Dissertations / Theses on the topic 'Rare earth element geochemistry'

Rare earth elements (REE) are known as the lanthanide series (La-Lu) plus yttrium (Y) and scandium (Sc). REE are essential materials for modern industries and especially for green technologies (wind turbines, batteries, lasers, catalysts, etc.). However, despite their high global demand, their supply is limited such that the EU has cataloged it as critical raw materials. In order to ensure the supply of REE in the future, the search for alternative sources of these elements worldwide has been promoted in recent years. Acid mine drainage (AMD) produced by the Fe-sulphide weathering can effectively leach Fe, Al, SO4, and REE from the host rock. This can lead to high concentrations of these liberated species in the affected waters. Thus, the REE concentrations in AMD can be between two and three orders of magnitude higher than natural waters, as such it can be considered as a complementary source of REE recovery. The increase of pH in AMD by mixing neutral waters results in the precipitation of iron oxy-hydroxysulfate (schwertmannite) from pH 3-3.5, and aluminum (basaluminite) from pH 4-4.5 in the river channels. This process may be accompanied by REE scavenging. Due to its acidity and high metal load, acid mine drainage presents a major environmental problem worldwide, therefore, different treatment systems have been developed to minimize its impact. Disperse Alkaline Substrate (DAS) passive remediation system neutralizes AMD by dissolving calcite, and allowing the sequential precipitation of schwertmannite and basaluminite in separated layers, where REE are preferably retained in the basaluminite-enriched waste. Despite this, there are still no studies describing the adsorption of REE on both basaluminite and schwertmannite in these environments. The REE scavenging mechanism is studied by adsorption on synthetic minerals of basaluminite and schwertmannite as a result of variation to the both the pH and sulfate concentration. A thermodynamic adsorption model is proposed based on experimental results in order to predict and explain the REE mobility in AMD mixtures with neutral waters and in a passive treatment system. Basaluminite and schwertmannite have a nanocrystalline character. Further, schwertmannite has been observed to transform into goethite on weekly timescales, resulting in sulfate release. However, there is a gap of knowledge about basaluminite stability at variable sulfate concentration and pH and its possible transformation to other more crystalline Al-minerals. In this study, basaluminite local order at different pH values and dissolved sulfate concentrations was characterized. Results demonstrate that basaluminite can transform to nanoboehmite in weeks under circumneutral pH. However, the presence of sulfate can inhibit this transformation. Separate adsorption experiments on both basaluminite and schwertmannite were performed with two different concentrations of SO4 while varying the pH (3-7). Results show that the adsorption is strongly dependent on pH, and to a lesser extent on sulfate concentration. Lanthanide and yttrium adsorption is most effective near pH 5 and higher, while that of scandium begins around pH 4. Due to the high concentrations of sulfate in acidic waters, the predominant aqueous REE species are sulfate complexes (MSO4+). Notably, Sc(OH)2+ represents a significant proportion of aqueous Sc. , A surface complexation model is proposed in which predominant aqueous species (Mz+) adsorb on the mineral surface, XOH, following the reaction: The adsorption of the lanthanides and yttrium occurs through the exchange of one and two protons from the basaluminite and schwertmannite surface, respectively, with the aqueous sulfate complexes. The sorbed species form monodentate surface complexes with the aluminum mineral and bidentate with the iron mineral. In the case of Sc, the aqueous species ScSO4+ and Sc(OH)2+ form bidentate surface complexes with both minerals. EXAFS analysis of the YSO4+ complex adsorbed on the basaluminite surface suggests the formation of a monodentate inner sphere complex, in agreement with the proposed thermodynamic model. Once the surface complexation model was validated, it was used to asses and predict the REE mobility in passive remediation systems and acidic water mixing zones with alkaline inputs from the field. The REE are preferentially retained in basaluminite-rich waste during passive remediation due to its sorption capacity between pH 5-6. In contrast, schwertmannite waste contains very little REE because the formation of this mineral occurs at pH lower than 4, which prevents REE adsorption. Further, Sc may be scavenged during schwertmannite precipitation as a result of this low pH The model correctly predicts the absence of REE in schwertmannite precipitates and the enrichment of the heavy and intermediate REE with respect to the light REE in basaluminite precipitates collected in the water mixing zones. However, there is a systematic overestimation of the fractionation of rare earths in basaluminite precipitate. This inaccuracy is mainly due to the fact that the mineral precipitation and adsorption are not synchronous process, while basaluminite precipitates from pH 4, REE adsorption occurs at higher pH values, between 5 and 7, when the water mixture reaches these values and a fraction of the particles have been dispersed.
Las tierras raras (en inglés rare earth elements, REE) son conocidas como el conjunto de la serie de los lantánidos (La-Lu), itrio (Y) y escandio(Sc). Las tierras raras son materiales indispensables para las industrias modernas y en especial para las tecnologías verdes (aerogeneradores, baterías, láseres, catalizadores, etc.). Sin embargo a pesar de su gran demanda mundial, su abastecimiento es limitado, por lo que han sido catalogadas por la UE como materias primas críticas (Critical Raw Materials). Con el objetivo de asegurar el abastecimiento de REE en el futuro, en los últimos años se ha promovido la búsqueda de fuentes alternativas de estos elementos en todo el mundo. El drenaje ácido de mina (en inglés acid mine drainage, AMD) producido por la meteorización de sulfuros de Fe, tiene un alto poder de lixiviación de las rocas, por lo que las aguas afectadas adquieren elevadas concentraciones en disolución de Fe, Al, SO4 y otros metales, como las REE. Así, las concentraciones de REE en AMD son entre dos y tres órdenes de magnitud superiores al resto de las aguas naturales y pueden suponer una fuente complementaria de recuperación de REE. El aumento de pH del AMD por mezcla con aguas neutras da lugar a la precipitación en los cauces de los ríos de oxy-hidroxisulfatos de hierro (schwertmannita), a partir de pH 3-3.5, y de aluminio (basaluminita), a partir de pH 4-4.5; acompañado de la eliminación de las tierras raras. Debido a su acidez y carga metálica, el drenaje ácido de mina presenta un problema medioambiental de primera magnitud, por lo que se han desarrollado diferentes sistemas de tratamiento para minimizar su impacto. El sistema de tratamiento pasivo Disperse Alkaline Substrate (DAS) produce la neutralización de las aguas ácidas por la disolución de la calcita presente en el sistema, permitiendo la precipitación secuencial, de schwertmannita y basaluminita. Las tierras raras quedan retenidas preferentemente en el residuo enriquecido en basaluminita. A pesar de ello, aún no existen estudios que describan la adsorción de tierras raras tanto en basaluminita como schwertmannita en estos ambientes. En esta tesis se estudia el mecanismo de retención de las tierras raras mediante adsorción en minerales sintéticos de basaluminita y schwertmannita, en función del pH y del contenido de sulfato disuelto. Con los resultados experimentales obtenidos, se propone un modelo termodinámico de adsorción para predecir y explicar la movilidad de las tierras raras observada en mezclas de AMD con aguas neutras y en un sistema de tratamiento pasivo. La basaluminita y la schwertmannita presentan un carácter nanocristalino. Es conocido que la schwertmannita se transforma en goethita en semanas, liberando sulfato. Sin embargo, nada se sabe de la basaluminita y su posible transformación a otros minerales de Al más cristalinos. De este modo, la caracterización del orden local de la basaluminita a diferentes valores de pH y sulfato se expone en primer lugar. Dependiendo del pH y el sulfato en disolución, la basaluminita se transforma en diferentes grados a nanoboehmita en semanas, pero tiende a estabilizarse con la presencia de sulfato en solución. Los experimentos de adsorción en basaluminita y schwertmannita con diferentes concentraciones de SO4 realizados para cada mineral y en rangos de 3-7 de pH han demostrado que la adsorción es fuertemente dependiente del pH, y en menor medida del sulfato. La adsorción de los lantánidos y del itrio es efectiva a pH 5, mientras que la del escandio comienza a pH 4. Debido a las altas concentraciones de sulfato en aguas ácidas, las especies acuosas predominantes de las tierras raras son los complejos con sulfato, MSO4+. Además del complejo sulfato, el Sc presenta importantes proporciones de Sc(OH)2+ en solución. En función de la dependencia del pH y de la importancia de la especiación acuosa, se propone un modelo de complejación superficial donde la especie acuosa predominante (Mz+) se adsorbe a la superficie libre el mineral, XOH, cumpliendo la siguiente reacción: La adsorción de los lantánidos y del itrio se produce a través del intercambio de uno o dos protones de la superficie de la basaluminita o de la schwertmannita, respectivamente, con los complejos sulfato acuoso, formando complejos superficiales monodentados con el mineral de aluminio y bidentados con el de hierro. En el caso del Sc, las especies acuosas ScSO4+ y Sc(OH)2+ forman complejos superficiales bidentados con ambos minerales. Complementando el modelo propuesto, el análisis de EXAFS del complejo YSO4+ adsorbido en la superficie basaluminita sugiere la formación de un complejo monodentado de esfera interna, coincidiendo con el modelo termodinámico propuesto. El modelo de complejación superficial, una vez validado, ha permitido evaluar y predecir la movilidad de REE en los sistemas de tratamiento pasivos y en zonas de mezcla de aguas ácidas con aportes alcalinos estudiados en el campo. La preferente retención de las tierras raras en la zona de la basaluminita precipitada en los sistemas de tratamiento pasivo ocurre por adsorción de las mismas a pH entre 5-6. La ausencia de tierras raras en la zona de schwertmannita se debe al bajo pH de su formación, inferior a 4, que impide la adsorción de las mismas. Sin embargo, debido a su menor pH de adsorción, una fracción de Sc puede quedar retenida en la schwertmannita. El modelo también predice correctamente la ausencia de REE en los precipitados de schwertmannita y el enriquecimiento de las tierras raras pesadas e intermedias respecto a las ligeras en los precipitados de basaluminita recogidos en el campo en las zonas de mezcla de aguas. Sin embargo, se ha observado una sistemática sobreestimación del fraccionamiento de las tierras raras en los precipitados de basaluminita. Este hecho se debe principalmente a que la precipitación del mineral no ocurre de forma síncrona con la adsorción, precipitando la basaluminita a partir de pH 4 y adsorbiendo tierras raras a pH más altos, entre 5 y 7, cuando las partículas sólidas han sido parcialmente dispersadas.

