Дисертації з теми "Geochemical signatures"

Master of Arts
Department of Geography
Kendra K. McLauchlan
The importance of local parent material has been recognized as a fundamental control on the geochemistry of lake sediments, but there have been relatively few broad-scale surveys of catchment sources of terrigenous lake sediments. In this paper, I present a geochemical study of catchment parent materials and lake sediments from four lakes in Northern Minnesota. Similar climate and vegetation conditions are present at all four lakes, which vary mainly in catchment parent material and lake morphometry. Geochemical data including major, trace and rare earth elements (REEs) from catchment parent material samples was compared with lake sediment geochemical data using PCA, linear regression, geological indices and elemental ratios. In homogenous till-dominated catchments, patterns of elemental variation in the catchment till could be extended to predict elemental concentrations in the lake sediments. Simple ratios, which are commonly used to analyze lake sediment geochemical data, were not good predictors of lake sediment composition, however. Catchments with mixed bedrock and till were compositionally heterogeneous, and comparison with lake sediments was difficult. Lack of grain size control and biogenic silica measurements further confounded analysis. However, ΣREE/Y ratio was found to be diagnostic of the catchment parent materials and present within the lake sediments. This study makes a contribution to an improved understanding of lacustrine sedimentary archives by analyzing the spatial linkages among catchment, water and sedimentary geochemistry.

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

This study utilized freshwater mussel shells to assess the role of mercury contamination in the North Fork Holston River, an aquatic habitat affected by extensive extirpations of mussel populations starting in the early 1970â s. Mussel shells (n=366) collected from 5 sites, upstream and downstream of Saltville (where mercury was used from 1950-1972) were analyzed to test if: (1) geochemical signatures of shells record variation in mercury levels relative to the contamination source; and (2) shell taphonomy could be used to differentiated affected and unaffected sites. Analysis of 40 shells for geochemical signatures using atomic absorption spectroscopy indicated a strong longitudinal pattern. Mercury content was as follows: upstream sites had low Hg concentrations (<5 to 31ppb), shells directly below Saltville had high concentrations (23-4,637ppb), shells 18km downstream of Saltville displayed intermediate values (7-115ppb), and those 38.4km downstream were comparable to upstream sites (<10ppb). Two pre-industrial shells collected from Saltville in 1917 also yielded Hg estimates (5-6ppb) comparable with upstream estimates. The Hg content was not correlated with shell length (r=-0.3; p=0.2) or degree of taphonomic alteration (r=0.18; p=0.28). Analysis of 366 shells for taphonomic signatures indicated that shells are most heavily altered and fragmented directly downstream of Saltville. In contrast, upstream sites, inhabited by reproducing mussel populations, contain many fresh-dead shells. Taphonomic signatures can thus be used to differentiate sites with different extirpation histories. Relic mussel shells can provide useful spatial and temporal data on Hg concentrations in polluted ecosystems and offer a tool for delineating areas with unknown extirpation histories.
Master of Science

