The super-giant Oyu Tolgoi porphyry copper-gold deposits in the South Gobi desert, Mongolia, consist of multiple discrete porphyry centers aligned within a north-northeast trending, >6.5 km long, arc-transverse mineralized corridor. The porphyries are linked to a tectono-magmatic event at ~372 Ma within a Devonian to Carboniferous volcanic arc, and U-Pb (zircon) geochronology records magmatic activity from ~390 Ma to ~320 Ma. The Oyu Tolgoi district underwent at least three discrete periods of syn- to post-mineral shortening and there is evidence for at least three unconformities within the Paleozoic sequence. Although the deposits were formed in an active orogenic environment characterized by rapid uplift, their preservation is a reflection of climactic effects as well insulation from erosion by rapid burial under mass-wasted and pyroclastic material in the volcaniclastic apron of late-mineral dacitic volcanoes. The porphyry copper-gold deposits are spatially and temporally related to medium- to high-K calc-alkaline quartz monzodiorite (~372 Ma) and granodiorite (~366 Ma) intrusive phases that comprise the Late Devonian Oyu Tolgoi Igneous Complex (OTIC). Adakite-like wholerock compositions as well as zircon grains with high CeN/CeN*, EuN/EuN* and Yb/Gd in the sample populations from syn- and late-mineral porphyry intrusions are different from younger intrusions that are not related to porphyry Cu-Au deposit formation. Moreover, mixed zircon populations within OTIC intrusions indicate that efficient assimilation of material from different host rocks by a convecting magma chamber occurred. Mafic to intermediate volcanic units evolved from tholeiitic to calc-alkaline compositions, which is interpreted to be a reflection of marine arc maturation and thickening. Felsic rock suites are dominantly high-K calc-alkaline, regardless of age. Nd-isotopic geochemistry from all suites is consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc and lead isotopic compositions indicate that the sulfides in the porphyry Cu-Au deposits are genetically linked to the Late Devonian magmas. Magma mixing, adakite-like magmatism and rapid uplift and erosion in a juvenile marine arc setting differentiate the ore-stage geologic environment at Oyu Tolgoi from other settings in active and fossil volcanic arcs.

The super-giant Oyu Tolgoi porphyry copper-gold deposits in the South Gobi desert, Mongolia, consist of multiple discrete porphyry centers aligned within a north-northeast trending, >6.5 km long, arc-transverse mineralized corridor. The porphyries are linked to a tectono-magmatic event at ~372 Ma within a Devonian to Carboniferous volcanic arc, and U-Pb (zircon) geochronology records magmatic activity from ~390 Ma to ~320 Ma. The Oyu Tolgoi district underwent at least three discrete periods of syn- to post-mineral shortening and there is evidence for at least three unconformities within the Paleozoic sequence. Although the deposits were formed in an active orogenic environment characterized by rapid uplift, their preservation is a reflection of climactic effects as well insulation from erosion by rapid burial under mass-wasted and pyroclastic material in the volcaniclastic apron of late-mineral dacitic volcanoes. The porphyry copper-gold deposits are spatially and temporally related to medium- to high-K calc-alkaline quartz monzodiorite (~372 Ma) and granodiorite (~366 Ma) intrusive phases that comprise the Late Devonian Oyu Tolgoi Igneous Complex (OTIC). Adakite-like wholerock compositions as well as zircon grains with high CeN/CeN*, EuN/EuN* and Yb/Gd in the sample populations from syn- and late-mineral porphyry intrusions are different from younger intrusions that are not related to porphyry Cu-Au deposit formation. Moreover, mixed zircon populations within OTIC intrusions indicate that efficient assimilation of material from different host rocks by a convecting magma chamber occurred. Mafic to intermediate volcanic units evolved from tholeiitic to calc-alkaline compositions, which is interpreted to be a reflection of marine arc maturation and thickening. Felsic rock suites are dominantly high-K calc-alkaline, regardless of age. Nd-isotopic geochemistry from all suites is consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc and lead isotopic compositions indicate that the sulfides in the porphyry Cu-Au deposits are genetically linked to the Late Devonian magmas. Magma mixing, adakite-like magmatism and rapid uplift and erosion in a juvenile marine arc setting differentiate the ore-stage geologic environment at Oyu Tolgoi from other settings in active and fossil volcanic arcs.