In the Mojave Pegmatite district, located in northwestern AZ, numerous pegmatites intrude syn- to post-collisional Paleoproterozoic granitic rocks. The slightly older Cerbat plutons are associated with the suturing of the Mojave and Yavapai terranes whereas Aquarius granites were emplaced during the Yavapai Orogeny as the sutured terranes docked with North America. A detailed study of 5 pegmatites shows that they are zoned with composite cores and contain REE minerals characteristic of NYF pegmatites. However, they exhibit characteristics atypical for NYF pegmatites including F depletion, white microcline, an absence of columbite and, in the Rare Metals pegmatite, have muscovite and beryl. With the exception of the Kingman pegmatite, they exhibit normal LREE-HREE distributions. The Kingman pegmatite is extremely LREE enriched, HREE depleted and exhibits an unusual Nd enrichment which, in some cases, is sufficiently high that allanite is Nd dominant, thus a new mineral species, allanite-Nd.

Silicate melt inclusions (MI) are small samples of melt that are trapped during crystal growth at magmatic pressures and temperatures. The MI represent a sample of the melt that was isolated from the magma during host crystal growth. Thus, MI provide a valuable tool for constraining the magmatic history of igneous systems because they provide an unambiguous method to directly determine compositions of melts from which the host crystal grew. As such, coupled petrographic examination and geochemical analyses of MI and host crystals can reveal information about crystal/melt processes in igneous systems that are difficult (or impossible) to assess through conventional methods. Many studies have used MI to monitor large scale petrogenetic processes such as partial melting and fractional crystallization. The research presented below focuses on using MI to constrain processes that operate at the crystal/melt interface because MI are samples of melt that resided adjacent to the host crystal prior to entrapment as an inclusion. Chapter one addresses challenges associated with preparing small crystals containing MI for geochemical analysis. In chapter two trace element analyses of MI and the immediately adjacent host zircon crystals are used to determine zircon/melt partition coefficients. In chapter 3 the significance of boundary layer development adjacent to growing crystals is evaluated by comparing the trace element compositions of MI host crystals that have significantly different trace element mineral/melt partitioning behavior.
Ph. D.

This thesis consists of three main chapters preceded by an introduction that discusses the importance of diffusion in minerals to constrain the geochemistry of various magmatic processes. The first chapter deals with the experimental technique and measurement of tracer element diffusion data in garnet and clinopyroxene. Self-diffusion coefficients of selected REE have been measured as a function of temperature (770°C-1050°) at 1 bar and oxygen fugacity (fO₂) corresponding to that defined by the iron-wustite buffer. The experimental results indicate small variations of diffusivity for REE in both garnet and clinopyroxene and an activation energy which is similar to the activation energy for diffusion of major components. In the second chapter the atomistic mechanism of Nd diffusion in garnet is investigated by molecular dynamics (MD) simulation. An optimization procedure based on genetic algorithm provides the semi-empirical coefficients that are used to reproduce the repulsive forces between atoms. Results from MD simulations at high pressure and temperature show that Schottky defect is the most favorable mechanism for vacancy formation in the intrinsic region. The preferred reaction to incorporate neodymium in the dodecahedral site involves transferring an iron atom to the octahedral site after removing the aluminum atom from the lattice site. A model of diffusion in the extrinsic region with a prescribed vacancy defect fraction in the garnet (10⁻⁴) also provides an acceptable result. The third chapter considers some of the potential applications of the REE diffusion data in garnet and clinopyroxene to magmatic processes. REE patterns obtained from the solution of a moving boundary problem shows that incompatible elements are more sensitive to disequilibration controlled by diffusion. Melt generated by disequilibrium melting is less enriched in incompatible elements than melt produced by an equilibrium melting process. Solution of a multiphase flow model, including the chemical transport equations with diffusion in a solid phase, permits a more realistic investigation of the disequilibrium melting process. During the ridge evolution the model predicts negligible effect of solid state diffusion on the geochemical evolution of the partial melt and the residual solid.

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.

Rare Earth Element (REE) determination in samples of coal and fly ash was undertaken by gradient high performance ion chromatography (HPIC). Ion chromatographic analysis requires that samples be in solution and that the matrix transition metals be removed. Coal samples, weighing 0.20g, were successfully dissolved in sealed pressure vessels in a microwave oven. Standard ashing procedures, followed by acid dissolution, were carried out to allow comparison with the microwave digestion technique. A lithium metaborate/tetraborate fusion and acid dissolution technique was used for the dissolution of fly ash. For the technique of REE determination the sample matrix was removed by off-line cation exchange. In an initial stage of the HPIC analysis the transition metals were removed by anion exchange using pyridine-2,6 dicarboxylic acid. The REE were then analysed using gradient elution of oxalic and diglycolic acid. Typically a 100μ1 volume of sample solution was employed for REE determination, but in the case of low ash (low REE) coal samples, prepared by microwave digestion, on-line concentration of 3-5 ml of sample, was necessary. The separated REE were reacted with 4-(2-pyridylazo)-resorcinol (PAR) and detected photometrically using a visible light detector at a wavelength of 520nm. Reproducibility for each REE was typically better than 5%CoV. Results from the analysis of coal and fly ash international standard reference materials were in acceptable agreement with values from alternative analytical procedures. Smooth, coherent trends obtained when the data were plotted on chondrite and "shale composite" normalised diagrams provided some support for the accuracy of the technique. The application of HPIC to the determination of REE in coals was demonstrated by the analysis of a new international reference coal sample, USGS CLB-1. Differences in REE concentrations between coal samples prepared by microwave digestion and ashing were observed. The HPIC analytical technique was also applied to the determination of REE in fly ash. The REE concentrations of fly ash from sequential electrostatic precipitators, from Lethabo and Kendal power stations, were determined to elucidate the behaviour of REE after the combustion of coal. REE concentrations increased through the sequential precipitators.

A novel and simple "constant-addition" technique was used to study calcite precipitation kinetics and the partitioning of REE between calcite overgrowths and their parent seawater solutions under steady state conditions.
As a consequence of solute interactions in solution and at the growing mineral surface, the calcite precipitation mechanism in seawater is complex. It is dominated by the following reversible overall reaction: $ rm Ca sp{2+}+CO sbsp{3}{2-} rightleftharpoons CaCO sb3.$ A kinetic expression is proposed which describes the precipitation rate according to this reaction. A partial reaction order of 3 with respect to CO$ sb3 sp{2-}$ is obtained.
REE have a strong affinity for calcite and substitute for Ca$ sp{2+}$. REE partition coefficients in calcite overgrowths were calculated from their concentrations in the overgrowths and their parent solutions using a non-thermodynamic homogeneous model. The concentrations were determined by chelation and gradient ion chromatography (CGIC) using a revised procedure. REE partition coefficients decrease gradually with increasing REE atomic number. They are sensitive to changes in (REE): (Ca$ sp{2+}$) and the presence of O$ sb2$ in solution, but unaffected by the precipitation rate, $ rm lbrack CO sb3 sp{2-} rbrack$ or Pco$ sb2$ of the solution. The partitioning behaviour of REE is negatively correlated to the solubility of their respective carbonates and influenced by speciation, adsorption, and subsequent surface reactions (e.g., dehydration).

Master of Science
Department of Geology
Matthew Totten
The REE distribution patterns and total concentrations of the organic matter of the Woodford shale reveal a potential avenue to investigate hydrocarbon maturation processes in a source rock. Ten samples of the organic matter fraction and 10 samples of the silicate-carbonate fraction of the Woodford shale from north central Oklahoma were analyzed by methods developed at KSU. Thirteen oil samples from Woodford Devonian oil and Mississippian oil samples were analyzed for REE also. REE concentration levels in an average shale range from 170 ppm to 185 ppm, and concentration levels in modern day plants occur in the ppb levels. The REE concentrations in the organic matter of the Woodford Shale samples analyzed ranged from 300 to 800 ppm. The high concentrations of the REEs in the Woodford Shale, as compared to the modern-day plants, are reflections of the transformations of buried Woodford Shale organic materials in post-depositional environmental conditions with potential contributions of exchanges of REE coming from associated sediments. The distribution patterns of REEs in the organic materials normalized to PAAS (post-Archean Australian Shale) had the following significant features: (1) all but two out of the ten samples had a La-Lu trend with HREE enrichment in general, (2) all but two samples showed Ho and Tm positive enrichments, (3) only one sample had positive Eu anomalies, (4) three samples had Ce negative anomalies, although one was with a positive Ce anomaly, (5) all but three out of ten had MREE enrichment by varied degrees. It is hypothesized that Ho and Tm positive anomalies in the organic materials of the Woodford Shale are reflections of enzymic influence related to the plant physiology. Similar arguments may be made for the Eu and the Ce anomalies in the Woodford Shale organic materials. The varied MREE enrichments are likely to have been related to some phosphate mineralization events, as the Woodford Shale is well known for having abundant presence of phosphate nodules. The trend of HREE enrichment in general for the Woodford Shale organic materials can be related to inheritance from sources with REE-complexes stabilized by interaction between the metals and carbonate ligands or carboxylate ligands or both. Therefore, a reasonable suggestion about the history of the REEs in the organic materials would be that both source and burial transformation effects of the deposited organic materials in association with the inorganic constituents had an influence on the general trend and the specific trends in the distribution patterns of the REEs. This study provides a valuable insight into the understandings of the REE landscapes in the organic fraction of the Woodford Shale in northern Oklahoma, linking these understandings to the REE analysis of an oil generated from the same source bed and comparing it to oil produced from younger Mississippian oil. The information gathered from this study may ultimately prove useful to trace the chemical history of oils generated from the Woodford Shale source beds.

