The giant Kidd Creek Mine is an Archean Cu-Zn-Ag deposit in the Abitibi Greenstone belt, located in the Superior Province of Canada and is one of the largest known base metal massive sulfide mines in the world with a tonnage of 170.7 Mt (Past production, Resource and Reserve). The massive sulfides in Mine D comprise a number of ore lenses that are interpreted to be the downplunge continuation of the Central orebody from the upper mine. These are referred to as the West, Main, and South lenses. The massive sulfides overlie a silicified rhyolitic unit at the top of a mixed assemblage of rhyolite flows, volcaniclastic sediments and ultramafic flows. The sheared nature of the fragmental units in the hanging wall of the deposit, at depth, illustrates the greater deformation that has occurred than in the upper mine. Metal zonation and the distribution of Cu stringer mineralization suggest that the West and Main lenses may be part of a single massive sulfide body (Main orebody) that has been structurally dismembered. The South Lens is a detached body, separated by late faults. The large Cu stringer zone beneath the West and Main lenses has a thickness of up to 150 metres, and is much broader and structurally remobilized in Mine D partially due to a newly identified series of vertically trending offset faults, that extends along the entire length of the massive sulfide bodies. A number of features of the North, Central and South orebodies in the upper part of the mine (e.g., Se-rich halo around Cu-rich zones) have been recognized in Mine D and provide an important framework for correlating the deep orebodies with the upper levels of the mine. Drilling below the current mine levels indicates that the massive sulfide and Cu stringer zones continue below 10,200 feet (3109 m) and highlight the remarkable continuity of the deposit downplunge with no end in sight. Two main ore suites have been recognized in the upper part of the mine and in Mine D: a low-temperature, polymetallic assemblage of Zn, Ag, Pb, Cd, Sn, Sb, As, Hg, ±Tl, ±W, and a higher-temperature suite of Cu, Co, As, Bi, Se, In, ±Ni. More than 25 different ore minerals and ore-related gangue minerals are present, including Co-As-sulfides, Cu-Sn-sulfides, Ag-minerals, and selenides. The massive ores consist mainly of pyrite, pyrrhotite, sphalerite, magnetite and chalcopyrite, together with minor galena, tetrahedrite, arsenopyrite, and native silver with a quartz and siderite gangue. Despite the high Ag content of the ores, the majority of the massive sulfides are remarkably Au poor except for a local gold zone that has been recognized in the deep mine in association with high-temperature mineralization. The trace elements in the ores exhibit strong zonation and diverse mineralogy. Spectacular albite porphyroblasts, up to 1 cm in size occur in the most Cu-rich ores of Mine D which are coincident with the peak of regional metamorphism and likely represent higher metamorphic or hydrothermal temperatures. Overall the orebodies have remained remarkably similar downplunge. However, unlike the upper part of the mine, pyrrhotite is dominantly hexagonal, only tetrahedrite was observed as the dominant sulfosalt, and magnetite occurs as both blebby porphyroblasts and as abundant intergrowths with sphalerite-chalcopyrite ores and siderite. These characteristics suggest that the deep mine has been subjected to higher metamorphic temperatures, possibly related to depth of burial, and that the original hydrothermal fluids may of had a lower H2S/CO2 and/or higher temperatures.

The North Caribou Greenstone Belt (NCGB) lies at the core the granitoid-dominant North Caribou Terrane (NCT). Two sedimentary assemblages; the Eyapamikama (ELS) and Zeemal-Heaton Lake (ZHA) form the core of the NCGB. Geochemistry of garnets from the orogenic Au deposit at Musselwhite suggest that the auriferous fluids have a contribution of metamorphic fluids and mineralization consisted of prolonged, multi-stage periods. Chemical zoning suggests changes in the influx of chalcophile and lithophile elements and that Au/sulphide ratios during nucleation were lower relative to later growth events. Zircons from the ELS and ZHA suggest a c. 100 My hiatus in the onset of sedimentation, with the ZHA showing younger, “Timiskaming-type” ages. Age distributions from each assemblage reflect proximal, igneous sources. Nd isotopic compositions of the ZHA suggest a mixture of ancient and contemporaneous sources which are similar to external TTG rocks. Deplete mantle model ages of the ZHA rocks indicate a Mesoarchean inheritance.