The super-giant Oyu Tolgoi porphyry copper-gold deposits in the South Gobi desert, Mongolia, consist of multiple discrete porphyry centers aligned within a north-northeast trending, >6.5 km long, arc-transverse mineralized corridor. The porphyries are linked to a tectono-magmatic event at ~372 Ma within a Devonian to Carboniferous volcanic arc, and U-Pb (zircon) geochronology records magmatic activity from ~390 Ma to ~320 Ma. The Oyu Tolgoi district underwent at least three discrete periods of syn- to post-mineral shortening and there is evidence for at least three unconformities within the Paleozoic sequence. Although the deposits were formed in an active orogenic environment characterized by rapid uplift, their preservation is a reflection of climactic effects as well insulation from erosion by rapid burial under mass-wasted and pyroclastic material in the volcaniclastic apron of late-mineral dacitic volcanoes. The porphyry copper-gold deposits are spatially and temporally related to medium- to high-K calc-alkaline quartz monzodiorite (~372 Ma) and granodiorite (~366 Ma) intrusive phases that comprise the Late Devonian Oyu Tolgoi Igneous Complex (OTIC). Adakite-like wholerock compositions as well as zircon grains with high CeN/CeN*, EuN/EuN* and Yb/Gd in the sample populations from syn- and late-mineral porphyry intrusions are different from younger intrusions that are not related to porphyry Cu-Au deposit formation. Moreover, mixed zircon populations within OTIC intrusions indicate that efficient assimilation of material from different host rocks by a convecting magma chamber occurred. Mafic to intermediate volcanic units evolved from tholeiitic to calc-alkaline compositions, which is interpreted to be a reflection of marine arc maturation and thickening. Felsic rock suites are dominantly high-K calc-alkaline, regardless of age. Nd-isotopic geochemistry from all suites is consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc and lead isotopic compositions indicate that the sulfides in the porphyry Cu-Au deposits are genetically linked to the Late Devonian magmas. Magma mixing, adakite-like magmatism and rapid uplift and erosion in a juvenile marine arc setting differentiate the ore-stage geologic environment at Oyu Tolgoi from other settings in active and fossil volcanic arcs. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The majority of economic gold deposits in NSW are associated with Ordovician-aged igneous rocks and are examples of the Cu-Au porphyry-skarn-epithermal association commonly developed in convergent margin to orogenic settings. They are among the oldest porphyry Cu-Au deposits in the Pacific Rim region. They are similar to younger deposits in terms of tectonic setting and structure, but the largest are chemically distinct, being associated with shoshonite magmas (Cadia, Ridgeway and Northparkes). The Lachlan Fold Belt (LFB) porphyries are subdivided into four sub-groups based mainly on their age relative to development of the Lachlan Transverse Zone (LTZ) structure. Two subgroups pre-date the LTZ, one group is syn�LTZ and one group post-dates the LTZ. No mineralisation has been found or reported among pre-I.TZ porphyries. but it is common in post- . l Z_ porphyries. Petrographic analysis and microprobe results establish a wide range of primary and secondary features within the Ordovician rocks examined in this study. Cale alkaline to shoshonitic affinities are supported by the variable abundance of primary K-feldspars. Primary mineral phases such as pyroxenes and igneous magnetite provide an indication of fractioning mineral assemblages responsible for igneous trends in magma chemistry. The hydrothermal mineral assemblages documented in these LFB study areas are characteristic of younger Cu-Au Porphyry style mineralisation. As expected, the most pervasive alteration is associated with highly mineralised shoshonitic Ordovician rocks at Ridgeway, and Cadia. the less strongly mineralised calc alkaline Ordovician