Ni laterites are considered worthy targets for critical metals (CM) exploration as rare earth elements (REE), Sc and platinum group elements (PGE) can be concentrated during weathering as a result of residual and secondary enrichment. In this investigation geochemical and mineralogical data of CM from two different nickel laterite types (i) from the Moa Bay mining area in Cuba (oxide type) and (ii) from the Falcondo mining area in the Dominican Republic (hydrous Mg silicate type) are presented. Emphasis is given on examining their potential to accumulate CM and on processes involved. Results show that CM are concentrated towards the surface in specific zones: (i) REE in clay minerals rich horizons and within zones composed of secondary Mn oxide(s) (ii) Sc within zones rich in secondary Fe and Mn bearing oxide(s) and (iii) PGE in zones with high concentrations of residual chromian spinel and secondary Fe and Mn bearing oxide(s) at upper levels of the Ni laterite profiles. Concentration factors involve (i) residual enrichment by intense weathering (ii) mobilization of CM during changing Eh and pH conditions with subsequent reprecipitation at favourable geochemical barriers (iii) interactions between biosphere and limonitic soils at highest levels of the profile (critical zone) with involved neoformation processes. Total contents of CM in both Ni laterite types are low when compared with conventional CM ore deposits but are of economic significance as CM have to be seen as cost inexpensive by-products during the Ni (+Co) production. Innovative extraction methods currently under development are believed to boost the significance of Ni laterites as future unconventional CM ore deposits. Two Ni laterite profiles from the Falcondo mining area have been compared for their platinum group element (PGE) geochemistry and mineralogy. One profile (Loma Peguera) is characterized by PGE-enriched (up to 3.5 ppm total PGE) chromitite bodies incorporated within the saprolite, whereas the second profile is chromitite-free (Loma Caribe). Total PGE contents of both profiles slightly increase from parent rocks (36 and 30 ppb, respectively) to saprolite (-50 ppb) and reach highest levels within the limonite zone (640 and 264 ppb, respectively). Chondrite-normalized PGE patterns of saprolite and limonite reveal rather flat shapes with positive peaks of Ru and Pd. Three types of platinum group minerals (PGM) were found by using an innovative hydroseparation technique: (i) primary PGM inclusions in fresh Cr-spinel (laurite and bowieite), (ii) secondary PGM (e.g., Ru-Fe-Os-Ir compounds) from weathering of preexisting PGM (e.g., serpentinization and/or laterization), and (iii) PGM precipitated after PGE mobilization within the laterite (neoformation). Results provide evidence that (i) PGM occurrence and PGE enrichment in the laterite profiles is independent of chromitite incorporation; (ii) PGE enrichment is residual on the profile scale; and (iii) PGE are mobile on a local scale leading to in situ growth of PGM within limonite, probably by bioreduction and/or electrochemical metal accretion. Free grains of PGM with delicate morphologies were discovered in limonite hosted chromitite samples (“floating chromitites”) from highest levels in the Falcondo Ni laterite deposit (Dominican Republic). Textural and chemical evidence obtained via SEM and EMP analysis points to a multistage formation: (i) primary PGM formation at magmatic stage; (ii) transformation to highly porous secondary Os-Ru PGM during serpentinization; (iii) neoformation of Ir-Fe-Ni-(Pt) mineral phases during early stages of lateritization; (iv) neoformation of Pt-(Ir) mineral phases within the critical zone of the profile resulting in nugget shaped accumulation of rounded particulates during late stages of lateritization. The observation of accumulations of most likely biogenic mediated in situ growth of Pt rich nanoparticles in supergene environments could help to explain (i) why Pt bearing nuggets are the most abundant PGM found in surface environments, (ii) why Pt nuggets from placer deposits generally surpass the grain sizes of Pt grains found in parent rocks by several orders of magnitude (few micrometers vs. several millimeters) and (iii) how anthropogenic PGE contamination may affect our biosphere. Osmium chromitite, saprolite and limonite (Falcondo mining area), suggest that serpentinization of the Loma Caribe peridotite has not significantly affected the Re-Os system in Os-rich PGM. This is noted by the fact, that primary PGM formed at magmatic stage and secondary Ru-Os-Mg- isotope characteristics from primary and secondary PGM, separated from Si PGM formed due desulphurization of primary PGM with significant incorporation of Mg silicates, have almost identical Os isotope characteristics, typical of the mantle. However, the Re-Os system can be significantly disturbed during stages of lateritization when porous secondary PGM react with Fe-rich fluids, thus forming hexaferrum and magnetite in the 187 188 interstices of secondary PGM. Here presented data indicate that more radiogenic ratios in higher levels of the weathering profile are linked to steady mobilization of PGE within secondary PGM resulting in subsequent loss of Os counterbalanced by the incorporation of Fe. Os/ Os In this investigation presented data clearly states that PGE are neither noble nor inert in surface environments, at least in those related to tropical Ni laterites from the Northern Caribbean.

It is well known that the release of long-lived radionuclides to the water path is probably the most relevant radiological risk originating from an underground repository. Transuranic elements (ie. all elements with an atomic number greater than 92 (U)) do not have any non-radioactive isotopes and are very rare in natural materials. The long term geochemical behaviour of these elements must thus be derived from chemical analogues such as the rare earth elements (REE), Th and U. Steenkampskraal monazite mine, situated 350 km north of Cape Town, has been found to be an excellent locality for the study of these elements, due to the high concentration of these elements in the ore as well as the ideal geology, which consists of low permeability rocks with groundwater flow governed by fractures. The ore body consists of a monazite [(REE, Th, U)P04], apatite [Ca₃P0₄)₂], chalcopyrite [CuFeS] and magnetite [FeP₄] veindeposit. Water was sampled from six boreholes in the vicinity of the mine and five wi.ndpumps on the surrounding farm Nabeep and Brandewynskraal. Surface water samples were taken from the slimes dam, an ephemeral stream on the western side of the mine, as well as from the surface of a road shortly after rain, below the tailings. Four water samples were taken from within the underground mine workings (Mainshaft, Main shaft extension, Sump on level 3 and Inclined shaft). Colloids were sampled from three of the boreholes and a precipitate was taken from the surface of the main shaft water. Soils were sampled along two transects away from the mine on the eastern and western side of the ore body. Due to the topography of the area, surface contamination could only occur on these two sides. Stable isotopes of oxygen (8 180) and hydrogen ((8 180) indicated the presence of two distinct groups of waters within the vicinity of the mine. One group is composed of unevaporated waters and includes all borehole sand the water sampled in the inclined shaft. The water moving through the inclined shaft is in contact with the ground water. A second group of highly evaporated waters was present in the slin1es dam samples as well as the underground water samples not directly in contact with groundwater. Groundwater contamination by REE-bearing phosphate minerals has resulted in measurable concentrations of U, Th and REE in all mine waters and boreholes in the near vicinity of the mine. The chondritenormalized REE patterns of the water samples are sin1ilar to those displayed by monazite, with a distinctive Eu depletion and an obvious enrichment in LREE with respect to HREE. Monazite-normalized REE patterns for the selected borehole waters show a marked fractionation between LREE and HREE, with the HREE strongly enriched in the aqueous phase. Heavy REE have been shown to have a greater tendency for complexatioi1 and a greater affinity for mineral surfaces. In the present study, the three boreholes in which colloids were found had high concentrations of U, Th and REE. It is likely that colloidal transport of these elements is the dominant mechanism of transport.

Microbes exert extensive control on redox element cycles. They participate directly orindirectly in the concentration and fractionation of elements by influencing the partitioningbetween soluble and insoluble species. Putative microbially mediated manganese (Mn) oxidesof the birnessite-type, enriched in rare earth elements (REE) + yttrium (Y) were recentlyfound in the Ytterby mine, Sweden. A poorly crystalline birnessite-type phyllomanganate isregarded as the predominant initial phase formed during microbial Mn oxidation. Owing to ahigher specific surface area, this biomineral also enhances the known sorption property of Mnoxides with respect to heavy metals (e.g. REE) and therefore has considerable environmentalimpact.The concentration of REE + Y (2±0.5% of total mass, excluding oxygen, carbon and silicon)in the Ytterby Mn oxide deposit is among the highest ever observed in secondary precipitateswith Mn and/or iron. Sequential extraction provides evidence of a mineral structure where theREE+Y are firmly included, even at pH as low as 1.5. Concentration ratios of Mn oxideprecipitates to fracture water indicate a strong preference for the trivalent REE+Y overdivalent and monovalent metals. A culture independent molecular phylogenetic approach wasadopted as a first step to analyze the processes that microbes mediate in this environment andspecifically how the microbial communities interact with the Mn oxides. Plausible players inthe formation of the investigated birnessite-type Mn oxides are mainly found within theferromanganese genera Hyphomicrobium and Pedomicrobium and a newly identified YtterbyBacteroidetes cluster most closely related to the Terrimonas. Data also indicate that thedetected microorganisms are related to the environmental constraints of the site including lowconstant temperature (8°C), absence of light, high metal content and possibly proximity to theformer storage of petroleum products.