Les plus anciens gisements d’uranium connus sur Terre sont les gisements de type paléo-placer hôtes de conglomérats à cailloux de quartz d’âge compris entre 3,09 et 2,2 Ga. Ces gisements représentent les reliques de l’ancienne croûte continentale archéenne maintenant érodée. L’origine de leurs concentrations primaires, correspondant à des accumulations de grains détritiques d’uraninite, est toujours sujette à controverse et la nature et les processus de formation des roches sources archéennes demeurent incertains.Ce travail présente l’analyse minéralogique et géochimique détaillée des minéralisations de différents paléo-placers (Witwatersrand en Afrique du Sud, Elliot Lake au Canada et séries Jatuliennes en Russie) ainsi que de granitoïdes archéens et paléoprotérozoïques enrichis en uranium (séries granitiques calco-alcalines à potassiques du craton de Kénéma Man en Guinée, granites tardi-orogéniques du craton de Pilbara en Australie Occidentale, pegmatite peralumineuse de Tanco du Bouclier Canadien et pegmatites à uraninite du Bouclier Baltique en Finlande et Russie). L’étude comparative de ces roches uranifères échantillonnées tout autour du globe prouve à la fois i) l’existence précoce (>3,1 Ga) de granitoïdes différenciés produits par la fusion partielle d’une croûte pré-enrichie tels que des granites peralumineux ou de type S, ii) nécessairement la présence d’un mécanisme permettant de produire ce type de granites comme les zones de subduction ou de collision générées par le mouvement des plaques tectoniques, iii) l’origine magmatique des uraninites thorifères des paléo-placers, iv) la présence d’une atmosphère réductrice avant 2,2 Ga permettant la préservation des uraninites durant leur transport, v) et finalement l’augmentation de l’oxygène libre dans l’atmosphère paléo-protérozoïque à partir de 2,2 Ga provoquant la disparition des paléo-placers uranifères en faveur de l’altération et de l’oxydation des concentrations préexistantes, de la remobilisation de l’uranium et de la formation de dépôts secondaires / The oldest known uranium deposits on the Earth are the paleoplacer-type deposits hosted in quartz-pebble conglomerates from 3.09 to 2.2 Ga in age. These deposits are representative of the ancient Archean continental crust now eroded. The origin of the primary ores corresponding to accumulation of detrital uraninite is still controversy and the nature and forming processes of the Archean source rocks remain uncertain.This work provides the detail mineralogical and geochemical analysis of mineralization from different paleoplacer-type deposits (Witwatersrand in South Africa, Elliot Lake in Canada and the Jatulian series in Russia) and from Archean and Paleoproterozoic U-enriched granitoids (calco-alkaline to potassic granite series from the Kenema Man Craton in Guinea, late-orogenic granites from the Pilbara Craton in West Australia, the Tanco pegmatite from the Canadian Shield and uraninite bearing pegmatites from the Baltic Shield in Finland and Russia). The comparative study of these worldwide uraniferous rocks prove either i) the existence of highly differentiated granitoids produced by the partial melting of a pre-enriched crust as peraluminous and S-type granites in early time (>3.1 Ga), ii) obviously the presence of an effective mechanism to produce such granites as tectonic plate systems with subduction or collisional zones, iii) the magmatic origin of the thorian uraninites in paleoplacers, iv) the efficiency of a reductive atmosphere prior to 2.2 Ga permitting the preservation of uraninite during transportation, v) and finally the rise of the oxygen-free level in the paleoproterozoic atmosphere providing the disappearance of uraniferous paleoplacers in favour of weathering, oxidation of pre-existing concentrations, remobilization of uranium and formation of secondary deposits