In the James Bay Lowlands of northern Ontario, kimberlite pipes are concealed by peat, thick layers of till, and Tyrell sea sediments. Studies have shown that buried ore bodies produce geochemical signatures in surface media. This thesis explores the geochemistry of near-surface groundwater above concealed kimberlite pipes using factor analysis to determine whether (1) a factor analysis can reveal an underlying structure (factors) in a multivariate groundwater geochemical dataset, and whether (2) those factors are related to the presence of concealed kimberlite. Factor analysis was performed on two datasets of nearsurface groundwater, collected at 0.2 m and 1.1 m below ground surface in peat. Results revealed that (1) there is a significant difference in the behaviour of elements in groundwater near the surface compared to those in deeper groundwater, which is sheltered from the effects of the atmosphere; (2) for both datasets, the first factor is dominated by elements known to be enriched in kimberlite, notably rare earth elements (REE), U, Th, Ti – the composition of factor one is consistent with their derivation from kimberlite in a limestone background where such elements are in very low concentration; (3) high-valence and lowvalence kimberlite indicator elements (KIE) are found separated into distinct factors suggesting that once released from the kimberlite after weathering, KIE are subjected to various geochemical processes to be differentiated as they migrate upward to the surface; and (4) Fe and Mn load on a factor distinct from other metals, suggesting that in this environment Fe-Mn-O-OH is not a significant controller of metal mobility in groundwater. Overall, this research has further highlighted the multivariate nature of geochemical processes in groundwater. Compared with previous work in geochemical exploration where often only univariate or bivariate statistics or single element profiles over concealed ore bodies were used, this thesis has shown that factor analysis, as a multivariate data analysis technique, is a robust exploration tool, able to shed light on relevant geochemical processes hidden within geochemical datasets. This thesis shows that high-valence KIE, notably U,V, Th, Ti and the REE, as a group, are better indicators of the presence of kimberlites than other well-known KIE. Single element concentration profiles such as Ni or Cr (known KIE) show similar anomalies over a concealed kimberlite as a factor score profile for factor one (U, V, Th, Ti, REE, Ni) would; however, it is the peculiar assemblage of elements in factor one that makes it unique to kimberlites, a feature that can be used in future exploration work for concealed kimberlites in similar surficial environments, such as the Siberian wetlands. The results suggest that future geochemical exploration work involving groundwater should focus on the more stable groundwater located below the zone of oxidation, sheltered from the effects of the atmosphere.

Actuellement, la Loire, voit sa géodynamique de plus en plus détériorée. Le déficit du transport solide provoque un enfoncement du lit mineur sur plusieurs secteurs du bassin Amont. Ceci a pour conséquence une déstabilisation progressive des ouvrages (digues, ponts) et l'érosion ou le colmatage des berges ainsi qu'une baisse du niveau piézométrique des nappes alluviales. Le traitement de ces problèmes passe par une meilleure connaissance des processus d'érosion et d'incision fluviale, le premier laissant place au second une fois que la couche « alluviale » a été totalement emportée, laissant apparaître un affleurement rocheux dans le lit du cours d'eau. Ce phénomène complexe est actuellement constaté en divers endroits de la Loire, dans la plaine du Forez. Nous proposons trois approches pour l'analyser.La première approche est fondée sur la modélisation numérique utilisant les équations de Barré-Saint-Venant, pour l'écoulement, couplées aux équations d'Exner et de Meyer-Peter Müller pour le transport solide. Ce modèle monodimensionnel permet d'obtenir la côte du fond du lit de la rivière et le flux solide au droit de chaque point de calcul.La seconde approche, mécaniste, consiste à déterminer de façon semi-empirique le taux d'incision du substratum marneux à partir de deux variables majeures: la puissance hydraulique totale et le coefficient d'abrasion en un point donné. La puissance hydraulique est calculée à l'aide d'un modèle hydraulique tandis que le nombre d'abrasion est une propriété mécanique de la marne qui est déterminée à partir d'essais en laboratoire. La troisième approche relève de la géochimie. Elle consiste à déterminer les provenances des matériaux contribuant à la recharge latérale des sédiments, à partir de leurs signatures géochimiques. Ceci a fait l'objet d'analyses en laboratoire sur des échantillons prélevés sur l'ensemble du linéaire entre Grangent et Balbigny. Les résultats obtenus montrent que ces approches indépendantes sont complémentaires et permettent une description à la fois qualitative et quantitative de l'enfoncement du lit de la Loire dans le secteur d'étude
Currently, the Loire river, sees its geodynamic increasingly deteriorated. The deficit of sediment transport causes erosion of the bed on several areas of the basin. This results in a gradual destabilization of structures (dams, bridges), erosion or clogging of banks or a decline in piezometric level alluvial.Treating these problems requires a better understanding of the processes of erosion and river incision, the second succeeding the first, once the alluvial material of the bottom was completely removed, revealing a bed outcrop.This complex phenomenon is currently found in various parts of the Loire river, in the plain of Forez.We propose three approaches for this analysis.The first approach is based on numerical modeling using the equations of Barre-de-Saint-Venant, for flow, coupled with the equations of Exner and Meyer-Peter Müller for sediment transport. This monodimensional model allows the simulation of riverbed changement and sediment discharge, right each calculation point of grid mesh.The second approach is mechanistic and consists of determining the rate of marly bedrock incision by a semi-empirical method by the use of two major variables: the total hydraulic power and an abrasion coefficient. The hydraulic power is calculated using a hydraulic model, while the abrasion coefficient is a mechanical property of the marl which is determined from laboratory tests.The third approach is the geochemistry. It consists in determining the provenance of the materials from tributaries and in the main chanel by analyzing their geochemical signatures. This has been the subject of laboratory tests on samples taken across the linear from Grangent to Balbigny.The results obtained show that these independent approaches are complementary and provide both a qualitative and quantitative description of the incision of the Loire river in the study area