Les interactions fluide-roche intervenant dans les systèmes hydrothermaux océaniques ont été étudiées expérimentalement en surveillant les isotopes du Mg et Sr. Les résultats suggèrent que les réactions rapides à températures moyennes pourraient expliquer en partie les divergences identifiées précédemment dans le bilan marin du Sr. De plus, la ré-dissolution de l'anhydrite dans les stades avancés peut expliquer les faibles quantités d'anhydrite trouvée dans les échantillons de basalte océanique altérés. L'évolution du δ26/24Mg dans les fluides indique que le Mg isotopiquement lourd a été incorporé préférentiellement dans les minéraux des argiles.Le fractionnement entre les terres rares et le Ca pendant la précipitation de calcite a été étudié expérimentalement. Ces données suggèrent que l'incorporation du REE3+ dans la structure de la calcite est probablement équilibrée par l'incorporation de Na+ et que les coefficients de partage déduits pour les conditions marines peuvent varier considérablement selon la composition du fluide. Enfin, l'étude de la solubilité de l'hydroxylbastnasite (REE(CO3)(OH)), conduite au cours de ce travail, indique que cette phase est moins soluble que les autres carbonates des terres rares connus
The fluid-rock interactions occurring in hydrothermal systems at or near mid-oceanic ridges (MOR) were studied experimentally while monitoring the Mg and Sr isotopic evolution. The results suggest that fast intermediate-temperature reactions could partly explain previously identified discrepancies in the marine 87Sr/86Sr budget. Furthermore, late-stage anhydrite re-dissolution caused by fluid reduction and temperature decreases in our experiments represent a potential explanation for the low amounts of anhydrite found in altered oceanic basalt samples. The fluid δ26/24Mg indicate that isotopically heavy Mg was preferentially incorporated into the clays. Towards the interpretation of rare earth element (REE) patterns in marine calcite, the fractionation between the REEs and Ca during the precipitation of calcite was studied experimentally. These data suggest that the incorporation of REE3+ ions into the calcite structure was likely charge balanced by incorporation of Na+, and that inferred partition coefficients for marine conditions can vary substantially depending on the fluid composition. Furthermore, the solubility of hydroxylbastnasite (REE(CO3)(OH)) was determined, indicating that this phase is less soluble than other known REE carbonates

Geoscience
Ph.D.
Karst aquifers are dynamic hydrologic systems which are sensitive to short-term recharge events (storms) and heterogeneous recharge characteristics (point recharge at sinks, irregular soil thicknesses). These aquifers are highly productive yet also vulnerable to contamination, in large part because the conduit network is a significant unknown for predicting karst flow paths. To address these uncertainties, two adjacent karst springs, Tippery Spring and Near Tippery Spring, were monitored to better understand flow and source mixing characteristics. The two springs in central Pennsylvania’s Nittany Valley have similar discharges and are only 65 meters apart, yet they show unique behaviors in terms of water chemistry and discharge response to storms. First examined for flow characterization in 1971 by Shuster and White, the springs were analyzed in this study using high-resolution logging and new tracers such as rare earth element (REEs) and Ca/Zr ratios. This research contributes to the field of karst hydrology through innovative water sampling and monitoring techniques to investigate karst recharge and flow behavior along with conduit flow models incorporating multiple calibration target datasets such as water temperature and dye tracing. Stable isotope signatures (δD & δ18O) of storm water samples at the two springs varied based on storm intensity, but also due to their unique recharge behaviors. Increased spring discharge preceded the arrival of storm water as conduits were purged of pre-storm water, indicated by no change in isotopic composition on the rising limb. The isotopic signature then became progressively more enriched at both springs, indicating storm water recharge. At Tippery, this enrichment began around peak flow, sooner than at Near Tippery where enrichment began during the descending limb. Thus, isotopes indicated a stronger surface connection at Tippery Spring. Storm intensity also affected the relative contribution of recharging water reaching both springs, with a larger storm producing a larger recharge signature compared to a smaller storm. At Tippery Spring, for a short time the majority of emerging water was storm water, which may indicate a reversal in water exchange between the conduits and the surrounding matrix, an important consideration in karst contaminant transport. Two natural tracers were applied in new ways for this study: Ca/Zr ratios and REE patterns. Both tracers provided additional information about flow paths and recharge sources as they varied during the storm hydrograph. Ca/Zr ratios changed in timing and intensity with storm intensity, and both springs exhibited a decline in Ca/Zr ratios as calcium-rich carbonate matrix water was displaced by zirconium-rich storm recharge water from sinking streams off the clastic upland ridges. Being a storm water arrival indicator in clastic-ridge-fed Valley and Ridge springs, this relationship made Ca/Zr ratios a useful substitute for stable water isotopes while also providing information on source area. In response to storm water recharge, REE concentrations increased with the arrival of storm water. The timing and magnitude of concentration increases were influenced both by the degree of surface connectivity intrinsic to each spring and the intensity of the recharge event. Elevated REE concentrations persisted after other parameters recovered to pre-storm levels, suggesting water which has interacted with either the local carbonate matrix or the upland siliciclastics. These slower flow paths recharging the two springs were not apparent from other geochemical parameters. This study illustrated the relationships among multiple tracers to understand source waters in different periods of storm hydrographs. A flow and transport model using the Finite Element Subsurface Flow Model (FEFLOW) was calibrated using quantitative dye trace and high resolution temperature data to simulate the connection between a sinking stream and Tippery Spring. Dye was injected at the sink and monitored at the spring while temperature data was collected using loggers at both the sink and the spring. FEFLOW was used to simulate the connection between sink and spring through varying conduit geometries, sink and spring discharges, conduit conductivity, conduit cross-sectional area, matrix transmissivity, matrix porosity, and dispersivity. Single conduit models reproduced larger peak and recession concentrations than observed. A forked conduit model diverted flow from the main conduit, reducing the concentration of dye reaching the spring, provided a better match. Latin Hypercube sensitivity analysis indicated that dye concentration breakthrough curves were most sensitive to conduit conductivity and less sensitive to other model parameters. Temperature data from high-resolution loggers at the sink and spring were then incorporated into the model scenarios to reproduce seasonal spring temperature using the conduit configuration fit to the dye trace. Simulated temperature signals at the spring were sensitive to parameters in addition to conduit conductivity, most notably matrix transmissivity and inflow rates at the sink. The dual approach to karst model calibration using a temperature model set up from an initial dye trace results in greater model confidence due to a limited possible range in conduit conductivity. This study improved conceptual and numerical models for karst by examining how data from storm events and tracers can be used to better understand recharge and flow paths.
Temple University--Theses

Master of Science
Department of Geology
Sambhudas Chaudhuri
The exploration and development of unconventional shale plays provide an opportunity to study the hydrocarbon generation process. These unconventional plays allow one to investigate the interactions between the fluid, mineral, and organic material that occur in a hydrocarbon-generating source bed, before any changes in composition that may occur during secondary migration or post migration processes. Previous studies have determined the chemical constituents of formation waters collected from conventional reservoirs after secondary migration has occurred. This investigation targets formation waters collected from the Woodford shale that acts as both source and reservoir, therefore samples have yet to experience any changes in composition that occur during secondary migration. This investigation focuses on the major element and trace element chemistry of the formation water (Cl, Br, Na, K, Rb, Mg, Ca, Sr, and Rare Earth Elements), which has been compared to chemical constituents of the associated crude oil and kerogens. Analytical data for this investigation were determined by the following methods; Ion Chromatography, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The information is used to assess the presence of different sources of water that constitute the formation water, and also to investigate interaction between different minerals and formation waters within the source beds. The formation water data also yields new insights into compartmentalization of oil-gas rich zones within the source beds.

Rare earth elements (REEs) and their isotopes (such as Nd isotopes) can be potentially used to trace a wide range of oceanic processes in both modern and ancient oceans, but their successful application as tracers requires a comprehensive understanding of REE cycling in the modern ocean. Previous studies of REEs in seawater were largely constrained by analytical difficulties in generating accurate and precise REE data from seawater, which typically contain REE concentrations at a sub-ppt to ppt level. A new, and relatively simple, analytical method for precise and accurate determination of all dissolved REE concentrations in reasonably small (∼100 ml) seawater samples is presented in this thesis. With the application of the new method, this thesis reports the first full-depth, zonal ocean section of all dissolved REE concentrations, collected during the CoFeMUG cruise along ∼12°S in the South Atlantic. The section approach of this study places the distribution of dissolved REE concentrations in a well-constrained hydrographic context, allowing the first quantitative assessment (by an inverse model) of the relative importance of hydrographic controls resulting from advection/mixing of ocean circulation, together with non-conservative controls resulting from local particle scavenging and remineralization, in controlling the distribution of dissolved REEs in this region. A noteworthy decoupling of Ce and Mn with respect to their cycling in the water column was also observed in this study. The application of Nd isotopes as a tracer to reconstruct changes in ocean circulation in the NW European chalk shelf sea during rapid climatic events, including the mid-Cenomanian Event and oceanic anoxic event 2 (OAE 2), suggests a tight coupling between ocean circulation and transient climatic cooling during the general warm Late Cretaceous. An advected volcanic signal during OAE 2 was registered in the seawater Nd-isotope record from the English Chalk, probably suggesting a period of enhanced ocean ventilation/mixing at this time.

The lower Mount Rogers Formation (LMRF) is described by Rankin (1993) as a sequence of intercalated metabasalts and volcanogenic sediments with minor metarhyolite. We have chosen to examine the sequence of the LMRF units exposed along Elk Garden Ridge, a high shoulder between the summits of Whitetop Mountain and Mount Rogers in the Mount Rogers National Recreation Area in SW Virginia. This sequence represents an uplifted block of LMRF units enclosed by exposures of Whitetop and Wilburn metarhyolites. In the field, progressive lithologic changes can be observed walking up-section along Elk Garden ridge that are indicative of changes in lava compositions and eruptive environments. From the bottom of the section, massive basalts with distinctive 1-2 cm long swallowtail plagioclase phenocrysts grade into vesicular basalts, then into sheet flow basalts, followed by a thick sequence of aphyric and amygdaloidal pillow basalts. Further up section, eruptive products transition into rhyolitic ignimbrites and ash and lapilli tuffs. Boulders of cobble conglomerates near the middle of the sequence and sedimentary layers in between individual sheet flows suggest short periods of relative eruptive quiescence. The only unit broken out in the LMRF by Rankin (1993), Fees Rhyolite, is not observed in the field area, suggesting local differences in topography, eruptive products and eruptive styles across the outcrop area during the deposition of these eruptive products. Petrographically, the rocks reflect the regional greenschist facies metamorphic conditions with chlorite and epidote as primary metamorphic minerals, and unakite-like zones of mineralization. Relict plagioclase and pyroxene phenocrysts persist, as do primary igneous textures and structures. Compositionally, all of the rocks in the Elk Garden Ridge sequence are strongly enriched in alkali metals, with elevated Na2O and K2O contents, and high TiO2 in the basalts. Major and trace element systematics suggest that the chemical signatures of the metabasalts are primary controlled by shallow-level crystallization processes. The LMRF metabasalts share many compositional affinities with later (~570 Ma) rift-related basalts preserved in the Appalachians, suggesting that all of these lavas were formed by melting of a compositionally uniform mantle source, followed by shallow crystallization, despite being separated from one another by large stretches of time and space.

