36 research outputs found
A New Mapping Protocol for Laser Ablation (with FastâFunnel ) Coupled to a TimeâofâFlight Mass Spectrometer ( LAâFFâICPâToFâMS ) for the Rapid, Simultaneous Quantification of Multiple Minerals
Although in situ analysis by LA-ICP-MS is considered a rapid technique with minimal sample preparation and data reduction, mapping areas of millimetres in size using a small beam (<â15 ÎŒm) can be time consuming (several hours) when a quadrupole ICP-MS is used. In addition, fully quantitative imaging using internal standardisation by LA-ICP-MS is challenging in samples with more than one mineral phase present due to varying ablation rates. A new protocol for the quantification of multiple coexisting phases, mapped at a rate of about 12âmm2 h-1 and a resolution of 12 ÎŒm Ăâ12 ÎŒm per pixel, is presented. The protocol allows mapping of most atomic masses, ranging from 23Na to 238U, using a time-of-flight mass spectrometer (ICP-ToF-MS, TOFWERK) connected to a 193 nm excimer laser. A fast-funnel device was successfully used to increase the aerosol transport speed, reducing the time usually required for mapping by a factor of about ten compared with a quadrupole ICP-MS. The lower limits of detection for mid and heavy masses are in the range 0.1â10 ÎŒg g-1, allowing determination of trace to ultra-trace elements. The presented protocol is intended to be a routine analytical tool that can provide greater access to the spatial distribution of major and trace elements in geological materials
Formation of Bushveld anorthosite by reactive porous flow
Bushveld anorthosites commonly contain the so-called âmottlesâ comprising irregular, typically centimetric domains of oikocrystic pyroxene or olivine enclosing small, embayed plagioclase grains. The mottles were traditionally interpreted to result from solidification of trapped intercumulus liquid or via in situ crystallisation at the top of the crystal mush. Here, we present microtextural and compositional data of a mottle to place further constraints on the formation of anorthosite layers. Element maps generated by scanning electron microscopy reveal that plagioclase within and around the mottle has markedly elevated An contents (up to An95) relative to the host anorthosite and is strongly reversely zoned. Other unusual features, some of which were reported previously, include a halo of sub-vertically oriented, acicular phlogopite around the mottle, elevated contents of disseminated sulfides, and relatively evolved yet Ni-rich olivine (Fo71â75, 3000 ppm Ni). These features are interpreted to result from reactive porous flow of hot, acidic fluid enriched in nickel and sulfur through proto norite. The fluids dissolved mafic minerals and leached alkalis from the outer rims of plagioclase grains. Reconnaissance studies suggest that reversed zoning of plagioclase is a common feature in Bushveld norite and anorthosite. This implies that reactive porous flow could have been far more pervasive than currently realised and that Bushveld anorthosite layers formed through recrystallisation of norites
Using sulphide indicator mineral chemistry for ore discrimination and targeting in the Churchill Province, northern Quebec, Canada
The Churchill Province in northern Quebec consists of Archean to Proterozoic basement rocks, which have undergone a complex orogenic and metamorphic history. The vast majority of these rocks are covered by Quaternary glacial deposits that display a complex geomorphology reflecting important variations in the glacial dynamics. Occasional mineralized outcrops have been identified south from the Ungava Bay in the Churchill Province during mapping surveys. However, this area has been underexplored owing to the thick sedimentary cover, which limits the effectiveness of conventional exploration methods. Heavy mineral separation from till and esker samples reveals the presence of thousands of sulphide grains, namely pyrite and chalcopyrite, and lesser amounts of sulfarsenides (löllingite and arsenopyrite), which is indicative of the presence of underlying mineralized rocks. As a result, this area is ideal to test the use of sulphide indicator mineral chemistry for mineral assessment and vectoring. In this study, we focus on integrating sulphide indicator mineral chemistry determined by laser ablation inductively coupled mass spectrometry (LA-ICP-MS) with the geology of glacial deposits. Trace-element signatures of pyrite and chalcopyrite grains indicate two distinct compositions for the sulphide minerals present in the glacial deposits and suggest there is strong potential for magmatic and hydrothermal mineralisation. Integrated maps combining sample locations and sulphide grain compositions and populations allow to delineate vectors toward potential economic targets
Ătude du comportement gĂ©ochimique du sĂ©lĂ©nium, sa relation avec le soufre dans le bushveld (Afrique du sud) et dĂ©veloppement des techniques analytiques
L'Ă©tude du comportement gĂ©ochimique du sĂ©lĂ©nium et sa relation avec le soufre dans les roches du complexe du Bushveld (Afrique du Sud) sont prĂ©sentĂ©es dans ce mĂ©moire. La dĂ©termination quantitative de ces deux Ă©lĂ©ments chimiques a Ă©tĂ© rĂ©alisĂ©e dans 157 Ă©chantillons provenant de la suite litĂ©e de Rustenberg (Bushveld) et des roches de la marge de l'intrusion reprĂ©sentant les magmas parentaux. Ătant donnĂ© que la plupart des roches analysĂ©es contiennent de trĂšs faibles teneurs en soufre et en sĂ©lĂ©nium, il a d'abord Ă©tĂ© nĂ©cessaire de mettre au point les techniques d'analyses appropriĂ©es. Au cours du dĂ©veloppement de ces techniques, des matĂ©riaux de rĂ©fĂ©rences gĂ©ologiques internationales (MRGI) ont Ă©tĂ© analysĂ©s pour valider les rĂ©sultats afin d'assurer une qualitĂ© constante et traçable lorsque cela est possible. Vingt-six MRGI ont Ă©tĂ© analysĂ©s pour le sĂ©lĂ©nium et vingt-neuf pour le soufre. Chaque technique dĂ©veloppĂ©e a Ă©tĂ© publiĂ©e dans un journal scientifique arbitrĂ© et les rĂ©sultats sont en accord avec ceux disponibles dans la littĂ©rature et/ou sur les certificats d'analyses. De plus, les rĂ©sultats des analyses du sĂ©lĂ©nium obtenus Ă l'UQAC dans les MRGI ont Ă©tĂ© greffĂ©s aux donnĂ©es disponibles dans la littĂ©rature et des traitements statistiques ont Ă©tĂ© rĂ©alisĂ©s pour produire un nouvel article dĂ©crivant les MRGI utiles, en termes de Se, servant Ă valider et Ă contrĂŽler les dĂ©terminations. Une fois Ă©tablies les bases analytiques, les rĂ©sultats obtenus dans l'Ă©tude du Bushveld ont menĂ© Ă l'Ă©laboration de trois modĂšles pour expliquer les relations gĂ©ochimiques observĂ©es. Le premier modĂšle suggĂšre que les sulfures qui Ă©taient prĂ©sents dans l'empilement cristallin aient pu migrer dans les roches encaissantes ou au centre de l'intrusion. Le deuxiĂšme modĂšle suggĂšre quant Ă lui que le magma ait Ă©tĂ© saturĂ© en soufre en profondeur et que, durant le transport, des sulfures aient Ă©tĂ© emprisonnĂ©s dans de petites cavitĂ©s prĂ©sentes dans la matrice cristallinevisqueuse. Finalement, le troisiĂšme modĂšle suggĂšre que les roches aient Ă©tĂ© appauvries en S et en Se Ă tempĂ©rature Ă©levĂ©e aprĂšs la solidification de l'intrusion. Ă ce jour, il est impossible d'Ă©valuer lequel de ces modĂšle est le plus plausible, mais les deux premiers modĂšles ont une implication importante pour l'exploration de nouvelles ressources. En effet, si l'un des modĂšles s'avĂšre ĂȘtre exact, cela signifierait qu'il y a dans le centre de l'intrusion ou Ă sa pĂ©riphĂ©rie une rĂ©serve en mĂ©taux de base importante et possiblement aussi en mĂ©taux prĂ©cieux, associĂ©e aux sulfures. Il a Ă©galement Ă©tĂ© possible de calculer un coefficient de partage du Se dans les sulfures Ă partir des roches de la portion supĂ©rieure de l'intrusion. Les proportions Se/Cu augmentent avec la stratigraphie, ce qui suggĂšre que le coefficient de partage du Se dans les sulfures est plus bas que celui du Cu (1,200 versus 1,700). Le coefficient de partage aide Ă comprendre le comportement gĂ©ochimique des Ă©lĂ©ments et leur relation avec les sulfures et les autres phases prĂ©sents dans les roches