Les découvertes de systèmes hydrothermaux marins ont permis de dire qu'ils réunissaient les conditions favorables à l'apparition des premières formes de vie car des concentrations appréciables en N2, CO2, H2S, CH4, C2H6 et C3H8 ainsi que des quantités détectables (10-9 mol) de n-alcanes de poids moléculaire élevé (C16-C29) ont été mesurées dans les fluides hydrothermaux de la ride médio-Atlantique. Les premières formes de vie étaient sans doute des êtres microbiens simples et unicellulaires qui ont pu trouver dans les composés organiques l'énergie nécessaire à leur évolution. Les systèmes hydrothermaux marins peuvent avoir constitués un environnement favorable à l'apparition de la vie car ces systèmes sont caractérisés par des fumeurs noirs et des fumeurs blancs avec un écosystème indépendant de l'énergie solaire où vivent les organismes les plus primitifs trouvés dans les environnements actuels, les hyperthermophiles. Ces arguments sont très importants en ce qui concerne les conditions qui régnaient à l'Archéen. Les systèmes hydrothermaux Archéens sont les seuls environnements où la vie primitive a pu être protégée des impacts des météorites et de la vaporisation partielle de l'océan. Ces systèmes sont compatibles avec l'origine et l'évolution de la vie. Les études expérimentales, sur la synthèse et la stabilité des composés prébiotiques dans des conditions hydrothermales sont couplées aux études théoriques en thermodynamique permises par les travaux de mesure expérimentales. L'origine abiogéniques des composés organiques azotés dans les conditions hydrothermales est primordiale dans l'histoire de la Terre / Hydrothermal Systems discovery involve it gather favorable conditions to act for the appearing of the first living shape, because significant concentrations in N2, CO2, H2S, CH4, C2H6 and C3H8 and detectable quantities (10-9 mol) of heavy weights n-alcanes (C19-C29) were measured in hydrothermal fluids of the mid-Atlantic ridge. The first living shape were without no doubt simple or unicellular microbes being which finding in organic compounds the satisfying energize for their evolution. Hydrothermal systems could have constitute a favorable environment for the appearing of life because these systems are characterized by black smokers and white smokers with an ecosystems independent of solar energize where the most primitives organisms live, found in actual environments, the hyperthermophiles. These arguments are very important concerning the conditions ruling in Archean. The hydrothermal systems of Archean were the only environment where the primitive life was protect of meteoritic impact and partial vaporization of the ocean. These systems are compatible with origin and evolution of life. The experimental study, on the synthesis and stability of prebiotic compounds in hydrothermal conditions are gathered with thermodynamic studies permit by the works of experimental measures. Abiogenic origin of nitrogen organic compounds in hydrothermal conditions is primordial in the history of the Earth

Les komatiites sont des roches volcaniques ultrabasiques caractéristiques de l'Archéen et du Protérozoïque. Nous présentons ici une étude de la pétrogénèse des komatiites de la ceinture de Barberton en Afrique du Sud. Celle-ci comprend un modèle de fusion original bâti à partir de la constatation expérimentale qu'à très forte profondeur (P>13GPa), les liquides komatiitiques sont plus denses que la péridotite solide et donc ne peuvent pas s'échapper de leur source. Nous proposons que la fusion des sources des komatiites de Barberton ait commencée à une pression supérieure à 13GPa dans le manteau mais que les liquides produits soient restés retenus dans les sources jusqu'à ce que celles-ci n'aient dépassé, au cours de leur remonté, la limite de densité à laquelle le liquide devient moins dense que le résidu solide (à ~13GPa). Alors, les liquides auraient commencé à quitter leur source, d'abord doucement, puis de plus en plus vite alors que la différence de densité entre le liquide et le résidu solide s'accroissait. Les komatiites appauvries en Al, qui sont les plus abondantes à Barberton, auraient été produites par les premiers liquides qui ont quitté la source peu après le franchissement de la limite de densité. Les liquides qui quittèrent ensuite cette même source à moins forte pression, auraient formé les komatiites enrichies en Al. Les komatiites non-appauvries en Al auraient été produites par le même mécanisme mais par des sources de température potentielle plus forte. Une étude parallèle des trois systèmes isotopiques Sm-Nd, Lu-Hf et Re-Os nous a permis de contraindre l'histoire chimique des sources de komatiites de Barberton. Les systèmes Sm-Nd et Lu-Hf indiquent des sources appauvries et le système Re-Os une source chondritique. Nous proposons que les sources des komatiites aient été appauvries par l'extraction de croûte, mais qu'ensuite, leur composition en Re et Os aient été ramenées à leur valeur chondritique par le dernier épisode massif d‟accrétion de la Terre : « le vernis tardif ». / Komatiites are ultrabasic volcanic rocks characteristic of the Archean and Proterozoic eras. In this study, we investigate the petrogenesis of the komatiites of the Barberton greenstone belt in South Africa. We present an original melting model developed on the experimental observation that, at great depths (P>13GPa), komatiitic liquids are denser than solid peridotite, and therefore cannot escape their source. We propose that the fusion of the sources of Barberton komatiites began at pressures greater than 13GPa in the mantle but that the liquids produced were retained in the sources until they crossed, during their ascent, the density limit at which the liquid becomes less dense than the residue (at ~13GPa). Then, the liquids would have started to escape their source, slowly at first, and faster and faster as the density contrast between liquid and solid residue increased. Al-depleted komatiites, which are the most common type in the Barberton belt, were produced as the first liquids that escaped the source soon after they crossed the density limit. The liquids that later escaped the same source at shallower depth, formed Al-enriched komatiites. Al-undepleted komatiites were produced by the same mechanism but from hotter sources. From complementary studies of the three isotopic systems Sm-Nd, Lu-Hf and Re-Os, we constrained the chemical history of the sources of Barberton komatiites. The Sm-Nd and Lu-Hf systems indicate depleted sources whereas the Re-Os system indicates a chondritic source. We propose that the sources of the komatiites had become depleted by the extraction of early crust, and that their compositions in Re and Os were then reset to their chondritic value by contamination by material from the last massive accretion stage of the Earth: “the late veneer”.