The Andean Southern Volcanic Zone (SVZ) is a vast and complex continental arc that has been studied extensively to provide an understanding of arc-magma genesis, the origin and chemical evolution of the continental crust, and geochemical compositions of volcanic products. The present study focuses on distinguishing the magma/sub-arc crustal interaction of eruptive products from the Azufre-Planchon-Peteroa (APP 35°15’S) volcanic center and other major centers in the Central SVZ (CSVZ 37°S - 42°S), Transitional SVZ (TSVZ 34.3-37.0°S), and Northern SVZ (NSVZ 33°S - 34°30’S). New Hf and Nd isotopic and trace element data for SVZ centers are consistent with former studies that these magmas experienced variable depths of crystal fractionation, and that crustal assimilation is restricted to the lower crustal depths with an apparent role of garnet. Thermobarometric calculations applied to magma compositions constrain the depth of magma separation from mantle sources in all segments of the SVZ to(70-90 km). Magmatic separation at the APP complex occurs at an average depth of ~50 km which is confined to the mantle lithosphere and the base of the crust suggesting localized thermal abrasion both reservoirs. Thermobarometric calculations indicate that CSVZ primary magmas arise from a similar average depth of (~54 km) which confines magma separation to the asthenospheric mantle. The northwards along-arc Sr-Nd-Hf isotopic data and LREE enrichment accompanied with HREE depletion of SVZ mafic magmas correlates well with northward increasing crustal thickness and decreasing primary melt separation from mantle source regions indicating an increased involvement of lower crustal components in SVZ magma petrogenesis. The study concludes that the development of mature subduction zones over millions of years of continuous magmatism requires that mafic arc derived melts stagnate at lower crustal levels due to density similarities and emplace at lower crustal depths. Basaltic underplating creates localized hot zone environments below major magmatic centers. These regions of high temperature/partial melting, and equilibration with underplated mafic rocks provides the mechanism that controls trace element and isotopic variability of primary magmas of the TSVZ and NSVZ from their baseline CSVZ-like precursors.

Master of Science
Geology
Matthew W. Totten
The most common practice of typing crude oils utilizes biomarkers to gain insight on the history of the oil. This practice only considers the organic chemistry of the oil, and does not consider the trace element concentrations within the oil. Rare earth element and other trace element concentrations in crude oil might provide further insight into the oil’s source and origin. This study analyzed REE and other trace metal concentrations of crude oil in the Spivey-Grabs field of south-central Kansas through analysis by ICP-MS and ICP-AES that, coupled with visual physical characteristics of oil and FT-IR analysis, could explain the reported “compartmentalization” of the field and provide insight on the origin of the oils. Analysis of physical characteristics of the crude oils suggested the presence of two types of oil, of differing viscosities, in the field. FT-IR confirmed the presence of these two oil types based on functional groups present in the oils. The existence of a high viscosity oil could potentially explain the compartmentalization behavior in the field. PAAS-normalized REE distribution patterns showed a general LREE enrichment, a positive cerium and negative europium anomaly, and a MREE and HREE depletion, but higher viscosity oils showed additional MREE and HREE enrichment. K/Rb values ranged from 2,864 to 44,118, with oils from mixed-viscosity wells having lower ratios overall. K/Rb values of Spivey-Grabs crude oils more closely resembled those of the Lansing-Kansas City formation than the K/Rb values of the Woodford shale and Mississippian formation of the Anadarko basin. Comparing the rare earth element distribution patterns and K/Rb values from this study to those of the Woodford shale suggests the Spivey-Grabs oil originated from a local source and not from the Woodford shale.

Ce travail est axé sur l’étude d’un profil de sol et des solutions de sol prélevés sur une parcelle expérimentale couvertes d’épicéas. Tous ces échantillons proviennent du Bassin Versant du Strengbach (Observatoire HydroGéochimique de l’Environnement – OHGE), ont été échantillonnés à différentes profondeurs (5, 10, 30 et 60 cm) et durant la période comprise entre 2009 et 2013.Les caractérisations des extraits des sols par spectroscopie Infra-Rouge ont permis de mettre en évidence les modifications des groupements fonctionnels organiques avec la profondeur et que ces modifications ont une forte incidence sur le comportement des cations (majeurs et traces) dans le sol. Des expérimentations d’ultra-filtration ont permis d’identifier les flux colloïdaux et dissous du carbone organique ainsi que ceux des éléments majeurs et traces présents dans les solutions de sol. L’utilisation conjointe des traceurs isotopiques (87Sr/86Sr et δ44/40Ca) et chimiques (Terres Rares) ont mis en évidence des processus ayant lieu aux interfaces eau-sol-plante, comme le prélèvement racinaire ou l’altération des sols
This work is focused on the study of a profile of soil and soil solutions collected on an experimental plot covered with spruce. All these samples come from the watershed of the Strengbach (environment - OHGE Hydrogeochimique Observatory), were sampled at different depths (5, 10, 30 and 60 cm) and during the period between 2009 and 2013. Characterizations of soil extracts by infrared spectroscopy allowed to highlight changes in the organic functional groups with depth and that these changes have a significant impact on the behaviour of the cations (major and trace) in the soil. Ultrafiltration experiments helped to identify flows of colloidal and dissolved organic carbon as well as those of the major and trace-element present in soil solutions. The joint use of isotope tracers (87Sr / 86Sr and δ44 / 40 Ca) and chemical (Rare Earth Elements) have highlighted processes taking place at the water-soil-plant interface, as the uptake by root or soil alteration

Master of Science
Department of Geology
Matthew Totten
Oil production in Kansas has a long history with plays being found on all sides of the state. The source of Kansas’s hydrocarbons has been traditionally thought to be outside the state due to low thermal maturity and the shallow burial of potential source rocks within Kansas. This research addresses the question regarding the source of the oil in Kansas, at least within a small geographic area of roughly 146mi[superscript]2. The Spivey-Grabs-Basil Field has been one of the more successful fields within the state of Kansas since the 1960’s. This field is compartmentalized and offers a natural laboratory in which to conduct the field’s first formal oil-source rock correlation since oils are locked into place. While the main focus of this research relies heavily on pyrolysis and GCMS for biomarker analysis, it also investigates the possibility of using rare earth element (REE) concentrations as a possible fingerprint of organic matter within a source bed. TOC values of the Chattanooga shale samples from the Spivey-Grabs-Basil filed range from 0.75 and 3.95 wt. %, well within productive capacity. Pyrograms show both the potential for additional production, and the likely previous expulsion of hydrocarbons. Biomarker concentration percentages between C[subscript]27, C[subscript]28, and C[subscript]29 steranes, as well as pentacyclic terpane ratios compared between crude oil from the Spivey-Grabs-Basil and the Chattanooga shale show a definite genetic relationship. REE values of the organic fraction of the Chattanooga inversely correlate with those of the crude oils, suggesting fractionation during oil generation. After comparison of results with the Woodford shale in Oklahoma, the conclusion of this study is that the Chattanooga shale which underlies the Spivey-Grabs-Basil oil field of southern Kansas is the probable source rock which generated the oil now being produced.

The quartz dioritic Quottoon Igneous Complex (QIC) is a major Paleogene (65-56 Ma) magmatic body in NW British Columbia and SE Alaska that was emplaced along the Coast shear zone (CSZ). The QIC contains two different igneous suites that provide information about source regions, magmatic processes and evolving tectonic regimes that changed from a dominantly convergent to a dominantly strike-slip regime between 65 to 55 Ma. Heterogeneous suite I rocks (e. g. along Steamer Passage) have a pervasive solid-state fabric, abundant mafic enclaves and dikes, metasedimentary screens, and variable color indices (25-50). The homogeneous suite II rocks (e. g. along Quottoon Inlet) have a weak (to absent) fabric developed in the magmatic state (aligned feldspars, melt filled shears), and more uniform color indices (24-34) than in suite I. Suite I rocks have Sr concentrations <750 ppm, avg. LaN/YbN = 10.4, and initial 87Sr/86Sr ratios that range from 0.70513 to 0.70717. The suite II rocks have Sr concentrations >750 ppm, avg. LaN/YbN = 23.1, and initial 87Sr/86Sr ratios that range from 0.70617 to 0.70686. This study proposes that the parental QIC magma (initial 87Sr/86Sr = 0.706) can be derived bypartial melting of an amphibolitic source reservoir at lower crustal conditions. Geochemical data (Rb, Sr, Ba and LaN/YbN) and initial 87Sr/86Sr ratios preclude linkages between the two suites by fractional crystallization or assimilation and fractional crystallization (AFC) processes. The suite I rocks are interpreted to be the result of magma mixing between the QIC parental magma and a mantle derived magma. The samples do not lie along a single mixing line due to continued evolution through fractional crystallization/AFC processes subsequent to magma mixing. The suite II rocks may be generated by AFC. Initial 87Sr/86Sr ratio data suggests that similar processes to those that affected the QIC may also have operated during the generation of other portions of the Great Tonalite Sill of southeast Alaska.
Master of Science

