Дисертації з теми "Geochemical alteration"

Discoveries of porphyry copper deposits (PCDs) in British Columbia have declined over the past 20 years. Undiscovered PCDs are predicted to occur in the Intermontane Belt, an assemblage of volcanic arc terranes considered important for hosting large porphyry deposits. The Deerhorn Cu-Au porphyry, located within this belt, is covered with up to 60 m of undisturbed moraine. Detailed regolith mapping based on a new classification scheme for BC, combined with aqua regia and deionised water assays, sequential leaching, physicochemical measurements and hydrocarbon analysis, was undertaken to determine the response in the till to buried mineralisation. Geochemical relationships dependent on the regolith type were identified and are particularly evident in organic rich areas. To minimise background noise, data analysis was constrained to the dominent regolith unit: the undisturbed moraine (DrM), resulting in enhanced anomaly identification. Regolith mapping in advance of a soil survey can therefore allow targeted efficient sampling. Normalisation to organic carbon (Corg) to counteract the influence of organic matter on trace element variability resulted in anomalous response for elements As, Cs, Cu, Mo, Tl, U and W by conventional aqua regia on a 180-micron fraction B-upper-horizon soil. The response for six of these elements is peripheral to mineralisation in the surface environment. Multi-element evaluation is superior for mineralisation detection than individual element evaluation. Light hydrocarbon results indicate a surface response with a distinct depletion over mineralisation. Sequential leaching on selected anomalous Cu samples indicates that an aqua regia extraction was the optimal first choice for anomalous Cu detection. Copper-Fe-oxide-bearing grains interpreted as oxidised sulphides were recovered from an anomalous Cu-bearing sample and confirm a contribution of glacial clastic transport. Visual screening for clastic fragments allows a reprioritisation of anomalous response. Copper isotope results do not support Cu-ion migration from the buried mineralisation, but instead support a clastic contribution. Anomaly formation is interpreted as a combination of clastic transport, ionic migration of H⁺, vegetation uptake and surface redistribution.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

The Pozzolane Rosse ignimbrite [PR] (457±4 ka) in the Alban Hills Volcanic District, Rome, Italy was exposed ~ 40 ka prior to a subsequent volcanic event which coverd it entirely. XRF, XRD, and clay separation results from PR samples from INGV and CA1 boreholes and Castel di Leva quarry show evidence of paleopedogenesis. All locations display loss of base cations, loss of K is consistent with XRD datat showing dissolution or alteration of leucite to analcime. Accumulation of Al and high L.O.I. support XRD evidence of 1:1 clay species at upper depth. Data suggest alteration extent can be determined by geochemistry. Hydrothermal alteration is assessed from geochemistry showing significant leaching of major and trace elements, primary mineralogy loss and iron sulfide and sulfate mineral development. Deep samples of PR may show groundwater influenced alteration with the presence of expandable 2:1 clays, zeolites, and possible mixing with the underlying Vallerano Lava.

Abstract Orogenic gold deposits from the Reefton goldfield in New Zealand hosted in Ordovician metasediments of the Greenland group have produce 67 tons of gold before 1951. The Blackwater mine in Waiuta account for about 1/3 of the gold production at Reefton prior 1951. The ore system at Blackwater consist of NE trending steeply dipping gold-bearing quartz veins (Birthday reef) occurring in faulted, sheared and folded alternating sequence of sandstone-mudstone metamorphosed to low greenschist facies and hydrothermally altered proximal to distal from the quartz vein. Host rock and ore forming fluids interaction resulted in a systematic change in the mineralogy and geochemistry of the wallrock developing a distinctive footprint of the ore system. The mineral assemblage subsequent to hydrothermal alteration is formed by quartz veining, chlorite, carbonates (minor calcite-dolomite-ankerite-siderite), albite, K-Mica and composite quartz-carbonate veining, carbonates spotting, pyrite, arsenopyrite, chalcopyrite, cobaltite, galena and in a lesser extent ullmannite, gersdorffite, pentlandite, millerite and sphalerite. Mass balance calculation based on geochemical data obtained by ultra-low detection analysis with a detection limit in part per trillion of Au, As and Sb provide new insight in the geochemical footprint of the ore system at Blackwater. A clear zone of roughly 40 meters (20 meters above and below the birthday reef) is enriched in Au, As and Sb up to respectively 6806%, 605% and 891% compared to the un-mineralised protolith. Furthermore, mass changes in K2O and Na2O indicate a consistent decrease in Na and increase in K in the vicinity of the Birthday reef reflecting the replacement of albite by K-mica. This is corroborated by pattern of alkali alteration index Na/Al for albite and 3K/Al for K-Mica showing similar trend. Carbonation and de/-hydration index also exhibits peaks in samples adjacent to the Birthday reef, though carbonation index is also influenced by carbonates content in the protolith or late carbonation that may not related to gold mineralisation. Using the indicators above-mentioned it is possible to define the mineralogical and geochemical “footprint” for the ore system in the host rock allowing to use this footprint as a tool for mineral exploration for orogenic gold deposits similar to Blackwater. Given that the geochemical footprint of orogenic gold deposit such as Blackwater is significantly wider than the economically viable part of the deposit defining the footprint of the ore system offers the potential for vectoring from sub-economic mineralisation towards higher-grade ore that is economically viable.