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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
Granites underlie large land areas and play a key role in global weathering patterns. This study provides insights into the effects of I- and S-type granites on weathering, pedogenesis, mineralogy and soil geochemistry of major, trace and rare earth elements across a climosequence in a tropical environment. We hypothesized that soils derived from I-type granites lead to huge differences in weathering, pedogenesis, mineralogical and geochemical patterns in comparison to those derived from S-type granites. The study was carried out in Borborema Province, NE Brazil, using petrological, mineralogical, geochemical and soil standard analyses; multivariate analysis and geographic information system approaches were used to evaluate such data. In general, results showed that the highest major, trace and rare earth element concentrations in soils derived from I-type granites are related to their higher proportion of accessory minerals: allanite, titanite, apatite, amphibole and opaque minerals. Bastnaesite and monazite seems to the major sources of rare earth elements in soils derived from I- and S-type granites, respectively. Geophysical field measurements show different magnetic susceptibilities, whereby I-type granites have substantial higher magnetic properties than S-type granites. Soils originated from I-type granites are quantitatively more significant carbon pools. Multivariate statistical techniques are useful to guide and support environmental management decisions not only to understand soils variability but also to contribute to agriculture production and soil-related environmental issues. Spatial distribution maps are suitable for supportting soil fertility management and crop specific fertilization. These results highlight the following issues: i) The importance of detailed characterization of granite types to understand the weathering patterns and carbon stocks in tropical settings; ii) Granitic composition and climate-related weathering processes are soil formation key factors to understanding major, trace and rare earth element distributions in soils; iii) The geologic factor on soil formation cannot be neglected in climosequence studies aiming to allow the understanding of environmental issues such as pedogenesis, soil geochemistry and carbon stocks. In addition, our findings provide wider implications in large parts of the tropics (S-America, sub-Saharan Africa, India, SE and East Asia, Australia) which are underlying by igneous rock types including I- and S-type granites and where effective management tools are needed to increase nutrient use efficiencies for increased productivity of food, fodder and energy crops.
Os granitos são a base de grandes áreas de terra e desempenham um papel fundamental nos padrões globais de intemperismo. Este estudo fornece insights sobre os efeitos dos granitos do tipo I e S sobre o intemperismo, a pedogênese, a mineralogia e a geoquímica do solo de elementos principais, traços e terras raras, em uma escala climática em um ambiente tropical. Nossa hipótese é que os solos derivados de granitos do tipo I levam a enormes diferenças nos padrões de intemperismo, pedogênese, mineralogia e geoquímica, em comparação àqueles derivados de granitos tipo S. O estudo foi realizado na Província de Borborema, nordeste do Brasil, utilizando análises petrológicas, mineralógicas, geoquímicas e de padrões de solo; análise multivariada e abordagens do sistema de informações geográficas foram utilizadas para avaliar tais dados. Em geral, os resultados mostraram que as maiores concentrações de elementos principais, traços e terras raras em solos derivados de granitos do tipo I estão relacionadas à maior proporção de minerais acessórios: allanita, titanita, apatita, anfibólio e minerais opacos. Bastnaesita e monazita parecem ser as principais fontes de elementos terras raras em solos derivados de granitos tipo I e tipo S, respectivamente. As medições geofísicas do campo mostram diferentes susceptibilidades magnéticas, pelo que os granitos do tipo I têm propriedades magnéticas substancialmente mais altas do que os granitos do tipo S. Solos originados de granitos tipo I são conjuntos de carbono quantitativamente mais significativos. As técnicas estatísticas multivariadas são úteis para orientar e apoiar as decisões de gestão ambiental, não apenas para entender a variabilidade dos solos, mas também para contribuir para a produção agrícola e questões ambientais relacionadas ao solo. Mapas de distribuição espacial são adequados para apoiar o manejo da fertilidade do solo e adubação específica da cultura. Esses resultados destacam as seguintes questões: i) A importância da caracterização detalhada dos tipos de granito para entender os padrões de intemperismo e os estoques de carbono em ambientes tropicais; ii) A composição granítica e os processos de intemperismo relacionados ao clima são fatores-chave na formação do solo para entender as distribuições de elementos principais, traços e terras raras nos solos; iii) O fator geológico na formação do solo não pode ser negligenciado estudos de climosequência visando a compreensão de questões ambientais como pedogênese, geoquímica do solo e estoques de carbono. Além disso, nossas descobertas fornecem implicações mais amplas em grandes partes dos trópicos (América do Sul, África Subsaariana, Índia, sudeste e leste da Ásia, Austrália) que são subjacentes por tipos de rochas ígneas, incluindo granitos do tipo I e S e onde São necessárias ferramentas de gestão eficazes para aumentar as eficiências de uso de nutrientes para aumentar a produtividade de alimentos, forragem e culturas energéticas.