rocks at Cargo. Copper Ilill and Fairholme. are correspondingly less strongly altered overall. although secondary mineral assemblages are locally abundant. Many varieties of oxides and carbonates are observed at the different study localities. Most of the studied samples conform to igneous chemical trends because they are weakly altered, although post magmatic processes, such as veining, are detectable in certain trends. The K2O enrichment of the studied samples is consistent with subductionmoditied mantle wedge sources. A few effects, such as the high Fe203 contents of some Ridgeway samples, probably reflect porphyry-style hydrothermal alteration processes. Host rocks at the Cadia and Ridgeway are entirely alkalic on the K2O versus SiO2 plot and shoshonitic on the Total Alkalies versus SiO2 plot. Igneous rocks at the other deposits display a range of compositions between low K tholeiites to shoshonites that in some cases reflects multiple igneous suites. The LREE and L1LE enrichments, and HFSE depletions (Nb, Ta and Ti) of the magmas associated with these deposits are characteristics of a subduction-related tectonic setting. They all fall in the volcanic-arc granite and syn-collisional granite field of the Nb-Y tectonic discrimination diagram. Several magma types are identified by differences in the HFSE and REE trends. Differences in the extent and style of magma fractionation are evident in the trace element data. The Ridgeway samples define a wider range of trace element concentrations than the Cadia samples that may indicate a greater extent of fractionation during emplacement of the Ridgeway magmas. Fairholme samples display a high Nh and /If trends that are distinct from the main fields on Zr variation diagrams. Compositional differences between larger Cu-Au deposits, Cadia-Ridgeway and smaller deposits, Copper Ifill, Cargo and Fairholme are evident in terms of Nb-Ta depletion and variation. The smaller deposits show constant Nb/Ta or negative Nb/Ta trends that extend to high Nb. The larger deposits display positive Nb/Ta trends that do not extend to high Nb. This distinction reflects a difference of preferential incorporation of Nb in a mineral phase (magnetite). Comparisons between Cadia-Ridgeway and other shoshonite (altered samples of Bajo de la Alumbrera, Argentina), calc alkaline magmas from New Zealand and rocks from other areas indicate that Nb/Ta is not directly correlated with the shoshonitic classification, K2O vs. SiO2, and that the Cadia-Ridgeway Nb and Ta variation is not the result of alteration. The fact that the weakly altered LFB Capertee shoshonites exhibit a narrow range of Nb and low Nb/Ta suggest the shoshonite trend for the LFB as a whole is a steep one on the Nb/Ta versus Nb plot. The results of this study could provide important information for exploration within the LFB. Only the Cadia and Ridgeway deposits display a wide range of Nb/Ta values and lack the near-horizontal trend seen for other localities associated with smaller deposits. The tectonic evolution of the LFB is a major factor contributing to occurrence of large porphyry Cu-Au deposits. The sequence of important events, however, commences with sub-crustal generation of oxidised magma and finishes with efficient Cu-Au accumulation by hydrothermal processes at favourable structural sites. The increase in Au-Cu deposit size from small (Copper Hill-Cargo) to world class (Cadia-Ridgeway) indicates the importance of magma composition during this process. The most obvious differences between the Cadia-Ridgeway and New Zealand rocks is that the latter are volcanic in origin and associated with an arc-back arc system. Therefore, they did not form in a tectonic regime suitable for the evolution of porphyries and the focussed movement of hydrothermal fluids during dilatant episodes. As a result, they are not linked to mineralisation despite having Nb-Ta and Nb/Ta variations that are typical of the high oxidation states in Au-prospective magmas of the LFB.

