Orientador: José Ricardo Sturaro / Banca: Gilda Carneiro Ferreira / Banca: César Augusto Moreira / Resumo: A viabilidade econômica da exploração de um depósito mineral envolve diversas variáveis, como teor e volume do minério, método de lavra, infraestrutura e mão de obra próxima à localização do depósito. Desta forma, se faz necessário quantificar os recursos minerais para reduzir o risco financeiro do empreendimento. A área de estudo está inserida na porção sudoeste do Greenstone Belt de Pilar de Goiás, constituída por uma sequência de metassedimentos químicos, metassedimentos clásticos, pequenos corpos intrusivos e rochas gnáissicas. As ocorrências de ouro estão associadas às camadas de clorita e grafita xistos. O objetivo deste trabalho consiste em caracterizar a distribuição espacial dos teores de ouro da mina Pilar de Goiás-GO, utilizando as técnicas de Krigagem Ordinária e Simulação Sequencial Gaussiana. O trabalho teve início com a validação do banco de dados dos furos de sondagens e a regularização das amostras para o comprimento de um metro. Com base nas descrições dos furos de sondagens, obteve-se a atitude das camadas dos litotipos, constituindo o modelo geológico que foi elaborado no programa Leapfrog Geo®. As amostras conferidas foram então submetidas às análises estatísticas e geoestatísticas. Em ambas as técnicas, realizou-se a modelagem dos variogramas e do elipsoide de busca dos dados. Para a krigagem ordinária, a filtragem restringiu os dados ao intervalo de 0 a 4,38 ppm, sendo que os outliers foram substituídos pelo valor máximo de teor. Verificou-se que os resultados obtidos pela krigagem são válidos, pois respeitam a distribuição de frequência dos dados originais. A análise da superfície do comportamento dos teores regionais permitiu concluir que não há uma direção preferencial de crescimento de teores de ouro, porém esta superfície... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The economic viability of a mineral deposit exploration involves many variables, such as content and ore volume, mining method, infrastructure and workers next to the location of the deposit. It is necessary to quantify the mineral resources to reduce the financial risk of the project. The study area is located in the southwest portion of the greenstone belt of Pilar de Goias, which is composed of a sequence of chemical and clastic metasediments, small intrusive bodies and gneissic rocks. The gold occurrences are associated with layers of chlorite schist and graphite. The objective of this study is characterize the spatial distribution of gold grades in the Pilar de Goiás mine (GO) by the Ordinary Kriging and Simulation Sequential Gaussian methods. The study started with the database validation of boreholes and the regularization of samples for the length of one meter. Based on the descriptions of the boreholes, it was obtained the attitude of the layers of rock types and, therefore, the geological model, developed in the Leapfrog Geo® program. The checked samples were then used for the statistical and geostatistical analyses. In both methods, the variograms were modeled and the search ellipsoid was defined. For Ordinary Kriging, the data filter restricted to the range 0 to 4.38 ppm and the outliers were replaced by the maximum content value. The results of kriging are valid because the frequency distribution is consistent with the original data. The analysis of the surface containing the higher levels implied that there is no preferential direction of growth of gold content, but this surface follows the regional foliation of the host rocks. The estimation by Simulation Sequential Gaussian were effective to model the layer of interest, which are the highest gold grades / Mestre

