En Afrique du Sud, le supergroupe Pongola s’est déposé sur le craton du Kaapvaal à environ 3 milliards d’années. Le groupe Mozaan repose sur le groupe basal Nsuze et contient des pélites, des arénites quartziques, des grès et des conglomérats. Dans ce type de conglomérat, des gisements d’uranium et des minéralisations d’or ont été reconnus dans le monde, au Canada, au Brésil, en Australie et en Afrique du Sud. Des petites minéralisations ont été avérées dans le groupe Mozaan, très différentes de celles qui ont été exploitées dans le bassin voisin du Witwatersrand. Ce travail pétrographique, minéralogique et géochimique concerne les formations conglomératiques et gréseuses basales du Mozaan Group dans le Denny Dalton. Il est fondé sur l’étude de deux carottes dans lesquelles des minéralisations en uranium ont été reconnues. Une attention particulière a été portée sur le matériel détritique car, dans ces conglomérats, les gisements sont de type placer avec des remobilisations plus ou moins marquées. Les grains détritiques identifiés associés à la pyrite détritique, sont la monazite fréquente, les oxydes de titane, les minéraux d’uranium thorium (coffinite, thorite, thorianite), le zircon, l’apatite, la chromite ainsi que d’autres sulfures (chalcopyrite, arsénopyrite). La roche source est vraisemblablement de matériel acide avec un faible apport basique ainsi que métamorphique. La morphologie des minéraux suggère un transport court de la source vers le bassin de Pongola. Les analyses pétrographiques et chimiques mettent en évidence les différentes minéralisations qui caractérisent les processus diagénétiques et hydrothermaux qui ont affecté le groupe Mozaan. Des observations nouvelles ont été réalisées sur les minéraux d’uranium avec la mise en évidence de phospho-coffinite, de phosphates alumineux hydratés de terres rares et des altérations très développées qui affectent les grains de monazite. Ces assemblages minéralogiques révèlent une diagenèse avec la circulation de fluides acides comme l’atteste la présence de pyrite et des APS dans la porosité secondaire des roches. Aucun grain d’uraninite détritique ni d’uraninite authigène n’a été observé dans cette étude. L’hypothèse la plus vraisemblable est que l’uranium des zones minéralisées provient de l’altération des grains de monazite à 2.54 Ga par des fluides acides. La remobilisation se fait en milieu ouvert et l’uranium cristallise essentiellement en bordures des grains de pyrite sous forme de phospho-coffinite. / In South Africa, the Pongola Supergroup was deposited on the craton Kaapvaal about 3 Ga years. The Mozaan group based on the basal Nsuze group and contains mudstones, arenites, sandstones and conglomerates. In this type of conglomerate, uranium and gold mineralization deposits have been recognized in the world, Canada, Brazil, Australia and South Africa. Small mineralization have been proved to in the Mozaan group, very different from those that have been exploited in the the neighbor of the Witwatersrand Basin. The petrographic, mineralogical and geochemical work concerns basal conglomerate and sandstone formations of Mozaan Group in Denny Dalton. It is based on the study of two cores where uranium mineralizations have been recognized. Particular attention was focused on the detrital material, because in these conglomerates, the deposits are placer type with the remobilizations more or less marked. The detrital grains identified associated with the detrital pyrite are frequent monazite, titanium oxides, thorium uranium minerals (coffinite, thorite, and thorianite), zircon, apatite, chromite and other sulphides (chalcopyrite, arsenopyrite). The source rock is likely acidic material with low basic contribution and metamorphic.The mineral morphology suggests a short transport the source to the Pongola basin. Petrographic and chemical analyzes show that characterize the different diagenetic mineralization and hydrothermal processes that have affected the Mozaan group. New observations were made on uranium minerals with the detection of phospho-coffinite, aluminous hydrated rare earth phosphates and highly developed alterations affecting monazite grains. These mineral assemblages reveal a diagenesis with the flow of acidic fluids as evidenced by the presence of pyrite and APS in the secondary porosity of the rocks. Detrital and authigène uraninite grains were not observed in this study. The most likely hypothesis is that the uranium mineralized zones comes from the weathering of monazite grains to 2.54 Ga by acidic fluids. Remobilization is done in open and uranium mainly crystallizes edges of pyrite grains in the form of phospho-coffinite.