A petrographic, geochemical, and molecular assessment was performed on a series of Illinois Basin coal samples that were collected at various distances from a Permian-age igneous dike. Standard coal characterization techniques such as vitrinite reflectance, proximate, and ultimate analyses provide valuable insights to maturation pathways experienced by rapidly heated coals. These techniques were coupled with reflectance micro-FTIR and KBr-FTIR analysis to provide a deeper understanding of the molecular changes that occur in the coal structure during relatively short-lived, intensive heating events. With increasing proximity to the contact with the dike, coals and coals macerals exhibit increased maturation on both petrographic and molecular scales. KBr-FTIR spectra were collected to distinguish bulk trends expressed in coals with increasing maturity, whereas reflectance micro-FTIR spectra were collected to analyze characteristics of vitrinite macerals in-situ. With increasing proximity to the intrusion, coals have higher mean random vitrinite reflectance values (Rr) within the dike alteration zone. Liptinite macerals are not distinguishable at reflectances equal to or higher than 1.36%, and coking textures are developed within 2 m of the intrusion. Geochemical data indicate an overall loss of H, O, and N and an increase in C approaching the dike. Carbonate minerals contribute significantly to geochemical data, specifically volatile matter (VM), C content, and O content. Even after carbonate removal with HCl, coals have higher VM contents at high rank than expected compared to normal coalification trends. When plotted on a van Krevelen diagram or Seyler chart, intruded coals follow different coalification trends than coals matured through normal burial metamorphism. FTIR analysis shows increased aromaticity with rank, with the ratio of the aromatic CHx band at 3100-3000 cm-1 versus the aliphatic CHx band at 3000-2800 cm-1 (AR1), and the ratio of the aromatic out-of-plane deformation band at 900-700 cm-1 versus the aliphatic CHx band (AR2) becoming larger with increasing Rr. Within the 3000-2800 cm-1 bandwidth, there is an increase in the area under the asymmetric CH3 peak at ~2960 cm-1 relative to the asymmetric CH2 peak at ~2920 cm-1 with increased rank. The overall intensity of the aromatic out-of-plane deformation modes at 900-700 cm-1 increase relative to aliphatic CHx bandwidth response at high rank as well. This trend is much more traceable in micro-FTIR spectra, which avoids the influence of mineral matter bands in the 900-700 cm-1 range. Within the 900-700 cm-1 band, the overall intensity of the ~750 cm-1 peak relative to the ~870 cm-1 peak increases with rank, likely reflecting a lower degree of substitution (DOS) of alkyl groups on aromatic ring sites in high rank coals. This trend likely also represents the building of large aromatic clusters at high rank. General FTIR spectral trends for whole-coals and individual vitrinite macerals are similar. Semi-quantitative measurements become less reliable at high coal ranks, mostly due to very small aliphatic bandwidth areas. FTIR analysis of coals and coal macerals provides insight to the molecular changes that occur in coals during rapid heating. Research of this nature can offer deeper insights into coalbed methane development in response to localized heating (Gurba and Weber, 2001).

Northern Norrbotten County is one of the three major ore producing districts in Sweden. Based on the predominance of epigenetic Cu-Au and Fe-oxide mineralization this region is regarded as a typical IOCG province. The massive to layered Viscaria Cu-deposit is proposed to be a VMS deposit of Besshi-type and is unique in deposit type of the region. The volcaniclastic rocks of the Viscaria Formation hosting the Viscaria deposit belong to the rift related Kiruna Greenstone Group. The Viscaria deposit consists of three stratiform-stratabound mineralized zones: A-, B- and D-zone. Sulphide mineralization of the D-zone differs in structural features, host rock, mineralization style and Fe-oxide dominance over Cu-sulphides compared to the main Cu-ore in the A-zone. These differences between A- and D-zone mineralization styles raise the subject that the D-zone could be of a different origin.   The Kiruna area is mainly covered by glacial-till, which contributes to limited bedrock exposure. This becomes a challenge when exploring for new deposits and highlights the importance of good geological knowledge obtained from existing deposits to carry through successful exploration programs. The objective of this study is to characterize the Fe-Cu-occurrence and the associated alteration halo of the Viscaria D-zone. Alteration halos can reach several kilometres away from the main ore zone and provides mineralogical and chemical signatures that extend the target area significantly in exploration for new deposits. Detailed core logging, optical microscopic studies, lithogeochemistry and electron microprobe analyses was utilized to contribute to a better genetic understanding of the D-zone and the associated hanging wall and footwall alteration features. The study shows that the main ore minerals of the D-zone consist of magnetite and chalcopyrite, and minor pyrite and hematite. The major alteration minerals associated with mineralization are calcite, actinolite/tremolite, epidote, chlorite and also biotite and scapolite in the hanging wall. The most prominent potential ore vector is calcite veins and biotite, as the abundance increase towards the D-zone. D-zone are further characterised by low REE concentrations, similarly to the calcic-dolomite host. The study also shows that the alteration halo of the D-zone is different in the hanging wall compared to the footwall, which is confirmed by the lithogeochemistry and mineral chemistry. The footwall is characterized by spilitization and chlorite alteration. The lithogeochemistry of the D-zone and the hanging wall reveals element mobility of Mg, Ba, Fe, Na, K, Cu and Zn. Mineral chemistry of epidote, amphibole and chlorite shows chemical changes in Fe/Al- and Mg/Fe-ratios. According to the result of this thesis and earlier studies, the D-zone mineralization is suggested to be part of the VMS system forming the stratigraphically above laying A-zone of the Viscaria Cu-deposit.

Archean lode-gold deposits are a significant source of gold. However, exploration of this deposit type is hindered by their poorly understood genetic models and geochemical features. This project investigated the geochemical expression surrounding the Archean lode-gold Red Lake Gold Mines (RLGM) in the Superior Province, Canada. Mineral chemistry, whole rock and isotope geochemistry were used to establish how hydrothermal and metamorphic events influenced ore genesis. The RLGM is a basalt-hosted lode-gold deposit that formed from multiple superposed hydrothermal and metamorphic events. This study defined three significant superposed events which were important for gold mineralization. The first event was a widespread hybridized seafloor-magmatic event which caused reduction with FeO, MnO, K2O, SO3, SiO2, Rb, As and Cu enrichment. Seawater interaction created abundant micas-clays-chlorite-carbonate-FeMn oxides. Localized acidic magmatic fluids, in syn-volcanic faults, caused advanced argillic alteration. Subsequent peak-regional metamorphism created a widespread (>7km) occurrence of metamorphosed altered basalts. The micas-clays-chlorite-carbonate-FeMn oxides were metamorphosed to form Fe-biotite-Ti-magnetite±carbonate and Fe-chlorite-Fe-amphibole-FeMn-garnet-epidote/clinozoisite-magnetite-calcite-biotite assemblages. The metamorphosed argillic alteration created a quartz-muscovite-andalusite assemblage. Overprinting the widespread metamorphosed altered basalt was the significantly narrower (<1km), and structurally-controlled main vein and mineralization event. Abundant ankerite-calcite±quartz veins with replacement sulfide assemblages of pyrrhotite-pyrite-arsenopyrite-magnetite-gold-quartz-Mg-brown biotite were formed. The replacement ore-forming fluid enriched the basalt in CaO, MgO, SiO2, K2O, Ag, Au, Ni, Cu, Sb and Zn. Sulfides were created by sulfidation reactions between the host rock and ore-forming fluid. Redox differences during sulfidation reactions between the reduced wall rock and relatively oxidized fluid were identified as the main influence on gold precipitation. Carbon isotopes from the ankerite-calcite±quartz veins ranged from -4 to +4‰ δ13C which is consistent with a metamorphic origin by devolatilization reactions of pre-existing marine carbonates. Sulfur isotope from mineralized samples ranged from δ34SH2S 0–9‰. These are consistent with a magmatic source as well as metamorphic desulfidation of pre-existing sulfides (-7 to +6‰ 34S). The stable isotopes are most consisted with an evolved ore-forming fluid derived from a magmatic intrusion emplaced during regional-metamorphism. Therefore, gold mineralization at the RLGM was formed during ongoing, but post-peak regional metamorphism from an evolved magmatic source emplaced during a regional-contact metamorphic event.