The majority of economic gold deposits in NSW are associated with Ordovician-aged igneous rocks and are examples of the Cu-Au porphyry-skarn-epithermal association commonly developed in convergent margin to orogenic settings. They are among the oldest porphyry Cu-Au deposits in the Pacific Rim region. They are similar to younger deposits in terms of tectonic setting and structure, but the largest are chemically distinct, being associated with shoshonite magmas (Cadia, Ridgeway and Northparkes). The Lachlan Fold Belt (LFB) porphyries are subdivided into four sub-groups based mainly on their age relative to development of the Lachlan Transverse Zone (LTZ) structure. Two subgroups pre-date the LTZ, one group is syn�LTZ and one group post-dates the LTZ. No mineralisation has been found or reported among pre-I.TZ porphyries. but it is common in post- . l Z_ porphyries. Petrographic analysis and microprobe results establish a wide range of primary and secondary features within the Ordovician rocks examined in this study. Cale alkaline to shoshonitic affinities are supported by the variable abundance of primary K-feldspars. Primary mineral phases such as pyroxenes and igneous magnetite provide an indication of fractioning mineral assemblages responsible for igneous trends in magma chemistry. The hydrothermal mineral assemblages documented in these LFB study areas are characteristic of younger Cu-Au Porphyry style mineralisation. As expected, the most pervasive alteration is associated with highly mineralised shoshonitic Ordovician rocks at Ridgeway, and Cadia. the less strongly mineralised calc alkaline Ordovician rocks at Cargo. Copper Ilill and Fairholme. are correspondingly less strongly altered overall. although secondary mineral assemblages are locally abundant. Many varieties of oxides and carbonates are observed at the different study localities. Most of the studied samples conform to igneous chemical trends because they are weakly altered, although post magmatic processes, such as veining, are detectable in certain trends. The K2O enrichment of the studied samples is consistent with subductionmoditied mantle wedge sources. A few effects, such as the high Fe203 contents of some Ridgeway samples, probably reflect porphyry-style hydrothermal alteration processes. Host rocks at the Cadia and Ridgeway are entirely alkalic on the K2O versus SiO2 plot and shoshonitic on the Total Alkalies versus SiO2 plot. Igneous rocks at the other deposits display a range of compositions between low K tholeiites to shoshonites that in some cases reflects multiple igneous suites. The LREE and L1LE enrichments, and HFSE depletions (Nb, Ta and Ti) of the magmas associated with these deposits are characteristics of a subduction-related tectonic setting. They all fall in the volcanic-arc granite and syn-collisional granite field of the Nb-Y tectonic discrimination diagram. Several magma types are identified by differences in the HFSE and REE trends. Differences in the extent and style of magma fractionation are evident in the trace element data. The Ridgeway samples define a wider range of trace element concentrations than the Cadia samples that may indicate a greater extent of fractionation during emplacement of the Ridgeway magmas. Fairholme samples display a high Nh and /If trends that are distinct from the main fields on Zr variation diagrams. Compositional differences between larger Cu-Au deposits, Cadia-Ridgeway and smaller deposits, Copper Ifill, Cargo and Fairholme are evident in terms of Nb-Ta depletion and variation. The smaller deposits show constant Nb/Ta or negative Nb/Ta trends that extend to high Nb. The larger deposits display positive Nb/Ta trends that do not extend to high Nb. This distinction reflects a difference of preferential incorporation of Nb in a mineral phase (magnetite). Comparisons between Cadia-Ridgeway and other shoshonite (altered samples of Bajo de la Alumbrera, Argentina), calc alkaline magmas from New Zealand and rocks from other areas indicate that Nb/Ta is not directly correlated with the shoshonitic classification, K2O vs. SiO2, and that the Cadia-Ridgeway Nb and Ta variation is not the result of alteration. The fact that the weakly altered LFB Capertee shoshonites exhibit a narrow range of Nb and low Nb/Ta suggest the shoshonite trend for the LFB as a whole is a steep one on the Nb/Ta versus Nb plot. The results of this study could provide important information for exploration within the LFB. Only the Cadia and Ridgeway deposits display a wide range of Nb/Ta values and lack the near-horizontal trend seen for other localities associated with smaller deposits. The