Research and Evidence-based Librarianship in the Corporate and Academic Library: Two Recent Graduates\u27 Perspectives
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Determination of Te, As, Bi, Sb and Se (TABS) in Geological Reference Materials and Geo<i>PT</i> Proficiency Test Materials by Hydride GenerationâAtomic Fluorescence Spectrometry (HGâAFS)
The study of Te, As, Bi, Sb and Se (TABS) has increased over the past years due to their use in the development of lowâcarbon energy technologies. However, there is a scarcity of mass fraction values of TABS in geological reference materials. This underlines the difficulty in undertaking routine determinations of these elements. The mass fractions of TABS were determined in geological reference materials using hydride generationâatomic fluorescence spectrometry (HGâAFS), calibrated with standard solutions. Comparisons with literature values were used to validate the method. Samples from the GeoPT proficiency test were also analysed. For most elements, there are no assigned or even provisional values for many of the GeoPT and reference materials because of the wide range of results reported. For mass fractions above the quantification limit of the method, our results are in good agreement with the median of GeoPT results. Thus, we propose GeoPT median values as informational values for these elements. In contrast, at mass fractions â1 median values of Se from GeoPT are systematically higher than our results. Our Se results are in agreement with the reference materials down to 0.02 ”g gâ1, which suggest that many of the results for Se reported in GeoPT testing are too high
Comparison between nickelâsulfur fire assay Te coâprecipitation and isotope dilution with highâpressure asher acid digestion for the determination of platinumâgroup elements, rhenium and Gold
The accurate determination of platinum-group elements (PGE), rhenium and gold is important in both fundamental research and ore deposit studies. Questions have been raised by some authors as to whether the nickel-sulfur fire assay technique (NiS-FA) efficiently collects all the PGE. On the other hand, most isotope dilution (ID) techniques can only treat small test portion masses (2 g was used for high-pressure asher digestion; HPA) and this makes them more vulnerable to nugget effects. We determined PGE concentrations in ten reference materials with the aim of comparing the performance characteristics of the two methods. Both methods determine Ru, Pd, Os, Ir and Pt and we found that there were no significant systematic differences in the recovery. The advantages of NiS-FA were that: (a) it is capable of determining Rh and Au; (b) the relatively large test portion mass (15 g) reduces the nugget effect and (c) it is faster and less expensive than HPA-ID. The advantages of HPA-ID were that: (a) it determined Re and (b) it had low level blanks, lower detection limits and hence better precision in low-level homogeneous samples. Each technique had advantages and limitations; they should be considered as complementary rather than competing techniques.
Lâanalyse quantitative des Ă©lĂ©ments du groupe du platine (ĂGP), du rhĂ©nium et de lâor est importante pour la recherche fondamentale et la prospection. Certains doutes existent concernant lâefficacitĂ© de la pyro-analyse par nickel-soufre (PA-NiS) pour quantifier les ĂGP. Dâun autre cĂŽtĂ©, la plupart des techniques dâanalyse par dilution isotopique (DI) ne peuvent quâanalyser de petites masses dâĂ©chantillon (2 g pour la digestion haute pression; DHP-DI), les rendant vulnĂ©rable Ă lâeffet de pĂ©pite. Nous avons quantifiĂ© les ĂGP dans dix matĂ©riaux de rĂ©fĂ©rence pour comparer les performances de chaque mĂ©thode. Chaque mĂ©thode peut quantifier le ruthĂ©nium, palladium, osmium, iridium et le platine. Les rĂ©sultats ne montrent pas de diffĂ©rences significatives. Les avantages de la PA-NiS sont : (a) sa capacitĂ© de dĂ©terminer lâor et le rhodium, (b) la masse dâĂ©chantillon plus Ă©levĂ©e (15 g) rĂ©duisant « lâeffet de pĂ©pite » et (c) sa rapiditĂ© et son coĂ»t moins Ă©levĂ©. Les avantages de la DHP-ID sont : (a) capacitĂ© de dĂ©terminer le rhĂ©nium et (b) blancs plus bas, limites de dĂ©tection plus basses donc plus de prĂ©cision pour lâanalyse en basses teneurs des matĂ©riaux gĂ©ologiques homogĂšnes. Chaque technique a des avantages et des limites et devraient ĂȘtre considĂ©rĂ©es comme complĂ©mentaires plutĂŽt que compĂ©titives