The United Verde orebody, a Proterozoic volcanogenic massive sulfide deposit, is hosted by the Cleopatra Formation. The Cleopatra Formation is subdivided into two distinct members, the Upper and Lower, on the basis of alteration facies, whole rock geochemistry and the chemistry of alteration minerals. The Lower member was deposited prior to ore deposition and consists of five major alteration facies. Facies Bl, the most distant from the orebody represents the recharge area for the ore-forming fluid. Facies B2 surrounds the major discharge area or the chlorite pipe. These three facies contain chlorite and quartz as alteration minerals in variable amounts. Two facies, 81 and S2, contain quartz and sericite as alteration minerals. Mass balance calculations show progressive removal of Na and Ca, and addition of MgO and FeO* from the area of recharge (facies Bl) to facies B2 to the chlorite pipe. Whole rock δ¹⁸O values are high relative to least altered Cleopatra Formation in the recharge area and low in the discharge zone. Mineralogy and geochemistry of samples from the Upper member indicate that it was deposited following ore deposition and interacted with fluids rich in silica and iron. The hydrothermal fluid, which is interpreted to have been seawater, evolved to a high temperature slightly acidic, reduced fluid during water-rock interaction(log a₀₂ = -33 to -41; log a(H2S) = -2.6 to -5.0). The fluid δ¹⁸O and δ¹³C₀₂ values increased. Calculated δ¹³C₀₂ and δ¹⁸O fluid values, and sphalerite and chlorite chemistry imply that mixing of the hydrothermal fluid with seawater occurred in the orebody. the upper The levels of the chlorite pipe and in limited range in δ³⁴S values of sulfides is consistent with the derivation of the oreforming fluids from the reduced basal layer of a stratified basin. The study area represents only a small part of the United Verde circulation cell. Increased δ¹⁸O values of the fluid, and the need for a source of Mg, Fe and other metals suggest that the fluids may have circulated into the Shea Basalt.

Bibliography: leaves 134-147.
The Otavi Mountain Land is a base metal ore province in which base metal sulphide deposits are hosted by platform carbonates in a foreland fold-and-thrust belt on the northern edge of the PanAfrican Damara Belt. Deposits have been classified as the Berg Aukas- and Tsumeb- types, based on differences in ore association, stratigraphic position and geochemistry of ores and gangue carbonates. Mineralisation at each of these deposits is accompanied by carbonate alteration in the form of dolomite and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Optical cathodoluminescence imaging, electron probe micro analysis, X-ray fluorescence spectrometry, X-ray diffraction, high performance ion chromatography, proton probe micro analysis, stable isotope techniques, and fluid inclusion microthermometry were employed (i) to differentiate between carbonate generations associated with the alteration and mineralisation, particularly for the more economic Tsumeb-type deposits, represented by Tsumeb and Kombat, as well as in comparing between Berg Aukas- and Tsumeb-type deposits; (ii) to set constraints on the fluids effecting such alteration and associated mineralisation; (iii) to determine the relationship of the Khasib Springs deposit, for which little geochemical data exists, to deposits of the Tsumeb-type, and (iv) to identify those parameters which are diagnostic of Tsumeb-type mineralisation.

A funnel-shaped alteration pipe in Archean tholeiitic to transitional rhyolite and andesite underlying massive Zn-Cu sulphide ore at the Norbec mine in northwestern Quebec was outlined from drill core samples. Geochemical parameters, including mass changes and mobile element ratios were used with normative alteration mineralogy and thin section petrography to determine the extent of the alteration. The alteration was initially characterised by a peripheral zone of sericite-chlorite-quartz and a central chlorite-quartz zone. Isochemical metamorphism of the alteration pipe within the contact aureole of the Lac Dufault stock has converted these assemblages to cordierite-anthophyllite-biotite bearing rocks.
Bulk oxygen isotope data for the altered rhyolite suggest that the Norbec deposit formed at temperatures between 200$ sp circ$C and 300$ sp circ$C, with highest temperatures in the central chloritic zone of the alteration pipe. Calculations using SiO$ sb2$, K and Fe solubilities in typical sea-floor hydrothermal fluids suggest that water/rock ratios of 250 to 900 were necessary to introduce the added mobile elements to the alteration pipe.

Des blocs de verre archéologique provenant d’une épave découverte près de l’île des Embiez (Var) en mer Méditerranée ont été étudiés en raison de leur analogie morphologique avec les verres nucléaires et de leur environnement connu et stable. Fracturés à l’issue de leur élaboration (comme les verres nucléaires), ces verres se sont altérés près de 1800 ans en eau de mer. Ce travail a abouti au développement et à la validation d’un modèle géochimique capable de simuler l’altération d’un bloc de verre archéologique fracturé au bout de 1800 ans. Les expériences ont permis de déterminer les constantes cinétiques des mécanismes en jeu (interdiffusion et dissolution du réseau vitreux) et les paramètres thermodynamiques (affinité, phases secondaires) de ce modèle. Celui-ci, implémenté dans HYTEC a permis de simuler l’altération de fissures sur 1800 ans. La cohérence des épaisseurs d’altération simulées et des valeurs mesurées sur les blocs valide la capacité prédictive du modèle. Ce modèle permet alors d’expliquer les résultats issus de la caractérisation du réseau de fissures et de son état d’altération. Les fissures de la zone externe du bloc sont les plus altérées du fait du renouvellement rapide de la solution, alors que les fissures internes ont des épaisseurs très fines à cause du couplage entre l’altération du verre et le transport des éléments en solution (effet de l’ouverture initiale et du colmatage). Les résultats expliquent non seulement les épaisseurs les plus fines, mais aussi leur variabilité. Le comportement analogue des verres archéologiques et nucléaires permet d’envisager une transposition de ce modèle aux verres nucléaires en condition de stockage géologique
Fractured archaeological glass blocks collected from a shipwreck discovered in the Mediterranean Sea near Embiez Island (Var) were investigated because of their morphological analogy with vitrified nuclear waste and of a known and stable environment. These glasses are fractured due to a fast cooling after they were melted (like nuclear glass) and have been altered for 1800 years in seawater. This work results in the development and the validation of a geochemical model able to simulate the alteration of a fractured archaeological glass block over 1800 years. The kinetics associated with the different mechanisms (interdiffusion and dissolution) and the thermodynamic parameters of the model were determined by leaching experiments. The model implemented in HYTEC software was used to simulate crack alteration over 1800 years. The consistency between simulated alteration thicknesses and measured data on glass blocks validate the capacity of the model to predict long-term alteration. This model is able to account for the results from the characterization of crack network and its state of alteration. The cracks in the border zone are the most altered due to a fast renewal of the leaching solution, whereas internal cracks are thin because of complex interactions between glass alteration and transport of elements in solution (influence of initial crack aperture and of the crack sealing). The lowest alteration thicknesses, as well as their variability, can be explained. The analog behavior of archaeological and nuclear glasses from leaching experiments makes possible the transposition of the model to nuclear glass in geological repository