The research described in this thesis has led to an understanding of the geochemical conditions controlling the formation, paragenesis and distribution of oxide zoner copper species in the Eastern Fold Belt of the Mt. Isa Inlier. This area is also known as the Cloncurry Complex. The regional geology and genesis of the copper deposits is reviewed and the deposits of particular interest to the study are described. Oxidation of pyrite and chalcopyrite by oxygen-bearing groundwater and the sources and mechanisms by which anions are carried by groundwater to reaction sites to form secondary copper species are discussed. Physical and chemical conditions control the development of particular species. Equilibrium phase diagrams have been constructed to represent stability fields. An explanation for the relative abundance and spatial distribution of the basic copper phosphates is provided. Stability field data supported by observations made on deposits in the Cloncurry district and elsewhere provides a basis for assessing the paragenesis and distribution of secondary copper species in this and similar environments. This is discussed and illustrated using the Great Australia mine as a model / Master of Science (Hons)

No description available.

M.Tech. (Extraction Metallurgy) / Please refer to full text to view abstract

The distribution of trace elements in bedrock, soils and plants, was studied in twelve areas of British Columbia where mineralization was known to occur below different kinds and depths of overburden. Samples were taken from two soil profiles and the bedrock at each location, and second and third year twigs of the principal vegetation found within a radius of fifty feet of each profile were also collected. The bedrock, soil and plant samples were analysed. The soil samples were used for the determination of pH, organic matter content, percentage of material <80 mesh, cation exchange capacity, exchangeable heavy metals, and content of Cu, Mo, Zn, Pb, As, Co, Ni, Fe and Hg. The same elements were determined in the bedrock and vegetation samples. The results were examined graphically for relationships between elemental contents of the bedrock, soil horizons and vegetation. The data were then statistically analysed.(a) soil horizons and plant relationship with bedrock. (b) inter-elemental relationship of individual horizons of soils and of plants, as well as all horizon relationships. (c) multiple correlation study of cation exchange capacity, percentage of organic material and -80 mesh of element content of individual and all soil horizons. These studies showed that, although most of the soil horizons were developed from transported materials, (glacial, alluvial, etc.), there was a highly significant correlation with B and C horizons and bedrock that confirmed the value of soil sampling in prospecting, since horizon development includes the upwards migration of the elements from bedrock. The secondary dispersion of the halo elements (Mo, Zn, Pb, As, Co, Ni, Hg) proved useful as pathfinders where major economic elements may have been masked during the upward migration process. Secondary dispersion may also be in some degree, helpful in identifying the origin of soils and plants. A great divergence in the affinity of various plants for different elements, and of the same species at different locations, was noted. It was also observed that plants have a closer relationship to the soils than to the bedrock itself, but even so, indicate mineralization. The important relationships between elemental distributions in soil horizons and in plants with bedrock, indicated a logarithmic relationship. The multiple correlation study indicated that some of the major factors of influencing the level of element content in soils developed on transported material-covered areas, are the size of the soil particles and frequently the pH of the soil. In general, the study indicated that the distribution of trace elements is highly complex and that bedrock, soils, and plants, should all be combined into one study; since the study of one of these alone would be incomplete without the others. / Land and Food Systems, Faculty of / Graduate

