Dissertations / Theses: 'Carbonatiite'

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Church, Abigail Ann. "The petrology of the Kerimasi carbonatite volcano and the carbonatites of Oldoinyo Lengai with a review of other occurrences of extrusive carbonatites." Thesis, University College London (University of London), 1996. http://discovery.ucl.ac.uk/1349623/.

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Extrusive carbonatites are rare igneous rocks with just 37 known localities. The majority are calciocarbonatites, the principal exception being those of the active volcano, Oldoinyo Lengai, which are strongly alkaline. Unresolved questions concerning extrusive carbonatites include: 1. Why are extrusive carbonatites at Lengai chemically different from all others? 2. Could the extrusive calciocarbonatites originally have had alkaline compositions? In order to address these questions extrusive carbonatites from both Lengai and the adjacent volcano, Kerimasi, were collected and compared. A compilation of all the available data on known extrusive carbonatites is also presented. The major results documented in this thesis are: 1. Alkali carbonatites from Oldoinyo Lengai erupted in 1993 contain petrographic evidence for an origin by liquid immiscibility from a highly fractionated peralkaline silicate melt (wollastonite nephelinite). 2. The suite of silicate rocks at Kerimasi are derived from a primary olivine nephelinite by fractional crystallisation and cumulus processes. 3. Extrusive carbonatites at Kerimasi are not genetically related to the silicate suite. By contrast intrusive sovites also present, originated by liquid immiscibility from a primitive silicate magma, equivalent to a melilite, nephelinite, at low pressure. 4. Extrusive calciocarbonatites from Kerimasi were erupted directly from the mantle. They contain phenocrysts (previously interpreted as pseudomorphs after alkali carbonate) which are now thought to have been dolomite containing calcite exsolution lamellae. 5. Of the 35 other extrusive carbonatite occurrences, none show any petrographic or geochemical evidence of having originally being alkaline. Therefore extrusive carbonatites from Oldoinyo Lengai are thought to be unique. 6. Of the 37 extrusive carbonatites, 50% are associated with melilitites or melilitebearing rocks, 27% are associated with nephelinites and the remaining 23% were erupted with no associated silicate magmas.

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Anzolin, Henrique de Maman. "Multigerações de apatitas no carbonatito Três Estradas, sul do Brasil : significado físico-químico e implicações para a qualidade do minério fosfático." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/184646.

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As recentes descobertas de corpos carbonatíticos no estado geram interesse sobre o potencial econômico destas rochas. Associada ao Complexo Granulítico Santa Maria Chico, o carbonatito Três Estradas apresenta um elevado teor de apatita torna-o um alvo para a implantação de um empreendimento de produção de fosfato, importante para a produção de insumos na indústria agrícola. Neste projeto procurou-se examinar este mineral associado ao carbonatito Três Estradas no estado do Rio Grande do Sul, bem como no perfil de alteração intempérica gerado sobre estas rochas. Foi realizado um estudo detalhado das ocorrências deste mineral associado a este corpo carbonatítico que mostrou a presença de diferentes gerações de apatita ao longo do perfil de alteração intempérica, evidenciando processos de dissolução parcial, substituições químicas e precipitação. Confirmada a existência de apatitas de diferentes gerações, o estudo foi direcionado para caracterizar as populações de apatitas e o ambiente geoquímico associado. Dentre os métodos que foram utilizados cita-se a análise química das amostras por espectrometria de fluorescência de raios-X, microssonda eletrônica, espectroscopia de infravermelho por transformada de Fourier e espectroscopia micro Raman, análise mineralógica através da difratometria de raios X e análise petrográfica e dos elementos texturais por microscopia ótica complementada pela microscopia eletrônica de varredura. Com os resultados obtidos foi possível compreender as variações na composição química das apatitas proveniente do carbonatito e no perfil de alteração destas rochas, identificando distintos tipos de ocorrência deste mineral e caracterizando-os quimicamente, além de especular sobre as condições supergênicas que propiciaram a formação de gerações tardias do mineral elevando consideravelmente as concentrações de fosfato.
Recent discoveries of carbonatite bodies in the state of Rio Grande do Sul created interest about the economic potential of these rocks. Associated with the granulitic complex Santa Maria Chico, the Três Estradas carbonatite presents a high content of apatite, making it a target to the implementation of an adventure for the production of phosphate, an important mineral for the production of inputs for the agricultural industry. In this project, this mineral was examined, as well as the weathering profile occurring in these rocks. A detailed study of the occurrence of this mineral associated with this carbonatite body was elaborated and revealed the presence of different generations of apatite along the weathering profile, evidencing processes of partial dissolution, chemical substitutions and precipitation. Once confirmed the existence of apatite of different generations, the study was directed to characterizing the populations and the geochemical environment associated with each one. Among the methods applied were the chemical analysis of the samples by x-ray fluorescence spectroscopy, electronic microprobe, Fourier-Transform infrared spectroscopy and micro Raman spectroscopy, the mineralogic analysis by x-ray diffraction, and the petrographic and textural analysis by optic microscopy complemented by scanning electron microscope. With the results obtained it was possible to comprehend the variations in the chemical composition of the apatite from the carbonatite and in the weathering profile of these rocks, allowing the identification of different types of occurrence and its chemical characteristics, as well as speculate about the supergenic condition that favored the formation of late generations of the mineral, what elevates considerably the phosphate concentration.

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Luciano, Rejane Lima [UNESP]. "Petrografia e geoquímica das rochas metacarbonatíticas do Complexo Angico dos Dias, divisa Bahia/Piauí, Brasil." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/138310.

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Este trabalho verificou que as rochas metacarbonatíticas do Complexo Metacarbonatítico de Angico dos Dias (CMCAD), constituídas principalmente por calcita, apatita, olivina, flogopita e magnetita dispõem-se em dois conjuntos: um localizado na mina de fosfato da Galvani (corpo principal, Campo Alegre de Lourdes-BA) e o outro na Fazenda Pimenteira (Caracol-PI). Variação no conteúdo de apatita, minerais ferro-magnesianos e magnetita configura um acamadamento cumulático e permite individualizar cinco fácies petrográficas (contatos graduais). Além disso, exibem manto intempérico, que resulta no minério de fosfato residual (apatitito). Registram pelo menos três fases deformacionais marcadas por estruturas primárias (acamamento reliquiar - S0) que devido aos processos de transposição (D1) da foliação S1 e da deformação D2 associada às zonas de cavalgamento (S2) se mantêm de forma escassa nas áreas menos deformadas. D2 evolui para um bandamento tectônico vertical (S3) nas zonas de cisalhamento (D3). Dados isotópicos indicam que as rochas metacarbonatíticas, datadas em 2.011±6Ma (U-PB em badeleíta e zircão), originaram-se de uma fonte mantélica enriquecida e que o enriquecimento em 18O é reflexo do reequilíbrio durante o metamorfismo/ hidrotermalismo relacionado ao Evento Brasiliano. Dados petrográficos e de química mineral apontam: que a olivina altera para serpentina, tremolita, antofilita e magnetita; que é comum a exsolução de dolomita em calcitas e de ilmenita em magnetitas e; que os carbonatitos foram parcialmente silicificados. As demais rochas do CMCAD, milonitizadas e metamorfizadas em fácies anfibolito alto (mesopertitas), exibem processo de potassificação (fenitização), metassienito e metassienogranito, além de processos de sericitização, saussuritização e epidotização dos plagioclásios. O evento metassomático/hidrotermal (fácies xisto verde médio a alto) tem caráter regional e atinge além das rochas do CMCAD as rochas do Complexo Sobradinho-Remanso. Dados geoquímicos classificam as rochas metacarbonatíticas principalmente como calciocarbonatitos. Aquelas intensamente hidrotermalizadas são classificadas como ferrocarbonatitos e magnesiocarbonatitos. Indicam filiação magmática comum para todos os cinco litofácies, associada a processos de diferenciação magmática por segregação mineral.
This study found that the metacarbonatite rocks of the Angico dos Dias Metacarbonatite Complex (CMCAD), consisting mainly of calcite, apatite, olivine, phlogopite and magnetite are arranged in two sets: one located at the phosphate mine Galvani (main body, Campo Alegre de Lourdes-BA) and the other at the Farm Pimenteira (Caracol-PI). Variation in the content of apatite, iron-magnesium minerals and magnetite sets up a cumulatic layering and allows individualize five petrographic facies (gradual contacts). Furthermore, exhibit weathering mantle, which results in the residual phosphate ore (apatite-rock). Register at least three deformational phases marked by primary structures (layering reliquiar - S0) that due to the transposition process (D1) of the foliation S1 and D2 deformation associated with thrust zones (S2) remain scantily the least deformed areas. D2 evolves into a tectonic vertical banding (S3) in the shear zones (D3). Isotopic data indicate that metacarbonatite rocks, dated at 2,011 ± 6Ma (U-PB in baddeleyite and zircon), originated from a mantle source enriched and the enrichment in 18O reflects the rebalancing during metamorphism/hydrothermalism related the Brasiliano Event. Petrography and mineral chemistry data point: the olivine changes to serpentine, tremolite, anthophyllite and magnetite; which it is common to exsolution of dolomite in calcite and ilmenite in magnetite and; that carbonatites were partially silicified. The other rocks CMCAD, mylonite and metamorphosed to amphibolite facies high (perthites) exhibit potassification process (fenitization), metasyenite and metasyenogranite, and sericitization, saussuritization and epidotization processes of plagioclase. The metasomatic/hydrothermal event (medium to high greenschist facies) has regional character and reaches beyond CMCAD rocks the rocks of Sobradinho-Remanso Complex. Geochemical data classify metacarbonatite rocks mainly as calcium carbonatites. Those intensely hydrothermalized are classified as iron metacarbonatites and magnesium carbonatites. Indicate common magmatic membership for all five lithofacies, associated with magmatic differentiation processes for mineral segregation.

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Cerva-Alves, Tiara. "Geologia dos carbonatitos ediacaranos de Caçapava do Sul, Rio Grande do Sul, Brasil." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/157570.

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A avaliação integrada de dados de geoquímica do solo, aerogamaespectrometria (eTh), mapeamento geológico e estrutural associado à descrição de furos de sondagem e afloramentos da região de Caçapava do Sul, sul do Brasil, levou à descoberta de dois corpos de carbonatitos. Estes corpos estão localizados próximos aos limites sudeste e leste do Granito Caçapava, intrudindo o Complexo Passo Feio. O sistema é composto por alvikitos de coloração rosada seguidos por beforsitos brancos tardios, ambos na forma de corpos tabulares deformados concordantes com a xistosidade e dobras das rochas encaixantes. Análises petrográficas e avaliações utilizando microscópio eletrônico de varredura demonstraram que a calcita é o mineral predominante nos alvikitos, sendo os seguintes minerais acessórios e traço: apatita, magnetita, ilmenita, biotita, badeleita, zircão, rutilo, minerais do grupo do pirocloro e minerais de elementos terras raras (ETR). O beforsito, caracterizado pela presença abundante de dolomita, possui os mesmos minerais acessórios e traço observados nos alvikitos. A metodologia utilizada para geocronologia foi U-Pb em zircões via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), executada em uma amostra de beforsito. A idade de cristalização fornecida pelo método foi de 603,2 ± 4,5 Ma, colocando a intrusão em um contexto de ambiente pós-colisional ediacarano, com tectonismo transpressivo predominante e atividade vulcânica marcada por características shoshoníticas.
The integrated evaluation of soil geochemistry, aerogammaspectrometry (eTh), geological and structural mapping associated with description of boreholes and outcrops of Caçapava do Sul region, southernmost Brazil, led to the discovery of two carbonatite bodies. They are located near to the east and southeast of Caçapava Granite, intruding the Passo Feio Complex. The system is composed by early alvikite pink-colored rock followed by late white beforsite dikes in deformed tabular units concordant with the host rock schistosity and folds. Petrographic and scanning electron microscopy show that the alvikites are dominantly by calcite with subordinate apatite, magnetite, ilmenite, biotite, baddeleyite, zircon, rutile, pyrochlore-like and rare earth element minerals. Beforsites have the same minor and accessory minerals of the alvikites. U-Pb zircon geochronology via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was performed on a beforsite sample, yielding a 603.2 ± 4.5 Ma crystallization age, in an Ediacaran post-collisional environment with transpressive tectonism and volcanic activity market by initial shoshonitic characteristics.

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Mäder, Urs Karl. "The Aley carbonatite complex." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26006.