tectonic evolution of the LFB is a major factor contributing to occurrence of large porphyry Cu-Au deposits. The sequence of important events, however, commences with sub-crustal generation of oxidised magma and finishes with efficient Cu-Au accumulation by hydrothermal processes at favourable structural sites. The increase in Au-Cu deposit size from small (Copper Hill-Cargo) to world class (Cadia-Ridgeway) indicates the importance of magma composition during this process. The most obvious differences between the Cadia-Ridgeway and New Zealand rocks is that the latter are volcanic in origin and associated with an arc-back arc system. Therefore, they did not form in a tectonic regime suitable for the evolution of porphyries and the focussed movement of hydrothermal fluids during dilatant episodes. As a result, they are not linked to mineralisation despite having Nb-Ta and Nb/Ta variations that are typical of the high oxidation states in Au-prospective magmas of the LFB.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia, 2018. / Submitted by Raquel Almeida (raquel.df13@gmail.com) on 2018-05-15T16:26:56Z No. of bitstreams: 1 2018_VictorBotelhoPerezGarcia.pdf: 2313547 bytes, checksum: d593399c348afe0ec7985407648f4b34 (MD5) / Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2018-05-23T10:30:14Z (GMT) No. of bitstreams: 1 2018_VictorBotelhoPerezGarcia.pdf: 2313547 bytes, checksum: d593399c348afe0ec7985407648f4b34 (MD5) / Made available in DSpace on 2018-05-23T10:30:14Z (GMT). No. of bitstreams: 1 2018_VictorBotelhoPerezGarcia.pdf: 2313547 bytes, checksum: d593399c348afe0ec7985407648f4b34 (MD5) Previous issue date: 2018-05-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). / O depósito GT-34, localizado a 12 km a SW da mina Sequerinho, Carajás, norte do Brasil, representa uma ocorrência incomum de Ni relacionado ao sistema Iron-OxideCopper-Gold (IOCG) regional. Ocorre ao longo de uma zona de cisalhamento subvertical de orientação NE-SW marcado por zonas de alteração alcáli-Fe encaixado em granitos a tonalitos. A aleração inicial Na-Mg e alteração Ca pervasiva formam, respectivamente, marialiate-ortopiroxênio e hornblenda-plagioclásio-clinopiroxênio. A mineralização de Ni ocorre na forma de brechas com a matriz rica em pentlandita-pirrotita-apatita e fragmentos arredondados compostos dominantemente por fragmentos da alteração Ca. Veios tardios de alteração K-Fe com magnetita ou hematita (alteração K-Fe (Mt) e alteração K-Fe (Hem), respectivamente) remobilizam parcialmente a mineralização, reprecipitando-a como calcopirita-pirrotita-magnetita (alteração K-Fe (Mt)) e como milerita-pirita-apatita (alteração K-Fe (Hem)). A alteração K-Fe (Mt) ocorre como veios irregulares ricos em flogopita-talco, enquanto a alteração K-Fe (Hem) ocorre como veios bem delimitados com K-feldspato-albita-quartzo-clorita-calcita-epidoto. As características iniciais do fluido associado a alteração Na-Mg precisam ser anidras para a estabilização do ortopiroxênio e de elevada salinidade para formação da marialita. Um fluido imiscível composto por CO2-NaCl é sugerido para a atingir tais características. A presença do ortopiroxênio indica temperaturas >700°C. Estudo experimentais indicam que marialiata não se forma a partir de fluidos ricos em NaCl a pressões >7 kbar a temperatura >700°C. A ausência de quartzo pode ocorrer devido a sua dissolução causada por fluidos ricos em NaCl sob pressões >5 kbar e temperaturas similares, também determinado experimentalmente. Cristais de zircão foram recuperados da alteração NaMg inicial e da alteração tardia K-Fe (Mt) fornecendo uma idade concordante de 2.724±4 Ga, corroborando a formação Neoarqueana do depósito GT-34, similar aos demais depósitos IOCG em Carajás. A temperatura >700°C e pressão entre 5–7 kbar, eventuais fluidos evaporíticos não podem estar presentes, sendo necessário uma fonte magmática. As idades obtidas nesse estudo se sobrepõe a idade do magmatismo bimodal Neoarqueano (2.75-2.70 Ga), suportando uma origem magmática-hidrotermal. As condições determinadas para o depósito GT-34 elevam a temperatura inicial do sistema IOCG de Carajás em pelo menos 200°C com pressões podendo chegar até 7 kbar, tornondo-o a mais profunda ocorrência associada ao sistema IOCG de Carajás conhecida até então. / The GT-34 deposit, which is located 12 km SW of the Sequerinho copper-gold mine, Carajás Province, northern Brazil, represents an unusual Ni occurrence related to a regional Iron-Oxide-Copper-Gold (IOCG) system. It occurs along a NE-SW-trending sub-vertical shear zone marked by progressive alkali-Fe alteration zones hosted in tonalite to granite intrusions. Initial