O significado da idade do magmatismo, reconhecimento das séries magmáticas e ambientes tectônicos que controlaram a origem das rochas metavulcânicas do Greenstone Belt da Vila Nova (GBVN), é uma importante ferramenta para entender a evolução do Escudo das Guianas durante o Paleoproterozóico. Este trabalho apresenta novos dados geoquímicos de rochas metavulcânicas e de U/Pb em zircão (LA-MC-ICPMS), que foram suplementados por petrografia, dados estratigráficos e estruturais obtidos através de mapeamento geológico e descrição de furos de sondagem. Na região de Vila Nova, as unidades do GBVN repousam sobre o embasamento Arqueano composto por ortognaisses, metagranitos e anfibolitos do Complexo Tumucumaque. A base do GBVN é composta por metabasaltos e metabasaltos andesíticos, sotoposto por um domínio superior metassedimentar com rochas químico exalativas e metavulcânicas subordinadas. As rochas metavulcânicas incluem anfibolitos e anfibólio xistos, cujos corpos estão alongados segundo a xistosidade regional de direção NW-SE. A geocronologia pelo método U-Pb em zircão mostra uma idade de 2.154 ± 6 Ma para um meta-andesito da porção inferior do GBVN. O evento de metamorfismo orogênico esteve associado a três eventos deformacionais. Os eventos D1 e D2 formaram a xistosidade (S1), preservada como dobras intrafoliais (F2) e a clivagem de crenulação (S2), originadas a partir de movimentos de cavalgamento. O pico metamórfico (M1) está marcado pela assembleia plagioclásio+hornblenda+granada e, plagioclásio+hornblenda+diopsídio, indicando temperaturas entre 450 e 650 °C e pressão entre 4 e 6 kbares. Os metabasitos compreendem Fe-toleítos e Mg-toleítos com afinidade komatitica, composições geoquímicas enriquecidas em LILE e ETR e empobrecidas em HFSE (com anomalias negativas de Nb, Ti e P) e padrões de ETR semelhantes ao MORB. As características observadas indicam um magmatismo toleítico relacionado à bacias de retro-arco e arco de ilhas de 2.15 Ga no Escudo das Guianas. / The significance of the age of magmatism, magma series and tectonic settings that controls the origin of metavolcanic rocks of Vila Nova Greenstone Belt (VNGB) is an important issue in order to understand the evolution of Guiana Shield in Paleoproterozoic times. This work presents new U-Pb LA-ICP-MS geochronological and geochemical analyzes carried out on zircon grains and metavolcanic rocks of the Vila Nova greenstone belt (VNGB) which were supplemented by petrography, and stratigraphic and structural data acquired through description of boreholes and field work. In the Vila Nova region, the VNGB units rest on the Archaean basement composed of orthogneisses of the Tumucumaque Complex. The lower portion of the VNGB is composed of metabasalts and andesitic metabasalts, supported by an upper metasedimentary domain with exhalative chemical rocks and subordinate metavolcanic rocks. The metavolcanic rocks include amphibolites and amphibole schists, whose bodies are elongated according to the regional NW-SE schistosity. U-Pb zircon geochronology data showed an age of 2154 ±6 Ma for a meta-andesite of the lower portion of VNGB. Orogenic metamorphism event followed by three deformation events were recognized. The D1 and D2 events formed the schistosity (S1), preserved as intrafolial folds (F2) and the crenulation cleavage (S2), derived from thrust movements. The assemblages plagioclase + hornblende + garnet and plagioclase + hornblende + diopside define the metamorphic peak (M1-M2) with temperatures from 450-650 °C and lithostatic pressure between 4 and 6 kbars. The metabasites comprise Fe-tholeiites and Mg-tholeiites with komatiitic affinity, geochemical compositions enriched in LILE and REE and depleted in HFSE (with negative Nb, Ti and P anomalies) and MORB-like REE patterns. The observed features indicate an expressive magmatism related to back-arc basins and island arcs at 2.15 Ga in Guiana Shield.