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The Aley carbonatite complex, a property belonging to Cominco Ltd., is 140 km north-northeast of Mackenzie, British Columbia at latitude 56°27' N, longitude 123°45' W. The complex intruded Cambrian rocks 345 ma ago near the shelf / off-shelf boundary of ancient North America and is now contained in an imbricate thrust sheet of the Northern Rocky Mountains. The circular complex is 3 km in diameter, cylindrical with respect to the third dimension and little affected by structures of the Rocky Mountains. The relationship of nearby lamprophyric dikes and the lamproitic Ospika diatreme, closely related in time, is unclear. The Aley carbonatite complex consists of an older, outer "syenite" ring (33% of the area) and a younger dolomite carbonatite core with minor calcite carbonatite "sweats". Rare-earth rich ferro-carbonatite dikes intruded the contact aureole. The contact aureole is composed of recrystallized rocks characterized by brownish weathering, but is little affected by metasomatism and shows no indication of high temperature contact metamorphism. The mineralogy and mineral chemistry were studied in detail. Over forty mineral species are described, including rare-earth carbonates (burbankite, ancylite, cordylite, huanghoite etc.), niobium oxides (pyrochlore, fersmite, columbite) and alkali-rich silicates (arfvedsonite, aegirine, richterite). Dolomite carbonatite contains apatite, pyrite and fersmite pseudomorphs after pyrochlore. Calcite carbonatite is composed of apatite, magnetite, biotite, pyrochlore, pyrite, ± richterite. The inner part of the contact aureole forms an annular, cylindrical ductile shearzone suggesting that doming was the major mechanism of emplacement. This is consistent with the circular structural trends in the carbonatite core. Temperatures deduced from field observations and mineralogy (250°C-400°C) disagree with temperatures calculated for a cooling igneous body based on a simple heat conduction model (500°C-600°C) further supporting the view that the complex was emplaced at subsolidus temperatures. Oxygen and carbon isotope ratios (δ¹⁸O = 7.7-15.4, δ¹³C = -4.7 - -6.1) and some initial Sr isotope ratios (⁸⁷Sr/⁸⁶Sr = 0.7034-0.7036) are indicative of a mantle source of carbonatite and syenite. Ceochemically, the carbonatites are enriched in the incompatible elements LREE, Th, U, Nb, Ta, Zr. The rare-earth carbonatite dikes represent a residual liquid extremely enriched in Fe, S, LREE, Sr and Ba. The "syenite" is not a .typical alkali-syenite, bearing quartz instead of felspathoids. A strong metasomatic overprint is marked by secondary aegirine and metamorphic textures. Processes by which the rocks of the Aley may be related genetically are discussed in the light of petrography, geochemistry and experimental studies.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

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Djeddi, Asma. "Pétrogenèse des carbonatites et magmas alcalins protérozoïques d’Ihouhaouene : terrane de l’In Ouzzal, Hoggar occidental, Algérie." Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTG022/document.

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Le craton archéen de l’In Ouzzal représente une succession d'événements intrusifs et métamorphiques depuis l’Eburnéen qui en font un marqueur important des processus géodynamiques à travers les temps géologiques. La région d’Ihouhaouene située au N-W du terrane de l’In Ouzzal en Algérie est unique de par la présence d’intrusions protérozoïques de carbonatites associées à des roches alcalines saturées. Ces carbonatites intracontinentales comptent parmi les plus anciennes et inhabituelles de par leurs diversités et la présence de minéraux à terres rares. Les carbonatites sont pegmatitiques ou bréchiques avec des fragments de syénite. Elles sont des calciocarbonatites composées de calcite (>50 vol.%), apatite, clinopyroxène et wollastonite et sont associées à des syénites rouges ou blanches présentes sous forme massive. Les syénites sont composées d’alternance de niveaux clairs de feldspaths alcalins rouges ou de wollastonites associées aux feldspaths blancs et de niveaux sombres d’apatites et de clinopyroxènes. Les carbonatites et syénites forment une suite cogénétique caractérisée par une augmentation en SiO2 et une diminution en CaO et CO2. Les carbonatites ont des compositions en silice comprises entre 5 et 35 pds.%, 28 et 53 pds.% CaO et 11 à 36 pds.% CO2. Les syénites montrent une forte teneur en K2O (12 pds.%) et des teneurs très faibles en Na2O (1 pds.%). Les carbonatites et syénites sont riches en éléments incompatibles avec des teneurs en REE supérieures à 7000 fois les chondrites et 1000 fois les chondrites dans les syénites, respectivement, et de fortes teneurs en U, Sr et Th. Les éléments en trace dans les minéraux magmatiques (apatite et pyroxène) mettent en évidence des processus complexes à l’origine de ces roches impliquant plusieurs étapes de cristallisation fractionnée et d’immiscibilité à partir d’un magma mélilititique riche en CO2. Les minéraux des carbonatites riches en silice et des syénites blanches ont des signatures géochimiques similaires et se caractérisent par des rapports élevés en Nb/Ta typiques de magmas riches en carbonate par immiscibilité. Les syénites rouges ont des caractéristiques de liquides silicatés évolués par différentiation. Les minéraux des carbonatites pauvres en silice ont des rapports Nb/Ta très variables, sub-chondritiques (<10), indiquant une cristallisation à partir de liquides très évolués et la présence de magmas carbonatitiques tardifs. Les apatites, en particuliers, enregistrent divers épisodes magmatiques et également supergènes. Elles présentent dans certaines roches une redistribution et un enrichissement en terres rares variables qui se caractérisent par des exsolutions de britholite dans les carbonatites riches en silice et monazite dans les carbonatites pauvres en silice. Ces exsolutions traduisent des rééquilibrations locales sub-solidus avec des fluides tardi-magmatiques de composition riche en Cl-Th-REE pour l’exsolution de la britholite et S-Ca-P-CO2 pour les inclusions de monazite. L’apatite et le zircon présents dans ces roches alcalines et carbonatites, ont permis de déterminer l’âge de mise en place du complexe magmatique de Ihouahouene à 2100 Ma syn-métamorphique et de confirmer l’âge panafricain de son exhumation. L’étude pétrologique, géochimique et géochronologique des carbonatites et syénites d’Ihouhaouene a permis de mettre en évidence l’origine magmatique de ces roches et de définir les interactions fluides-roches supergènes à l’origine des enrichissements en REE. Les carbonatites et syénites d’Ihouahouene proviennent d’un faible taux de fusion partielle d’un manteau Précambrien riche en CO2. Plusieurs étapes de cristallisation fractionnée et d'immiscibilité ont permis la genèse de ces roches hybrides, piégées le long de grandes zones de cisaillement durant la période de transition Archéen /Eburnéen dans un régime extensif à l’In Ouzzal caractérisé par un environnement granulitique d’ultra-haute-température
The In Ouzzal Archaean craton represents a succession of intrusive and metamorphic events since Eburnean, and an important marker of geodynamic processes through geological time. The Ihouhaouene area located in the N-W of In Ouzzal terrane in Algeria is unique by the presence of Proterozoic carbonatite intrusions associated with silica-saturated alkaline rocks. These intracontinental carbonatites are among the oldest and exceptional because of their diversity and the presence of unusual rare earth minerals. Carbonatites are pegmatitic or brecciated with fragments of syenite. They are calciocarbonatites with calcite (> 50 vol.%), apatite, clinopyroxene and wollastonite and are associated with red or white syenites in massive outcrops. Syenites are composed of alternating light levels of red alkaline feldspar or wollastonite associated with white feldspar and dark levels of apatite and clinopyroxene. Carbonatites and syenites form a cogenetic suite characterized by an increase in silica and decrease in calcium and CO2 content. The carbonatites have silica content ranging from 5 to 35 wt.%, 28 to 53 wt.% CaO, and 11 to 36 wt.% CO2. Syenites have high K2O (12 wt.%) and low Na2O content (1 wt.%). Carbonatites and syenites have high incompatible element concentrations with high REE content (7000*chondrites and 1000*chondrites, respectively) and high U, Pb, Sr and Th content. Trace elements (eg. Rare Earths, Nb-Ta, Zr-Hf) in magmatic minerals (apatite-pyroxene) of carbonatites and syenites reveal complex magmatic processes at the origin of these rocks involving several stages of fractional crystallization and immiscibility from a CO2-rich melilititic magma. Silica-rich carbonatites and white syenites are characterized by high Nb/Ta, Y/Zr and Rb/Sr ratios, typical of carbonate-rich magmas by immiscibility. The red syenites have characteristics of immiscible differentiated silicate melt. Silica-poor carbonatite minerals have variable subchondritic Nb/Ta (<10) indicating crystallization from highly evolved liquids and the presence of late carbonatitic magmas. Apatites, in particular, record various magmatic and supergene processes. They present, in some rocks, redistribution and enrichment in rare earth elements, which are characterized by exsolutions of britholite in silica-rich carbonatites and monazite-quartz-calcite inclusions in silica-poor carbonatites. These minerals reflect local sub-solidus re-equilibration with late-magmatic fluids rich in Cl-Th-REE for the exsolution of britholite and S-Ca-P-CO2 for monazite inclusions. The apatite and zircon present in these alkaline and carbonatite rocks, allow determination of the syn-metamorphic crystallization age of the Ihouahouene magmatic complex at 2100 Ma and confirm the pan-African age of its exhumation. The petrological, geochemical and geochronological study of Ihouhaouene carbonatites and syenites highlights the magmatic origin of these rocks and constrains the fluid-rock interactions at sub-solidus conditions leading to REE-enrichment. The carbonatites and syenites result from a low partial melting rate of a CO2-rich Precambrian mantle. Several fractional crystallization and immiscibility stages allowed the genesis of these hybrid magmas, trapped along large shear-zones during the Archean/Eburnean transition period in the In Ouzzal terrane, characterized by extensive deformation in ultra-high-temperature granulitic environment

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Rahman, Aklaqur. "Alnö Carbonatite: A Future Moneymaker?" Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-328062.

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Carbonatites are rare igneous rocks, which contain at least 50 %, carbonate minerals. They are often found along with alkaline silicate rocks, meaning that they contain relatively large amounts of Na2O and K2O, and important tools to understand mantle processes. Importantly, carbonatites are known to be rich in REE (Rare Earth Elements), compared to other magmatic rocks. The Alnö complex is located in the northern part of the island of Alnö, northeast of Sundsvall and is one of the biggest ring-shaped intrusions of the alkaline and carbonatite sort. The origin of carbonatites is not fully known yet but they may have resulted from a mantle plume, and absolute dating methods indicate that the age of the Alnö carbonatites are around 600 Ma. A large amount of carbonatites have been found in the Alnö complex and the purpose of this thesis is to assess whether the Alnö complex and its carbonatites can become a potential source of REEs and if it can be profitable to mine these. The research has been conducted by first analyzing samples from the Alnö complex in thin sections through a light polarising microscope. The thin sections were photographed with a focus on apatite crystals, since apatite are hosts of REE. The apatites in the thin sections are crystals with high relief, sub-rounded and white-grey in color in a calcitic matrix. The images of the apatite were then edited with photoshop, to graphically isolate the apatite. The processed images were then analyzed in a program called “ImageJ” to calculate the total area of apatites in the thin sections and the area percentage of apatites. The area percentage helps to give an estimation of how much REE that can occur in the carbonatites of the Alnö Complex. A recent 3D- analysis of the Alnö complex using petrophysical and geophysical methods indicated the volume of the complex, which when coupled with our apatite data, allows us to estimate the total REE volume. The estimation of occurrences of apatites was calculated to around 13 % of the carbonatites in the Alnö complex. The cost to mine the REEs was much higher than the market price of the REEs. So the Alnö carbonatites are not profitable to mine for REEs today.
Karbonatit är en ovanlig bergart som innehåller minst 50 procent karbonater, därav namnet. De hittas ofta i samband med alkaliska silikat-bergarter, vilket innebär att de innehåller till stor del natriumoxid och kaliumoxid samt kisel, och är viktiga för att kunna förstå processer i manteln. Karbonatiter är kända för att vara innehållsrika på sällsynta jordartsmetaller, även kända som REE, jämfört med andra magmatiska bergarter. Alnökomplexet ligger i den norra delen av Alnön, nordost om Sundsvall och är ett av världens största alkaliska och karbonatit-ringkomplex, med en radie på 2,5 km. Dess ursprung i jordens inre är okänt men det tros vara ett resultat av en mantelplym, smältor från manteln som stiger mot ytan, och åldersdatering via absoluta dateringsmetoder tyder på att karbonatiterna är nästan 600 Ma. Stora mängder karbonatiter har hittats i Alnökomplexet och syftet med detta arbete är att bedöma om Alnökomplexet potentiellt kan bli gynnsam som källa för prospektering av sällsynta jordartsmetaller, ur ekonomisk synpunkt. Detta utfördes genom att analysera prover från Alnökomplexet samt studera data från Magnus Anderssons arbete om Alnökomplexet. Proverna analyserades med hjälp av en mikroprob som fotograferade apatiten, vita kristaller i ett mörkgrå matrix, då apatit indikerar på hög sannolikhet för REE-förekomst. Sedan redigerades dessa bilder med Photoshop och Paint, där andra kristaller redigerades bort så att det enda som var kvar var de vit-gråa utåtstickande kristallerna mot ett kalcitrikt matrix. Med ett annat program som heter ImageJ beräknades arean av dessa kristaller samt procenten av arean som apatiterna utgör i tunnslipen. Detta gav en viss uppskattning på hur stor mängd REE som kan förekomma i Alnökarbonatiter. Resultatet jämfördes med data från Magnus Andersson som har gjort en 3D- undersökning av karbonatiter under Alnö-komplexet. Apatiten utgjorde en area på 13 % och mängden REE var inte tillräckligt stor mängd relativ marknadspriserna samt utvinningskostnader för att räknas som vinstgivande.