Na-Mg and pervasive Ca alteration forms the unique marialite-orthopyroxene and hornblende-plagioclase-clinopyroxene associations, respectively. Nickel mineralization occurs as breccias in a pentlandite-pyrrhotite-apatiterich matrix with rounded fragments chiefly of Ca-alteration parageneses. Late-stage veins of K-Fe magnetite and hematite (K-Fe (Mt) and K-Fe (Hem)) alterations partially remobilize the mineralization, reprecipitating as chalcopyrite-pyrrhotite-magnetite and as millerite-pyrite-apatite, respectively. Potassium-Fe (Mt) occurs as irregular phlogopitetalc-rich veins, while K-Fe (Hem) occurs as sharp K-feldspar-albite-quartz-chloritecalcite-epidote veins. Initial fluid characteristics associated with Na-Mg alteration require anhydrous conditions for orthopyroxene stability and high salinity for marialite formation. An immiscible CO2-NaCl fluid is therefore associated with such conditions. The presence of orthopyroxene indicates temperatures >700°C. Experimental studies indicate that marialite does not form with NaCl-rich fluid at pressures >7 kbar under such temperatures. The absence of quartz might be caused by NaCl dissolution at pressures >5 kbar, as determined experimentally with the same temperature conditions. Zircon crystal were recovered from the initial Na-Mg alteration and late-stage K-Fe (Mt) alteration yielding a concordant 2.724±4 Ga age, corroborating the GT-34 Neoarchean formation similar to other IOCG deposits in Carajás. At >700°C and 5–7 kbar, an eventual evaporitic fluid source would not be present, making a magmatic fluid source necessary. The age constrains obtained in this study overlaps the bimodal Neoarchean magmatism (2.75-2.70 Ga), supporting a magmatic-hydrothermal origin. Determination of such conditions raises the initial temperature of the Carajás IOCG system at least 200°C and pressure up to 7 kbar, making GT-34 the deepest IOCG-related occurrence known to date for this province.

Student Number : 9210081T - MSc dissertation - School of Geosciences - Faculty of Science / The occurrence of large, massive iron oxide deposits throughout the Bushveld Complex, South Africa, and its associated roof-rocks is well known. The style of mineralisation and the associated alteration exhibits many characteristics of iron oxide-copper-gold (IOCG) type deposits. The contained mineralisation is dominated by iron oxide and fluorite and is accompanied by a diverse polymetallic association, with anomalous fluorite, copper, gold, barite, uranium and LREE. The Ruigtepoort orebody, located in the western Bushveld Complex, is such an example and is surrounded by some 20 smaller occurrences in the upper stratigraphic portions of the Bushveld Complex, all displaying strong structural control. These IOCG bodies occur as narrow veins, hydrothermal breccias, subhorizontal sheets, or as pipe-like intrusions usually utilising pre-existing structures. Set in red Nebo granite, the mineralised core consists of severely chloritised rock that is haloed by progressively less-altered granite. The alteration passes from the chlorite core to more hematite-phyllosilicate-dominated alteration, to sericite-illite-dominated alteration; followed by the relatively fresh country granite. These alteration haloes dissipate rapidly away from the body over only a few metres. Sodic-calcic alteration described in other IOCG is not locally observed. Extensive zones of barren feldspar-destructive alteration exist, including K-metasomatism, sericitisation and silicification. Multiple alteration episodes appear to have occurred, resulting in extensive overprinting and a very complex paragenesis. The primary mineral assemblage consists of Fe-chlorite, fluorite, quartz, hematite, and specularite, with accessory pyrite and chalcopyrite. Multiple generations of hematite, quartz, fluorite and chlorite are also observed. At other localities, the assemblage is dominated by magnetite-actinolite-britholite. Significantly enriched concentrations of Au (2 g/t), Cu (0,45 wt%), Ba, Y and LREE are encountered in the small, mineralised core. A fluid mixing model is proposed characterised by an initial highly-saline, sulphur-poor magmatic fluid which mixed with a lower temperature oxidised, surficial fluid. Structure was probably a significant factor in determining the initial distribution of hydrothermal centres and the overall morphology of the entire system. Subsequently, continuous brecciation, alteration, mineral precipitation and fault activity helped develop the hydrothermal centres into a complex array of variably mineralised, lenticular, pipe-like and irregularly shaped breccia bodies.