L’enregistrement géologique de l’Hadéen et de l’Eoarcheén étant limité, la composition et l’évolution de la Terre silicatée au cours de ces périodes reste très débattue et peu connue. La première évidence d’un événement de différenciation précoce du manteau provient de l’étude du système éteint 146Sm-142Nd. En effet, les excès en 142Nd détectés dans les échantillons âgés de 3.7 milliard d’années (Ga) d’Isua (Sud-Ouest du Groenland) par rapport aux échantillons modernes, impliquent que leur source fût appauvrie en éléments incompatibles et formée durant l’Hadéen. Dans cette thèse nous avons étudié les systèmes isotopiques 146Sm-142Nd, 147Sm–143Nd et 176Lu–176Hf d’une collection d’échantillons mantelliques âgés de 3.8 Ga, 3.7 Ga, 3.4 Ga et 3.3 Ga et provenant de différentes unités géologiques de la région d’Isua. Cette collection d’échantillons couvre ~500 millions d’années de l’histoire précoce terrestre et a permis d’apporter des informations précieuses sur l’évolution de la composition et la dynamique du manteau au début de l’histoire de la Terre. Nous avons démontré un découplage des systèmes isotopiques de longue-vie Sm-Nd et Lu-Hf dans la source des roches âgées de 3.7 Ga, alors que ces deux systèmes sont généralement couplés lors des processus magmatiques de basse pression. Pour expliquer ce découplage, nous proposons que la source des laves d’Isua avait une origine profonde (manteau inférieur). Nous avons également confirmé les excès en 142Nd dans ces échantillons, ce qui implique que leur source a été appauvrie en éléments incompatibles dans les premiers 100 Ma de l’histoire de la Terre. L’évènement responsable de la différenciation du réservoir appauvri aurait également formé un réservoir complémentaire enrichi, enregistré dans les roches de 3.4 Ga. Cependant, les échantillons de 3.3 Ga ne montrent pas d’anomalies en 142Nd par rapport aux standards terrestres. Ceci suggère que les hétérogénéités chimiques hadéennes aient résisté au mélange convectif pendant plus de 1 Ga, puis qu’elles aient disparu et soient remélangées au reste du manteau à 3.3 Ga. Le mélange à 3.3 Ga pourrait aussi s’expliquer par les processus de subduction initiées par la tectonique de plaques récemment proposée comme ayant démarrée autour de 3.2 Ga. / The composition and the evolution of the silicate Earth during the Hadean-Eoarchean is widely debated and largely unknown due to the limited geological record. The first undisputable evidence for a very early differentiation of the mantle came from the extinct 146Sm-142Nd chronometer. The 142Nd excesses measured in 3.7 billion year (Ga) old rocks from Isua (Southwest Greenland) relative to modern terrestrial samples imply their derivation from a depleted mantle formed in the Hadean. We have studied 146,147Sm–142,143Nd and 176Lu–176Hf isotope systematics in 3.8 Ga, 3.7 Ga, 3.4 Ga and 3.3 Ga mantle-derived samples from different tectonic domains of the Isua region. This dataset covers ~ 500 million years of the early history of the Earth and revealed precious information about the compositional evolution and dynamics of the early Earth mantle. Combined Lu-Hf and Sm-Nd of the 3.7 Ga Isua samples revealed that these isotopic systematics were decoupled, suggesting a deep-seated source for the Isua lavas. We have further expanded the dataset and confirmed the 142Nd excesses in these rocks, implying that their source was depleted and differentiated during the first 100 Ma of Earth’s history. The differentiation event that created this early-depleted reservoir had to also form a complementary enriched component. We have found the first evidence for this reservoir recorded in the 3.4 Ga samples that yielded negative 142Nd anomalies. However, the 3.3 Ga analyzed samples showed no resolvable 142Nd anomalies compared to terrestrial Nd standards. This suggests that the Hadean heterogeneities were likely isolated for more than 1 Ga before being completely rehomogeneized by 3.3 Ga. The remixing by 3.3 Ga could have been achieved by subduction processes due to the onset of modern plate tectonics at ~3.2 Ga, as proposed by other recent studies.