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8

Mollex, Gaëlle. "Architecture de la plomberie du volcan carbonatitique Oldoinyo Lengai : nouvelles contraintes sur la source, les transferts hydrothermaux, et la différenciation magmatique dans la chambre active." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0123/document.

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La particularité de l’Oldoinyo Lengai à émettre des laves natrocarbonatitiques fait de ce volcan un laboratoire naturel pour l’étude de la genèse de ces magmas. De nouvelles mesures isotopiques en hélium nous ont permis de constater que la signature des fumerolles est constante depuis 1988 malgré le changement morphologique considérable du cratère sommital lors de la dernière éruption subplinienne de 2007-2008. L’alternance des éruptions explosives et effusives n’engendre donc aucune modification majeure dans l’organisation du système hydrothermal qui est par conséquent profondément enraciné. Les xénolites cogénétiques qui ont été émis lors de l’éruption de 2007-2008 permettent d’étudier directement les processus magmatiques qui se déroulent dans la chambre magmatique active. La comparaison des signatures isotopiques des gaz rares (hélium) de la chambre magmatique et des volcans silicatés de la région d’Arusha montre que les deux types de magmatisme ont une source analogue identifiée comme un manteau lithosphérique subcontinental préalablement métasomatisé par des fluides asthénosphériques. De plus, ces signatures isotopiques confirment l’absence de contaminations crustale lors de la remontée du magma entre le manteau source et la surface. Une description pétrographique de détail couplée à une approche thermobarométrique, ainsi qu’à la détermination des modèles de solubilité des volatils dans les liquides phonolitiques, nous a permis d’identifier l’évolution du liquide dans la chambre magmatique et ses paramètres de stockage. Les résultats nous révèlent que le magma injecté en 2007 a une composition phonolitique et des teneurs élevées en volatils (3.2 wt.% de H2O et 1.4 wt.% de CO2) ainsi qu’une température d'environ 1060° C. Ce magma évolue ensuite dans la chambre magmatique crustale se trouvant à 11.5±3.5 km de profondeur jusqu’à atteindre une composition de néphélinite et une température de 880°C. Pendant sa différenciation, le magma silicaté s’enrichit en calcium, sodium, magnésium et fer alors que sa concentration en silice, potassium et aluminium décroit. Ces résultats concordent avec les précédents relatifs à cette éruption, ou aux produits volcaniques plus anciens émis tout au long de la vie du volcan. Cette similarité suggère qu’aucun changement majeur n’ait eu lieu dans l’organisation de la plomberie du volcan Oldoinyo Lengai au cours de son évolution. Les mesures en éléments traces (REE, HFSE et LILE) dans les minéraux cristallisés lors de cette séquence de différenciation, et les inclusions magmatiques associées montrent un enrichissement pouvant atteindre de 100 à 1000 fois la composition du manteau primitif. Une étude expérimentale préliminaire s’appuyant sur la composition du liquide de recharge (phonolite) et les conditions (P, T) identifiées pour la chambre magmatique nous a permis de reproduire l'immiscibilité entre un liquide silicaté et carbonatitique, processus à l’origine de la formation des carbonatites de l’Oldoinyo Lengai. La poursuite de ces travaux expérimentaux permettra de mieux contraindre la genèse des magmas carbonatitiques et ainsi comprendre les processus en jeux dans l’enrichissement en éléments traces des magmas carbonatitiques
The uniqueness of Oldoinyo Lengai to emit natrocarbonatite lavas makes this volcano a natural laboratory to study the genesis of these magmas. New helium isotopic data permit to assert that the signature of the fumaroles has been constant since 1988 despite the radical morphological change of the summit crater after the last sub-Plinian eruption in 2007-2008. The alternation of the effusive and explosive eruptions does not cause major modifications in the hydrothermal system architecture, which is inferred to be deeply rooted. Cognate xenoliths that were emitted during the eruption in 2007-2008 represent a unique opportunity to document the igneous processes occurring within the active magma chamber. The comparison between the noble gas (helium) isotopic compositions of the active magma chamber and those of the other silicate volcanoes of the Arusha region indicates that both types of magmatism have similar sources, identified as being a typical sub-continental lithospheric mantle, which was previously metasomatized by asthenospheric fluids. Moreover, these isotopic signatures confirm that no crustal contamination has occurred during the magma ascent from the mantle to the surface. Detailed petrographic descriptions coupled to a thermo-barometric approach, and to the determination of volatile solubility models for a phonolite composition, allow us to identify the melt evolution at magma chamber conditions and the storage parameters. These results indicate that the magma injected in 2007 has a phonolitic composition and contains a high amount of volatiles (3.2 wt.% H2O and 1.4 wt.% CO2) as well as a temperature around 1060° C. This magma subsequently evolved in the crustal magma chamber located at 11.5 ± 3.5 km depth until reaching a nephelinite composition and a temperature of 880°C. During the differentiation in the magma chamber, the silicate magma is enriched in calcium, sodium, magnesium and iron, whereas the content of silicate, potassium and aluminum decreases. Our results support previous studies related to this eruption, and are similar to the historical products emitted during the whole volcano history, permitting the suggestion that no major modification in the plumbing system has occurred during the Oldoinyo Lengai evolution. The trace elements (REE, LILE and HFSE) measured in the minerals and melt inclusions reveal a concentration reaching 100 to 1000 times the primitive mantle composition. A preliminary experimental study based on the recharge melt composition (phonolite) and identified magma chamber conditions (P, T) permits to reproduce the immiscibility between silicate and carbonatite liquids, key processes at the origin of the Oldoinyo Lengai carbonatites. The continuation of this experimental study will lead to a better comprehension of the carbonatite genesis, thus improving our understanding of the processes that are responsible for the enrichment in trace elements

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9

Broom-Fendley, Sam Louis. "Targeting heavy rare earth elements in carbonatite complexes." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18490.

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The HREE are generally considered to be the most critical of the REE, indispensable for many high-tech applications such as smart-phones and electric vehicles. Currently, carbonatites are the main source of REE due to their high REE grade; most carbonatites, however, are HREE-poor. This thesis presents the findings on HREE mineralisation at the Songwe Hill carbonatite, in the CAP of south-eastern Malawi. Across all carbonatite types at Songwe, whole-rock Y and P2O5 concentrations correlate positively, indicating that phosphate minerals have a strong control over the HREE contents. This is confirmed through textural and geochemical analyses (LA ICP-MS and EPMA) of apatite, which show that it can be subdivided into 5 different types (Ap-0–4), found at different stages of the paragenetic sequence. The chemistry of each of these apatite types becomes progressively more HREE-enriched, up to 3 wt. % Y2O3, and ultimately culminating in xenotime crystallisation. Cross-cutting relationships indicate that HREE-enriched apatite formed as an early crystallisation product from a late-stage, carbonatite-derived hydrothermal fluid. It is evident that LREE-fluorcarbonate mineralisation occurred after apatite crystallisation and it is assumed that crystallisation of all hydrothermal phases was though the evolution of a single fluid, rather than several different fluids. The apatite composition is compared to a compilation of analyses of apatite from other carbonatites and granitoids, as well as new analyses of late-stage apatite from the Kangankunde and Tundulu carbonatites, Malawi. Based on these analyses, it is concluded that apatite from Songwe has the highest HREE concentration compared to apatite from any previously analysed carbonatite. However, apatite from the Tundulu carbonatite has a similar geochemistry and paragenesis to the HREE-rich apatite from Songwe, suggesting that late-stage HREE enrichment may be a common process in carbonatites. In order to elucidate the fluid conditions which led to HREE mineralisation, new fluid inclusion and stable isotope data are presented to complement the mineralogical data. The fluid inclusions constrain the minimum temperature of apatite crystallisation of 160 °C, and most homogenisation temperatures in apatite are between 160-360 °C. Inclusions from apatite are CO2-rich, and it is suggested that transport of the REE occurred in carbonate complexes. Stable isotope data were obtained from both conventional C and O analyses of carbonates and from a novel method developed for acquiring δ18OPO4 from apatite. A conceptual model involving the simultaneous cooling and mixing of magmatically-derived and meteoric fluids is suggested. Two possible causes of REE fractionation are suggested: (1) a crystal-chemical control and (2) control through preferential stability of LREE and HREE complexes. However, neither mechanism is equivocal and further work on the stability of carbonate complexes is suggested in order to better understand REE mineralisation at carbonatites In addition to results on the HREE mineralisation in carbonatites, new data on the mineralogy, geochemistr y and age of the Songwe Hill carbonatite and the closely-associated Mauze nepheline syenite intr usion are presented. Songwe compr ises three stages of intr usion (C1–3): (C1) sovitic calcite carbonatite, (C2) alvikitic calcite-carbonatite and (C3) Fe-rich carbonatite. The LREE grade increases with the increasing Fe-content of the intrusion, as is common at many REE-rich carbonatites. Later-stages of the intrusion include apatite-fluorite veins (C4) and Mn-Fe-veins. The former is a volumetrically minor stage, but can contain up to 1 wt. % Y2O3, and the latter is formed through oxidation of carbonatite by supergene fluids. Samples analysed from Mauze show that it is REE- and P2O5-poor, with MREE-depleted REE distributions. U-Pb dating of zircons from Songwe and Mauze show that they are 131.5 ± 1.3 and 133.1 ± 2.0 Ma, respectively. The close temporal association of each intrusion suggests that Mauze could be a ‘heat-engine’ for hydrothermal mineralisation at Songwe.

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10

Norton, Gillian Elizabeth. "The physical properties of carbonatite and silicate magmas." Thesis, Lancaster University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316563.

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11

Sharpe, Joanna Carleton University Dissertation Geology. "Geochemistry of the Cargill Carbonatite Complex, Kapuskasing, Ontario." Ottawa, 1987.

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12

Moore, Meghan. "Carbonatite-related rare-earth mineralization in the Bear Lodge alkaline complex, Wyoming: Paragenesis, geochemical and isotopic characteristics." ElSevier, 2014. http://hdl.handle.net/1993/23991.

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The Bear Lodge alkaline complex in northeastern Wyoming (USA) is host to potentially economic rare-earth mineralization in carbonatite and carbonatite-related veins and dikes that intrude heterolithic diatreme breccias in the Bull Hill area of the Bear Lodge Mountains. The deposit is zoned and consists of pervasively oxidized material at and near the surface, which passes through a thin transitional zone at a depth of ~120-183m, and grades into unaltered carbonatites at depths greater than ~183-190m. Carbonatites in the unoxidized zone consist of coarse and fine-grained calcite that is Sr-, Mn- and inclusion-rich and are characterized by the presence of primary burbankite, early-stage parisite and synchysite with minor bastnäsite that have high (La/Nd)cn and (La/Ce)cn values. The early minerals are replaced with polycrystalline pseudomorphs consisting of secondary rare-earth fluorocarbonates and ancylite with minor monazite. Different secondary parageneses can be distinguished on the basis of the relative abundances and composition of individual minerals. Variations in key element ratios, such as (La/Nd)cn, and chondrite-normalized profiles of the rare-earth minerals and calcite record multiple stages of hydrothermal deposition involving fluids of different chemistry. A single sample of primary calcite shows mantle-like δ18O V-SMOW and δ13C V-PDB values, whereas most other samples are somewhat depleted in 13C (δ13C V-PDB ≈ –8 to –10‰) and show a small positive shift in δ18O V-SMOW due to degassing and wall-rock interaction. Isotopic re-equilibration is more pronounced in the transitional and oxidized zones; large shifts in δ18O V-SMOW (to ~ 18‰) reflect input of meteoric water during pervasive hydrothermal and supergene oxidation. The textural relations, mineral chemistry, and C and O stable-isotopic variations record a polygenetic sequence of rare-earth mineralization in the deposit. With the exception of one Pb-poor sample showing an appreciable positive shift in 208Pb/204Pb value (~39.2), the Bear Lodge carbonatites are remarkably uniform in their Nd, Sr and Pb isotopic composition: (143Nd/144Nd)i=0.512591-0.512608; εNd=0.2-0.6; (87Sr/86Sr)i=0.704555-0.704639; εSr=-1.5-2.7; (206Pb/204Pb)i=18.071-18.320; (207Pb/204Pb)i=15.543-15.593; (208Pb/204Pb)i=38.045-39.165. These isotopic characteristics indicate that the source of the carbonatitic magma was in the subcontinental lithospheric mantle, and modified by subduction-related metasomatism. Carbonatites are interpreted to be generated from small degrees of partial melt that may have been produced via interaction of upwelling asthenosphere giving a small depleted MORB component, with an EM1 component likely derived from subducted Farallon crust.

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13

Brod, José Affonso. "Petrology and geochemistry of the Tapira alkaline complex, Minas Gerais State, Brazil." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4971/.