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Master of Science, November 2019
The Sadiola goldfield is located in the eastern Kédougou Kéniéba Inlier of the West African Craton. The study area is located in the western region of the Republic of Mali close to the international border between Mali and Senegal, and approximately 75 km south of the regional capital of Kayes in the sub-Sahelian region of West Africa. The goals of this research are to study the different geological relationships: oxide and unaltered rock (calc-silicate, siltstone-shale-greywacke); oxide and structure; oxide and mineralisation; supergene alteration and mineralisation; supergene alteration and structure. To achieve the Sadiola Hill oxide zone geochemical complexities and alteration signatures study, many research studies were conducted such as lithological and oxide 2D mapping, lithological and oxide 3D modelling. The oxide profiles were sampled for gold analysis, XRF, and XRD analysis. The found minerals were separated into light and heavy. The key minerals identified by XRD are alunite (K2Al6 (SO4)4(OH)12) and jarosite (K2Fe63+ (SO4)4(OH)12). The mineral association suggests a highly acidic environment and acidic supergene conditions. The examination of oxides also allowed distinguishing the different ferricrete horizons in the Sadiola goldfield. Significant gold mineralisation is hosted in the oxide profile (weathered calc-silicate) in the Sadiola Hill opencast pit. Sadiola gold plant at Sadiola gold mine is fed oxide ore mined from the oxidation profile in the weathered rock. The oxide ore fed into the Sadiola gold plant includes laterite, transitional oxide and saprolitic oxide. The age of oxide saprolite and oxide transitional zones is assumed to have formed during recent weathering by deeply penetrating meteoric waters. In general, the geology of the oxide feed is assumed to be derived from weathering and decomposition of rocks of the Birimian Supergroup. The need of oxide-feed to sustain Life of Mine of the Sadiola goldfield mean that exploration for oxide ore is critical but understanding the geology and geochemistry of the oxide is also vital, particularly in terms of ore optimization. Five main lithologies are identified from mapping the Sadiola Hill area and these include calc-silicate, siltstone-shale-greywacke, metasandstone, diorite and quartz-feldspar porphyry. Furthermore, six calc-silicate sub-facies are identified as (1) thick-bedded (more than 0.5-1 cm) marble with an alternation of white and black layers, (2) thin-bedded (3-5 mm), (3) massive marble, (4) slump-folded marble, (5) carbonaceous siltstone and (6) pure marble. Oxide mapping in the Sadiola Hill opencast pit identified three oxide profiles and three distinct alteration types as follows (Type 1) decarbonated calc-silicate alteration, (Type 2) Fe alteration (oxide-jarosite-siderite), and (Type 3) potassic clay alteration. The Fe-oxide and potassic clay alteration profile are related to the gold mineralisation at the Sadiola goldfield. 3D lithological modelling conducted in the Sadiola goldfield has established a significant relationship between gold mineralisation and the calc-silicate unit. The 3D oxide profiles and hard rock modelling defined three types of gold mineralisation according to the age of the host. Young gold is found in the ferricrete of Eocene-Miocene age, the second type of gold is found in the oxide profile (oxide saprolite and transitional) of unknown age and the third type is found in the hard rocks of Birimian age. Gold mineralisation is associated with the (1) lithological contacts, (2) north-south trending structure (Sadiola Fracture Zone), (3) northeast trending faults, while it is proportionally with iron (Fe) and potassium (K) alteration. The three-oxide development has been sampled individually to characterise the oxide geochemistry and alteration signature. The geochemistry study of the oxide zone of the opencast mine identified the following minerals (1) Silica or quartz (SiO2), (2) Goethite (Fe+ 3O.OH), (3) Muscovite (KAl3Si3O10 (OH) 2), (4) Siderite (FeCO3), (5) Biotite KFeMg2 (AlSi3O10) (OH) 2, (6) Bernalite (Fe (OH) 3), (7) Orthoclase (KAlSi3O8), (8) Alunite (K2Al6 (SO4)4(OH)12) and (9) Jarosite (K2Fe63+ (SO4)4(OH)12). The presence of jarosite and alunite are an indicator of an acidic pH condition. The XRF analysis results established the relationship between the gold grade and silica, potassium, and iron. The presence of alunite and jarosite highlight a highly acidic environment and acid supergene conditions. The oxidation of the calc-silicate rock caused the diminution of volume and subsequent concentration of the gold mineralisation in the decarbonated calc-silicate mainly along the structures. This diminution of volume also caused the collapse of the contact between the siltstone-shale-greywacke in the west of the Sadiola Hill opencast pit and the decarbonated calc-silicate rock in the east. This contact is known as Sadiola Fracture Zone. The collapses of the decarbonated calc-silicate is associated with the flexure of the Sadiola Fracture Zone, a number of discontinuous bodies of diorites and quartz-feldspar porphyry units, and possibly produced the soft sediment deformation in the Sadiola Hill opencast pit. Sadiola goldfield can be classified as an oxide gold enrichment deposit.
XN2020

