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This thesis presents the results of a detailed study of the mineralogy and paragenesis of gold at the Sunrise Dam gold deposit. The Sunrise Dam mine is the largest gold deposit in the Archean Laverton Tectonic Zone of the Eastern Goldfields Province, Yilgarn Craton, Western Australia. A number of previous studies have established the geology, geochemistry and geochronology, but the nature of the gold mineralogy and distribution has remained poorly characterized. Mineralogical studies have established a paragenetic sequence consisting of five hydrothermal stages (D1, D2, D3, D4a and D4b) which are generally in accord with the major deformation events at Sunrise Dam gold deposit. The D4a stage was the dominant episode of Au deposition, followed, in importance by the D4b stage, which is characterized by more diverse ore mineralogy including base metal sulfides, sulfosalts, and telluride minerals. Based on EPMA results, native gold in D4a stage has higher purity, with a small range of Ag variations (fineness 923 ~ 977, average 945), than that of the D4b stage (fineness 596 ~ 983, average 899), in which fineness values decrease systematically in accord with mineral paragenesis, reflecting that gold deposition was from a progressively compositionally evolving hydrothermal fluid with respect to Au/Ag ratios. The occurrences of As-rich pyrites are restricted to steeply-dipping ore bodies, which are most likely structurally connected at various level by channel ways through which As-rich (D4a) hydrothermal fluid migrating upward. There is a systematic variation in composition of the tetrahedrite-group minerals ranging from Sb to As end-members with highly variable Zn:Fe ratios, which correlates with the later paragenetic stages (D3, D4a, and D4b) and mineral associations. The composition of the tetrahedrite-group minerals is useful as a petrogenetic indicator of the evolution of the hydrothermal mineralizing systems with time. A total of thirteen telluride mineral species, including two unnamed phases, were identified in the D4 veins. Among them nagyágite, the complex Pb-Sb-Au tellurosulfide is most abundant. The deposit is the second occurrence of this mineral in the Yilgarn Craton. Compositionally, nagyágite from Sunrise Dam conforms to ideal stoichiometry, with negligible As content and Au/(Au+Te) ratio of 0.325. The diverse mineralogy of the post-D4 veinlets relative to the host veins is attributed to small-scale reaction fronts established along zones of replacement. The presence of Au-Ag tellurides in D4 veins and the character of their breakdown products have implications for the gold recovery as well as for the genetic interpretation of the deposit. During the D4b stage, Au-richer telluride and Au-richer native gold mineralization formed earlier than Ag-(Au)-telluride and Ag-richer gold mineralization. Values of f(Te2) and f(S2) for the early telluride assemblages were determined at 300°C to be -10.7 to -7.8 (log fTe2) and 11.4 to -8.6( log fS2 ). The Au content of arsenian pyrite and arsenopyrite from four mineralizing stages (D1, D3, D4a and D4b) was measured using in-situ LA-ICP-MS. The average Au concentration is 44.5 ppm in pyrite (n = 224) with maximum value of 3,067 ppm, and 1,483 ppm in arsenopyrite (n = 35) with maximum value of 5,767 ppm, which are the highest concentrations reported for the Yilgarn Craton. The concentrations of invisible Au in arsenian pyrite at Sunrise Dam varies with mineralizing events, mineral paragenesis, and textural type. Gold is strongly enriched in D4a stage pyrite (average 80.8 ppm) and to a lesser extent in D4b pyrite (average 16.8 ppm). Pyrite from D1 (average 3.55 ppm) and D3 (average 2.96 ppm) show much lower levels of Au enrichment. The presence of metallic Au below the Au solubility limit in the Sunrise Dam pyrite is interpreted as evidence of an epigenetic origin for Au mineralization. Small-scale remobilization during dissolution-reprecipitation (D4a) and recrystallization (post-D4b) processes resulted in the Au enrichment and the upgrading of Au during successive hydrothermal events in the deposit. The speciation of Au at Sunrise Dam and the exceptional size of the deposit are the result of multiple fluid flow and multiple Au-precipitating mechanisms over a single plumbing system.