L'alteration supergene de trois indices de cuivre du bresil, localises entre 5**(o) et 24**(o) de latitude sud est etudiee. On determine les differentes phases d'alteration (smectitique et lateritique) correspondant a une grande mobilite geochimique. La plus grande partie du cuivre est lisciviee et le cuivre restant est associe a la goethite. Une application de cette etude a la prospection geochimique et a la mineralurgie est proposee

Intrusion-related, carbonate rock–hosted replacement deposits are an important source of global base metal production that includes: Cu-Zn skarn, Zn-Pb-Ag carbonate replacement and Ag-base metal deposits. These deposits are located in multiple geological settings and are commonly associated with low-grade Cu-Mo calc-alkaline porphyry districts. Visible alteration halos to these deposits range from ten to hundreds of metres around high temperature skarn deposits, being small to imperceptible around the distal relatively low temperature members of this clan. Patterns of visible and cryptic alteration are described and constrained in this study particularly around paleo-fluid flow zones at different distances and elevations from the ore centre. This was done in order to identify the large-scale zonation, mechanisms, and effects of fluid infiltration especially into the distal portions of these deposits. The main alteration tracers employed included mineralogy, major and trace element geochemistry, oxygen and carbon isotopes, and the fluorescent signature of calcite veins associated with the fluids conduits. Two areas were selected for this study: the large Cu-Zn Antamina skarn and the Ag-base metal Uchucchacua vein deposits in the Peruvian Central Andes as these deposits represent the end-members of the polymetallic carbonate rock-hosted deposits and hence, provide an excellent opportunity to examine the margins and upper sections of these hydrothermal systems. Geochronological analyses of intrusive dikes were used to establish the magmatic and hydrothermal evolution associated with mineralization, as well as the genetic linkage between proximal and distal portions of the mineralizing system at Antamina. Oxygen, carbon and strontium isotope data of vein minerals is also used to constrain the temperature of the fluids proximal and distal to the magmatic centre. Chemical data of fluorescent and non-fluorescent veins were used to determine the main activators of fluorescence and to constrain its relationship with mineralizing fluids. In summary, results of this research identify a large-scale zonation of visible and cryptic alteration around paleo-fluid flow zones demonstrating the linkage between Ag-base metal veins, replacement and skarn deposits. Anomalous halos determined throughout Antamina and Uchucchacua deposits may contribute to the development of a more systematic exploration methodology for these types of deposits.

On etudie la couverture ferralitique rouge de la zone forestiere du sud cameroun du point de vue petrographique, mineralogique, geochimique et cristallochimique. Son evolution correspond a deux mecanismes de pedogenese, l'une a l'amont a evolution verticale descendante, l'autre a l'aval a evolution verticale ascendante, cette derniere du niveau de la nappe phreatique

The present study provides the results of detailed mapping and analysis of structures encountered in Seguelen pit of Siguiri gold mine, Guinea, where the Siguiri mine is geo-tectonically located in the Baoulé-Mossi domain of Man Shield in West African craton. The gold deposit is hosted in low-grade metamorphic sediments of turbidites sequences which form part of the Lower Proterozoic of Birimian Super group. Three rock formations of Balato, Fatoya and Kintinian underlay the overall pits. The Siguiri gold mine is characterized by the deep weathering profile, developed over the rocks reaching 200 m below the surface in some areas and often capped by the lateritic gravel or duricrust. The rock formations at Seguelen area are characterised by strong bedding monotonously dipping towards SW and trending NW-SE. The lithology of the host rocks has strong control on the disseminated mineralisation throughout the deposit. Two domains of rock formations are clearly distinguished at Seguelen:  Fatoya Formation(Ffm) domain ; and  Kintinian Formation (Kfm) domain. The two domains are separated by a contact zone of 1.7 m wide parallel to bedding and characterised by the presence of quartz fragments as well as thinly sheeted shale and black shale. This contact zone is identified as disconformity. The major tectonic deformation which has affected the region is known as D2 corresponding to the Eburnean orogeny. The major D2 related structures is the regional thrust striking N-S over an area of 12 km long and 3 km wide and within which corridors all Siguiri gold Mine open pits are located. In the N-S trending structures, there is east-northeast shortening and north-northwest extension. There is pervasive hydrothermal alteration (carbonatization and sideritization) and supergene alteration in the all pits. The hydrothermal alteration attests the intensity of hydrothermal fluid-flow over the host rocks. The hydrothermal fluids flowed along the fractures and within the wall rocks through bedding plans to form numerous auriferous quartz veins bearing disseminated sulphides through chemical reaction between fluids and wall rocks, which are remarkable at Seguelen pit. Three quartz vein sets are distinguished at Seguelen:  NNE-SSW quartz vein set  NE-SW quartz vein set  NW-SE quartz vein set The NE-SW and NNE-SSW quartz veins are often lenticular and associated with the bulk mineralisation.