Stream capture is a major driver of the retreat of the Blue Ridge Escarpment, but timescales of capture are not well understood. This study examines stream sediment geochemistry to establish a set of sediment source fingerprints which can be used to identify and date the capture of the Tallulah River. Statistical analyses show significant differences in U, Th, and certain REE enrichment. These differences result from variations in bedrock along the lengths of each river and a shift in relative stream powers after capture to favor mobilization or deposition of heavy elements. The observed differences should be sufficient to identify where Tallulah sediment appears in floodplains of the capturing Tugaloo River, facilitating future dating of the capture event. Understanding the timing of river capture will provide insight into the ongoing reshaping and redistribution of river systems and interactions of geomorphic processes in the continuing evolution of the southern Appalachian Mountains.

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Mineralisation overlain by extensive cover can be identified through the geochemical signature dispersed through the surrounding regolith. This project aimed to use portable XRF (pXRF) analysis to increase the understanding of the regolith geochemistry in the proximity of the Cygnet-Snelling Shear Zone (CS-SZ), Kangaroo Island. The shear zone is significant as it hosts several potentially economic deposits including the Bonaventura Copper (Cu) deposit as well as the Dewrang and Kohinoor Lead - Zinc (Pb-Zn) prospects. By using pXRF analysis at 2m intervals on drill hole transects taken from the vicinity of the CS-SZ it was hoped to be able to discern known pathfinder elements associated with Cu, Pb and Zn mineralisation. The data collected from these transects can be used to develop a model of the regolith sequence lithogeochemistry, and to determine which elements can be reliably analysed by pXRF within a regolith sequence such as that seen on Kangaroo Island. The study has also attempted to identify any geochemical signatures associated with Cu, Zn or Pb mineralisation, their spatial extent and potential as geochemical vectors towards mineralisation.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2014