This work computationally investigates the partial oxidation of ethylene (i.e. ethylene epoxidation) using periodic Density Functional Theory (DFT) on slab models that represent the catalyst surfaces. The mechanical aspects of the reaction were investigated on silver surfaces, which are industrially applied catalysts, for a wide range of surface models varying from metallic surfaces with low oxygen coverage to oxide surfaces. For comparison, the metallic and oxide phases of copper and gold were also studied. On these surfaces, the reaction paths and the transition states along these paths for the selective and non-selective reaction channels were obtained using the climbing image nudged elastic band (CI-NEB) method. In order to answer the question &ldquo / what is the relation between the surface state and the ethylene oxide selectivity?&rdquo / metallic (100), (110) and (111) surfaces of Cu, Ag and Au / and, (001) surfaces of Cu2O, Ag2O and Au2O oxides were studied and compared. For the studied metallic surfaces, it was found that the selective and non-selective reaction channels proceed through the oxametallacycle (OMC) intermediate, and the product selectivity depends on the relative barriers of the these channels, in agreement with the previous reports. However for the studied metallic surfaces and oxygen coverages, a surface state that favors the ethylene oxide (EO) formation was not identified. The studied Au surfaces did not favor the oxygen adsorption and dissociation, and the Cu surfaces favored the non-selective product (acetaldehyde, AA) formation. Nevertheless, the results of Ag surfaces are in agreement with the ~50% EO selectivity of the un-promoted silver catalyst. The catalyst surface in the oxide state was modeled by the (001) surfaces of the well defined Cu2O, Ag2O and Au2O oxide phases. Among these three oxides, the Cu2O is found not to favor EO formation whereas Au2O is known to be unstable, however selective for epoxidation. The major finding of this work is the identification of a direct epoxidation path that is enabled by the reaction of the surface oxygen atoms, which are in two-fold (i.e. bridge) positions and naturally exist on (001) oxide surfaces of the studied metals. Among the three oxides studied, only Ag2O(001) surface does not show a barrier for the formation of adsorbed epoxide along the direct epoxidation path. Moreover, the overall heat of reaction that is around 105 kJ/mol agrees well with the previous reports. The single step, direct epoxidation path is a key step in explaining the high EO selectivities observed. Also for the oxide surfaces, the un-selective reaction that ends up in combustion products is found to proceed through the OMC mechanism where aldehyde formation is favored. Another major finding of this study is that, for the studied oxide surfaces two different types of OMC intermediates are possible. The first possibility is the formation of the OMC intermediate on oxygen vacant sites, where the ethylene can interact with the surface metal atoms directly. The second possibility is the formation of a direct OMC intermediate, through the interaction of the gas phase ethylene with the non-vacant oxide surface. This occurs through the local surface reconstruction induced by the ethylene. The effect of Cl promotion was also studied. Coadsorption of Cl is found to suppress the oxygen vacant sites and also the reconstruction effects that are induced by ethylene adsorption. Thus, by preventing the interaction of the ethylene directly with the surface metal atoms, Cl prevents the OMC formation, therefore the non-selective channel. At the same time Cl increases the electrophilicity of reacting surface oxygen. The direct epoxidation path appears to be stabilized by coadsorbed oxygen atoms. Thus, we carry the discussions on the silver catalyzed ethylene epoxidation one step further. Herein we present that the EO selectivity will be limited in the case of metallic catalyst, whereas, the oxide surfaces enable a direct mechanism where EO is produced selectively. The role of the Cl promoter is found to be mainly steric where it blocks the sites of non-selective channel.