L’objectif de cette thèse est d’utiliser la géochimie des spéléothèmes à travers une étude multi-proxy afin de reconstituer des changements environnementaux et climatiques dans le Sud-Ouest de l’Europe au cours de l’Holocène. Ce travail basé sur trois sites répartis entre l’Espagne et la France couvre les 14 000 dernières années. Cette région du sud-ouest de l’Europe, située à la confluence des hautes et des basses latitudes en fait une région particulièrement sensible à la fois à l’influence climatique de la région Nord-Atlantique mais également des régions Méditerranéenne et subtropicales Africaines et Asiatiques. Ce contexte particulier permet d’étudier idéalement l’impact des différents mécanismes climatiques agissant sur les modifications de son environnement. La répartition des sites d’étude a pour but de comparer les sites sous influence majeure Atlantique (Candamo, Nord Espagne), Méditerranéenne (Salamandre, SE France) ou sous influence mixte (Nerjà, sud Espagne). La compréhension des comportements géochimiques d’éléments clés, a constitué la première partie de cette étude. Après avoir établi un cadre temporel bien contraint (14C, U/Th), la géochimie élémentaire (éléments traces et terres rares) a été couplée à l’étude isotopique (87Sr/86Sr, d18O, d13C). Le rapport 87Sr/86Sr traditionnellement utilisé comme traceur de sources du Sr a été couplé à l’étude des variations élémentaires des éléments alcalins (Li, Rb, Cs) afin de déterminer des changements de sources des éléments (roche-mère ou de sol) dans les spéléothèmes. Le comportement de ces alcalins s’est également révélé lié à des modes de transports différents (particulaire, dissous ou liés à des complexes organiques) et l’utilisation du d13C et des terres rares (fractionnement terres rares légères et terres rares lourdes et anomalie en cerium) a permis de confirmer ou non ces hypothèses. La deuxième partie de ce travail a été d’appliquer ces mécanismes géochimiques à la détermination des processus hydrologiques et environnementaux et de les replacer dans le cadre climatique propre à chaque site d’étude. Ainsi, les éléments alcalins (Li, Rb, Cs) se sont révélés de bons indicateurs de phénomènes d'altération pouvant être liés à des changements climatiques (comme la transition entre le Bölling-Alleröd et le Younger-Dryas dans le site de la Salamandre), et/ou environnementaux (période de déforestation ou de mise en place de végétation à l’Holocène moyen dans le cas du site de Nerjà ou de Candamo). Ces événements pouvant donc se dérouler en contexte très différents (climat sec, déforestation, apports détritiques en climat humide par lessivage), le couplage à d’autres proxis est alors nécessaire pour préciser les conditions d'enrichissement de ces éléments alcalins
The purpose of this thesis is to use speleothem geochemistry through a multi-proxy study to reconstruct environmental and climatic variations in southwestern Europe during the Holocene. This work, based on three sites distributed between Spain and France, covers the last 14,000 years. Due to its location at the confluence of the high and low latitudes, this region of south-western Europe is especially sensitive to both the influence of the North Atlantic climate but also the Mediterranean and subtropical African and Asian climate. This particular context allows to study ideally the impact of the different climatic mechanisms driving the modifications of its environment. The choice of the study sites’ distribution aims to compare sites with main Atlantic influence (Candamo, N Spain), Mediterranean (Salamandre cave, SE France) and mixt one (Nerjà, S Spain). The understanding of geochemical behavior was the first part of this study. After the establishment of a chronological frame (14C, U/Th), elemental geochemistry (trace elements and rare earth elements) and isotopic (87Sr/86Sr, d18O, d13C) was coupled. The 87Sr/86Sr isotope ratio, traditionally used as a source tracer for Sr, has been coupled to the study of elementary variations of alkali elements (Li, Rb, Cs) in order to determine changes in the contribution of bedrock and soil in speleothems. The behavior of these alkalis has also been shown to be related to different modes of transport (particulate dissolved or bound to organic complexes) and the use of d13C and rare earths (light rare earth and heavy rare earth fractionation and cerium anomaly) made it possible to confirm or not these hypotheses. The second part of this work was to apply these geochemical mechanisms to the determination of the hydrological and environmental processes and to place them in the specific climatic context of each study site. Thus, the alkali elements (Li, Rb, Cs) have proved to be good indicators of weathering phenomena that may be related to climate change (such as the transition between Bölling-Alleröd and Younger-Dryas in the Salamandre site), and/or environmental changes (period of deforestation or establishment of vegetation in the Middle Holocene in the case of the sites of Nerjà or Candamo). These events can thus take place in very different contexts (dry climate, deforestation, detrital inputs during wet climate by leaching) the coupling to other proxis is then necessary to specify the conditions of enrichment of these alkali elements

Les processus d’interaction solide-liquide régulent les mécanismes qui régissent la disponibilité des oligo-éléments en phase liquide. Dans cet article, ces processus ont été étudiés grâce à l'utilisation des éléments de terres rares (REE), car ils sont d'excellents traceurs des processus géochimiques. Le but de la première partie de ce travail était d'étudier la réactivité des particules volcaniques lors de l'interaction avec l'eau de la mer synthétique. Les résultats montrent que en dehors de la dissolution, qui est le processus principal, un procédé d'adsorption de surface se produit également, probablement sur la surface des cristaux nouvellement formé. La présence supposée de ces minéraux est suggéré par la variation temporelle de l'Y/Ho, des observations SEM et analyse XRD. Enfin, l'ajout des ligand dissous ne pas augmenter le taux de dissolution des particules volcaniques, mais modifiant la distribution de REE en phase liquide. Dans la deuxième partie de ce travail, l'étude des terres rares a été appliquée à un système humain. Ces éléments ont été utilisés, en fait, d'enquêter sur les fluides du poumon (BAL) chez les personnes exposées aux retombées de cendres volcaniques. Le résultat suggère que la co-précipitation du YLn-phosphates se produisent dans les poumons, à la suite de l'inhalation de particules volcaniques. Ce processus est confirmé par des simulations thermodynamiques et cinétiques indiquant que la cristallisation de YLn-phosphates et d'autres phases authigènes apparaît comme la conséquence de la dissolution de la fraction solubles de cendres
The solid-liquid interaction processes regulate the mechanisms governing the availability of trace elements in liquid phase. In this paper, these processes have been studied through the use of the Rare Earth Elements (REE) since they are excellent tracers of geochemical processes. The purpose of the first part of this work was to study the reactivity of volcanic particulates during the interaction with synthetic seawater. The results show that apart from the dissolution, which is the main process, a surface adsorption process also occurs, probably on the surface of newly formed crystals. The supposed presence of these minerals is suggested by the temporal variation of the Y/Ho ratio, by SEM observations and XRD analysis. Finally the addition of ligand species to dissolved media does not increase dissolution rate of volcanic particles but modify the YLn distribution in liquid phase. In the second part of this work, the Rare Earth study was applied to a human system. These elements were used, in fact, to investigate the effects due to the interactions between the inhaled atmospheric particulate matter and the lung fluids (BAL), in people exposed to fallout of volcanic ash. The results suggest that YLn-phosphate co-precipitation occurs in lungs as a consequence of inhalation of volcanic particles and their interactions with lung fluids. This process is confirmed by thermodynamic and kinetic simulations indicating that crystallisation of YLn-phosphates and other authigenic phases occurs as a consequence of the soluble ash fraction dissolution. The combination of YLn fractionation in bronchial fluids can represent a potential tracer of exposure to atmospheric fallout

Thesis (Ph. D.)--Georgia State University, 2008.
Title from file title page. Eirik J. Krogstad, committee chair; Andrey Bekker, committee co-chair; W. Crawford Elliott, Timothy E. LaTour, committee members. Description based on contents viewed Aug. 27, 2009. Includes bibliographical references (p. 207-219).

Cette thèse de doctorat traite du comportement géochimique de Zr, Hf et Terres Rares dans des environnements aqueux extrêmes. Les études ont été effectuées dans les eaux hyper-salines long de la faille de la Mer Morte (Israël), les eaux hyper-acides dans le système volcanique hydrothermal du Nevado del Ruiz (Colombie) et les eaux riches en CO2 du système volcanique hydrothermal de l'île de Pantelleria, en comprenant le lac alcalin “Specchio di Venere”. Haute appauvrissement en Terres Rares légères a été trouvé dans les eaux acides dominées par le sulfate où on a reconnu la formation d’alunite et jarosite. Certaines eaux long de la faille de la Mer Morte montrent des enrichissements en Terres Rares intermédiaires, causés par la dissolution des minéraux évaporitiques. Les grandes variations redox et de pH observées dans ces systèmes hydrothermaux sont la cause des anomalies de Eu et Ce. Les eaux sulfates acides (1 < pH < 3.6) se caractérisent par des relations de Zr/Hf sous-condritiques et des relations condritiques de Y/Ho. Les rapports de Zr/Hf augment à l'augmentation du rapport Cl/SO4 en suggérant un comportement différent de Zr et Hf. Contrairement aux eaux acides, les relations de Y/Ho et Zr/Hf dans les eaux proches de la neutralité avec valeurs de Eh positives augmentent vers des valeurs super-condritiques, en raison de l'élimination préférentielle par les oxyhydroxydes de fer, de l'Hf et Ho que de Zr et Y. Le distribution des Terres Rares, avec les rapports de Y/Ho et Zr/Hf du “Specchio di Venere” montrent l’interaction entre les particules atmosphériques qui viennent du désert du Sahara et le lac “Specchio di Venere”, démontrent qu’ils sont de traceurs géochimiques
This thesis concerns the geochemistry of Zr, Hf and REE (Rare Earth Elements) in extreme water environments. The investigations were carried out in hypersaline waters covering a wide range of Eh values along Dead Sea Fault (Israel), in hyperacid waters circulating in Nevado del Ruiz volcano-hydrothermal system (Colombia) and in CO2-rich waters in Pantelleria volcano-hydrothermal system (Italy), including the alkaline lake “Specchio di Venere” within a calderic depression. The acidic sulphates waters characterized by the precipitation of alunite and jarosite show a strong LREE depletion. The REE in waters along Dead Sea Fault show MREE enrichments in waters with relative high Ca and SO4 concentrations due to the water interaction with MREE-enriched salt minerals. In the natural waters, changing of pH and Eh induce variations of Ce and Eu anomalies, due to the different behaviour of these elements with respect to the neighbours REE. In sulphate acidic waters, Zr/Hf ratios are very low down to 4.7, while quite constant Y/Ho ratio (close to the local rock value) indicates the lack of decoupling. Zr/Hf ratio increases as Cl/SO4 ratio increases. On the contrary, Zr/Hf and Y/Ho ratios in near-neutral pH waters with positive Eh values change from near-chondritic to super-chondritic. The precipitation of Fe-oxyhydroxides removes preferentially Hf and Ho with respect to Zr and Y. The interaction of atmospheric fallout from the nearby Sahara Desert with the water of the lake “Specchio di Venere” was recognized by the Zr, Hf and REE distribution. Zr, Hf and REE show the capability to trace the interaction process between open water bodies and atmospheric fallout