L'activité volcanique Cénozoïque de la plaque arabique offre l’exemple d’un volcanisme intra-plaque développé dans un contexte géodynamique complexe. Après la construction des trapps basaltiques du plateau yémeno-ethiopien, vers 31 Ma, à partir de l’Oligocène terminal, une importante activité volcanique se développe, liée à la déchirure du bouclier arabo-nubien (l’ouverture de la Mer Rouge) et la convergence des plaques Arabique et Eurasienne (zone de suture du Bitlis-Zagros). Au nord de la plate-forme arabique, le volcanisme syrien s’implante dans un contexte général de compression, autour de la ceinture de plissement des Palmyrides et des zones de déformation adjacentes (graben de l'Euphrate et système de faille de la Mer Morte). Cette thèse porte sur l'évolution volcano-tectonique de la partie nord de la plaque Arabique, en particulier celle de la Syrie, combinant des études géochronologiques, géochimiques et morpho-structurales et modélisation géophysique. Notre analyse morpho-structurale de la province volcaniques de Harrat Ash Shaam (HASV), au sud des Palmyrides, a permis de caractériser numériquement plus de 800 cônes volcaniques monogéniques répartis entre le Sud Syrien, la Jordanie et le Nord de l’Arabie Saoudite. Cette étude de la distribution des cônes volcaniques, jointe aux données existantes sur l’épaisseur de la couverture sédimentaire traversée démontre que la corrélation négative constante entre l’intensité des éruptions volcaniques et la profondeur au socle est, de fait, influencée par le contexte tectonique. L’analyse normative de la distribution des cônes volcaniques, comparée à l'épaisseur des sédiments, est essentielle pour caractériser la tectonique d'extension dans des différentes zones. La télédétection, les observations sur le terrain, et notre base de données de plus de 40 nouvelles datations potassium-argon, entre 50 ka et 18 Ma, nous permettent de préciser l’évolution volcano-tectonique de la Syrie. Cette approche pluri-disciplinaire, appliquée au plateau du Al-Lajat, le champ volcanique le plus récent de HASV, nous a permis, d’abord, de proposer un modèle chronologique pour le processus d'altération en relation aux changements paléoclimatiques du Quaternaire. Elle a surtout permis de reconstituer l'évolution volcano-tectoniques du Nord de la plaque arabique, au cours du Cénozoïque et de situer différents styles d’extension responsables de l’activité volcanique. Le volcanisme commence à la fin de l’Oligocène et au Miocène inférieur, entre ~ 26 Ma et ~ 16 Ma, au sud des Palmyrides, dans la province de HASV, dans un contexte tectonique extensif. Du Miocène au Quaternaire, entre ~ 19 Ma et ~ 0,08 Ma, des champs volcaniques se développe au nord des Palmyrides, conséquence d’extensions tectoniques de second ordre. A partir du milieu du Miocène, la compression augmente et le développement magmatique se poursuit potentiellement dans une ambiance tectonique de rotation antihoraire. Au sud des Palmyrides cela correspond à l’activité volcanique constante au cours des 13 derniers millions d’années. Au nord, cette phase d’activité liée à la tectonique de rotation est concentrée dans l’espace et le temps ; elle correspond au Plateau d’Homs, dans le NW Palmyre, entre 6,3 et 4,3 Ma.Nous proposons un nouveau modèle d'évolution volcano-tectoniques pour la province volcanique de HASV. Il souligne le rôle essentiel joué par l'hétérogénéité de la lithosphère (sous les chaînes du Liban – anti-Liban et la zone de plissement des Palmyrides) dans la formation du volcanisme à partir du milieu du Miocène. Nos modèles géophysiques permettent d’estimer à ~150 km la profondeur moyenne de la limite lithosphère-asthénosphère. A l’analyse des données géochimiques des laves, la zone à l’ouest de HASV où cette limite apparaît moins profonde, à ~ 110 km, s’expliquerait par une anomalie thermique plutôt que par une remontée asthénosphérique. Géochimiquement, les laves Cénozoïques syriennes sont alcalines et sub-alcalines et présentent les caractères de magma émis dans un contexte continental intra-plaque. Ce sont des basanites et des téphrites, des basaltes, des andésites et des trachy-andésites basaltiques et des trachybasaltes. 30 échantillons des différentes provinces volcaniques syriennes montrent une variation significative des signatures des éléments traces incompatibles. Le processus de genèse de ces magmas montre une influence négligeable de la contamination crustale, et un effet de la cristallisation fractionnée limité à l'olivine et au clinopyroxène. Nos résultats montrent que les laves syriennes ont été produites par des taux variables de fusion partielle à partir de niveaux différents dans le manteau lithosphériques présentant localement des hétérogénéités. Le rapport LREE / MREE nous permet de montrer non seulement comment le degré de fusion partielle varie spatialement et temporellement au cours des derniers 18 Ma, mais encore d’illustrer comment varie le degré et le style de la tectonique au cours de cette période. L’une des conséquences de ce contexte tectonique pourrait être la migration d’hydrocarbures vers l’ouest du fait de l’extension crustale au Plio-Quaternaire dans la zone du graben de l’Euphrate à l’Est ; cette migration pourrait être guidée vers une zone de la croûte préalablement fracturée située au NW de la Syrie.En conclusion, le volcanisme cénozoïque de la Syrie résulte d’une tectonique extensive, influencée périodiquement par la convergence arabo-eurasienne, au nord et à l’est, convergence qui provoque des styles tectoniques de rotation ; cette tectonique contrôle la fusion partielle à différents niveaux dans le manteau. Le volcanisme du Nord de la plaque arabique se développe dans le cadre de l’ouverture de la Mer Rouge et débute en même temps que l’activité au sud de la mer Rouge. Il se poursuit jusqu’à la période historique, progressivement amorti vers le nord, l’extension étant contrariée par le cadre compressif à la marge Arabie-Eurasie
The Cainozoic volcanic activity in the Arabian plate offers an excellent opportunity to study the intra-plate volcanism related to a complex tectonic setting. After the emplacement of the Yemeni-Ethiopian continental flood basalt plateau, ~ 31 Ma, since the Late Oligocene, widespread volcanic activity has erupted, accompanying the separation of the Arabian-Nubian Shield (development of Red Sea rifting) and the convergence between the Arabian and Eurasian plates (building of the Bitlis-Zagros thrust belts). In the northern part of the Arabian platform, the Syrian volcanism has taken place in a general compressional context, surrounding the Palmyride fold belt and adjacent to other deformation zones (e.g. the Euphrates graben and Dead Sea fault system). This thesis focuses on the volcano-tectonic evolution of the northern part of the Arabia plate, particularly in Syria, and essentially combines geochronological, geochemical, and morpho-structural studies, in addition to supplementary geophysical models. Our morpho-structural analyses of the Harrat Ash Shaam volcanic province (HASV) to the south of Palmyride, digitally characterise more than 800 monogenic volcanic cones placed in Syria, Jordan, and Saudi Arabia. These new data, together with the availability of sediment thickness data, give rise to a new volcano-tectonic approach. This study shows that the consistent negative correlation between the intensity of volcanism and basement depth is influenced by the tectonic setting. The normative analysis of the distribution of volcanic cones in relation to sediment thicknesses is critical when comparing the extension of tectonics in different zones. Remote sensing imagery, field work and our > 40 new K-Ar ages dataset ranging from ~0.05 million years (Ma) to ~18 Ma allow us to precise the Syria volcano-tectonic evolution through time. Regarding the youngest lava flows of HASV, the integration of the results makes it possible to suggest a chronological model for the alteration processes in relation to Quaternary palaeoclimatic changes. We reconstruct the volcano-tectonic evolution in Syria during the Cainozoic, and suggest different extension styles to explain the volcanism. It started during the Late Oligocene and the Early Miocene, between ~26 Ma and ~16 Ma to the South of Palmyride at HASV in an extensional tectonic context. From the Miocene to the Quaternary, between ~19 Ma and ~0.08 Ma, the volcanism developed to the North under second order extension tectonic conditions. Since the Mid-Miocene, the compression has increased and the magma erupted in relation with a possible counter-clockwise rotation tectonic relative motion. South of Palmyride it corresponds to the widespread eruptive phase during the last 13 Ma. To the North, this phase, linked to rotational tectonics appears concentrated in superficies and time; it corresponds to the Homs plateau, NW Palmyride, between 6.3 and 4.3 Ma. We suggest a new volcano-tectonic evolution model for the HASV. It highlights the essential role of lithosphere heterogeneity beneath Lebanon, in particular the anti Lebanon Mountains and Palmyride thrust belts, in triggering the Mid-Miocene volcanism. Our geophysical models estimate mean lithosphere – asthenosphere boundaries at about 150 km depth. According to geochemical data, the zone of shallowest depth ~110 km, W of HASV, could be the result of a thermal anomaly, instead of an asthenospheric upwelling. Geochemically, the Cainozoic Syrian lavas are alkaline and subalkaline rocks, typical of magma emitted in continental intraplate contexts. They are basanites and tephrites, basalts, basaltic andesites, basaltic trachyandesites, and trachybasalts. Thirty samples from different Syrian volcanic provinces show significant variation in terms of incompatible trace element signatures. Crustal contamination plays a negligible role in the process of magma genesis, as does crystal fractionation, essentially restricted to olivine and clinopyroxene. Our results show that the Syrian lava has been generated by variable rates of partial melting from different levels of a locally heterogeneous lithospheric mantle. The LREE/MREE ratio not only illustrates how the degree of partial melting was changed spatially and temporally during the last ~18 Ma, but it also illustrates how the degree and style of extension tectonics changed through time