Au Maroc, de nombreux filons à Pb-Zn-Ag sont encaissés dans des séries paléozoïques recoupées par des granitoïdes tardi-varisques. L'association spatiale de ces filons avec ces intrusions magmatiques a souvent été interprétée comme la preuve d'un lien génétique entre la mise en place des granitoïdes et l'hydrothermalisme minéralisateur. Toutefois, des observations récentes permettraient d'envisager que ces minéralisations puissent être post-hercyniennes, remettant en cause les modèles génétiques, et donc les stratégies d'exploration de ces métaux. Le district polymétallique de Tighza-Jbel Aouam (Maroc central) où des minéralisations à Pb-Zn-Ag sont concentrées autour de petits stocks granitiques est un site privilégié pour étudier les relations spatio-temporelles entre les granitoïdes et les minéralisations associées. Les objectifs de la thèse ont donc été : (i) d'approfondir la minéralogie des minéralisations, (ii) d'utiliser les méthodes géochronologiques les plus pertinentes pour dater les minéralisations, (iii) d'étudier les transferts magmas-fluides-métaux depuis les zones profondes (manteau, croûte inf.) vers les zones les plus superficielles de la lithosphère, à l'aide de traceurs géochimiques. Les stocks et dykes granitiques de Tighza ont été analysés et datés par U/Pb sur zircons. Ces roches appartiennent à une lignée calco-alcaline potassique et les datations mettent en évidence trois évènements magmatiques et hydrothermaux associés: (i) entre 320 et 300 Ma, mise en place de quelques dykes et des stocks granitiques ; (ii) entre 300 et 280 Ma, mise en place d'un pluton, actuellement non affleurant, accompagné par un hydrothermalisme responsable de la formation d'une auréole de métamorphisme hydrothermal, et du développement de minéralisations à W-Au ; (iii) entre 280 et 240 Ma, mise en place d'un réseau important de dykes NE-SW, accompagné par un hydrothermalisme minéralisateur en Pb-Zn-Ag caractérisé par une altération à chlorite-muscovite-calcite des métasédiments encaissants. L'étude détaillée des paragenèses des filons à Pb-Zn-Ag a permis d'établir le caractère pulsatoire de la précipitation des minéralisations. Quatre paragenèses successives ont été identifiées : (P1) stérile à sidérite ± quartz ; (P2) à calcite ± ankérite + sphalérite + galène ± sidérite ± quartz ± calcédoine ; (P3) à sidérite + sphalérite + galène ± quartz ; (P4) stérile à quartz + calcite + pyrite. Ces assemblages minéralogiques synchrones s'accompagnent de minéraux accessoires à éléments des terres rares (monazite, xénotime, synchisite), responsables des hautes teneurs en REE des carbonates de gangue (≃ 700 ppm). Des monazites d'un filon à Pb-Zn-Ag ont pu être datées par Th/Pb à 255 ± 15. L'étude des sources des métaux (isotopes Pb) indique que le plomb des minéralisations Pb-Zn-Ag provient du lessivage de la croûte supérieure. L'étude des sources des fluides minéralisateurs en Pb-Zn-Ag indique une origine crustale (isotopes He, Ar), avec un fort effet tampon par les schistes encaissants les minéralisations (isotopes C, O). Les fluides minéralisateurs en W-Au, sont eux issus d'un mélange entre une source météorique et une source mantellique (isotopes He, Ar), et ont donc une origine distincte du système à Pb-Zn-Ag. Le gisement polymétallique de Tighza-Jbel Aouam est donc caractérisé par le télescopage de plusieurs épisodes magmatiques et hydrothermaux guidés par un accident d'échelle lithosphérique et conduisant à la formation : (i) de minéralisations W-Au mésothermales pouvant être assimilées à un type porphyre, suivies pas (ii) des minéralisations à Pb-Zn-Ag épithermales. Ces épisodes magmatiques et métallogéniques s'étalent sur une durée de près de 80 Ma à la fin de l'orogenèse varisque, et caractérisent parfaitement le contexte post-collisionnel de cet orogène, notamment les effets associés au réequilibrage thermique de la croûte pendant la période permo-triasique et le prérifting Atlantique. / In Morocco, many Pb-Zn-Ag vein-type deposits are hosted in paleozoic series crosscut by variscan granitoids. The spatial association of these veins with the magmatic intrusions has often been interpreted as evidence of a genetic link between the granitoids emplacement and the mineralizing hydrothermal event. However, recent data allow to consider a late-variscan emplacement of these mineralizations. Genetical models must thus be reviewed, as well as the exploration of these base metals strategy. The polymetallic district of Tighza-Jbel Aouam (Central Morocco), were Pb-Zn-Ag vein-type deposits are located around small granitic stocks, has been selected to study the spatial and temporal relationships between granitoids and associated mineralizations. The aims of this work have been: (i) to go further into the mineralizations mineralogy, (ii) to use appropriate geochronological methods to date the mineralizations, (iii) to study the magma-fluids-metals transfers from the deeper areas (mantle, deep crust) to the upper lithosphere, using geochemical tracers. Granitic stocks and dykes of Tighza have been