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The Tapira alkaline complex is the southernmost of a series of carbonatite-bearing intrusions occurring in the Alto Paranaíba region, western Minas Gerais State, Brazil. Together with kamafugites, lamproites and kimberlites, these complexes form part of the Late-Cretaceous Alto Paranaíba Igneous Province (APIP). The Tapira igneous complex is emplaced into rocks of the Late-Proterozoic Brasilia mobile belt, adjacent to a major cratonic area (the Sāo Francisco craton).The complex is formed by the amalgamation of several intrusions, comprising mainly ultramafic rocks (wehrlites and bebedourites), with subordinate syenite, carbonatite and melilitolite. At least two separate units of ultramafic rocks (B1 and B2) and five episodes of carbonatite intrusion (CI to C5) are recognised. The plutonic rocks are crosscut by fine-grained ultramafic and carbonatite dykes. Two varieties of ultramafic dykes are recognised: phlogopite-picrites are the most primitive rocks in the complex; low-Cr dykes are more evolved, and typically lack olivine. The ultramafic dykes are carbonate-rich, and may contain carbonate ocelli, indicating that immiscibility of carbonatite liquid occurred early in the evolution of the complex. The ultramafic dykes are chemically similar to the APIP kamafugites. The primitive Tapira magmas underwent some differentiation in the crust, before their final emplacement. Crystal fractionation from the phlogopite-picrite magma may have produced olivine and chromite-rich cumulates, but these rocks are under- represented in the complex. Crystal fractionation from low-Cr dykes may have produced the bebedourites. The Tapira complex contains examples of carbonatites that originated by either liquid immiscibility or crystal fractionation. These contrasting petrogenetic mechanisms have produced distinct geochemical and mineralogical signatures, which have been used to pinpoint specific events in the evolution of the complex, and to test the consanguinity of carbonatites and associated silicate rocks.

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14

Salo, A. (Aleksi). "Geology of the Jaakonlampi area in the Siilinjärvi carbonatite complex." Bachelor's thesis, University of Oulu, 2016. http://urn.fi/URN:NBN:fi:oulu-201604091452.

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The objective of this work was to describe the lithology and structures of the Jaakonlampi area of the Siilinjärvi alkali complex, eastern Finland. The research area is located directly north of the currently mined Särkijärvi open pit of the Siilinjärvi apatite mine. A drilling project to increase the knowledge on the phosphorus-bearing mineralization in the Jaakonlampi area was commenced in 2014. The defined lithological units and structural model were based on field observations and Yara Siilinjärvi Mine’s geological database and employed in resource estimation on the Jaakonlampi area. The Jaakonlampi area consists of carbonatite, silicocarbonatite, carbonate-glimmerite and glimmerite, with fenite xenolith-bearing margins in contact with metasomatically produced fenite halo. A regional NE-SW-trending shear zone affects the northern part of the Jaakonlampi area. The alkali complex is cut by Svecofennian mafic and intermediate dikes, with varying age and composition. A previously unknown felsic pegmatitic dike was identified from the northwest part of the Jaakonlampi area. Four deformation phases were identified in the study area. The use of structural geology gives the ore evaluation process a better control over the calculation parameters in different areas, as all the lithological domains are affected by regional and local faulting and shearing.

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15

McMahon, Sorcha Ciara. "New insights into deep mantle melts: the carbonatite-melilitite connection." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680375.

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The study of carbonatites and their genesis is an active area of research, with significant implications for carbon in the mantle and the global carbon cycle. In this thesis, possible theories of carbonatite petrogenesis are investigated using two main approaches. Firstly, natural examples of extrusive calciocarbonatites in the Calatrava Volcanic Province (CVP), Spain, are explored. Secondly, experiments at mantle conditions in piston cylinder apparatus are used to reproduce characteristic textures and compositions observed at the CVP, and examine the melting behaviour of potassic carbonated lherzolite in the mantle. The extrusive pyroclastic carbonatite deposits at the CVP can potentially provide· insights into deep mantle melts. Carbonate-rich volcanism is prevalent, and closely associated with silica-undersaturated magmas such as melilitites, nephelinites and leucitites. Rounded calcium carbonate globules within silicate melt fragments in carbonate tuffs are described and analysed in detail in this study. A variety of methods are used to characterise the textures and geochemistry of the carbonate globules, to investigate whether they represent quenched immiscible carbonatite liquids or solid calcite crystals with a rounded shape. Results from trace element partitioning studies of the natural samples, and experiments based on the Calatrava compositions, suggest that the carbonate globules are rounded carbonate crystals, and do not support an immiscible origin in their formation. In an effort to understand carbonatite melting at a more general scale, experimental results in the simple synthetic system, CaO-MgO-Ah03-Si02-K20-C02, at 30 kbar are presented. A low variance approach is utilised to maximise the proportion of melt to aid in identification and analysis of small-degree partial melts. Potassium-rich carbonatite melt is found to be in equilibrium with phases typical of a carbonated lherzolite assemblage over a large temperature interval. Melt composition changes very little over the temperature range, corresponding to a region of highly potassic (rv20 wt.% K20) carbonatite metasomatism at mantle depths.

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16

Pollock, Stephen John Carleton University Dissertation Geology. "The isotopic geochemistry of the Prairie Lake carbonatite complex, Ontario." Ottawa, 1987.

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17

Morisset, Natalie Carleton University Dissertation Geology. "Stableisotope and radioisotope geochemistry of the Panda Hill carbonatite, Tanzania." Ottawa, 1992.

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18

Preci, Lorenzo. "Concrezioni Carbonatiche Metano-derivate nella valle del Secchia." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

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19

Mungall, James E. "Geochemistry of carbonatite and alkali pyroxenite, Bancroft Terrane, Grenville Province, Ontario." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59521.

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Alkali-rich pyroxenite and sovitic carbonatite intruded amphibolite grade metamorphic rocks of the Bancroft terrane, Grenville province, in the Eganville-Pembroke region, Ontario, between 1090 and 1038 Ma ago. Intrusive field relationships, metastable feldspar mineralogy and oxygen isotope geothermometry indicate temperatures of emplacement above 650$ sp circ$C and locally rapid cooling rates. Clinopyroxene compositions from pyroxenites, carbonatites and fenites show identical sodium and iron enrichment trends. REE and C and O isotope ratios in carbonate dikes are typical of carbonatites. The presence in nearby carbonate metasediments of diopside- and apatite-rich skarn zones resulting from regional metamorphism explains the confused state of literature concerning the intrusive suite. Previously recognized resetting of radiogenic isotope systems may have resulted from a regional fenitization event associated with the emplacement of this suite.

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20

Bédard, L. Paul. "Pétrographie et géochimie du stock de Dolodau : syénite et carbonatite associée /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1988. http://theses.uqac.ca.

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21

Roopnarain, Sherissa. "Petrogenesis of Carbonatites in the Alnö Complex, Central Sweden." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-215436.

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The Alnö Complex is a Late Precambrian alkaline and carbonatite intrusion (c. 30km2) into Early Proterozoic country rock that extends from the north east, to the north western shoulder of Alnö Island. Carbonatites are rare among volcanic provinces, with Oldoinyo Lengai of northern Tanzania being the only active carbonatite volcano in the world today. The high carbonate mineral volumes and rare earth element (REE) concentrations of carbonatites, in combination with the intrusive-extrusive nature of their suites contribute to the rarity of these rocks. Carbonatites, through their peculiar petrological and geochemical compositions, provide vital insights to the composition and condition of the Earth’s mantle. The genesis of the Alnö carbonatites and their relation to other lithological units at the complex is however, only partially understood. This stems from the epistemological division of carbonatites as having either a ‘magmatic’ or ‘reactive’ origin. This study focuses on sampled carbonatites from the Alnö Complex, employing an oxygen and carbon isotope approach on their native calcite, complemented with petrological and mineralogical methods in order to constrain petrogenesis. As a reference, oxygen and carbon isotope data of calcite from an earlier Alnö investigation as well as from an array of data from comparative alkaline complexes elsewhere are also discussed. The combined data and the derived findings support a scenario that is consistent with the ‘magmatic’ model wherein carbonatites have a primary mantle-derived origin, and prospectively stem from a parent magma akin to that of Oldoinyo Lengai, but have experienced a degree of silicate and sedimentary assimilation. The extraction of the Alnö carbonatites for their rare earth metals is a looming possibility due to the current volatility in the rare earth market. The risks and opportunities involved in this kind of natural resource extraction provide a context wherein sustainable development paradigms can be applied. The capacity of the Alnö environment to withstand the impact of development in the mining sector is discussed through a perspective of establishing a quarry, and quarry-related methods for rare earth extraction.

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22

Hodgson, Neil Andrew. "Carbonatites and associated rocks from the Cape Verde Islands." Thesis, University of Leicester, 1985. http://hdl.handle.net/2381/35041.

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Carbonatite magmas are alkali-bearing, ionic melts, analogous to synthetic carbonate melts. REE complexing suggests that carbonato-complexes dominate the melt, and these are more stable for the LREE than the HREE, leading to the extreme LREE/HREE enrichments characteristic of carbonatites. Crystal settling is viable in static magma chambers. however in thin carbonatite dykes as seen on San Vicente, turbulent flow velocities preclude vertical particle transfer against the flow of liquid, and favour fractionation by rapid crystal growth in a boundary layer close to the dyke margins, and particle accretion to the dyke walls. The Vale de Cavaleiros sovite on Fogo, displays mineralogical variation as a result of adcumulation, gravitationally controlled sedimentalogical sorting and post-lithification deformation. Minor and trace element variations are explained partly as a function of the heterogeneity of mineralogy, but require chemical modification of the magma by fractional crystallization and auto-metasomatizm. O18o and O13C of the carbonatites on San Vicente are decoupled, however calcite and dolomite may have equilibrated with seawater at temperatures close to 100°C. Fractionation of calcite and apatite from a carbonatite magma, produces cumulate microsovite and conjugate evolved carbonatite liquids which form the ferrocarbonatite suite. Trace element variations within the ferrocarbonatite suite indicate that the unstained ferrocarbonatites (unaltered 'quench' carbonatite) are heterogeneously metasomatized and mineralized by evolved (contaminated) orange ferrocarbonatites to produce brown-black ferrocarbonatites. The degree of dolomitization of the Camile dyke on San Vicente, relates to the activity of Ba2+ released during recrystallization of the original carbonate minerals. The arrays on plots of 87Sr/86Sr vs 143Nd/144Nd vs. 206Pb/204Pb for rocks from the Cape Verde Islands are interpreted as a two component mixing lines between recycled pelagic sediment and recycled altered MORB. The melilitites and nephelinites of the Malhada Pedra formation on Maio defines an array from CSn = 157. to CSN = 07 (in CSn-(Or+Ab) n-Din space), which may be interpreted as describing the loci of migration of the peritectic melt during the melting episode. There is little evidence for the genesis of carbonatite by ultra - fractionation of carbonated, alkalic, silicate magma. Neither major or trace element evidence can discriminate between liquid immiscibility, or direct partial melting of carbonated peridotite at pressures greater than 20kbar as mechanisms for generating carbonatite magmas.

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23

Chmyz, Luanna. "Géochronologie et pétrogenèse du complexe ultramafique-alcalin carbonatitique de Jacupiranga (BR)." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT080/document.