This study comprises a petrographical and mineralogical investigation of rocks from an area 850 sq. km in size, situated about 80km northeast of Middelburg. Roughly half of the area is occupied by rocks of the epicrustal phase of the Bushveld Complex, and consists largely of Rooiberg Felsite and granophyre as well as leptite, microgranite and granodiorite. Numerous veins of finegrained granite traverse the leptite which is considered to be highly metamorphosed felsite. These veins of fine-grained granite probably owe their origin to the melting of the leptite. The coalescence of these products of melting gave rise to the thick sheet of.granophyre between the leptite and the felsite. Rocks of the Layered Sequence occupy the eastern half of the area and consist of the Main and Upper Zones which were subdivided into various subzones on the basis of characteristic rock types and marker horizons. Mineralogical investigations are restricted to the minerals from rocks of the Layered Sequence, namely orthopyroxene, plagioclase, apatite and the sulphides of the Upper Zone. In Subzone A of the Main Zone, the orthopyroxene is present as cumulus crystals, but it changes in texture to ophitic in the lower half of Subzone B where small discrete grains of inverted pigeonite are also developed. Inverted pigeonite is present in the upper half of Subzone B and in rocks of the Upper Zone, whereas the orthopyroxene-pigeonite relationships in Subzone C of the Main Zone are a repetition of those observed in the underlying rocks. The phase-change from orthopyroxene to pigeonite takes place over a transition zone in which both phases crystallized from the magma. It is envisaged that the first pigeonite to have crystallized from the magma at high temperatures had a lower Fe/Mg ratio than the hypersthene precipitating at slightly lower temperatures, with the result that the early formed pigeonite was unstable and reacted with the magma to form hypersthene. This caused the formation of groups of grains of hypersthene which are optically continuous over large areas and which may contain a few blebs of augite exsolved from the original pigeonite. A few pigeonite grains were effectively trapped in other minerals, mostly augite, and consequently escaped reaction with the liquid. These inverted to hypersthene at the appropriate temperature and contain numerous exsolution-lamellae of augite. As fractional crystallization of the magma continued, it moved further into the stability field of pigeonite and out of the stability field of hypersthene with the result that the formation of hypersthene by the reaction of pigeonite with magma was replaced by inversion of pigeonite to hypersthene. This inverted pigeonite is also present as groups of grains optically continuous and contains pre-inversion exsolution-lamellae of augite orientated at random, and post-inversion exsolution-lamellae which are orientated parallel to the (100) plane of the orthopyroxene throughout a unit. The inverted pigeonite is orientated in such a way that its crystallographic c-axis lies close to or in the plane of layering. This is explained as being due to the load pressure of the superincumbent crystal mass during the inversion. Textural features of the plagioclase revealed interesting information on the postcumulus changes in the rock. Reversed zoning, interpenetration and bending of plagioclase crystals as well as the presence of myrmekite are described. These are considered to be due to increased load pressure prior to and during crystallization of the intercumulus liquid. It is considered that the various types of pegmatoids may have originated by an increase in pressure on the intercumulus liquid which was concentrated to form pipe-like bodies by lateral secretion or filter pressing. Cumulus apatite is developed in the olivine diorites of Subzone D of the Upper Zone. From unit cell dimensions it seems as if it changes in composition from a fluor-rich hydroxyapatite at the base of this subzone to a relatively pure hydroxyapatite 70m below the roof. There seems to be a substantial increase in the fluor content of the apatite in the topmost 70m of the intrusion. Rocks of the Upper Zone contain considerably more sulphides than those of the Main Zone. This is ascribed to an increase in the sulphur content of the magma owing to fractional crystallization. The magma reached the saturation point of sulphur when rocks of Subzone D of the Upper Zone started to crystallize with the result that these rocks contain numerous small droplets of sulphide which constitute on an average about 0, 5 per cent by volume of the rocks. A concentration of the sulphides in these rocks would not yield a deposit of economic interest because of the unfavourable composition of the sulphide phase, which consits of more than 90 per cent pyrrhotite. Sulphides in the rocks below this subzone are intercumulus and a concentration could be of economic importance because the sulphide phase contains appreciable amounts of chalcopyrite and pentlandite. Although no economic concentration of sulphides are known from the Upper Zone, this study has revealed the presence of a mineralized anorthosite below Lower Magnetitite Seam 2 which contains in places up to 1 per cent Cu, 0, 18 per cent Ni and 1, 6g/ton platinum metals. Continuous, slow convection and bottom crystallization probably gave rise to the homogeneous rocks of the Main Zone. Injection of a considerable amount of fresh magma took place at the level of the Pyroxenite Marker which resulted in a compositional break and gave rise to a repetition in Subzone C of the rocks of the Main Zone below this marker. The oxygen pressure during crystallization of the magma was probably low, causing a gradual enrichment in iron in the magma and gave rise to the appearance of magnetite at the base of the Upper Zone. Intermittent increase in the oxygen fugacity is considered to be important in the formation of magnetitite seams. As a result of fractional crystallization the volatile content of the remaining magma gradually increased. This is seen firstly, by the appearance of biotite secondly by the appearance of cumulus apatite and droplets of sulphide and lastly by hornblende in the rocks of the Upper Zone. Some water-rich residual liquids apparently also intruded the overlying leptite, causing additional melting of the latter and the formation of irregularly shaped veins and pockets of granodiorite. A lateral change in facies of the rocks of the Layered Sequence in a southerly direction is described. This is considered to be due to crystallization of the magma at slightly lower temperatures because of the more effective heat loss where the magma chamber was thinner. Two parameters of differentiation for layered intrusions are proposed, viz. a modified version of the differentiation index and a modified version of the crystallization index. The former seems more applicable for intrusions such as the Bushveld Complex, whereas the latter seems to be more applicable for intrusions in which there is a considerable development of ultramafic rocks. These two parameters can also be used to indicate the differentiation trend if they are plotted against height in the intrusion. / Thesis (DSc)--University of Pretoria, 2012. / Geography, Geoinformatics and Meteorology / Unrestricted