No description available.

The North Caribou Terrane forms the core of Superior Province and records a protracted history of crustal growth and modification. At the centre of the North Caribou Terrane, lies the North Caribou greenstone belt, which is surrounded by granitoids of diverse compositions and ages. This study reports whole-rock geochemistry, zircon and titanite geochronology, and hornblende geobarometry on these plutonic rocks. Although zircons as old as 3132 ± 7 Ma were found, the main magmatic pulse occurred between 2880 and 2830 Ma, and geobarometry indicates tectonic thickening during this period. This was followed by widespread hydrothermal alteration and limited magmatism from 2760 to 2680 Ma, and shallow, brittle-ductile intrusions at circa 2630 Ma. From 2730 to 2630 Ma, intrusions were emplaced at increasingly shallow crustal levels. All of the rocks, except for the youngest pegmatitic intrusions, show similar patterns in major and trace elements, with a general trend toward more evolved compositions through time. These patterns indicate that the granitoids record mostly reworking of early intrusions, which is also consistent with patterns observed in the geochronology.

The Saglek-Hebron Gneiss Complex (SHC) is located in Northern Labrador within the Nain Province. It has recorded multiple magmatic events over more than 1 billion years, making it ideal to study the evolution of mantle-derived rocks through time. Here we present a 147Sm-143Nd isotopic study focussing on the different generations of mantle-derived rocks in the SHC. A total of 83 samples have been analysed, including: 1) mafic metavolcanic rocks; 2) ultramafic rocks divided into two distinct groups (a Fe-rich group enriched in incompatible elements and more depleted ultramafic rocks with lower Fe contents); 3) mafic metamorphosed dikes called the Saglek dikes; and 4) undeformed mafic dikes. Some samples exhibit evidence of post-magmatic geochemical and isotopic disturbance but only the least disturbed samples have been considered to constrain the timing of formation of the different lithologies and the isotopic composition of their mantle source. The mafic metavolcanic rocks combined with the co-genetic low-Fe ultramafic rocks yield an isochron age of 3819 ± 190 Ma (MSWD=34, n=25) with an initial εNd value of +2.3 ± 0.6. The high-Fe enriched ultramafic rocks yield a younger age of 3433 ± 220 Ma (MSWD=10.4, n=10) with an initial εNd= +1.8 ± 0.5. The two generations of mafic dikes appear to have been emplaced in the Mesoarchean and the Neoarchean. The Saglek dikes yield an isochron age of 3565 ±120 Ma (MSWD=1.17, n=10) with an initial εNd value of +1.7 ± 0.1, while the Sm-Nd isochron age for the undeformed mafic dikes is 2694 ±79 Ma (MSWD=3.2, n=21) with an initial εNd value of +1.7 ± 0.1. All generations of mantle-derived rocks yield positive initial εNd values, where only the Eoarchean rocks display an initial Nd isotopic composition similar to the depleted mantle. The Mesoarchean ultramafic rocks, Saglek dikes and Neoarchean mafic dikes display almost identical initial εNd values, despite an age difference of ~800 Ma. This could suggest the contribution of distinct mantle sources or, if all generations of mantle-derived rocks in the SHC were produced from the same mantle source, it implies that this source evolved with a nearly chondritic Sm/Nd ratio for almost the whole Archean Eon. The fact that the initial isotopic compositions of the mantle-derived rocks appear to deviate from the depleted mantle with time, could also suggest an increasing interaction with older evolved crust.

<p> The Archean pyroclastic conglomerate studied has six clast types which can be condensed to four clast families based on lithology. The quartz clasts have an average strain of X:Y:Z=1.21:1:0.55 while the pumice clasts have an average strain of X:Y:Z=1.27:1:0.47. The difference is strain between these clast families can be attributed to their different viscosities. The quartz clasts have an assumed viscosity ratio between the clasts and the matrix of unity and are taken to represent the strain in the rock as a whole. The sulphide and black clasts have strain ratios much higher than the quartz because of recrystallization of the sulphide and cleavage formation effecting the black clasts.</p> <p> The sedimentary structure of the deposit and its position between mafic pillow basalts indicate that the deposit is a result of the deposition of a subaqueous pyroclastic debris flow in a proximal environment.</p> / Thesis / Bachelor of Science (BSc)