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Le Complexe de Jacupiranga (Cajati, SP) est l’une de plusieurs occurrences alcalines du Méso-Cénozoïque situées aux bords de la bassin de Paraná, dans la région sud-est de la Plate-forme Sud-Américaine. Cette unité présente une grande variété de roches: dunites, wehrlites, clinopyroxènites, roches de la série ijolitique, diorite, syénite, monzonite, phonolites, lamprophyres et carbonatites. Considérant que les carbonatites ont été largement étudiés au cours des dernières décennies, grâce à l’importance de sa minéralisation en phosphate, les roches silicatées ont été très peu étudiées. Cette étude présente des nouvelles données géochronologiques, de chimie minérale, de géochimie et isotopique pour le Complexe Jacupiranga, visant à mieux comprendre l'origine et l'évolution de l'unité. Âge argon des différents lithotypes varient entre 133,7±0,5 Ma et 131,9±0,5 Ma, tandis que l’âge obtenu par U-Pb au zircon est de 134,9±0,65 Ma, indiquant que la mise en place de l'unité a été contemporaine à l’extrusion de tholéiites de la Province Magmatique du Paraná. Bien qu'il ne soit pas possible de définir une séquence de mise en place parmi la clinopyroxenite, la diorite et le lamprophyre, la monzonite présente l’âges argon et U-Pb plus âgés que les autres roches. Deux séries magmatiques sont proposées pour les roches silicatées, compte tenu de leurs compositions chimiques: (1) une série fortement sous-saturé en silice, éventuellement lié à un magma parental de composition néphélinitique et (2) une deuxième série modérément sous-saturé, lié à des magmas basanitiques. Les lamprophyres sont considérés représentatifs du magma basanitique. La composition du liquide calculé en équilibre avec les coeurs de la diopside aux clinopyroxénites est similaire aux lamprophyres, ce qui indique qu'une partie des clinopyroxénites est associée au magma basanitique. Monzonite et meladiorite présentent les caractéristiques pétrographiques, compositionnelle et isotopique (87Sr/86Sri: 0,705979 à 0,706086; 143Nd/144Ndi: 0,511945 à 0,512089) qui suggèrent le processus d'assimilation crustale, bien que de caractère local et limité à certains impulsions de magma basanitique. Les carbonatites ont des rapports isotopiques (Nd et Pb) et composition trace (e.g. Ba/La, Nb/Ta) qui exclurent un lien avec les roches silicatées par immiscibilité de liquide. Il est proposé deux scénarios: un magma carbonatitique primaire, généré directement par la fusion du manteau, ou un magma secondaire généré par l’immiscibilité d'un composant silicaté encore inconnu dans l'unité. Données Nd-Sr-Pb-Hf indiquent une contribution importante du manteau lithosphérique subcontinental dans la genèse des roches du complexe. Les lamprophyres et le liquide calculé en équilibre avec le clinopyroxène ont des rapports CaO/Al2O3 et La/Zr relativement élevés et faible Ti/Eu, ce qui indique un manteau lithosphérique métasomatisé par des fluides riches en CO2 et les mécanismes de fusion "vein-plus-wall-rock". Les différences de composition entre ces liquides sont interprétés comme comme résultant du mélange entre la fusion des veines métasomatiques avec la fusion des péridotites, ainsi des proportions différentes de clinopyroxène/grenade à la source. Les variations dans les valeurs ΔεHf suggèrent que le magma basanitique represente une contribution plus grande des vein wehrlitique, tandis que le magma nephelinitiquea été être généré à partir des contributions un peu plus important des peridotites, bien que les deux fluides sont enrichis. Appauvrissement en Nb, Yb, enrichissement en ETR lèger pour rapport le lourdes et l'enrichissement en Cs, Rb et Sr dans les lamprophyres réactions suggèrent que les reactions métasomatiques à la source mantellique ont été associées aux fluides dérivés de processus de subduction. Les âges modèles TDM indiquent l'hétérogénéité à la source et sont compatibles avec les valeurs généralement obtenues pour les occurrences alcalines au du Sud-Est de la Plate-forme Sud-Américaine
The Jacupiranga Complex (Cajati, SP) is one of several Meso-Cenozoic alkaline units intrusive along the Parana Basin margins, in the Central-Southeastern part of the South American Platform. This unit comprises a large variety of lithotypes: dunites, whehrlites, clinopyroxenites, rocks from the ijolite series, diorites, syenites, manzonites, phonolites, lamprophyres, and carbonatites. While carbonatites have been extensively investigated over the last decades, as they host an important phosphate ore deposit, little attention has been paid to the silicate rocks. The current study presents new geochronological, mineralogical, geochemical, and isotopic data on the Jacupiranga Complex, in order to better understand the origin and evolution of the unit. 40Ar/39Ar ages for different lithotypes range from 133.7±0.5 Ma to 131.9±0.5 Ma, while monzonite zircon analyzed by SHRIMP yields a U-Pb concordia age of 134.9±0.65 Ma, indicating that the Jacupiranga emplacement was contemporaneous with the extrusion of the tholeiites of the Paraná Magmatic Province. There seems to be no obvious age progression for clinopyroxenites, diorites, or lamprophyres, although the monzonite yield both 40Ar/39Ar and U-Pb ages older than those of the other rocks. Geochemical compositions of the silicate rocks are used to evaluate two main magma-evolution trends for that unit: (1) a strongly silica-undersaturated series, probably related to nephelinite melts and (2) a mildly silica-undersaturated series related to basanite melts. Lamprophyre dikes within the complex are considered as good representatives of the basanite parental magma. Compositions of the calculated melts in equilibrium with diopside cores from clinopyroxenites are quite similar to those of the lamprophyres, suggesting that at least a part of the clinopyroxenites is related to the basanite series. Meladiorite and monzonite show petrographic features and geochemical and isotope compositions (87Sr/86Sri: 0.705979-0.706086 and 143Nd/144Ndi: 0.511945-0.512089) suggestive of crustal assimilation, although it may be relegated to a local process and to some basanite batches. Carbonatites yield isotopic ratios (Nd and Pb) and trace elements composition (e.g. Ba/La, Nb/Ta) that preclude a link by liquid immiscibility with the silicate rocks. Two scenarios are envisaged: a primary magma of carbonatite composition originated by direct partial melting of the mantle or an origin by immiscibility from a hypothetical silicate magma currently unknown in the complex. Nd-Sr-Pb-Hf isotopic data indicate an important contribution of the subcontinental lithospheric mantle (SCLM) in the genesis of those rocks. Lamprophyres and calculated melts in equilibrium with clinopyroxene show relatively high CaO/Al2O3 and La/Zr ratios and low Ti/Eu, indicating a lithospheric mantle metasomatized by CO2-rich fluids and vein-plus-wall-rock melting mechanisms. Compositional variations among those liquids are attributed to the mixing between metasomatic veins partial melt and peridotite partial melt, besides as well as to the differences in the clinopyroxene/garnet ratios on in the mantle. ΔεHf variations suggest a slightly higher role of the wall-rock peridotite as a source component for the nephelinites, whereas the basanite parental magma is mainly related to the wehrlite veins, although both are enriched magmas. Depletion in Nb-Yb, enrichment of LREE relative to HREE, and enrichment in Cs, Rb and Sr in the lamprophyres suggest that the metasomatic reactions in the mantle source were caused by slab-derived fluids. TDM model ages indicate the heterogeneous nature of the mantle source and are coherent with the values generally obtained for the alkaline occurrences from the Central-Southeastern part of the South-American Platform

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24

Palmer, David A. S. "Geology and Geochemistry of the Amba Dongar carbonatite-hosted fluorite deposit, India." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68237.

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The Amba Dongar carbonatite complex, India is host to a large fluorite deposit. The complex consists of a small ring structure comprised of early carbonatite breccia, a large, outer lining of calcitite and a number of small ankeritic carbonatite plugs. Surrounding the carbonatite ring are numerous plugs of nephelinitic and phonolitic syenites. The complex was intruded into Late Cretaceous Bagh Sandstones and Late to Early Paleocene Deccan Volcanics.
The hydrothermal history of the complex is extensive, consisting of two main systems, the first resulted in large amounts of fenitization, causing extensive K and Na metasomatism of the surrounding sandstones and the second, dealt with here, was responsible for the silicification of large amounts of the calcitite and the deposition of economic quantities of fluorite.
The deposit consists of veins and vug fillings of blue, purple, white, yellow and colorless fluorite. The main ore zone, which is currently under production, and most other showings, are found near the carbonatite-sandstone contact.
Chemical analyses and mass balance calculations show that the fluids responsible for silicification removed significant quantities of Ca from the rock while adding large amounts of Si, Al and F. Alteration associated with fluorite deposition involved the removal of Al from the rock and the addition of large quantities of F and Si.
Fluid inclusions in fluorite point to a low temperature-low salinity ore fluid, which decreased in temperature and salinity with evolution. Crushing experiments performed on fluid inclusions in both fluorite and quartz reveal the presence of ${ approx0.08}$ m of dissolved CO$ sb2$ in solution while analyses of leachates and decrepitate residues from fluid inclusions show significant concentrations of Ca, Al, Na, Cl and S in their fluids. (Abstract shortened by UMI.)

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25

Dalsin, Mallory Linda. "The mineralogy, geochemistry and geochronology of the Wicheeda Carbonatite Complex, British Columbia." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45393.

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Carbonatites are rare magmatic rocks composed of greater than 50% carbonate minerals. They are generally associated with continental rift-related tectonic settings and are commonly enriched in rare earth elements (REE), Nb, and P. The Wicheeda carbonatite complex, located 80 km northeast of Prince George in British Columbia, Canada, has been historically explored for its REE potential, but until recently there has been very little scientific study. The purpose of this study was to explore the geology, mineralogy, geochemistry, and geochronology of the Wicheeda Carbonatite Complex. The complex consists of a carbonatite plug with a number of carbonatite and potassic-syenite dykes and sills emplaced into the sedimentary rocks of the upper Cambrian and lower Ordovician Kechika Group. Sodic-fenitization is common around the carbonatites and the degree of alteration and abundance of syenite outcrops increases away from the carbonatite plug. The complex was mapped over an area of 1.45 km². The REE mineralogy of the Wicheeda carbonatite was defined through optical petrography (86 thin sections), scanning electron microscopy, electron probe microanalysis (371 points on 14 mineral species), and single-crystal X-ray diffraction (7 samples). The REE mineralogy is complex, with multiple stages of primary, late-stage, rapidly cooling crystallization. It consists of Ca-REE-fluorocarbonates, Ba-REE-fluorocarbonates, ancylite-(Ce), monazite-(Ce), euxenite-(Y), and allanite-(Ce); the majority of these minerals are LREE rich. Whole rock isotopic analysis was completed for the Rb-Sr and Sm-Nd systems. An isochron age of 316 ± 36 Ma was determined using the Sm-Nd system, giving values for εNdT and ⁸⁷Sr/⁸⁶SrT that range from -0.5 to 0.5 and 0.70526 to 0.70659, respectively. Evidence from the Wicheeda Carbonatite Complex along with comparisons with other worldwide carbonatites, suggests that the complex formed from a dominantly silicate, parental, mantle melt emplaced into the continental lithosphere. The lithosphere underwent metasomatism and, potentially, low degrees of partial melting and/or the incorporation of previously subducted sediments for carbonatite generation.

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26

Ting, Wupao. "A fluid and solid inclusion study of the Sukulu carbonatite complex, Uganda." Thesis, Kingston University, 1994. http://eprints.kingston.ac.uk/20577/.

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The thesis consists of 8 chapters. The first Chapter gives an introduction to carbonatites and outlines the general aims of this study. The general geology of Sukulu, the methodology used in this research, and previous work are presented in Chapter 2. Detailed descriptions and analytical results on the principal minerals are given in Chapter 3. Chapters 4 and 5 focus on aqueous and solid inclusions in apatite, and detailed descriptions, microthermometric results and interpretations are presented. Determination of oxygen and carbon stable isotope compositions and their interpretations are covered in Chapter 6. Chapter 7 describes geothermometric and geobarometric investigations and the calculation of oxygen fugacities during the deposition of apatite and carbonate. The final chapter discusses evolution of the fluids in the Sukulu carbonatite complex and presents a petrogenetic model. Aqueous inclusions in apatite from the Sukulu carbonatite consist essentially of three types: CO[sub]2-bearing, H[sub]2 0-rich and CH[sub]4-bearing. The CO[sub]2- and CH[sub]4-bearing inclusions, in general, are not present together in individual apatite crystals. It is considered that these compositionally discrete inclusions represent different fluids trapped during different stages of apatite crystallisation. The CO[sub]2-bearing fluid probably formed from an originally H[sub]2 0-rich fluid containing significant CO[sub]2 by immiscible separation under high pressure and temperature. This precursor H[sub]2 0-CO[sub]2 fluid was probably derived from a carbonatite melt, also by a possible process of liquid immiscibility. The CH[sub]4-bearing inclusions were probably formed by late stage hydrothermal processes under different P-T conditions. Many solid inclusions occur in apatite of the Sukulu carbonatite, of which the most abundant are carbonate. They can be classified into Mg-calcite. (primary) and calcite (secondary) inclusions based on their morphology, texture and chemical composition. Although such carbonate inclusions are ubiquitous in carbonatite apatite and have been described by many other workers, this study provides new insight into their genesis and petrogenetic significance. Carbon and oxygen stable isotopic composition from fluid inclusions, in both apatite and matrix carbonate, suggest that the CO[sub]2-bearing fluid was equilibrated with carbonate fluids at an early stage, but it evolved along a different path. The CO[sub]2-bearing fluids which has a stable isotopic composition close to upper-mantle values, evolved in a closed-system after being trapped by apatite, but the carbonate fluid evolved in an open-system and its isotopic composition was elevated by assimilation and contamination during ascent. The results also reveal that post-magmatic processes played an important role in the development of the Sukulu carbonatite. P-T-X isochores calculated for each type of fluid indicate that their evolution was probably from a CO[sub]2-bearing fluid, through a moderate to highly saline one, to a CH[sub]4-bearing one, and took place under temperatures and pressures varying from >1000°C and >7.4kb, through >560°C and >5kb, to about 500°C and <3 kb. This trend represents evolution of the carbonatite from a deep magmatic (carbonate melt) environment towards a shallow level hydrothermal system. This study confirms that both apatite and carbonate-can be precipitated over a wide range of temperatures and melt fluid compositions. The present findings indicate that the compositions of the fluids associated with the Sukulu carbonatite complex appear to have evolved chemically from a Mg-bearing calcite melt, through aqueous CO[sub]2-bearing and bicarbonate-rich melts (NaHC0[sub]3 daughters) to a final aqueous CH[sub]4-bearing fluid.

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27

Onuonga, Isaac Oriechi. "Geochemistry and mineralization of Buru and Kuge volcanic carbonatite centres, Western Kenya." Thesis, University of St Andrews, 1997. http://hdl.handle.net/10023/15470.