Orientador: Elson Paiva de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-18T13:34:45Z (GMT). No. of bitstreams: 1 Piaia_Patricia_M.pdf: 22497674 bytes, checksum: ca688c1a7bfc4bf7fbbbc2fe2a92815e (MD5) Previous issue date: 2011 / Resumo: Complexos máfico-ultramáficos são comuns em faixas orogênicas e podem representar diferentes ambientes tectônicos, tais como raízes de arco, restos obductados de ofiolitos, platôs oceânicos, lascas do manto litosférico ou ainda ramos abortados de riftes. Características de campo, petrográficas, de química mineral e litogeoquímicas são importantes no intuito de diferenciar o ambiente de formação desses corpos. O orógeno Itabuna-Salvador-Curaçá corresponde a uma das faixas precambrianas do Brasil consolidada durante o Paleoproterozóico. Ele hospeda diversos complexos máficos-ultramáficos cuja compreensão petrogenética é dificultada por suas rochas muitas vezes se encontrarem metamorfisadas em fácies granulito. Um desses complexos é a Suíte metamórfica gabro-anortosítica São José do Jacuípe que compreende um conjunto de rochas cumuláticas estratificadas, formado por metaanortositos, meta-leucogabros, meta-leuconoritos, meta-gabros e meta-gabronoritos, com meta-piroxenitos subordinados. As rochas da suíte possuem características litogeoquímicas e de química mineral semelhantes ao magmatismo máfico de arco e foram interpretadas como pertencentes a um remanescente de arco, podendo representar um fragmento da raiz máfica de arco magmático que, no caso do cinturão Salvador-Curaçá, seria o Complexo Caraíba. Outros complexos máfico-ultramáficos que se destacam na região são os enxames de diques máficos que ocorrem em abundância na porção norte do Orógeno Itabuna-Salvador-Curaçá. Um deles é o enxame de diques máficos Aroeira, que ocorre na porção central e mais deformada do orógeno, cujas rochas de composição gabronorítica muitas vezes são confundidas com as rochas pertencentes à Suíte São José do Jacuípe. O enxame intrudiu a crosta continental, possui caráter tholeiítico e subalcalino, sendo que suas rochas possuem afinidade com magmas basálticos. Modelagem geoquímica indica que o derrame se formou provavelmente a partir de baixas taxas de fusão de uma fonte mantélica pobre em granada e, a partir de então, evoluiu por processos de cristalização fracionada - cujos principais minerais a cristalizarem foram plagioclásio, olivina e piroxênio - seguida de contaminação crustal. No que se refere aos aspectos petrográficos e litogeoquímicos, as rochas da Suíte São José do Jacuípe e do enxame de diques máficos Aroeira são muito semelhantes e de difícil diferenciação. No entanto aspectos macroscópicos das rochas pertencentes aos diques como presença de fenocristais, falta de outros litotipos associados, diferenças de granulação e no grau metamórfico entre diques, além das próprias relações de contato com as encaixantes, permitem separá-los dos meta-gabronoritos pertencentes à Suíte São José do Jacuípe / Abstract: Mafic and ultramafic complex are commons in orogenics belts and can represent differents tectonics environments like arcs roots, obducted parts of ophiolites, oceanic plateaus, litospheric mantle wedge or an aborted rift. Field, petrographic, mineral chemistry and litogeochemistry characteristics are important to characterize the formation environment. The Itabuna-Salvador-Curaçá belt is one of the Precambrian belts consolidated during the Paleoproterozoic. This belt hosts a lot of mafic and ultramafic bodies and the petrogenesis understanding of these bodies is difficult because they are often metamorphosed in granulite facies. The São José do Jacuípe metamorphic gabbro-anorthositic suit is one of these bodies. It's a conjunct of stratified cumulatic rocks constituted by metaanorthosites, meta-leucogabbros, meta-leuconorites, meta-gabbros and meta-gabbronorites with associated metapyroxenite. These rocks have lithogeochemistry and mineral chemistry characteristics similar to arc mafic magmatism. They are being interpreted as a remaining of a mafic root of a magmatic arc and, in case of Itabuna- Salvador Curaçá belt, this arc probably is represented by the Caraíba Complex. Others complex that stand out in this region are the mafic dykes swarms. They are abundant in the north part of the Itabuna-Salvador-Curaçá belt. One of them is Aroeira swarm that occurs in the central and more deformed part of the belt. Their rocks have a gabbronoritic composition and sometimes are confounded with São José do Jacuípe's rocks. The swarm intruded a continental crust, has a tholeitic and sub-alcaline character and affinity with basaltics magmas. Geochemistry modeling shows this magma was formed from low rates of melt of a mantle font poor in garnet and then, evolved by fractional crystallization and crustal contamination. The main minerals that crystallize were plagioclase, olivine and pyroxene. São José do Jacuípe and Aroeira's rock are petrographically and lithgeochemically similar and difficult to differentiate. However, characteristics of dyke's rocks like presence of phenocrysts, absence of any other litho type associated, differences of granulation and of the metamorphic degree between dykes and the relations of contact with the other rocks allow differentiate them of the meta-gabbonorites of São José do Jacuípe suite / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