Orientador: Elson Paiva de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-11T16:36:13Z (GMT). No. of bitstreams: 1 Costa_FelipeGrandjeanda_M.pdf: 10447471 bytes, checksum: c27e2dc3f77cf21b0841b3e40d6e57ae (MD5) Previous issue date: 2008 / Resumo: O greenstone belt do Rio Itapicuru é uma seqüência vulcano-sedimentar paleoproterozóica cortada por uma série de corpos plutônicos com idades entre 2160-2070 Ma. O Granodiorito Fazenda Gavião (GFG) é um corpo intrusivo em metabasaltos da porção ocidental do greenstone, próximo ao contato com o embasamento arqueano. Este pluton tem textura fanerítica média e hornblenda como mineral máfico dominante. Uma característica de campo é a presença de enclaves máficos magmáticos e diques máficos sinmagmáticos com evidências da mistura física de magmas (magma mingling). A analise geoquímica classifica o Granodiorito Fazenda Gavião como uma rocha intermediária (SiO2~63 wt%), com composição de granodiorito a quartzo-monzodiorito, da série cálcioalcalina de médio a alto-K, metaluminoso, espectro Terras Raras fracionado (razão (La/Yb)N = 22.81), alto Sr (900-800 ppm), alto Ba (1000-1500 ppm), e alta razão Sr/Y. Comparando com a geoquímica de outros plutons da área, o GFG apresenta assinatura dos elementos traço similar aos plutons alcalinos, sugerindo uma provável ¿consangüinidade¿ magmática entre estes plutons. A característica geoquímica dos diques máficos (appinitos) associados ao GFG é similar ao granodiorito em questão, porém com uma maior abundancia em Ba, Sr, MgO, Ni, Cr, K2O, e Terras Raras leves, sugerindo que estes diques são originados da fusão parcial de uma fonte mantélica enriquecida. O GFG apresenta semelhanças com rochas adakíticas e plutons TTGs, mas diferente destas rochas, apresenta maior conteúdo em K2O. É possível que o GFG foi originado pela fusão parcial de crosta máfica (crosta inferior?) (com granada e sem plagioclásio no resíduo) em função do acúmulo de magma máfico na base desta crosta (underplating of mafic magmas). O magma félsico gerado, provavelmente se misturou com uma pequena porcentagem do magma máfico, como é sugerido pelas feições de magma mingling observadas em campo. O GFG com idade de 2106 + 6 Ma (U-Pb SHRIMP em zircões) é mais jovem do que o magmatismo TTG/cálcio-alcalino (2163-2127 Ma) e é contemporâneo ao magmatismo potássicoultrapotássico (ca. 2110-2105 Ma) presente no contato embasamento-greenstone. O modelo de evolução geológica desenvolvido nesta dissertação sugere que os plutons ricos-em-K do greenstone belt do Rio Itapicuru são o registro da colisão de um arco oceânico com uma margem continental em ~2110-2105 Ma, precedendo outro evento colisional com retrabalhamento crustal em ~2080-2070 Ma / Abstract: The Rio Itapicuru greenstone belt is a gold-bearing Palaeoproterozoic volcanic-sedimentary sequence intruded by several granitic plutons in the time interval 2160-2070 Ma. The Fazenda Gavião granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with the Archaean basement complex. The FGG is largely composed of a homogeneous coarse-grained hornblende granodiorite, occasionally crosscut by appinitic mafic dykes. Minor mafic enclaves and amphibolite xenoliths are common close to the contact with the host metabasalts. The FGG is a metaluminous medium-K to high-K calc-alkaline body with relatively constant silica abundances (SiO2 ~ 63-66 wt %). It shows fractionated REE patterns (LaN/YbN ~22), high Sr (900-800 ppm), high Ba (1000- 1500 ppm), and high Sr/Y ratios. Comparing with the geochemistry of other plutons of the area, the trace elements signature of the FGG suggests a probable magmatic consanguinity between this pluton and the alkaline plutons of the area. Similar geochemical characteristics of the FGG are observed in the associated appinitic dykes, which show relatively higher abundances of Ba, Sr, MgO, Ni, Cr, K2O, and the light rare earth elements, suggesting they derived from partial melts of an enriched mantle source. The FGG shares several geochemical characteristics with adakites and TTG plutons, but unlike these series it shows relatively higher K2O abundance. It is suggested here that the FGG originated from partial melts of the mafic lower crust (with garnet and no plagioclase in the residue) possibly triggered by underplating of mantle-derived, enriched mafic magmas, of which the appinitic mafic dykes may be a