Geoheritage 4: Raising Public Awareness of Geological Heritage at LâUniversitĂ© du QuĂ©bec Ă Chicoutimi
Promotion of geological heritage is achieved through programs that increase the public awareness of geological phenomena and to draw attention to the importance of minerals in everyday life. Activities at the UniversitĂ© du QuĂ©bec Ă Chicoutimi (UQAC) are divided into two parts: conservation and popularization. At the UQAC Petit musĂ©e mineral exhibit, the minerals on display are predominantly from the province of QuĂ©bec, but samples from elsewhere in Canada and from the rest of the world are also presented to compare with QuĂ©becâs geoheritage. More than a hundred samples from the Petit musĂ©e are described and photographically illustrated in a mineral identification guide (BĂ©dard et al. 2008). Part of the collection can also be consulted on the web. The Petit musĂ©e is not simply a mineral collection. Elementary and secondary school groups routinely visit the museum in conjunction with science popularization activities. For younger students, a story has been developed to present, in a light-hearted manner, some information about minerals and their uses. This story is centred on a hero who has many adventures in which minerals provide solutions to a series of problems. Older students participate in laboratory experiments that include observation of melting a rock, tasting and measuring salts in water and playing with the concept of density. New exhibits presently being developed include a âlead pencilâ exhibit where the rich history of this common object is explored; another on mass extinctions presents the rich fossil heritage of QuĂ©bec.
Une bonne mise en valeur du patrimoine gĂ©ologique nĂ©cessite une conscientisation de la population Ă la prĂ©sence de phĂ©nomĂšnes gĂ©ologiques dans lâenvironnement immĂ©diat et Ă lâutilitĂ© des minĂ©raux dans la vie de tous les jours. Les interventions se divisent en deux grands volets, soit la conservation et la popularisation. Au Petit musĂ©e de lâUQAC, des Ă©chantillons minĂ©ralogiques provenant principalement du QuĂ©bec sont conservĂ©s. Quelques Ă©chantillons dâautres rĂ©gions du monde sont Ă©galement exposĂ©s en guise de comparaison avec le patrimoine du QuĂ©bec. Plus dâune centaine de minĂ©raux du Petit musĂ©e sont prĂ©sentĂ©s dans un livre grand public (BĂ©dard et al. 2008). De plus, une partie de la collection peut ĂȘtre consultĂ©e en ligne. Le Petit musĂ©e nâest cependant pas quâune simple collection de minĂ©raux. LâUQAC accueille rĂ©guliĂšrement des groupes scolaires de niveau primaire et secondaire qui viennent visiter le Petit musĂ©e. Les visites dâĂ©lĂšves sont gĂ©nĂ©ralement accompagnĂ©es dâactivitĂ©s de vulgarisation scientifique. Ainsi, pour les plus jeunes, un conte a Ă©tĂ© dĂ©veloppĂ© pour prĂ©senter de façon amusante quelques minĂ©raux et leurs utilisations. Le hĂ©ro vit de nombreuses aventures dans lesquelles les minĂ©raux offrent des solutions aux problĂšmes rencontrĂ©s. Pour les plus vieux, des activitĂ©s de laboratoire sont offertes dans lesquelles ils peuvent observer une roche en fusion, mesurer et goĂ»ter la salinitĂ© de lâeau et expĂ©rimenter sur la densitĂ©. Des nouveaux prĂ©sentoirs sont en dĂ©veloppement : une vitrine ayant comme thĂšme le « crayon plomb » nous fera dĂ©couvrir lâhistoire riche de cet objet commun et des dioramas sur les grandes extinctions pour valoriser le patrimoine fossilifĂšre quĂ©bĂ©cois