The effectiveness of catechol, an aromatic vic-diol, in dissolving silicate minerals was studied. A synthetic amorphous magnesium trisilicate, Mg₂Si₃O₈∙5H₂O, as well as the minerals olivine, sepiolite, diopside, augite, and enstatite were used to react with catechol in slightly acidic, basic, and neutral solutions. It was found, depending on the solvent used, that 33-52, 8-17, 14-30, 5-11, 3-6, and 0.5-1 % of the minerals dissolved, respectively. The reaction with Mg₂Si₃0₈·5H₂0 resulted in the formation of crystals of magnesium tris (catecholato) siliconate nonahydrate Mg[Si(Cat)₃]∙9H₂0. Dehydration of the crystals at room temperature resulted in the loss of 6 moles of water to form a trihydrated complex, Mg[Si(Cat)₃]·3H₂0; further dehydration at 100°C gave an anhydrous complex, Mg[Si(Cat)₃]. By adding guanidine hydrochloride, CN₃H₆Cl, to the reaction mixture after filtering, crystals of guanidinium tris (catecholato) siliconate monohydrate, (CN₃H₆)₂[Si(Cat)₃]∙H₂0, were obtained. Infrared and nmr spectra, and analytical and x-ray powder diffraction data are presented. The possible structures of the magnesium salts of tris (catecholato) siliconate are also discussed. The reaction of catechol with the minerals listed above gave a water soluble silicon-catechol complex, Si (Cat)₃⁼, which was isolated as (CN₃H₆)₂[Si(Cat)₃]·H₂0 by adding guanidine hydrochloride to the reaction mixture after filtering. The dissolution of these minerals by catechol to form Si(Cat)₃⁼ leads to the conclusion that aromatic vic-diols in nature may play a role in chemical weathering, in transport of silicon into rivers or seas, in soil development, in interconversion of minerals, and in accumulation of silica in plants.

No description available.

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirement for the degree of Master of Science. 2016. / An important feature of the Merensky Cyclic Unit in the Bushveld Complex is the association of platinum group metals with narrow chromitite layers. The appearance and removal of chromitite layers in this unit has been used to define facies types. This study explores the hypothesis that individual chromitite layers within the Merensky Cyclic Unit at Marikana have distinguishing major element concentrations or ratios which could assist in tracing the continuity of the chromitite layers between facies types which is characterized by single or multiple layers. The examination of field relationships of the chromitite layers at the transition between facies types will be useful to improve understanding of lithological continuity. This study has two approaches; the first being the examination of underground exposures and petrographic analysis, and secondly by chemical analysis of chromite grains within the chromitite layers. No chromite mineral compositional trends or similarities were observed for grains in chromitite layers hosted by the same silicate mineral. The mineral chemistry evidence suggests that post cumulus processes are considered to have changed the primary chromite compositions and that reequilibration has occurred due to reaction with trapped intercumulus liquid. Little to no reaction with the host silicates of plagioclase and pyroxene is envisaged. The slow cooling of the Bushveld Complex has allowed intercumulus liquid a greater opportunity to equilibrate with the early minerals, destroying the early magmatic history by reaction and recrystallization. The cumulate deposition model envisaged to have formed the Merensky Cyclic unit at Marikana is by the emplacement of several pulses of superheated magma, supported by the occurrence of several chromitite layers within the sequence. / LG2017