representative remnant. The granitic melt mixed with minor amounts of the appinitic magma, as suggest by magma mingling. The 2106 + 6 Ma-old (UPb SHRIMP in zircons) FGG is younger in age than the early (2163-2127 Ma) TTG/calcalkaline arc plutons of the greenstone, and is close-related in time to the young potassicultrapotassic plutons (ca. 2110-2105 Ma) emplaced along the basement-greenstone boundary. We suggest that the K-rich plutons in the Rio Itapicuru greenstone belt are the records of island arc-continent collision at ~2110-2105 Ma, preceding major continental rework and collision at ~2080-2070 Ma / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

Orientador: Elson Paiva de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-12T03:34:56Z (GMT). No. of bitstreams: 1 Ruggiero_Alberto_M.pdf: 5764806 bytes, checksum: cdadd28e98d86c8738fcf5955bd71eea (MD5) Previous issue date: 2008 / Resumo: Novos dados geoquímicos nas rochas vulcânicas andesíticas e dacíticas da Unidade Maria Preta (UMP), Greenstone Belt do Rio Itapicuru, revelaram a presença de dois grupos geoquímicos distintos: um de rochas com afinidade adakítica e outro com caráter cálcio-alcalino. A suíte adakítica (ADK), localizada nas porções oeste da UMP, é caracterizada pelos altos valores de Sr/Y (Sr ~900 ppm, Y~5ppm); Na2O ~ 4,5ppm (K2O/Na2O ~0,3). É caracterizada também pelo enriquecimento de LILE (elementos litófilos de alto raio iônico) relativos aos HFSE (elementos de elevado potencial iônico) e também pelo moderado fracionamento dos elementos terras-raras (La/Yb ~ 12). A suíte cálcio-alcalina (CA) apresenta baixas razões Sr/Y (Sr ~ 170 ppm, Y~ 22 ppm), menor fracionamento de elementos terras-raras (La/Yb ~8) e anomalias negativas de Eu. No entanto apresenta maiores concentrações de elementos incompatíveis (Y ~22ppm, Zr ~142ppm, Th ~6ppm) e também Cr e Ni. Foi revelado, através de modelagem geoquímica que as duas suítes não se relacionam por cristalização fracionada. Contudo a suíte Adk apresenta indícios de cristalização fracionada de hornblenda enquanto que na CA a cristalização fracionada de plagioclásio desempenhou papel importante. O ambiente mais provável para a formação das rochas vulcânicas cálcioalcalinas é fusão em baixas profundidades da cunha do manto metassomatizado por fluídos liberados a partir de uma crosta oceânica subductada, seguida por fracionamento de plagioclásio. A geoquímica dos adakitos requer fusão de meta-basaltos hidratados em pressões elevadas, onde granada+hornblenda são estáveis e constituem o restito da fusão. Em geral, as rochas adakíticas apresentam indícios de pouca interação do magma original com uma coluna de manto peridotitico, como visto em adakitos atuais, dados os baixos valores de Cr e Ni em relação aos adakitos cenozóicos. A suíte cálcio-alcalina apresenta menores valores de fugacidade de oxigênio no sítio de extração do magma (entre -3 e -1 FMQ). Ao contrário, os adakitos apresentam maiores valores (entre -1 e +0,5 FMQ), semelhantes aos valores encontrados em adakitos modernos formados por fusão de crosta oceânica subductada. Dados de isótopos de Sm-Nd forneceram idades modelo TDM para a suíte adakítica de 2.213 a 2.010 Ma, com valores de eNdT de +3,9 a +1,7. A suíte cálcio-alcalina revelou idades modelo mais antigas, entre 2.330 e 2.279 Ma e menores valores de eNdT de +0,7 a + 1,3. Estes valores indicam magmatismo juvenil para ambas as suítes, porém com maior tempo residência crustal para a fonte das rochas cálcio-alcalinas, ou interação do magma com crosta mais antiga. Datação U-P SHRIMP em andesito adakítico revelou idade de cristalização de 2.081 ±9 Ma e a presença de zircões herdados arqueanos (3364, 3017, 3064 Ma), evidenciando que o magma gerado em zona de subducção interagiu com crosta arqueana, provavelmente o embasamento do Greenstone Belt do Rio Itapicuru, sugerindo então um provável arco continental como origem da Unidade Maria Preta. Esses dados sugerem que o vulcanismo intermediário a félsico do Greenstone Belt do Rio Itapicuru foi formado ou teve relação direta com subducção. Esta possivelmente teve uma vergência de leste para oeste, evidenciada pela zonalidade na geoquímica das rochas vulcânicas (adakitos à oeste e cálcio-alcalinas a leste). / Abstract: New geochemical data on andesites and dacites of the Maria Preta Unit, Rio Itapicuru Greenstone Belt, revealed two distinct