The geochemical significance of on-axis diffuse fluids, in addition to those formed during the waning phases of hydrothermal systems and off-axis crustal ageing processes, has been investigated through a comparison of the rare earth element (REE) systematics of hydrothermal materials from the ore-forming hydrothermal systems of the TAG vent field, 26 N Mid-Atlantic Ridge, and 90 Myr Troodos Ophiolite, Cyprus. Ophiolites integrate a long (c. 20 Myr) history of seafloor alteration, which reflects both , axial and off-axis hydrothermal processes. Spatially-resolved laser ablation inductively coupled plasma-mass spectrometric (LA ICP-MS) REE analyses of individual alteration phases within stockwork-mineralised Troodos lavas have been used to deconvolve the complex alteration processes associated with crustal generation at an oceanic spreading ridge. REE mobility was associated with the development of both high- (-200 to 350 C) and lowtemperature (<100 C) secondary phases which precipitated within contrasting alteration regimes (discharge- and recharge-dominated respectively). Low-temperature alteration phases are the major repository for the REEs in lavas which are depleted in the light REE Eu relative to pristine volcanic glass compositions. These data indicate that much of the REE signature of the alteration pipe is a post-mineralisation overprint acquired in the waning stages of hydrothermal activity and during the protracted alteration of the oceanic basement, rather than on-axis greenschist facies hydrothermal alteration. Submersible and drilling studies of the TAG mound have led to the development of models of mound growth and fluid evolution within an actively-forming seafloor sulphide deposit. The REEs have been used to test the applicability of these models to processes of sulphide mound and metalliferous sediment formation which occurred within the Troodos ophiolite. The REE patterns of umber, ochre and sulphide sampled from a section through the top of the Skouriotissa ore body clearly demonstrate extensive seawater ingress and circulation throughout the upper ore body during waning hydrothermalism and cooling of the mound, which has resulted in the overprinting of any original hydrothermal signatures in both mound sediments and sulphides. This study has demonstrated that the geochemistry of the sulphide mound deposits continues to evolve following the peak of hydrothermal activity, and that the seawater overprinting of the Skouriotissa deposit is the end product of a process which we only see the initiation of on the modern seafloor. At TAG, the origin of far-field Mn and Fe-rich oxide crusts has remained controversial over 25 years of investigations of the vent field. The REE and Nd isotope data presented in this thesis indicate these ferromanganese deposits are forming by a combination of sedimentation of Mn-rich particulates from the TAG hydrothermal plume, and direct precipitation from diffuse hydrothermal fluids seeping from the rift valley wall. The REE data reveal that the separation of manganese from other hydrothermally-derived metals at TAG is due to both plume processes and the spatial distribution of diffuse flow within the vent field. The studies presented in this dissertation have demonstrated the use ofREEs as tracers of chemical processes in ancient and modem hydrothermal systems on a wide range of temporal and spatial scales.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN.
Bibliography: leaves 598-622.
by William Joseph Pegram.
Ph.D.

The work in this thesis had two main aims. The first aim was to study the use of a number of precipitation methods to control the size and morphology of precursor phosphor materials for potential applications in a new generation of high definition and field emission displays. The morphological and luminescent characteristics of these precursor phosphor materials were studied after they were annealed to form their respective luminescent oxides using electron microscopy and light measuring techniques. The first set of experiments presented describes the development of a range of spherical submicron europium-doped yttrium oxide phosphor particles and their optimisation for use in the aforementioned applications. A homogeneous precipitation technique exploiting a hydrothermal decomposition of urea that provides hydroxycarbonate phosphor precursor ligands is at the centre of this work. In the presence of rare earth element nitrates the hydroxycarbonate ligands form spherical phosphor precursor particles that after annealing yield the luminescent oxides. This is followed by the presentation of a novel synthetic method using a micellar phase of rare earth element chlorides, after annealing, yielding europium-doped yttrium oxide. This method produces a variety of morphologies with crystallites as small as a few nanometres and up to hundreds of nanometres. Next is described a new precipitation method using ammonia and carbon dioxide gases that are introduced in a controlled manner into a solution of rare earth element chlorides at room temperature. Rare earth element hydroxycarbonates rapidly precipitate upon supersaturation, yielding a range of morphologies and particles sizes. The second aim of the thesis was to prepare a novel range of three-dimensional photonic band gap materials composed of conventional phosphor materials.

Geology
M.S.
Grasslands provide fundamental ecosystem services in many arid and semi-arid regions of the world, but are experiencing rapid increases in fire activity making them highly susceptible to post-fire accelerated soil erosion by wind. A quantitative assessment that integrates fire-wind erosion feedbacks is therefore needed to account for vegetation change, soil biogeochemical cycling, air quality, and landscape evolution. We investigated the applicability of a novel tracer technique – the use of multiple rare earth elements (REE) - to quantify aeolian soil erosion and to identify sources and sinks of wind-blown sediments in a burned and unburned shrub-grass transition zone in the Chihuahuan desert, NM, USA. Results indicate that the horizontal mass flux of wind-borne sediment increased approximately three times following the fire. The REE-tracer analysis of aeolian sediments shows that an average 88% of the horizontal mass flux in the control area was derived from bare microsites, whereas at the burned site it was derived from shrub and bare microsites, 42% and 39% respectively. The vegetated microsites, which were predominantly sinks of aeolian sediments in the unburned areas, became sediment sources following the fire. The burned areas exhibited a spatial homogenization of sediment tracers, highlighting a potential negative feedback on landscape heterogeneity induced by shrub encroachment into grasslands. Though fires are known to increase aeolian sediment transport, accompanying changes in the sources and sinks of wind-borne sediments likely influence biogeochemical cycling and land degradation dynamics. Our experiment demonstrated that REEs can be used as reliable tracers for field-scale aeolian studies.
Temple University--Theses

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.

Geology
M.S.
Many grasslands in arid and semi-arid regions are undergoing rapid changes in vegetation, including encroachment of woody plants and invasive grasses, which can alter the rates and patterns of fire and sediment transport in these landscapes. We investigated the spatial distribution of sediments at the scale of vegetated microsites for three years following a prescribed fire using a multiple rare earth element (REE) tracer-based approach in a shrub-grass transition zone in the northern Chihuahuan desert (New Mexico, USA). To this end, we applied REE tracers – holmium, europium, and ytterbium on shrub, grass, and bare microsites, respectively in March 2016. Soil samples were collected from both burned and control (not burned) sites before (March) and after (June) the annual windy season, from 2016 through 2018. Results indicate that although the horizontal mass flux (HMF) of wind-borne sediment increased approximately threefold in the first windy season following the fire, and the HMF of both plots were not significantly different after three windy seasons. Comparing REE concentrations in sediments from both plots over the three years and three annual windy seasons, we observed a post-fire shift in source and sink dynamics of sediments. The tracer analysis of wind-borne sediments indicated that the source of the HMF in the burned site was mostly derived from shrub microsites following the fire, whereas the bare microsites were the major contributors for aeolian sediment in control areas. The shift in sources and sinks, and the spatial homogenization of REEs indicate that the removal of shrub vegetation resulted in sediment redistribution to the bare microsites even three years after the prescribed fire. The findings of this study will improve our understanding of post-fire geomorphic processes at a microsite scale in a grassland ecosystem undergoing land degradation induced by shrub encroachment.
Temple University--Theses

One of the largest environmental liabilities facing the Canadian and international mining industry includes the effects of acidic drainage to water resources. This thesis sought to determine biogeochemical mechanisms of rare earth element and yttrium (REY) enrichment in mine drainage, linkages between REYs and microbial populations, and whether REYs were present in water or biofilm at mineable quantities or toxic levels. Water and co-occurring biofilm samples were collected from North and South American mining and control sites, and a passive water treatment system in Pennsylvania. REY concentrations within mineralized biofilm were observed to occur at borderline mineable quantities within biofilm in coal mine drainage (1,000 mg/kg dry weight total REYs), where REYs were bound predominately to particulate organic matter, manganese and iron, limiting their bioavailability. Within the passive treatment system, REYs showed the greatest maximum water-biofilm partitioning coefficients after Al and Fe, and a strong inverse relationship with aqueous REY concentration. Photosynthetic eukaryotes were observed to occur within biofilms that contained an abundance of neutrophilic iron oxidizing bacteria.