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Western Kenya hosts a number of Tertiary and Quaternary alkaline volcanic carbonatite centres, such as Rangwa, the North and South Ruri centres, Kuge, Homa Mountain and Legetet which are located along an old Precambrian major shear zone lying within the Nyanza rift, off the main Kenyan (Gregory) rift. The centres consist of agglomerates and breccias with mixed clasts of silicate rocks and carbonatites, interbedded with carbonatitic and nephelinitic tuffs. The volcanic assemblage is transected by high level sheets and dykes of calcite carbonatite and ferrocarbonatite which were probably later feeders for the volcanic eruptions. Carbon, oxygen, and sulphur isotopic compositions were determined for calcite, siderite and barite from the Buru and Kuge carbonatite centres. Wide ranges in the isotopic compositions of the minerals were observed with values for delta13C and delta18O for the Buru calcites ranging from +1.27 to -3.23‰ (PDB) and +11.25 to +26.21‰ (SMOW). The delta13 C and delta18O for the Kuge calcites are -3.11 to -8.44‰ (PDB) and +18.09 to +25.73‰ (SMOW). The Buru siderites plot in a narrow and restricted range at -3.07 to -4.39‰ (PDB) and +12.61 to +16.10‰ (SMOW). Data on the sulphur isotopic composition from the Buru hill carbonatite show a fairly widespread variation in delta34S ranging from +4.50 to +12.40‰ (CDT), whereas Kuge hill displays a slightly more homogenous isotopic composition with values ranging from +1.10 to +5.10‰ (CDT). The carbon and oxygen isotopic compositions from the Buru and Kuge carbonatite centres do not retain the primary isotopic signatures expected for magmatic primary carbonatites. Most of the variations in isotopic composition have been attributed to secondary processes involving low temperature (60° to 144°C) hydrothemal alteration and isotopic exchange between the carbonatites and fluids (meteoric water). Higher delta18O values (+21.91 to +26.21‰) with a significant increase in delta13Cvalues (-1.48 to +1.27‰) shown by the most oxidized samples from the Buru carbonatite may indicate the involvement of supergene exchange with atmospheric CO2 at relatively lower temperatures (< 50°C). The variations in 34S shown by the two centres compared to mantle sulphur could be due to either redox processes and/or isotopic fractionations due to loss of volatiles. The Buru and Kuge carbonatite centres are characterized by enriched rare earth element (REE) values dominated by higher abundances of LREEs with steep chondrite-normalized distribution patterns. The lateritic zone at Buru hill, however, contains the greatest concentrations of REEs, barium, iron and manganese compared to the fresh carbonatite in which calcite and particularly siderite increase in abundance as the influence of supergene processes decrease with depth. The most common rare earth minerals encountered in the Buru and Kuge carbonatite centres are the fluorocarbonates (bastnaesite, synchysite and parisite), and monazite. The lanthanide fluorocarbonate and monazite control the concentration and bulk distribution of the REEs. The replacement textures of the lanthanide fluorocarbonates and monazite indicate that they are secondary in origin and appear to have been introduced by late stage, low temperature hydrothermal processes. The rare earth minerals are commonly accompanied by fluorite, and barite. Stable isotope studies suggest that the low temperature mineralogical changes and REE mineralization observed in western Kenyan carbonatites were controlled initially by hydrothermal activity and later by supergene processes. Higher delta18O and values, especially in the oxidized zones, correspond to higher REE abundances.

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28

Lee, Mi Jung. "Minéralogie, pétrologie et géochimie de l'association Phoscorite-Carbonatite du complexe alcalin de Sokli, Finlande." Saint-Etienne, EMSE, 2002. http://www.theses.fr/2002EMSE0020.

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Le complexe de Sokli, situé en Laponie finlandaise (67°48'N, 29°27'E), fait partie de la Province Alcaline de Kola, qui comporte 24 intrusions alcalines, mises en place au Dévonien, entre 370 et 340 Ma. Le complexe comprend principalement deux zones. La zone externe est constituée de roches modifiées ('métacarbonatites' et 'métaphoscorites', au sens de Verwoerd, 1967). La zone centrale est constituée pour l'essentiel de carbonatites associées à des phoscorites. Sur la base des assemblages minéraux et de la géochimie, trois paires principales ont été reconnues, C1-P1, C2-P2, C3-P3, qui se distribuent dans des zones successivement de plus en plus centrales du 'complex carbonatite-phoscorite' (CCP). A ces paires carbonatite-phoscorite succèdent des carbonatites à dolomite dominante (stade D4), puis un stade terminal, D5, de carbonatites à dolomite minéralisé en Strontium, Baryum et Terres Rares. Les minéraux de métaux rares (Zr, Nb, Ta,. . . ), préférentiellement concentrés dans les faciès phoscoritiques, passent de Baddeleyite seule dans CP1, à Baddeleyite+Pyrochlore dans CP2, puis à Pyrochlore dominant, et localement très abondant (quelques %), dans CP3
The Sokli complex (67°57'N, 29°05'E) is located in the north-eastern Finih Lapland, and belongs to the Paleozoic (380-360 Ma) Kola Alkaline Province (KAP). The complex comprises two main units organized as concentric zones. The outer zone is composed of alkaline silicate rocks intruded by numerous veins of carbonatites and largely transformed by the related fluids ; the inner zone is dominantly composed of carbonatites and subordinate phoscorites. Based on mineral assemblages, mineral compositions, and bulk chemical compositions, the Sokli phoscorites and carbonatites are classified in five stages of intrusion. In the early stages, phoscorites and calcite carbonatites are intimately associated with each other (P1-C1, P2-C2 and P3-C3 phoscorite-carbonatite pairs) ; in the later stages, the intrusive material is mostly dolomitic (D4 and D5 dolomite carbonatites) and lacks associated phoscorite. The latest stage rocks occur along a fracture zone in the centre of the 'magmatic core'

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29

Baghdadi, Bashar. "Géochimie analytique et prospection : application aux roches mantelliques de type péridotitique." Paris 6, 2013. http://www.theses.fr/2013PA066235.

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Les angrites forment un groupe d’achondrites rares dont la minéralogie est particulière. Ce sont les plus anciennes roches magmatiques du système solaire (~4. 564 Ga). Leur pétrogenèse est mal comprise, leur pétrographie inhabituelle place leur origine au cœur d’un grand débat. La présence de métal et des microstructures réactionnelles dans certains échantillons de ce groupe mérite d’être étudiée attentivement ce qui n’a pas été fait jusqu’à ici. La modélisation thermodynamique permettra de préciser les conditions de leur formation. Nous avons conduit des analyses pétrogéochimiques et minéralogiques sur des échantillons d’angrites de type péridotitique et sur des roches terrestres (enclaves carbonatées) de Tell Thennoun/Syrie. Les résultats nous ont permis de contraindre les conditions P-T nécessaires à l’existence du magmatisme parent des angrites et de vérifier dans quelle mesure les données sur les péridotites terrestres sont en accord avec ces résultats. La maîtrise des analyses géochimiques et leurs applications dans le domaine de la prospection des minéraux est un des objectifs de cette thèse, l’étude des roches carbonatées de Tell Thennoun en est un exemple. On en conclut que le corps parent des angrites est un planétoïde de grande taille avec une évolution métamorphique et dont le magmatisme associé est typique de l’évolution précoce des planètes. Quant aux roches carbonatées de Tell Thennoun, il semble qu’elles représentent des roches d’origine sédimentaire plutôt que magmatique, recyclées dans le volcanisme de rift syrien et dont l’intérêt économique est très faible
Angrites are a group of rare achondrites with particular mineralogy. They are the oldest igneous rocks in the solar system (~4. 564 Ga). Their petrogenesis is poorly understood, their unusual petrography put up their origin in the heart of a great debate. The presence of metal and reaction microstructures in some samples of this group deserve to be studied carefully what has not been done yet. The thermodynamic modeling would recognize the conditions of their formation. We carried out petrogeochemical and mineralogical analysis on some angrites of the peridotitic type and on some terrestrial rocks (carbonated enclaves) of Tell Thennoun/Syria. The results allow us to constrain the P-T conditions necessary for the existence of the parental magmatism of angrites and to verify the extent to which data on terrestrial peridotites are consistent with these results. The expertise of geochemical analysis and their applications to the field of mineral exploration is one of the objectives of this thesis, the study of carbonated rocks of Tell Thennoun is an example of the latter. We conclude that the angrites parent body is a large planetoid with a metamorphic evolution and the associated magmatism is typical of early evolution of planets. About the carbonated rocks of Tell Thennoun, it seems that they represent rocks of sedimentary origin, rather than magmatic ones, which have been recycled in the Syrian rift volcanism and show a low economic interest

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30

Bui, Andrea. "Studio della decarbonatazione durante l'interazione tra rocce carbonatiche e magma." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16264/.

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Approfondimento delle conoscenze petrografiche legate al processo metamorfico di decarbonatazione registrato dal marmo VV13L, proveniente dai depositi piroclastici eruttati nel 1631 d.C dal Mt. Somma-Vesuvio.

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31

Frejd, Julia. "Magnetic Mineralogy of Nb-bearing Carbonatites from Oldoinyo Dili (Tanzania)." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-445837.

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Niobium (Nb) and Rare Earth Elements (REE’s) have in recent years received considerable attention because of their importance to the modern technical industry, and more specifically the enhanced sustainability that comes with them. The main source for Nb and REE’s on Earth are carbonatites and associated alkaline silicate rocks. This report examines the magnetic properties of rocks from the Oldoinyo Dili carbonatite complex in northern Tanzania. Previous workers have suggested a link between the Fe-bearing mineralogy and the formation of Nb-mineralizations at Oldoinyo Dili. This hypothesis is further examined in this report by combining detailed petrographic observations and withnew measurements of magnetic susceptibility. The aim is to see if any correlation exists between occurrence of Nb-mineralizations and the types of Fe-minerals present at Oldoinyo Dili. Based on the magnetic susceptibility measurements, at least two different species of Fe-minerals arefound in the examined samples. These are characterized by different magnetic trends during heating/cooling and also by their separate Curie temperatures (Tc). In combination with the petrographic observations these minerals are interpreted to be magnetite (Fe2O4) with Tc ~580°C, and a mineral that most likely represents a solid solution between ilmenite (FeTiO3) and hematite (Fe2O3) with Tc ~300°C. Here, no clear link between the type of opaque mineral(s) present and the total Nb content of the carbonatites can be conclusively determined based on the petrography and the magnetic measurements alone. Although the results of this report provide an important first step towards understanding the relationship between Nb-mineralizations and the magnetic mineralogy at Oldoinyo Dili, more detailed analyses of the mineral chemistry is a necessity to fully understand their complex relations and the specific conditions under which they formed.
Niob (Nb) och sällsynta jordartsmetaller (REE’s) har på senare år fått stor uppmärksamhet för sin betydelse för den moderna tekniska industrin, och specifikt för den förhöjda hållbarhet som de bidrar med. Den huvudsakliga källan till Nb och REE’s på jorden är karbonatiter och associerade alkalisilikater. Denna rapport undersöker de magnetiska egenskaperna för karbonatit-komplexet Oldoinyo Dili i norra Tanzania. Forskare har tidigare anat att det finns en koppling mellan Fe-bärande mineralogi och bildandet av Nb-mineraliseringar vid Oldoinyo Dili. Denna hypotes undersöks vidare i denna rapport genom att kombinera detaljerade petrografiska observationer med nya mätningar av magnetisk susceptibilitet. Syftet är att undersöka om det finns någon korrelation mellan förekomst av Nb-mineraliseringar och de typer av järnmineral som finns vid Oldoinyo Dili. Baserat på de genomförda magnetiska susceptibilitets-mätningarna så finns det åtminstone två olika sorters järnmineral i de undersökta proverna. De karaktäriseras av olika magnetiska trender vid upphettning/nedkylning och även av sina olika Curietemperaturer (Tc). Kombinerat med petrografiska observationer uttolkas att dessa mineral är magnetit (Fe2O4) med Tc ~580°C, samt en mineral som troligen är en solid solution av ilmenit (FeTiO3) och hematit (Fe2O3) med Tc ~300°C. Det går inte att senågon tydlig koppling mellan förekommande opaka mineral och det totala Nb-innehållet i karbonatiterna med säkerhet enbart utifrån petrografin och de genomförda magnetiska mätningarna. Resultaten av denna rapport utgör ett bra första steg mot att förstå relationen mellan Nb-mineraliseringar och den magnetiska mineralogin för Oldoinyo Dili, men mer detaljerade analyser av mineralkemin är nödvändigt för att till fullo förstå de komplexa förhållanden som råder vid bildning av dessa.

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Bizzarro, Martin. "Major element and isotope geochemistry (Sr, Nd and Hf) of mantle derived peridotites, carbonatites and kimberlites from Canada and Greeland; insights into mantle dynamics." Thèse, Chicoutimi : Montréal : Université du Québec à Chicoutimi ; Université du Québec à Montréal, 2003. http://theses.uqac.ca.

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Thèse (D.Ress.Min.) -- Université du Québec à Chicoutimi, programme extensionné à l'Université du Québec à Montréal, 2002.
Bibliogr.: f. 105-109. Document électronique également accessible en format PDF. CaQCU

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Niegisch, Max, Andreas Kamradt, and Gregor Borg. "The upper zone of the Storkwitz Carbonatite: Geochemical and mineralogical characterization of the REE-mineralisation in the upper zone of the Storkwitz Carbonatite Complex from drill core SES-1/2012." Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie, 2020. https://slub.qucosa.de/id/qucosa%3A71506.