geochemical groups: one of adakitic affinity and another of typical calc-alkaline. The adakitic suite, localized west in the unit, is characterized by high values of Sr/Y and Ti/YN >1. It shows enrichment in LFSE (Low Field Strength Elements) relative to HFSE (High Field Strength Elements) and a moderate rare earth element fractionation. The calc-alkaline suite (CA) shows low Sr/Y ratios, less rare earth elements fractionation and negative Eu anomalies. On the other hand it shows higher incompatible elements abundances (Y, Zr, Th) and high Cr and Ni concentrations. The two suites cannot be linked by fractional crystallization and are derived from different sources (distinct initial Nd ratios). The most probable setting for the formation of CA is partial melting of mantle peridotite modified by hydrous fluids released from a subducting slab, followed by low pressure plagioclase fractionation. The adakite geochemical features require partial melting of hydrous metabasalts at depths high enough to stabilize garnet+hornblende as the residual phase. This suite does not reveal significant interactions with the mantle, as shown by its lower Cr and Ni values than Cenozoic adakites. For an assumed 2170 Ma age, the Sm-Nd isotope data show higher eNd(t) for the adakites (+4,8 to +2,5) than for the calc-alkaline suite (+1,9 to +1,4). These data indicate a juvenile source for the UMP volcanic rocks. U-Pb SHRIMP dating indicates a crystallization age of 2,081 ± 9 Ma for the adakitic volcanic. Inherited Archean zircons (3364, 3017, 3064 Ma) evidence a magma generated at a subduction zone followed by interaction with Archean lithosphere, probably the basement of the Rio Itapicuru Greenstone Belt. The calc-alkaline suite shows low oxygen fugacities at the magma extraction site (between -3 e -1 FMQ). On the other side, the adakites shows higher values (between -1 e +0,5 FMQ), similar to modern adakites formed by a subducting slab melt. This results suggests that the UMP volcanism was formed or was directly connected to a subduction. The geographic position of the two suites, i.e. adakites to the west of the calc-alkaline volcanics, suggests subduction of an oceanic plate to the west. / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

The distribution of gold in igneous rocks and minerals is described and discussed. Not all the gold in igneous rocks is contained within early formed crystal lattices. Evidence that gold can be associated with late stage crystallizing phases is described. It is concluded that some of the gold in hydrothermal and volcanogenic deposits may have come from a primary magmatic source rather than having been leached from solid country rock. Gold is probably transported as chloride complexes at temperatures greater than about 300°C. At lower temperatures it is probably transported with other metals as sulphide and thio-sulphide complexes. The precipitation of gold from the transporting medium is brought about by changes in the physico-chemical conditions within that medium. Decrease in pressure is probably not a major cause of precipitation in volcanogenic environments. The geology of volcanogenic iron-formations is described and discussed, relative to the development of greenstone belts. Oxide facies iron-formations were formed in shallow oxidizing environments. They are associated with volcanogenic and clastic sediments. Sulphide facies iron-formations were precipitated in the deeper parts of geosynclinal structures. They are associated with mafic and ultramafic rocks similar to modern oceanic volcanic assemblages. Carbonate facies iron-formations were deposited in the regions between oxide facies and sulphide facies. Other banded iron-formations are found associated with base metal massive sulphide deposits related to arctype volcanic centres. These deposits are found in the regions where carbonate facies iron-formations were formed. Exploration for and exploitation of gold deposits in Archaean iron-formations are discussed. Geochemical exploration programmes are aided by the association of gold with trace amounts of base metals. Geophysical exploration methods that can be employed include magnetometer, I.P. and E.M. surveys. The metallurgical treatment of the ores should include "roasting" because a large proportion of the gold occurs as submicroscopic grains within sulphide mineral crystals.