analyzed and dated using U/Pb method on zircons. These rocks belong to a high-K calc-alkaline association and datations show three magmatic and associated hydrothermal events: 320 to 300 Ma, stocks with few dykes emplacement; 300 to 280 Ma, pluton emplacement with associated hydrothermal event and responsible for a hydrothermal metamorphic halo, mineralizing the W-Au ore; (iii) 280 to 240 Ma, NE-SW dykes network emplacement, associated with a Pb-Zn-Ag mineralizing hydrothermal event, characterized by a chlorite-muscovite-calcite alteration of the hosting metasediments. The detailed study of Pb-Zn-Ag veins paragenesis showed the pulsated character of the mineralization precipitations. Four successive paragenesis have been identified: (P1) siderite ± quartz; (P2) calcite ± ankerite + sphalerite + galena ± siderite ± quartz ± chalcedony; (P3) siderite + sphalerite + galena ± quartz ; (P4) quartz + calcite + pyrite. These synchrone paragenese are associated with REE-minerals (monazite, xenotime, synchisite) responsible for the high amount of REE in the gangue carbonates (≃ 700 ppm). Some monazites from a Pb-Zn-Ag vein have been dated at 255 ± 15 Ma using the Th/Pb method. The metals source study (lead isotopes) shows that the Pb of Pb-Zn-Ag mineralizations come from the upper crust leaching. The fluid sources study of Pb-Zn-Ag veins indicates a crustal origin (He, Ar isotopes) strongly buffered by the hosting shales (C, O isotopes). W-Au mineralizing fluids are stemming from a mixing of meteoric and mantellic fluids (He, Ar isotopes). W-Au and Pb-Zn-Ag are thus distinguished mineralizations. The polymetallic district of Tighza-Jbel Aouam is thus characterized by the superposition of several magmatic and hydrothermal events controlled by lithospheric scale leap, leading to the formation of: (i) mesothermal W-Au deposit which can be considered as a porphyry-type mineralization; (ii) epithermal Pb-Zn-Ag mineralization. These magmatic and metallogenic events last over 80 Ma after the end of the varican orogenesis, and characterize the post-collisional context of this orogen, in particular the effects of the thermal balance of the crust during the permo-triassic period and the Atlantic pre-rifting.

Banded iron formations (BIFs) are iron oxide- and silica-rich chemical sedimentary rocks and the principal source of high-grade (HG) iron ore. Magnetic survey methods are commonly applied in the exploration for BIF-hosted iron ore deposits but the interpretation of total magnetic intensity (TMI) data is often complicated by the presence of strong remanent magnetization and anisotropy of magnetic susceptibility (AMS). This study evaluated a tri-axial fluxgate vector magnetometer system for ground-based high-resolution mapping of BIF-hosted HG iron ore deposits at a 16 ha site near Mary River, Baffin Island. Magnetometer orientation was measured using a MEMS (Micro Electro-Mechanical System) accelerometer and dual D-GPS receivers. 12-oriented block samples were collected for analysis of rock magnetic properties and supplemented with outcrop measurements using a hand-held susceptibility probe. The large (3 Gauss) dynamic range of the tri-axial vector magnetometer permitted mapping of HG magnetite ore zones, with TMI in excess of 400,000 nT. A 20 m-wide W-E trending HG zone and a narrow (<10 m) BIF zone were identified in RMV maps with distinctive dipole signatures. Within the HG zone a northwest-southeast oriented magnetic fabric was defined by linear magnetic lows that offset the strike of the HG ore zone and were interpreted as brittle faults or shear zones. The RMV orientation indicated the presence of strong bedding parallel magnetization, while its signal amplitude showed a wide variation between ore types and provided basis for ore grade differentiation. Paleomagnetic measurements revealed high Q ratios for hematite ores and strong AMS for BIF. The results from Mary River demonstrate that remanence and AMS effects are important in BIF-hosted iron ores and cannot be neglected in magnetic interpretation and inversion modelling of magnetic source bodies. / Thesis / Master of Science (MSc)

<p> Sulphur isotope data from coexisting sulphides and sulphates from the 120m level of the Shangtancen ore body of the Taolin Pb-Zn ore deposit have been used to estimate the temperatures of sulphur mineral precipitation. The data indicate that sulphide was the dominant species in solution at both high and low temperatures. The data also show that the 𝛿34S value of total sulphur in solution was close to zero at high temperatures, but had low negative values (about -6.7‰) at low temperatures. This is interpreted in terms of the effects of mineral precipitation on the isotopic 34 composition of the solution. The decrease of the 𝛿34S value of the total sulphur with decreasing temperature was brought about because the removal from the system, by precipitation, of isotopically heavy sulphate exceeded the removal from the system, by precipitation, of isotopically light sulphide.</p> / Thesis / Bachelor of Science (BSc)