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The search for economically viable ore deposits focuses increasingly on deeply buried deposits. This study was designed to highlight specific mafic/ultramafic igneous bodies in the western Gawler Craton, near Streaky Bay, South Australia, through the analysis of the behaviour of pathfinder elements within the regolith above anomalous aeromagnetic targets. In particular, the possibility of developing a rapid and inexpensive means of characterising the intrusions at depth by looking within the calcareous sediments located within the top two to twelve metres of regolith was evaluated. Data from 26 of the 53 holes drilled were analysed, covering an area of approximately 214 km2. This area covers a diverse lithological basement including ultramafics, gabbros, granitoids and felsic gneisses and is located near a strong magnetic anomaly. Given the significant difference in basement lithology of the target bodies (mafic to ultramafic) versus the variably magnetic felsic to intermediate granitoids, pathfinder elements including Ni, Cu, Cr, Mn and V, which are elevated in mafic to ultramafic rocks, were targeted. Depth plots and ratios of the transition elements are shown with simple graphing techniques are used to illustrate the behaviour of geochemical signatures throughout the profile and to display any correlation between basement rocks and the regolith. There was no discernible anomaly in any trace metals throughout the calcrete of the uppermost regolith unit. Calcrete pathfinder element abundances are uniformly low, which is to be expected, as the sediments are up to 75% carbonate, and any basement detrital signature is highly diluted. In the majority of holes, however, an abrupt increase in these element values occurred at the base of the calcrete or a few metres deeper within ferruginous sediments. The increase in values occurred in Ni, Cu and Cr, but was most prominent in V. This pattern is reflected in the plots for the basement saprolitic material. Unfortunately, sampling of the oxidised zones requires expensive and time­consuming air-core drilling through up to twelve metres of calcrete, and in places soft, unconsolidated sands. More detailed geochemical analyses of the calcrete layers in the 26 holes were undertaken to try to establish a method of identifying the basement lithology from the calcrete chemical data. Absolute abundances of pathfinder elements are too low in the calcrete to be useful in distinguishing differences in basement lithology. While calcareous sediments may contain subtle geochemical indicators of the differences in basement lithology, it alone is not adequate to confidently predict the basement lithology for drilling. Below the calcrete, within the oxidised zone, the geochemical anomalies are large enough to confidently conclude whether the basement is mafic or felsic.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2003

Temporal variations in gas hydrate related geochemical signatures under different deposition conditions are the primary purposes of this study. Accreted wedge located offshore Southwestern Taiwan receives high terrigenous river materials, 100 MT/yr, at present time. It is not clear how seep environment varied during the past glacial. A 25 meters long piston core was taken offshore Southwestern Taiwan on r/v Marion DuFresne. Short piston cores and box cores were also taken on r/v OR-1. Samples were analyzed for pore water dissolved sulfide, sulfate, methane, chloride, del O18, calcium, magnesium, alkalinity, pH, and sediment AVS, pyrite, inorganic carbon, del O- 18, C13. Changes in deposition environment play a major role in the study area. Three stages of geochemical processes are identified in the 25 meters long core, interchange between reduce and oxic depositional environments, with reducing condition in the top 10 m, oxic in between 10-20 meter and reducing below the 20 meter. High concentrations of dissolved sulfide, rapid sulfate depletion, increase of methane, decrease of calcium were found in pore water in the top 10 m of sediments together with high concentrations of pyrite, relatively higher proportion of coarsegrained sediment. Concentrations of pyrite were very low in sediments between 15 to 20 meters but increased rapidly from 20 to 25 meters with a maximum concentration at 400 umol/g. Chloride concentrations also increased to a maximum concentration of 630 mM at 20 m. The rapid increase of chloride indicated gas hydrate formation at this depth. Authigenic carbonate nodules were found in sediments below 20 m. The carbonate content also increased rapidly beneath this depth. Stable isotopic carbon composition of the carbonate varied rapidly beneath 20 m with a low at -28 per mil. The existence of oxic/reducing alterations indicates that methane seep may vary in the past in the study area.

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