The previously undifferentiated, "Melmoth Granite-Greenstone Remnant" (MGGR¹) crops out over an area of about 360 km² in northern Natal, South Africa. The greenstone sequence is comprised mainly of mafic metalavas with lesser serpentinite, talc schist, dacitic tuff, quartz-muscovite schist, quartzite and calc-silicate rocks. The greenstones are intruded by syntectonic trondhjemitic gneisses, late-tectonic granodioritic gneisses and post-tectonic granite dykes. Four phases of deformation and metamorphism are recognized. Epigenetic, disseminated and quartz vein-hosted gold mineralization is associated with D₂ shearing - a positive correlation existing between the intensity of the shearing, the thickness of the shear zone and the grade of ore it contains. Auriferous quartz veins are distinguished from an earlier generation of barren vein quartz on the basis of mineralogy, texture and relationship to the s-fabric. The mineralization occurs in zones of dilation associated with shear zone refraction. Associated wall rock alteration includes sericitization, argillization and chloritization. An ore genesis model based on the aforementioned parameters, is proposed. Finally, an exploration programme has been devised in order to locate undiscovered gold deposits in the MGGR. The programme could probably be applied, with minor modifications, to shear zone-hosted gold deposits in other granite-greenstone remnants in northern Natal. ¹- Name suggested by writer.

The study area comprises the Archaean Manica Greenstone Belt and the Vumba Granite Gneiss, the Proterozoic Messica Granite Gneiss of the Zimbabwe Craton, the possibly allochthonous metasedimentary sequence of the Frontier Formation, the granitoids of the Mozambique Metamorphic Province, which are subdivided into Vanduzi Migmatite Gneiss, the Chimoio Granodiorite Gneiss, the Nhansipfe Granitic Orthogneiss and the Pan-African Tchinhadzandze Granodiorite Gneiss. The rock sequences in the two provinces are cut by mafic intrusions. The greenstone belt comprises mafic to ultramafic and pelitic schists and serpentinites of the Macequece Formation and metasediments ofthe M'BezaNengo Formation. The mafic to ultramafic schists and the serpentinites have chemical signatures of komatiites. The Vumba Granite Gneiss comprises the northern and southern Vumba granitoids dated at 3885±255 Ma, and 2527±632 Ma respectively. They vary from metaluminous to peraluminous, have normative QAP compositions of granodiorites and monzogranites and chemical signatures of mantle fractionates and volcanic-arc granitoids. The Early Proterozoic Messica Granite Gneiss is 2348±267 Ma old, is metaluminous and has QAP compositions of monzogranites and chemical signatures suggesting a crustal source and a volcanic-arc environment. The Frontier Formation comprises quartzite and pelitic schists. The Vanduzi Migmatite Gneiss comprises stromatic and stictolithic types. Two mineral assemblages are distinguished as they contain either garnet or hornblende. The Mid-Proterozoic Chimoio Granodioritic Gneiss is 1236±201 Ma old. It is granodioritic and metaluminous with a chemical signature of volcanic-arc granitoids. The Late Proterozoic Nhansipfe Granitic Orthogneiss is dated at 981 ±83 Ma and varies from metaluminous to peraluminous. The Rb, Nb and Y contents are typical of within-plate granitoids, whereas Ga, Zr, AI, Ce andY are typical of A-type granitoids. The age of the mafic intrusions falls between ~500 and ~11 00 Ma. The rocks typically contain plagioclase, hornblende and clinopyroxene with or without garnet and orthopyroxene. The chemistry of the rocks is typical of sub-alkaline tholeiites. The Tchinhadzandze Granodiorite Gneiss may be part of a Pan African event which lasted till ~450-~500 Ma. The normative feldspar compositions and Rb, Ba and Sr contents are typical of granodiorites. It is metaluminous and has Rb, Y and Nb contents typical of volcanic arc granitoids. The planar