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The Gawler Range Volcanics (GRV) form part of a Mesoproterozoic Silicic Large Igneous Province (Gawler SLIP) within South Australia. The SLIP includes intrusive and extrusive rocks within the Gawler Craton and Curnamona Province that are dominantly felsic. Recent high precision dating of several GRV units has shown that they erupted between 1587 Ma and 1595 Ma allowing for geochemical comparisons with respect to a precise timeline. Trace element geochemistry has shown anomalies to be consistent through the lower and upper GRV demonstrating the main source in the GRV likely did not change. A mafic component is shown to have contributed to both the lower and upper GRV system. Eu anomalies and trace element geochemistry shows that there was a large change in magmatic evolution between the upper and lower GRV within a short time (<1 m.yr). This change is hypothesised to have occurred due to the tectonic regime during the SLIP emplacement. Hydrothermal alteration associated with the emplacement of the Gawler SLIP is known to have contributed to the formation of Iron-Oxide Copper-Gold (IOCG) and shear-hosted deposits in South Australia. More recent discoveries within the Southern Gawler Ranges display epithermal-porphyry characteristics associated with alteration in the lower GRV. Alteration within the GRV is hereby characterised in order to identify alteration associated with mineralisation. Alteration is shown to encompass a sericite – hematite dominated assemblage which has affected most of the GRV. Several other anomalous alteration assemblages exist in localised areas. Using direct evidence, it is suggested that epithermal-porphyry systems may be preserved within the upper GRV, which encompasses a larger outcrop area than the lower GRV which is underexplored.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2019

The report summarizes the results obtained by the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf within the BMWi-financed Joint Research Project “Geochemical retention of radionuclides on cement alteration phases (GRaZ)”. The project focused on the retention behavior of Ca-bentonite and cementitious material, both constituents of the geo-engineered barrier of deep geological repositories for high-level radioactive waste, towards radionuclides. Specifically, the influence of increased salinities and of hyperalkaline conditions on interaction processes in the system radionuclides – organics – clay/cementitious materials – aquifer was studied. For this purpose, complexation, sorption and desorption studies were performed at alkaline to hyperalkaline pH conditions (pH 8-13) and under variation of the ionic strength (0.1 to 4 M) applying complex solution compositions. For the U(VI) citrate system molecular structures dominating in the pH range 2-9 were studied spectroscopically (NMR, UV-Vis, FT-IR). As dominating species 2:2, 3:3, 3:2 and, above critical concentrations also 6:6 and 9:6 U(VI) citrate complexes were identified or confirmed and complex formation constants were determined. U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions in mixed electrolyte solutions was studied by means of batch sorption experiments. The U(VI) retention on Ca-bentonite was shown to be very effective at pH>10, even in the presence of carbonate and despite the prevalence of anionic aqueous uranyl species. The presence of two independent U(VI) surface complexes on Ca-bentonite at pH 8-13 was shown by site-selective TRLFS and EXAFS spectroscopy. The sorption of anionic uranyl hydroxide complexes to the mineral surface was shown to be mediated by calcium cations. In further experiments, the effect of isosaccharinic acid (ISA) and polycarboxylate ether (PCE) on U(VI) and Eu(III) sorption, respectively, on Ca-bentonite was studied. An effect of ISA on U(VI) sorption on Ca-bentonite only occurs when ISA is present in very high excess to U(VI). The effect of PCE, as a commercial cement superplasticizer, on Eu(III) sorption onto Ca-bentonite was negligible already at moderate ionic strengths. The retention of U(VI) and Cm(III) by various C-(A-)S-H phases, representing different alteration stages of concrete, was studied by batch sorption experiments. Sorbed or incorporated actinide species were identified by TRLFS. The stability of U(VI) and Cm(III) doped C-(A-)S-H phases at high ionic strengths conditions was studied in solutions simulating the contact with North German claystone formation water. Potential changes of actinide speciation as well as formation of secondary phases due to leaching effects were followed spectroscopically. The results of this project show that both bentonite and cementitious material constitute an important retention barrier for actinides under hyperalkaline conditions and increased ionic strength.

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Sedimentary uranium systems represent a significant source of economically recoverable material, with deposits frequently clustered where conditions are favourable for roll-front formation. Exploration for sedimentary uranium usually attempts to target redox fronts within paleochannels or clastic sedimentary sequences which could be potential sites for roll front style uranium mineralisation. Sediments altered by oxidation can be re-reduced at a later date by bacteria making it difficult to determine if an oxidised fluid has moved through the sequence. The movement of oxidising fluids through sediment will inevitably alter both the chemistry of the sediment and the fluid supplying uranium. Elements which are sensitive to redox conditions dissolve and precipitate as conditions change creating a recognisable geochemical footprint. In particular the uranium, molybdenum and arsenic contents of the sediments are changed in a way which is not reversed by re-reduction. These changes are distinctive enough to be detected using a handheld X-Ray fluorescence device which enables rapid decision making in the field even if traditional methods allow for far greater precision and accuracy. The findings of this study describe geochemical changes linked to oxidation in the Pepegoona East and Pannikan deposits, Lake Frome region, South Australia, for use as an exploration tool. It is hoped that by studying changes in the chemistry of these sediments that we may not only improve the efficiency of exploration but also gain a better understanding of how the fluids responsible for uranium mineralisation evolve over time. The addition of data from new deposits will enhance the accuracy of the data set and provide a better understanding of how sediment composition effects alteration.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2014