<p> The mean square displacement spectrum of a single mass defect and that of its neighbours is examined for both a light and a heavy defect to observe the extent of the perturbation of the pure crystal. </p> <p> Nearest neighbour force constant changes for a 3% random distribution of gold defects in a copper host are calculated by fitting to experimental elastic constants for this alloy. The phonon shifts and widths are calculated for the system with various sets of force constant changes, and comparison is made with experiment. </p> / Thesis / Master of Science (MSc)

Les zones de subduction présentent un intérêt majeur en termes de ressources minérales, notamment à cuivre et or. De nombreuses études se sont focalisées sur les mécanismes physico-chimiques de formation de ces minéralisations, mais très peu se sont intéressées aux processus géodynamiques qui contrôlent ces mécanismes. Dans cette étude, j’identifie les processus mantelliques et crustaux, liés à la dynamique tridimensionnelle (3D) de la subduction, qui favorisent la genèse de ces concentrations métalliques. La zone de subduction est-Méditerranéenne présente une évolution tectonique et magmatique complexe, avec de nombreuses données métallogéniques disponibles, ce qui en fait une zone d’étude privilégiée afin d’étudier ces interactions entre subduction et minéralisations. Ce travail a consisté à (1) réaliser un nouveau modèle de reconstructions cinématiques de la région, (2) caractériser la distribution spatiale et temporelle des occurrences magmatiques et minéralisées à partir de ce modèle, (3) mettre en évidence, via une étude de terrain, le contrôle structural de ces minéralisations et (4) apporter des contraintes physiques aux modèles conceptuels alors proposés, à l’aide d’une étude de modélisation numérique thermo-mécanique 3D. Deux provinces métallogéniques ont ainsi été mises en évidence : (1) au Crétacé supérieur, une province riche en cuivre qui s’est développée dans un environnement d’arc et (2) à l’Oligocène-Miocène, une province riche en plomb-zinc puis en or, qui s’est mise en place dans un contexte d’arrière-arc. Ces épisodes fertiles sont contrôlés par le retrait de la zone de subduction et les flux asthénosphériques associés qui permettent l’instauration d’un régime tectonique extensif (ou transtensif) dans la lithosphère, favorisant la genèse de ces systèmes minéralisés. Leur contenu métallique ainsi que leur typologie est alors fonction (1) de l’intensité avec laquelle ces processus influent sur la cinématique de subduction et (2) de l’histoire géodynamique antérieure de cette zone de subduction. / Subduction zones display a major economic interest, in terms of mineral resources, with mainly copper and gold deposits. While many studies focus on ore-forming physico-chemical mechanisms, the control of geodynamic processes on such deposits remains poorly investigated. In this study, I track tridimensional (3D) subduction-related mantle and crustal processes that promote ore genesis. The eastern Mediterranean subduction zone is a relevant study area to explore subduction-mineralization interactions, because of its complex tectonic and magmatic evolution and the large number of available metallogenic data. This work consisted in (1) performing a new kinematic reconstruction model of this region, (2) using this model, characterizing the spatial and temporal distribution of magmatic and ore occurrences, (3) evidencing, on the field, the relations between mineralization and large-scale tectonic structures and (4) providing physical constrains to proposed conceptual models, using 3D thermo-mechanical numerical modeling. Two main metallogenic provinces are evidenced: a late Cretaceous copper-rich and an Oligocene-Miocene lead-zinc- then gold-rich provinces emplaced in an arc and back-arc context, respectively. These metallogenic periods are controlled by the subduction zone retreat and associated asthenospheric flow that results in an extensional (or transtensional) tectonic regime in the overriding lithosphere, promoting ore genesis. Their metal content, as well as their typology then depend on (1) how much these processes affect the subduction kinematics and (2) the past geodynamic evolution of this subduction zone.