fabrics in the Archaean granite-greenstone belt are characterized by E-W to SW-NE strikes and steep dips to N and S and to NW and SE. The mineral lineations and fold axes plunge 60° and 30° respectively towards the E. Within the Mozambique belt, around the central part and in the extreme east of the study area, the planar fabrics have essentially N-S strikes and steep dips to E and Win contrast with complex deformation observed in the migmatites and megacrystic granitoids. The study area can be subdivided into three metamorphic blocks, namely, one of low-grade greenschist facies, one of medium-grade amphibolite facies and a third block of high-grade metamorphism. / Dissertation (MSc)--University of Pretoria, 2012. / Geology / unrestricted

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

Greenstone belts are dominated by volcanic rocks with lithogeochemical characteristics that reflect a range of possible geodynamic settings. Many analogies with modern tectonic settings have been suggested. Increasing exploration and comprehensive sampling of volcanic rocks in modern oceans provides the unique opportunity to characterize different melt sources from intraoceanic settings. This thesis examines geochemical data from more than 2850 submarine mafic and more than 2200 submarine felsic volcanic rocks, representing a wide range of settings. The results show significant geochemical variability spanning the full range of compositions of volcanic rocks found in ancient greenstone belts. This diversity reflects complex rift and spreading regimes, variations in crustal thickness, dry melting versus wet melting, mantle mixing and crustal contamination. Highly variable melting conditions are thought to be related to mantle heterogeneities, complex mantle flow regimes and short-lived tectonic domains, such as those caused by diffuse spreading, multiple overlapping spreading centers and microplate breakouts. Systematic differences in the volcanic rocks are revealed by a combination of principal components analysis and unsupervised hierarchical clustering. Rocks from most arc-backarc systems have strongly depleted mantle signatures and well-known subduction-related chemistry. This contrasts with rocks in Archean greenstone belts, which show no, or at least weaker, subduction-related chemistry and stronger mantle enrichment resulting from a less-depleted mantle, less wet-melting, and variable crustal contamination. The geochemistry of the modern volcanic rocks reflects lower mantle temperatures, thinner crust and subduction-related processes of present-day settings. However, rocks that are geochemically identical to those in Archean greenstone belts occur in many modern back-arc basins, such as the Lau Basin. Crustal growth and area-age relationships in the Lau Basin are similar to observed ages and compositions of volcanic assemblages in greenstone belts, such as the Blake River Group of the Abitibi Greenstone Belt. Such settings are recognized as favorable locations for volcanogenic massive sulfide (VMS) deposits, and therefore the particular geochemical signatures of the volcanic rocks are important for enhanced area selection in base and precious metal exploration.

The Round Lake Batholith is a composite granitic intrusion into the Archean metavolcanics of the Abitibi Greenstone Belt, Superior Province. The mafic metavolcanics are mainly high iron tholeiitic basalts of ocean floor origin. The intrusion of the batholith has metamorphosed the metavolcanics to amphibolite grade. Moving towards the contact there is no change in the metavolcanics grain size, but mineralogy changes quickly from the actinolite zone with relict pumpellyite to the hornblende zone. Field evidence as well as thin section and chemical analyses have shown that the dioritic appearing hybrid rock, near the contact, is a product of the mafic meta volcanics assimilation into the batholith. / Thesis / Bachelor of Science (BSc)