abstract: The hydrous alteration of ultramafic rocks, known as serpentinization, produces some of the most reduced (H2 >1 mmolal) and alkaline (pH >11) fluids on Earth. Serpentinization can proceed even at the low-temperature conditions (<50°C) characteristic of most of Earth’s continental aquifers, raising questions on the limits of life deep in the subsurface and the magnitude in the flux of reduced volatiles to the surface. In this work, I explored the compositions and consequences of fluids and volatiles found in three low-temperature serpentinizing environments: (1) active hyperalkaline springs in ophiolites, (2) modern shallow and deep peridotite aquifers, and (3) komatiitic aquifers during the Archean. Around 140 fluids were sampled from the Oman ophiolite and analyzed for their compositions. Fluid compositions can be accounted for by thermodynamic simulations of reactions accompanying incipient to advanced stages of serpentinization, as well as by simulations of mass transport processes such as fluid mixing and mineral leaching. Thermodynamic calculations were also used to predict compositions of end-member fluids representative of the shallow and deep peridotite aquifers that were ultimately used to quantify energy available to various subsurface chemolithotrophs. Calculations showed that sufficient energy and power supply can be available to support deep-seated methanogens. An additional and a more diverse energy supply can be available when surfacing deep-seated fluids mix with shallow groundwater in discharge zones of the subsurface fluid pathway. Finally, the consequence of the evolving continental composition during the Archean for the global supply of H2 generated through komatiite serpentinization was quantified. Results show that the flux of serpentinization-generated H2 could have been a significant sink for O2 during most of the Archean. This O2 sink diminished greatly towards the end of the Archean as komatiites became less common and helped set the stage for the Great Oxidation Event. Overall, this study provides a framework for exploring the origins of fluid and volatile compositions, including their redox state, that can result from various low-temperature serpentinizing environments in the present and past Earth and in other rocky bodies in the solar system.
Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2020

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy,
The Ventersdorp Contact Reef(VCR) is a major gold-bearing reef in the Witwatersrand Basin. It occurs between the overlying Klipriviersberg Group lavas and the underlying Central Rand Group sediments, and was strongly altered by hydrothermal fluids circulating in the Witwatersrand Basin. A detailed study of the mineralogy, geochemistry of rocks and minerals, physicochemical conditions, stable isotopes and ages of hydrothermal alteration zones associated with the VCR were carried out at Western Deep Levels South Mine, South Africa. ( Abbreviation abstract)
Andrew Chakane 2019

Anthropogenic disruptions in the form of hydrological alterations, such as dam construction and the associated water diversions are a cause of much upheaval to local and regional ecosystems. Lake 626 within the Experimental Lakes Area of north-west Ontario, along with its downstream wetlands, 626A and 626B are one such system. Construction of a dam at the L626 inflow has completely restricted water flow, reducing and reshaping the watershed, increasing water retention time, and decreasing outflow into the wetlands. This study investigates the state of each wetland through physical and geochemical characterization during the first year following the diversion. Previous studies have found that hydrological diversions in wetlands can lower water table levels, altering soil chemistry and producing a shift in floral and faunal communities. Ultimate consequences involve significant loss of wetland area through conversion to upland habitat. This provides a model for climatic warming scenarios, wherein sustained drought conditions can produce the same result. Boreal wetlands are surprising fragile ecosystems that store massive quantities of carbon and are at risk of releasing it in such situations. One study showed that an extended summer drought in an otherwise average year with above average precipitation produced losses of 90 g C/m2 over the course of the year. Maintenance of reduced-flow in wetlands 626A and 626B is expected to convert the system into a carbon source and reduce overall wetland area. Radiocarbon dating has revealed that following deglaciation, both 626A and 626B basins were open water wetlands, depositing limnic peat for about 3200 and 1300 years respectively. Each site then transitioned into open sedge dominated fen – 626B to the present and 626A until about 2.5 ka BP when Sphagnum began to develop. Wetland 626B is decidedly an open shrub/sedge fen, supporting Myrica gale, Chamaedaphne calyculata and Carex rostrata / lasiocarpa communities. Wetland 626A is a bog/fen complex, sharing similar communities in the fen areas, but housing a large, centrally located bog of shrub species overlying Sphagnum hummocks. Tritium values in 626A were similar to cosmic background levels, indicating that recharge of basal pore water has not occurred in at least 60 years. Tritium in 626B was much higher, suggesting a substantial difference in hydrology or peat hydraulic conductivity between the basins. Measurement of DOC profiles showed high concentrations in near-surface water, reaching over 80 mg/L, and dropping to about 20 mg/L at maximum depths. An opposite trend was seen for DIC and CH4 profiles which increased concentration with depth (25 – 70 mg/L DIC; 75 – 700 μmol/L CH4). Isotopically however, 13C signatures from basal DIC were more positive while signatures from CH4 were typically more negative (-6 ‰ to +4 ‰ DIC; -57 ‰ to -73 ‰ CH4). Breakdown of DOC by LC-OCD showed high concentrations of humic substances and low molecular weight neutrals. The origin of humic substances in surface water became more pedogenic with increasing distance from the L626 outflow, indicating the influence of decaying wetland vegetation on the DOC of adjacent water. A comparison between contemporary and future characterization of boreal peatlands under drought-like conditions will provide a better understanding of the impacts suffered by wetlands during hydrological alterations. The high sensitivity of wetlands to changing hydrology should also provide a measure for gauging the effects of long term climate warming. This will assist in the development of environmental policies to better govern both the establishment of water diversions and the multitude of other practices leading to climate change.