\(^{182}Hf-^{182}W\) chronometry is considered the most powerful tool to determine the formation timescale of the terrestrial planets. However, previous work employed oversimplified accretion and core formation models. The accretion and core formation models presented here for the \(^{182}W \) isotopic evolution in the mantles of the accreting Earth and Mars, can incorporate the core formation conditions constrained by siderophile element geochemistry and can be successfully applied to constrain the formation timescale of Earth and Mars. Elemental abundance analyses of the Allende meteorite and two martian meteorites lead to new estimates of core-mantle concentration ratios of Si, V, Cr and Mn for Earth and two distinct mantle Hf/W ratios for Mars respectively, and provide better constraints on the models. It is concluded that formation of the proto-Earth (\(\sim87\%\) of its present mass) has to complete rapidly in \(10.7 \pm 2.5 Myr\) after the onset of the Solar vSystem for a late \((\ge 52 Myr)\) Moon-forming giant impact. The mean time of Mars’ accretion is determined to be \(3.6 \pm 0.1 Myr\), meaning that Mars accretes to 95% of its present mass in \(10.8 \pm 0.3 Myr\) after the formation of the Solar System. Therefore, Mars is not a planetary embryo, and Mars and proto-Earth may be formed on a similar timescale if a late Moon-forming giant impact is assumed. In contrast, if the Moon formed early at \(\sim30 Myr\) then it takes about 3 times longer to form the protoEarth compared to Mars. A stochastic mantle stirring and sampling model was developed to investigate the evolution of W isotope heterogeneities in the mantles of Earth and Mars after accretion and core formation. Our results confirm the mantle stirring rate of \(\sim 500 Myr\) constrained by the long-lived isotope systems in Earth and suggest that the mantle stirring rate in Mars is much slower \((\sim 2 Ga)\). A new concept is developed: the core formation memory of a siderophile element. Siderophile elements are shown to have different capabilities in recording core formation history, a very important fact to consider in any core formation modeling.
Earth and Planetary Sciences

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, February 2011.
Cataloged from PDF version of thesis. "December 20, 2010." "This thesis was submitted to the Institute Archives without all the required signatures"--Disclaimer Notice page.
Includes bibliographical references (pages 33-34).
This paper seeks to describe an impact glass from the K/T boundary layer at Beloc that is depleted in rare earth elements (REE) relative to continental crust. It is widely agreed that a large bolide struck the Yucatan Peninsula roughly 65 Ma spreading a worldwide iridium anomaly. However, there is only one case of a piece of the impactor being found (Kyte et al., 1995). Impact glass from the K/T boundary at Beloc, Haiti has been widely researched with several types of glass documented. So far, all of the documented glass exhibits a crustal REE compositional pattern. In this study, REE composition from two glass types from the same K/T boundary layer sample are examined using a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). One glass type exhibits crustal REE composition which is enriched normalized to chondrite. The other glass type, however, displays a meteoritic REE composition signature. REE patterns for this glass are nearly flat when plotted normalized to chondrite with an average La/Sm ratio of 1.51 compared to 2.69 for crustal glass. Major element data were obtained through electron microprobe analysis and displays a composition that differs from one glass type to the other. Results suggest chondritic parent material from the Chicxulub impactor.
by Dennis W. Fantone.
S.B.

A significant knowledge gap between the fields of reflectance spectroscopy and rare earth element (REE) mineralogy prompted this research effort. It narrows the knowledge gap through detailed study of thirty three samples representing three important mineral classes: REE fluorocarbonates (bastnaesite, synchysite, and parisite), REE phosphates (monazite, xenotime, and britholite), and REE-bearing silicates (cerite, mosandrite, kainosite, zircon and eudialyte). Reflectance spectroscopy was carried out in the visible to short wave infrared regions (500 nm to 2500 nm) and each sample was characterized using scanning electron microscopy and electron microprobe analysis. Spectral features of these minerals are primarily related to numerous 4f-4f intraconfigurational electronic transitions of trivalent lanthanides (Ln³+), as well as 5f-5f electronic transitions of uranium and vibrational overtones and combinations of CO₃²-, H₂O, PO₄³- and OH- where applicable. In general, the respective spectra of these REE minerals are sufficiently distinct for spectral classifications, and compilation diagrams with representative spectra are given. Broadly speaking, the light REE-enriched minerals are dominated by sharp absorptions related to Nd³+, Sm³+, and Pr³+ with lesser input from Eu³+, whereas heavy REE-enriched minerals are dominated by sharp spectral features related to Er³+, Dy³+ and Yb³+ with lesser input from Nd³+, Tb³+, Ho³+ and Tm³+ depending on their specific concentrations. For those minerals that do not show strong preference for light or heavy REE, a mixed set of absorption patterns is seen. Spectral variability of specific 4f-4f absorptions were substantial between different minerals and these variations are interpreted to be driven by the specific anion coordination at the Ln³+site across various crystal structures. Shifts in wavelength position and relative strengths of related absorptions can be significant enough to be highly relevant for hyperspectral remote sensing. This is especially applicable for REE mineral identification in field-based settings and high spatial resolution imaging spectroscopy. Three themes of ongoing and potential research are discussed: additional REE mineral spectroscopy, exploitation of diagnostic features for REE mineral detection and identification, and REE ore grade estimation. Overall, the research presented in this dissertation sets the foundation for future interpretation and exploitation of reflectance spectra for the REE minerals.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

Many of the world's economic rare earth element (REE) deposits are formed from, or have been subsequently upgraded by, hydrothermal fluids. Some of the most important REE minerals are the light REE (LREE) enriched fluorocarbonates and carbonates, which are commonly found in carbonatites. Textural and mineralogical evidence from these and other sites point towards wall rock composition as a major control on the observed REE mineralisation, with the supply of carbonate, and possibly fluoride, thought to be the limiting factor. Despite theoretical and experimental studies focussed on REE speciation in hydrothermal fluids, and a few on REE mineral solubility, there remains a lack of understanding of the processes occurring at the uid-rock interface during REE carbonate and fluorocarbonate mineralisation. Many of the issues surrounding this topic stem from the difficulty of working at elevated temperatures, low REE concentrations, and with the corrosive fluoride ion. The synthesis of REE carbonates under simple, low temperature conditions is a useful starting point for understanding REE mineralisation, and as such has been the focus of research for decades. Despite this, cross-series trends are rarely assessed together under the same conditions, and multi-REE-bearing systems - useful for assessing REE fractionation - have scarcely been explored. Furthermore, wall rock experiments, whereby REE-rich fluids are reacted directly with carbonate rocks, are absent from the literature. The same is true for systems containing fluoride, necessary for studying the formation of fluorocarbonates. A fuller understanding of REE mineralisation cannot be achieved until empirical experimental results can be compared with theoretical data and field observations. This thesis documents the laboratory synthesis of single- and multiple-REE-bearing carbonates and fluorocarbonates, and compares the findings with a mineralogical and textural study of two REE-bearing carbonatite deposits. The REEs La, Nd, Gd, Er and Yb were investigated as representatives of the entire series. The experiments constituted titrations of REE chloride solutions with sodium carbonate, and `wall rock reactions' of REE chloride with dolomite, or dolomite plus fluorite. Batch and flow-through setups were used, and the experiments were performed, or the products aged, at temperatures ranging from ambient to 200 °C. Products were characterised by techniques such as PXRD and SEM to document their structure and morphology as a function of temperature, and assess the influence of single vs multiple REE on the final material (whether mixed or separate phases formed). Results showed that in titration experiments, the LREEs crystallised easily and at low temperatures (as low as room temperature), HREEs either do not crystallise (in some cases even at 200 °C) or are more diffcult to crystallise, and mixed LREE + HREE precipitates behaved more like HREE-only examples. The HREEs and LREEs + HREEs mostly produced X-ray amorphous materials, identified as carbonates using FTIR. These were analysed by XAS (XANES and EXAFS) to assess whether they possessed the same short-range structure as the crystalline phase into which are known to form, thus adding to the non-classical nucleation pathway argument as previously suggested for these materials. Results suggested the short-range order of most phases analysed were similar to known bulk phases, but that these were probably different to the earlier precipitates formed in solution. Additionally, in the mixed LREE + HREE systems (Nd+Er), REEs were well dispersed (as opposed to Nd- and Er-rich clusters). In contrast to the titration results were those of wall rock reactions, in which excellent crystallisation was observed for almost every REE configuration (single- or up to five- REE mix), or ageing duration. All but three of the phases produced were previously described natural or synthetic minerals. When fluorite was included in batch reactions the results were more varied: REE carbonates, fluorides and fluorocarbonates were all observed, but never together in the same sample (except in one example). A textural and mineralogical assessment of two carbonatite deposits, Bayan Obo, China and Tundulu, Malawi, which were analysed by EMPA, revealed multiple stages of hydrothermal activity, some of which related to REE fluorocarbonate mineralisation. REE fluorocarbonates, identified at both sites, were typically LREE enriched. No REE carbonates or fluorides were observed, despite the presence of fluorite (REE-barren) and carbonates at Bayan Obo, and carbonates (low REE content) at Tundulu. However, at both sites apatite contained considerable REE. The REE fluorocarbonates were not solely associated with carbonate wall rocks, although the Ca-REE fluorocarbonate synchysite was only observed in the significantly more carbonate-rock-rich Tundulu samples. At Bayan Obo, bastnasite and huanghoite (Ba-REE fluorocarbonate) were observed, the latter of which is reportedly replacing earlier Ca-REE fluorocarbonates. The results demonstrate the varying behaviour of REEs during precipitation under different conditions, and highlights the influence of dissolved carbonate supply rate to morphology, structure and crystallinity of the products. The occurrence of only one class of REE mineral (carbonate, fluoride or fluorocarbonate) in the synthetic experiments with fluoride may help explain the lack of natural REE carbonates and fluorides - and predominance of REE fluorocarbonates - in hydrothermal systems, as was observed in the natural samples studied. In addition, the lack (absence?) of naturally occurring HREE carbonates and fluorocarbonates in the studied carbonatites (and the literature) is suggested to result not from factors such as structural constraints, but instead from the relative crustal abundances of the individual REEs. It is shown that HREE carbonates and fluorocarbonates are valid species under certain conditions, but that these are not likely to occur naturally.

The Dumper Dew is a newly discovered pegmatite located on the eastfacing slope of Uncle Tom Mountain in Oxford County, Maine. It is a geochemically evolved LCT-type pegmatite petrogenetically linked to the middle Paleozoic Sebago batholith. Shallow emplacement of the Dumper Dew is evidenced by abundant miarolitic cavities found in the pegmatite. The sheet-like structure of the pegmatite coupled with its intrusion in lowmetamorphic grade country rock suggests rapid crystallization. Northern portions of the wall zone and intermediate zones have undergone hydrothermal alteration by the migration of late-stage fluids. The pegmatite hosts a diverse assemblage of rare-element mineral phases due to its high degree of geochemical fractionation. Trends of geochemical fractionation of individual mineral phases such as K-feldspar, muscovite, garnet, apatite, beryl, spodumene, triphylite-lithiophilite, tourmaline, cassiterite, and columbite-tantalite were attained via instrumentation assay. These trends illustrate an enhanced degree of magmatic differentiation relative to other pegmatites in the area.