for small particles. Tentatively, this behaviour is attributed to a disturbed zone, created by the mechanical treatment of the material during particle size reduction, extending throughout small particles, but not altering an undisturbed core of the larger particles. In agreement with this, measurements on large pieces show a surface area 5 to 150 times lower than expected from the linear trends observed for the crushed material, implying an overestimation of the surface area and possibly also of the sorption capacities of the rock material from simple extrapolations of experimental results employing finely crushed material to the field situation. / QC 20110929 / Äspö Radionuclide sorption

The geometry and mineralization features of small left-lateral strike-slip faults and associated fractures in Lake Edison Granodiorite of the central Sierra Nevada, California, were examined in order to model the three-dimensional structure of strike-slip faults. These faults, which are reactivated joints, were also examined to determine fault sizes, starting joint size, and evidence for fluid flow. The associated secondary fractures are usually found in the dilational quadrants of fault-tip regions. The longest fault-segment trace is 32.14 m; the longest joint trace is 22 m. The joint population length (l) is represented by a power-law distribution (l-n) and it is l-1.22. The fault-segment distributions are l-0.23~0.79, and the compiled fault-segment distribution is l-1.18. The data on fracture and fault spacing, along with the joint power-law distribution, will aid in the simulation and analysis of fault evolution. The splay-fracture traced in the faults are linear at depth and the average splay-fracture angle is 39° ± 13°. The dihedral angle of the splay plane and fault plane ranges from 20° to 65°. There is a high concentration of splay fractures near the fault. As distance increases perpendicular form the fault, the splay-fracture spacing increases and splay-fracture frequency decreases. The splay tracelength distributions have a high short tracelength concentration with a rapid decrease of long tracelengths. The maximum tracelength of multiple splay-fracture groups is restricted by their distance orthogonal to the fault trace. The three-dimensional relationship between the splay-fracture plane and fault plane can be inferred from these data. When present, mineralized quartz appears largely as lenses and few as single continuous veins along the faults. No consistent pattern exists between fault displacement and the locations and dimensions of quartz cavities. There is no visible damage zone near the fault termination or around the faults. Microstructures in the fault zone consist of cataclasites and patchy gouges, and zones of dynamically recrystallized fault walls. The three-dimensional geometry, along with quartz cavity distribution and thin section analysis, has led to the conclusion that fluid migrates vertically among the faults and fractures.

No description available.

<p> The Killarney Igneous Complex, composed of an intrusive granite and a hypabyssal or extrusive porphyry was implaced near and at the surface in the general locality of Killarney, Ontario. The crystallization age of the intrusive portion of the complex is approximately 1740 million years. These rocks have experienced deformation by forces which in some instances produced complicated shearing motions. Mesoscopic samples show a foliation and a lineation supporting a history of deformation. The foliation is clearly the more visible fabric and is interpreted as a plane of flattening.</p> <p> Kinematic indicators, specifically asymmetric pressure shadow wings, are present within the rocks; however the patterns are too complicated to interpret by a simple sense of shear. The geometry of these kinematic indicators does suggest an active plane of foliation.</p> / Thesis / Bachelor of Science (BSc)

<p> A detailed petrographic, geochemical and strontium isotope study of the rocks representing the variations observed across the Coe Hill granite, Grenville Province, southeastern Ontario provides the basis for the determination of the age and possible origin of this pluton. This study also provides insight into the relationships between similar granitoid plutons in the immediate vicinity.</p> <p> The Coe Hill granite is a medium to coarse grained hypidiomorphic to allotriomorphic, leucocratic quartz monzonite with subordinate isolated inclusions of dioritic and gabbroic gneiss. Variations upon this otherwise homogeneous granitoid occur in discordant aplite dykes, assimilating mafic xenoliths and along brecciated contact boundaries.</p> <p> Generally the rocks of this pluton are more basic than the average for similar granitoids in the area (12.4% vs. 6.0% mafics) as observed in both thin section and major element oxide diagrams. Besides this trend major element diagrams have uniform distributions. A Rb-Sr isochron was determined for the rocks of the pluton proper which gave an age representative of the emplacement of these rocks (t = 1063 ± 21 M.a.; Ri = 0.7040 ± 5). Trace element Rb shows a value similar to the norm for granitoids yet is enriched in comparison to values acquired from similar granitoids in the area (144 ppm vs. 63 ppm).</p> <p> Through a synthesis of the available data, and that which was acquired from this study on the Coe Hill granite, a comparison with the available data on the Loon Lake quartz monzonite can be made. This comparison illustrates a great deal of strikingly similar trends which have been taken to represent a lower crustal, or upper mantle origin, cogenetic relationship between these two granitoids.</p> / Thesis / Bachelor of Science (BSc)

<p> Samples from two granitic offshoot dikes from the Murray granite, and from the Murray granite itself were analysed for eight major elements using X-Ray Fluorescence, to determine whether or not the dikes represented remobilized parts of the Murray granite and as such could have a different chemical composition from the parent material.</p> <p> The analyses show that only very minor chemical differences exist between the two granitic dikes and the main Murray granite. However four samples of the dike rocks appear to show element exchange with the Sudbury norite surrounding them, resulting in increased Na2O and CaO contents and lower K2O contents, resulting in increased amounts of albitic plagioclase.</p> / Thesis / Bachelor of Science (BSc)