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Im Umfeld von Delitzsch befinden sich unter der etwa 100 m mächtigen Bedeckung aus tertiären Lockersedimenten mehrere magmatische Körper aus Karbonat. Im Jahr 2012 wurde durch die Deutsche Rohstoff AG bei Storkwitz eine 700 m tiefe Explorationsbohrung auf Seltene Erden Elemente abgeteuft. Im Rahmen eines Forschungsprojektes wurde der Frage nachgegangen, wie und woher die Seltenen Erden in das Gestein hineingelangten. Die Ergebnisse können Hinweise auf möglicherweise bisher unbekannte Anreicherungen von Seltenen Erden in anderen Nebengesteinen als den Karbonatiten geben. Die Veröffentlichung liegt nur in englischer Sprache vor.
The Storkwitz-Carbonatite is a Late Cretaceous intrusive complex, which is well-explored by a relatively large number of exploration bore holes both from the 1970ies, 1980ies and from one more recent bore hole, SES-1/2012. The carbonatite complex hosts a (currently) marginally economic mineralisation of rare earth elements (REE) and niobium, which is technically still difficult to recover. The upper part of the carbonatitic body is located some 100-120 m below the Pre-Cenozoic land surface, which in turn is overlain by approximately 100 m of glacial, fluvio-glacial, and fluviatile sediments. The aim of this study was to characterize the mineralisation in the upper part of the intrusion geochemically and mineralogically and to try to identify indications of a supergene overprint on the late magmatic to hydrothermal mineralisation. Fresh drill core samples from the exploration bore hole SES-1/2012 have revealed that the mineralisation is associated with a carbonatitic igneous breccia body and also with several alvikite veins. The breccia body is very heterogeneous, displays a variety of matrix colours and also a range of matrix-to-clast ratios.

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Fournier, Antoine. "Magmatic and hydrothermal controls of LREE mineralization of the St.-Honoré carbonatite, Québec." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68174.

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The St.-Honore alkaline complex is intruded along the Saguenay graben of the lapetan Rift System. Country rocks, in the vicinity, are Pre-Grenvillian syenites belonging to the Central Gneiss Belt of the Grenville Province. The complex has a reniform shape, and consists of a central portion of carbonatitic rocks enclosed in an alkaline syenite.
The carbonatite comprises concentric lenses which evolved from calcitite through dolomitite, to a brecciated core of ferrocarbonatite which hosts REE mineralization, mainly as REE flurocarbonates and monazite. This mineralization forms part of the breccia cement, and is associated with hematite, chlorite, ferroan dolomite, minor thorite, ilmenorutile and pyrite.
Apatite-phlogopite geothermometer yielded magmatic temperatures between 1150 and 800$ sp circ$C for the complex, and for the REE Zone, the temperatures range between 380 and 346$ sp circ$C, and are interpreted to reflect subsolidus conditions. An independent chlorite geothermometer yielded similar temperatures (364 to 321$ sp circ$C) for the REE Zone breccia cement.
A model is proposed in which REE concentration in the magma was initially buffered by the crystallization of pyrochlore and apatite, and was subsequently allowed to build up when these phases stopped crystallizing in the most evolved ferrocarbonatite. Saturation of this magma with water, late in its crystallization history, led to the separation of an acidic aqueous phase into which the REE were partitioned as fluorocomplexes. Fluid overpressure produced hydrobrecciation which led to adiabatic expansion of the fluid and rapid cooling. The precipitation of REE minerals was caused by a combination of the drop in temperature and an increase in pH due to the interaction of the fluid with the dolomite.

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Alves, Paula Regina. "The carbonatite-hosted apatite deposit of Jacupiranga, SE Brazil: styles of mineralization, ore characterization and association with mineral processing." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/prayb4_09007dcc804f7bd9.pdf.

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Thesis (M.S.)--Missouri University of Science and Technology, 2008.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 9, 2008) Includes bibliographical references (p. 131-139).

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Sage, R. P. "Alkali rock complexes - carbonatites of Northern Ontario and their economic potential." Ottawa, 1986.

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Chudy, Thomas Christof. "The petrogenesis of the Ta-bearing Fir carbonatite system, east-central British Columbia, Canada." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45749.

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This dissertation investigates the petrogenesis of the Fir carbonatite system (Monashee Mountains of British Columbia), which is particularly interesting because of its high degree of deformation, the relatively minor presence of associated silicate rocks and its comparably high content of Ta. A detailed examination of the rock textures and microstructures shows that the two main fabrics, a primary gneissic and a secondary fine-grained, foliated fabric, are the results of plastic flow and dynamic recrystallization during deformation. The primary fabric developed under peakmetamorphic conditions and was overprinted by retrograde mylonitic shear zones. The microtextural record and the equilibration temperatures are compared to regional marbles that share the same tectonometamorphic history. Both lithologies reveal a very similar petrological record indicative of metamorphic equilibration, however, some calculated temperatures in the carbonatites (∼700 °C) exceed the peak-metamorphic conditions (620 - 650 °C), which indicates that the magmatic crystallization temperatures are preserved despite amphibolite-facies metamorphism. Apart from minor calcium and sodium amphiboles the Fir system contains predominantly the sodium-calcium amphiboles winchite and katophorite which define two major mineralogical facies. The amphiboles have high F contents (<1.6 a.p.f.u.) and show a systematic increase in the Na₂O content from the margin to center of the carbonatite. This distribution is paralleled by the Nb-Ta mineralization with ferrocolumbite in the winchite facies and pyrochlore in the katophorite facies. The two Nb-Ta-oxide minerals are stable under acidic and alkaline conditions, respectively, which are strongly influenced by the proximity to the country rocks. The geochemical composition is characterized by low REE and LILE concentrations, elevated Ta₂O₅ contents and subchondritic Nb/Ta ratios. The observed compositional differences can be attributed to the simple mineralogy that developed by in-situ differentiation of a primary dolomitic weakly fractionated mantle melt. The key factors for the enrichment of Ta in the Fir system are the relatively high F content of the melt and the high emplacement temperatures which increased the solubility of Ta in the melt and favoured the relative late precipitation of pyrochlore leading to the accumulation of Ta₂O₅.

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Carmody, L. "Geochemical characteristics of carbonatite-related volcanism and sub-volcanic metasomatism at Oldoinyo Lengai, Tanzania." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1348540/.

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The eruption of xenolithic material during large explosive eruptions, at any volcano, supply vital samples of the sub-surface lithologies upon which it is built, which in turn provides an indication of the evolution of the volcanic complex, in particular the volcanic conduit, magma storage zones and crustal / mantle lithologies. This is particularly important at alkaline-carbonatite complexes which are known to have “exotic” chemistries and also cause extensive zones of alteration through fenitisation processes. As the only active carbonatite volcano on Earth and also the unusual nature of Oldoinyo Lengai, Tanzania, it is an excellent study site to better understand the generation and chemical influence of carbonate-rich melts and fluids from source to surface. This study has attempted to better constrain the sub-volcanic environment, the source of the carbon within the material and the processes which lead to the formation of such unique rocks. Using geochemistry, isotopic studies and fluid inclusions, this thesis highlights the importance of fluid circulation within the volcanic system, both at the surface but also within the sub-volcanic mantle, leading to metasomatised material rich in carbon and alkali elements from which natrocarbonatite and potentially kimberlitic material could be derived. Almost all of the geochemical evidence and composition of fluid inclusions trapped within fenitised aureoles indicates a mantle derivation of carbonatitic material with isotopic signatures typical of the pre-defined “mantle-box”. The nature of the fluids is also investigated using trace element modelling and argued to be both carbonatitic and siliceous in origin, which have been circulating within the mantle beneath the Gregory Rift since before the establishment of Oldoinyo Lengai. These themes of research are discussed in terms of the genesis of natrocarbonatite, focussing upon the notion that it may be an evolutionary feature of Oldoinyo Lengai rather than a constant eruptive product.

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Prud'homme, Nathalie. "Caractérisation pétrographique et géochimique de la carbonatite et de la syénite de la mine Lac Shortt /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1990. http://theses.uqac.ca.

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Mémoire (M.Sc.T.)--Université du Québec à Chicoutimi, 1990.
"Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en sciences de la terre" CaQCU Document électronique également accessible en format PDF. CaQCU

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Hode, Vuorinen Jaana. "The Alnö alkaline and carbonatitic complex, east central Sweden - a petrogenetic study." Doctoral thesis, Stockholm University, Department of Geology and Geochemistry, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-546.

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The Alnö complex on the central Swedish east coast is composed of a main composite intrusion (the main intrusion) and four smaller satellite intrusions (Söråker, Sälskär, Långharsholmen and Båräng) distributed around the main intrusion on Alnö Island and on the mainland north of the island. The major rock types exposed within the complex are melilitolite, pyroxenite, ijolite series (melteigite-ijolite-urtite), nepheline syenite, carbonatite and alnöite dykes. Melilitolite is only exposed within the Söråker intrusion. The intrusive sequence is melilitolite → pyroxenite → ijolite series → nepheline syenite → carbonatite → alnöite.

Mineralogical, whole rock geochemical and radiogenic isotope (Nd-Sr-Pb) studies of exposed rocks from the Alnö alkaline complex, east central Sweden, were performed in order to investigate the genetic relationships between the diverse rock-types, and to evaluate the contributions from mantle and crustal components in the genesis of the complex. Most analysed samples fall within the depleted quadrant in a eNd-eSr diagram, similar to carbonatites and alkaline silicate rocks from other complexes, indicating derivation of parental magma(s) from a source that had experienced time-integrated depletion in LIL elements. Contamination by local crust is indicated by Sr and Pb isotope data, but is geographically restricted to samples collected from the outer parts of the main intrusion and from satellite intrusions. This localized contamination is attributed to selective hydrothermal element leaching of surrounding bedrock during fenitization. Nd- and Sr-isotope data separates the carbonatites into two groups (group I and II), each related to a specific set of silicate rock types. The overlap of group II carbonatites with ijolite and nepheline syenite could indicate a common origin through liquid immiscibility but this hypothesis cannot be confirmed by trace element data because initial concentrations are obscured by fractionation processes. Interestingly, results from AFC-modelling suggest that production of ijolite residual magma requires addition of a small volume (2.4 %) of carbonatite component to the parental magma, whereas formation of nepheline syenite residuals requires removal of an almost equal amount of carbonatite (1.5 %) to yield a statistically significant result. AFC-modelling further suggests that the various silicate rock types exposed within the complex are related to the same parental olivine-melilitite magma through crystal fractionation of olivine, melilite, clinopyroxene, nepheline, Ti-andradite and minor phases. These results agree with compositional trends exhibited by clinopyroxene and Ti-andradite from the silicate rocks of the main intrusion, which suggests co-genesis of pyroxenite, ijolite series rocks and nepheline syenite. Production of ijolite-like residual liquids can be achieved by <40% fractionation whereas production of nepheline syenite residuals requires >80% fractionation.

An investigation of the origin of silicate minerals in carbonatites suggest that most silicate minerals observed in the carbonatites on Alnö Island are derived from surrounding wall-rock and/or produced through corrosive interaction between carbonatite liquid and assimilated phases. This leads to ambiguities when addressing the possible genetic link between carbonatites and associated silicate rocks as occurrences of identical “liquidus” phases in inferred immiscible liquids may not actually be such.

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Hode, Vuorinen Jaana. "The Alnö alkaline and carbonatitic complex, east central Sweden : a petrogenetic study /." Stockholm : Department of Geology and Geochemistry, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-546.

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Ya'acoby, Avee. "The petrology and petrogenesis of the Ren carbonatite sill and fenites, southeastern British Columbia, Canada." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46653.

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This thesis explores in detail the petrology and petrogenesis of the Ren carbonatite sill and associated fenites, located in the Monashee mountain range of British Columbia. The carbonatite body and fenites have been significantly deformed and metamorphosed, which has provided a unique petrological research opportunity, since only a few other carbonatite occurrences worldwide have been described from highly metamorphosed orogenic settings. This work aims to address knowledge gaps pertaining to the petrology, petrogenesis and economic exploration of comparable carbonatites in similar geotectonic settings. The effects of amphibolite facies regional metamorphism and progressive deformation are apparent throughout the carbonatite body and adjacent fenites. Many of the rocks display remobilized, passively mixed components, boudinaged structures, and rheomorphic bands, as well as foliation and porphyroblastic textures. Recrystallization of minerals at peak metamorphic conditions (580–730 °C) is indicated primarily in undifferentiated calcite for which metamorphic solvus temperatures (~690 °C) were derived. Other minerals related to metamorphic recrystallization include rims of monazite-(Ce) around earlier fluorapatite, interstitial REE-silicates, and Ca- and Mg-amphibole forming late in the paragenetic sequence, after primary silicates. Despite the metamorphic overprint and alteration, many petrological features pertaining to the igneous paragenetic record have been preserved, such as textures of primary minerals, compositional trends in phlogopite, clinopyroxene and amphibole, and whole-rock geochemistry of rock units. Solvus temperatures (~760 °C) of calcite, higher than peak metamorphic conditions, highlight preservation of the igneous component. The carbonatite is inferred to be a product of primitive mantle melts(s) that did not undergo significant fractionation processes, and intruded the crustal environment relatively undifferentiated. The whole-rock compositional trend of the fenites and partially fenitized host rocks suggests sodic-potassic alteration of the country rock during emplacement of the carbonatite sill. The Nb-Ta and REE mineralizations of the Ren occurrence are both insufficient for economic extraction. Nevertheless, rare and new mineral candidates, (Fe,OH)-analogue to västmanlandite-(Ce) and (Mg)-analogue to biraite-(Ce), discovered in the deposit by the author, emphasize its petrological and mineralogical significance.