Iron-oxide copper gold (IOCG) and banded iron formation (BIF)-hosted iron deposits are the dominant styles of mineralization in the Gawler Craton, South Australia. Multivariate geochemical datasets of various types and complexity collected from whole-rock samples and individual mineral grains from these deposits form a previously untapped source of information that can be applied to characterization and genetic modelling of such deposits. Moreover, such datasets carry major implications for new approaches to regional-scale exploration. Despite this, the ever-increasing complexity and size of geochemical datasets necessitates development of bespoke multivariate statistical analysis techniques as a prerequisite to any reproducible quantitative characterization of mineralization and/or alteration signatures, especially when detailed petrographic data are either limited or absent altogether. Left-censored values, i.e., those concentrations that fall below minimum limit of detection (reflecting the analytical limitation of the instrument used for acquisition), are present in all types of geochemical datasets but are amplified in trace element datasets such as those obtained by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A novel approach for imputation of values below detection limits using copula cumulative density functions (CDFs) is proposed. A case study involving imputation of left-censored data for Te in the presence of Au and Ag values is based upon fitting copula CDFs to the data and iteratively simulating new Te values from copula CDFs using the Metropolis-Hastings algorithm. Within BIF-associated iron ores of the Middleback Ranges, iron oxides display interconversion and replacement reactions between magnetite by hematite and reprecipitation of new generations of platy hematite. Quantitative assessment of such interconversions, when correlated with available textural evidence, allows definition of geochemical signatures associated with ore enrichment. Linear-mixed effects models support the statistically significant difference among prevailing textures. Such models can account for the high degree of correlation among the analyses within a single polished block and therefore respect the hierarchical structure of such data. The observed trace element signatures indicate the potential impact of hydrothermal fluids associated with the ~1.8 Myola Volcanics, ~1.6. Ga Hiltaba Suite granites and younger discordant mafic dykes on ore enrichment process in the Middleback Ranges. Statistical analyses of a large LA-ICP-MS dataset for pyrite shows the independence of several minor and trace elements of economic interest or of relevance to optimized ore processing. Principal Component Analysis shows that Au is contained in zoned pyrite, along with As-Co(- Ni), thus suggesting the presence of invisible Au as both nanoinclusions and within the sulphide lattice. Nevertheless, PC2 essentially discriminates Co-As-Au from Ni, thus suggesting that Co-As zoning in pyrite is not always accompanied by Ni. The clearly defined (by PC1) Ag-Bi-Pb association is likely present in the form of discrete inclusions of telluride minerals. Other elements certainly hosted as minerals inclusions in pyrite and not in the crystal lattice include Zn, Sn, Mn, Ti, Sb and Cu. Application of multivariate statistical analyses to whole-rock data from three different IOCG systems within the Olympic Dam district, coupled with geological 3D modelling, has resulted in recognition and specification of shared but subtly different mineralization and alteration signatures within each system. The novelty of such an approach lies in the direct comparison of lithological and mineralogical zonation with calculated parameters such as geochemical clusters and principal component scores, also taking into consideration an extended suite of elements representative of both protoliths and superimposed mineralization and alteration. Results showed that despite significant differences between the geological settings of individual IOCG systems (host lithologies, presence of mafic dykes, mineralization style etc.), all three (the Olympic Dam deposit and the Acropolis and Wirrda Well prospects) can be readily characterized by the presence of ‘granitophile’ signatures thus confirming a common source of fluids for IOCG mineralization across the Olympic Cu-Au Province. Multivariate statistical analysis is both flexible and adaptable and can readily complement and often outperform conventional approaches to interpreting different types of geochemical data. Although particularly applicable to larger, more complex datasets, this research also emphasizes the caution needed when working with datasets containing large proportions of left-censored values.
Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering & Advanced Materials, 2020

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Garnetiferous rocks show a spatial association with several base metal deposits in the Early Cambrian Kanmantoo Trough. These rocks include coticules (garnet-quartz rocks) and banded iron formation (BIF) and are hosted by pelitic metasediments of the Tapanappa Formation. Petrological and geochemical investigations have been made of garnetiferous rocks associated with the Scotts Creek Ag-Pb-Zn and Angas Pb-Zn deposits and in the vicinity of the Kanmantoo Cu deposit. Geochemical features indicate variations between coticules from the three localities but general similarities with coticules from Broken Hill, N S. W. BIF from the Kanmantoo area is also comparable to the equivalent lithologies in the Willyama Complex, at Olary and Broken Hill. Geochemical diagrams (Fe-Mn-(Co+Cu+Ni), Al/(Al+Fe+Mn ) vs Fe/Ti, Ti02 vs Al203 and chondrite-normalised rare earth element (REE)) for coticules and iron formations suggest variable contributions of detrital and hydrothermal components. The hydrothermal component, is generally 30 to 50 wt. percent for coticules, and >70 wt percent for BIF. The stratigraphic position, layer parallel banding and unusual geochemistry suggest the coticules associated with Scotts Creek, Kanmantoo and Angas deposits are exhalative in origin, and may be termed "meta-exhalites". The Kanmantoo BIF appears to have formed from high temperature submarine hydrothermal fluids and metalliferous sediments analogous to those of the Red Sea and the East Pacific Rise. Coticules and BIFs are indicators of hydrothermal activity and may be local guides to base­ metal mineralisation. The Mn content of garnet in coticules reflects proximity to Pb-Zn ore, and may be a useful exploration tool.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 1998

The sandstone-hosted McArthur River Zone 4 U ore body and alteration system, located in the Athabasca Basin, are the focus of a detailed mineralogical and geochemical study aimed at reconstructing its evolution. The oxidation state of Fe in clay alteration from Zone 4 is measured using 57Fe Mössbauer spectroscopy and compared with other mineralized and barren sandstone-hosted alteration systems in the Athabasca Basin. The aim is to ascertain the role of Fe in forming U deposits and determine whether Fe oxidation state in alteration minerals can indicate proximity to mineralization. At Zone 4, early diagenetic kaolin is overprinted by zones of dravite, illite, chlorite, and late kaolinite forming around the P2 fault. Uranium mineralization occurred at ca. 1600 Ma and was triggered by mixing between oxidizing U-bearing basinal fluids and reducing basement-modified basinal fluids, the latter forming when basinal fluids interacted with basement lithologies. Early pre-ore silicification in the lower 200 metres of the Manitou Falls Formation above the ore body created favourable conditions for mineralization by focusing basinal fluids into the reduction site and enhancing ore preservation. However, it obstructed the post-ore migration of radiogenic Pb and U pathfinder elements from the deposit and limited the extent of hydrothermal sudoite alteration in the overlying strata. Sandstone-hosted alteration systems in the Athabasca Basin are commonly surrounded by an outer illite and an inner chlorite zone. Illites have high Fe3+/ƩFe ratios characteristic of formation from oxidizing basinal fluids, whereas, chlorites have lower and more varied Fe3+/ƩFe ratios, reflecting their origin from reducing, Fe2+-bearing basement-derived fluids having undergone variable mixing with oxidizing basinal fluids. Chlorites in mineralized systems where fluid-mixing occurred, such as at McArthur River Zone 4 and Maurice Bay, record higher Fe3+/ƩFe ratios than barren systems where fluid-mixing did not, such as at Wheeler River Zone K and Spring Point. The scarcity of U-bearing basinal fluids available for mixing with Fe2+-bearing basement fluids is a critical geochemical factor precluding mineralization in barren sandstone-hosted systems. The Fe3+/ƩFe ratio of chlorites has potential applications for discriminating barren and mineralized systems and as spatial vectors to ore when coupled with Pb isotope ratios.
Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-11-01 14:08:33.51