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Subasinghe, Nalaka Deepal. "Formation of secondary phosphates by weathering of apatite rich carbonatite : an example from Sri Lanka." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270305.

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Marageni, Manoka. "The geochemistry and petrogenesis of the Saltpeterkop carbonatite complex near Sutherland, Northern Cape, South Africa." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29818.

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The Saltpeterkop Carbonatite Complex is a Late Cretaceous (≈76 Ma) volcanic and shallow intrusive magmatic feature located approximately 20 km southeast of Sutherland in the Northern Cape. It is unusual among southern African carbonatite complexes in that it has not been deeply eroded, and retains a significant vestige of its original volcanic features. The main geologic expression of the Complex is a ≈1.5 km diameter tuff ring, located on top of prominently updomed and fractured Beaufort Group (Karoo) sediments, that appears to have formed as the result of a major diatreme-type eruption. The volcaniclastic breccias making up the tuff ring have been heavily altered and silicified by hydrothermal activity, and thick (mm to tens of cm) Fe oxide-rich crusts, which appear to represent the alteration products of Fe-rich carbonatites, are common in this area. Outside of the central ring structure are numerous shallow intrusions (dykes, sills and irregular shapes), satellite breccia pipes and pipe-shaped intrusions that host fresh to only moderately altered igneous rocks. The main igneous rock types include (in decreasing order of abundance): carbonatite, potassic trachyte, olivine melilitite and ultramafic lamprophyre. This thesis provides the first detailed petrographic and geochemical description of these rocks (e.g., major and trace elements) and attempts to explain several aspects of their petrogenesis. The olivine melilitites and ultramafic lamprophyres are the most primitive igneous rocks in the complex and have experienced only minor to moderate extents of differentiation, respectively. They apppear to have been derived by low-degrees of partial melting of a carbonated, likely phlogopite-bearing mantle source. The lamprophyres appear to have been derived by melting at shallower depths than the melilitites based on REE constraints. The carbonatites range from relatively primitive to highly differentiated and they form a nearly continuous compositional range with the ultramafic lamprophyres and melilitites. This seems to argue against a major role for liquid immiscibility in their origin. Their REE content (up to 2 wt.% total REE oxides) correlates with their extent of differentiation. The potassic trachytes are plausibly linked to melts of mafic lower continental crust that has been metasomatised by hydrous potassium-rich carbonatitic melts and which have experienced significant fractional crystallization and assimilation of upper crustal sedimentary rocks during emplacement.

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Riley, Teal Richard. "Quaternary volcanism of the Rockeskyll Complex, West Eifel, Germany and the carbonatite-nephelinite-phonolite association." Thesis, University of Bristol, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260870.

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Nabyl, Zineb. "Caractérisation expérimentale du comportement des métaux rares au cours de la différenciation des carbonatites et des magmas alcalins." Thesis, Orléans, 2020. http://www.theses.fr/2020ORLE3048.

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Les carbonatites et les roches magmatiques alcalines constituent une faible fraction du magmatisme terrestre et sont essentiellement produits en contexte intraplaque. Ces magmas sont particulièrement riches en éléments volatils (dioxyde de carbone, halogènes et eau) et présentent aussi des fortes concentrations en métaux rares (REE, Hf, Zr, Nb, Ta). Les gisements associés à ces roches magmatiques sont souvent affectés par des stades hydrothermaux tardifs brouillant les relations entre les processus magmatiques à l’origine de la formation de ces magmas (immiscibilité, différenciation, cristallisation fractionnée) et cet enrichissement métaux et en constituants volatils. Des expériences haute pression et haute température ont été réalisées afin d’évaluer le comportement des métaux rares pendant la différenciation de ces magmas. Ces expériences adressent le comportement des métaux rares pendant les processus d’immiscibilité entre liquides silicatés et liquides carbonatés et pendant la cristallisation de ces magmas. Les conditions optimales d’enrichissement en REE des liquides carbonatés au cours de la différenciation des magmas alcalins sont identifiées : les liquides carbonatés les plus enrichis sont formés par immiscibilité avec des liquides silicatés très différenciés et polymérisés de type phonolite/phono-trachyte. Un modèle d’enrichissement en REE des liquides carbonatés basé sur la composition des liquides silicatés est proposé et permet d’identifier i) le potentiel en REE des carbonatites pouvant être formées par immiscibilité avec des magmas alcalins, et ii) le stade de genèse par immiscibilité des carbonatites tout au long de la différenciation alcaline. De plus, le degré de différenciation et de polymérisation des liquides silicatés joue également un rôle sur l’enrichissement en métaux rares des cristaux (clinopyroxène, grenat, titanite, calcite et apatite) : les métaux rares sont plus concentrés dans les minéraux coexistant avec des liquides silicatés plus différenciés et polymérisés. Ceci implique que les liquides silicatés alcalins tendent à s’appauvrir en REE au cours de la différenciation, en comparaison aux liquides carbonatés et aux cristaux
Carbonatites and alkaline magmatic rocks occur in intraplate context and constitute a small fraction of the earth magmatism. Those magmas are particularly enriched in volatiles (carbon dioxide, halogens, water) and also in rare metals (REE, Hf, Zr, Ta, Nb). The associated deposits are often affected by hydrothermal and supergen processes which erase any relation to the magmatic processes at the origin of these magmas (immiscibility, differentiation, fractional crystallization) and responsible of the rare metal and volatile enrichments.High pressure and high temperature experiments have been performed to characterize the behavior of rare metals during both magma differentiation. These experiments simulate the immiscibility between carbonate and alkaline silica-undersaturated melts, during the crystallization of the magma.The optimum of carbonate melt REE enrichments across alkaline magma differentiation course is identified : carbonate melts immiscible with highly differentiated and polymerised silicate melts of phonolitic/phono-trachytic compositions are the REE richest. A modelling of carbonate melts REE enrichment based on the silicate melt composition is suggested, to identify the REE potential of carbonatites which may be immiscible with an alkaline magmatic rock, or to identify at which differentiation stage the immiscibility has occurred. Moreover, the silicate melt degree of differentiation and polymerisation has also an impact on crystal rare metal enrichments : crystals which coexist with highly differentiated and polymerized silicate melts are highly enriched in rare metals. This implies that silicate melts become depleted in REE across the differentiation compare to crystals and carbonate melts

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Sumida, Viktor Yuri Doná. "Investigação geofísica (magnetometria) no carbonatito da Fazenda Varela, Domo de Lages, SC." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/44/44137/tde-26042018-090729/.

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O presente estudo teve como objetivo investigar o Carbonatito Fazenda Varela, envolvendo a aplicação de um método geofísico, a magnetometria, que apresenta destaque na investigação de intrusões alcalinas. Os resultados do levantamento geofísico realizado no carbonatito, localizado no Distrito Alcalino de Lages, Santa Catarina, mostram uma forte assinatura magnética, sendo três anomalias reconhecidas na área do estudo: uma delas evidencia a presença de intensa magnetização remanente, enquanto as outras duas possuem polarização normal, ou seja, apresenta uma componente remanente fraca. A partir dos dados coletados no levantamento de campo foi realizada a inversão para obter modelos 3D, que permitiram avaliar a extensão, a geometria e os contrastes de susceptibilidades dos carbonatitos com as rochas sedimentares do Grupo Guatá, pertencentes à Formação Rio Bonito. Porém, a presença da magnetização remanente em um dos corpos gerou resultados imprecisos na inversão do campo magnético residual. Em função disso, foram aplicadas duas técnicas, a Integral Vertical do Sinal Analítico e o Sinal Analítico da Integral Vertical, para atenuar ou minimizar sua influência. Os resultados dos modelos 3D da distribuição do contraste de susceptibilidades indicaram três anomalias com extensões de 70m, 15m e 80m, e profundidades de 90m, 50m, 115m, respectivamente, sendo aqui apresentados e avaliados.
The present study aimed to investigate the Carbonatito Fazenda Varela, through the application of a geophysic method, magnetometry, which presents as a stand out investigation of alkaline intrusions. The results from magnetic survey that was held in Carbonatito Fazenda Varela, located in Alkaline District of Lages, Santa Catarina, reveal a strong magnetic signature, with highlight to three anomalies in the studied region: one of them has a strong remanent magnetization, whereas the other two have normal polarization, therefore, presents a weak remanent component. From the data collected through the survey, 3D models were obtained by inversion, which allowed to evaluate the extent, geometry and the contrasts of susceptibilities of the carbonatites with the sedimentary rocks of the Guatá Group, belonging to the Rio Bonito Formation. However, the presence of the remanent magnetization in one of the bodies produced inaccurate results in the inversion of the residual magnetic field. Thus, two techniques, the Vertical Integral of the Analytical Signal and the Analytical Signal of the Vertical Integral, were applied to attenuate or minimize its influence. The results of 3D models of susceptibility distribution indicated three anomalies with lengths of 70m, 15m, 80m, and depths of 90m, 50m, 115m, respectively, being presented and evaluated here.

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Martin, Alexis. "Modélisation de saumures carbonatées et caractérisation hydrogéologique de la mine Niobec, Saint-Honore, Québec : /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1993. http://theses.uqac.ca.

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49

Ngwenya, Bryne Tendelo. "Magmatic and post-magmatic geochemistry of phosphorus and rare earth elements in carbonatites." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306803.

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Abstract:

This study documents the magmatic, hydrothermal and supergene mineralogy and geochemistry of phosphorus and rare earth elements in carbonatite complexes using examples from Tundulu (Malawi), Sokli (Finland), Siilinjarvi (Finland) and Kaluwe (Zambia). In carbonatites, phosphorus averages 1-2% P20S and forms the minerals fluorapatite and monazite. Hydrothermal and supergene processes enrich fluorapatite in Na and REEs through vitusite-type exchanges which lead to formation of vitusite, belovite and britholite; and in CO2 through anti-francolite substitutions. The highest rare earth element contents are found in late-stage ankerite carbonatites or similar rocks of low temperature origin (T < S(XtC) and in hydrothermally altered rocks, where they occur mainly as fluorocarbonates or carbonates. Such minerals are consistent with the REEs having been transported in form of mixed fluoride-carbonate complexes. The mineral paragenesis in hydrothermal veins suggests that different fluorocarbonates precipitated depending on the activity of Ca supplied to the fluid by the wall rocks. The various minerals are modelled to form by simple combinations of calcite (CaCO:v and bastnaesite (REEC03F) molecules. A secondary characteristic feature of these reactions is that extreme heavy rare earth enrichment occurs if the wall rocks are apatite-rich. Petrogenetic modelling using REEs suggests that carbonatites are unlikely to be derived from carbonated silicate magmas by fractional crystallisation or liquid immiscibility. These findings are supported by ex solution temperatures of about 9S0·C recorded using the calcitedolomite geothermometer for quenched lapilli from the Kaluwe carbonatite.

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50

Burger, Erasmus Petrus. "An Investigation of the carbonatites of the Kaapvaal Craton and their tectonic context." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/43297.

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Abstract:

Carbonatites are exotic rocks which usually occur in discrete intrusions. Considering the association of carbonatites with rifting environments, this dissertation proposes that: carbonatites occur in extensional tectonic settings and therefore carbonatite occurrence can be used to constrain an extensional setting for related occurrences. In order to give context in which to consider this hypothesis, the formation of carbonatites is reviewed. This work favours the direct mantle melting model as it is most relevant and consistent with observations of Kaapvaal Craton carbonatites. However the liquid immiscibility model cannot be entirely rejected with current knowledge. The hypothesis is applied to the Bushveld Igneous Complex after providing evidence of the rift-carbonatite association. The Bushveld Igneous Complex is considered to have been emplaced in the same tectonic setting as carbonatites. Therefore the Bushveld Igneous Complex was emplaced in an extensional tectonic setting. Finally the carbonatites which are part of the Pilanesberg Alkaline Province are considered in order to test the hypothesis. This work finds that the Pilanesberg carbonatites do occur with other rift related magmatism during the break-up of Nuna (Columbia) and therefore the hypothesis is not rejected. This work offers reviews of basic carbonatite background, formation models and carbonatite occurrences on the Kaapvaal Craton.
Dissertation (MSc)--University of Pretoria, 2013.
lk2014
Geology
MSc
Unrestricted

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Dissertations / Theses on the topic 'Carbonatiite'

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