93 research outputs found
Identificació d'intercreixements submicrosòpics de pigeonita de baixa temperatura en salita
Pigeonitic submicroscogic laminar (100) intergrowths, less than l um thin, in a salite of composition En 34, Wo 48, Fe 18, have been identified by electron microscopy and electron diffraction techniques. The parametres of the pigeonitic intergrowth were obtained from calibrated electron diffraction patterns, by wmparing the X-ray refined parameters of salite with those given by the electron diffraction patterns. We discuss the nucleation and growth mechanism of pigeonitic lamellae, and the thermal history of the whole rock, on the basis of these data and the images obtained by electron microscopy
Estructura cristal·lina i molecular de perclorbifenil (C12 Cl10)
C12C10 orthorhombic, Pbcn, a=13.375 Å, b=10.498 Å, c=12.001 Å. V=1685.07 Å 3,
Z=4, Dx = 1.96 g.cm-3, λ(Cu Kq)=1.54051 Å. Final residual R=0.043 for 841 observed reflexions. Two rings of molecule are perpendicular (87.0º) and related by a binary axis. All atoms of the pentachiorophenyl group lie on a plane. No significant molecular distortion due to the Cl atoms was observed
Talc- and serpentine-like 'garnierites' from Falcondo Ni-laterite deposit (Dominican Republic): a HRTEM approach
"Garnierites" represent significant Ni ore minerals in the lower horizons of many Ni-laterite deposits worldwide (e.g. Freyssinet et al., 2005). They consist of a green, fine-grained mixture of hydrous i-bearing magnesium phyllosilicates, including serpentine, talc, sepiolite, smectite and chlorite (e.g. Brindley and Hang, 1973; Springer, 1974; Brindley et al., 1979). Thus, "garnierite" is a general descriptive term and is not recognized as a mineral species by the IMA Commission on New Mineral and Mineral Names (CNMMN). For this reason, "garnierites" have been classified as "serpentine-", "talc-" and "clay-like garnierites", respectively (e.g. Brindley and Maksimovic, 1974)
Reactive transport modelling: the formation of Ni-laterite profiles (Punta Gorda, Moa Bay, Cuba).
Ni-laterites represent one of the main Ni sources worldwide, with about 40% of the annual production (Gleeson et al.,2003). The Punta Gorda Ni laterite deposit is part of a larger province of nickel laterites in northeast Cuba (Moa Bay district) (Lavaut, 1998) developed from serpentinized peridotites
New Insights into the Concept of Ilmenite as an Indicator for Diamond Exploration, Based on Kimberlite Petrographic Analysis
This study presents results of the initial phase of the research project, "Kimberlites associated to the Lucapa structure, Angola (Africa)", within the framework of a multilateral agreement between the Faculty of Geology Universitat de Barcelona, the Empresa Nacional de Diamantes de Angola and the Agostinho Neto University (LuandaAngola)
Ni-bearing phyllosilicates ('garnierites'): New insights from thermal analysis, μRaman and IR spectroscopy.
Ni-Mg-phyllosilicates, so-called 'garnierites', are significant Ni ores in Ni-laterite deposits worldwide. In addition, they are the natural analogues of synthetic catalysts involving Ni and phyllosilicate substrates used in reactions for the remediation of greenhouse gases. However, the nomenclature, classification and characterisation of Ni-Mg-phyllosilicates is a long-lasting problem, because of their fine-grained nature, poor crystallinity and frequent occurrence as intimate mixtures. This work presents and discusses DTA-TG, Raman and FTIR spectroscopy data of a series of well characterised, naturally occurring Ni-Mg-phyllosilicate samples with a variety of mineral compositions (including serpentine-dominated, talc-dominated and sepiolite-falcondoite, with various Ni contents). The results are compared to data obtained from crystalline, 1:1 and 2:1Mg-phyllosilicates and from the literature. DTA-TG confirmed that the talc-like fraction in garnierite mixtures belongs to the kerolite-pimelite series. The different garnierite types analysed are distinguishable from their Raman and FTIR spectra, and the serpentine, talc and sepiolite components could be identified (e.g. by Raman bands at ~690cm−1, ~670cm−1 and ~200cm−1, respectively). Knowledge of Raman and FTIR vibrations of garnierites with constrained structure and composition is paramount in order to effectively characterise these phyllosilicates, and can be applied to mineral identification in ore exploration and processing, and after synthesis for nanotechnology purposes
Ni-enrichment processes revealed by TEM imaging on garnierites
Ni-phyllosilicates, commonly grouped under the name of "garnierites", are significant nickel ores found in hydrous silicate-type Ni-laterite deposits worldwide. They usually occur as vein infillings in the lower parts of laterite profiles, and consist of fine-grained, often intimately mixed, nickelmagnesium phyllosilicates, including serpentine, talc, sepiolite, smectite and chlorite (e.g. Brindley & Maksimović, 1974)
Micro-Raman spectroscopy of garnierite minerals: a useful method for phase identification
Garnierites are important Ni-Ores found in worldwide hydrous silicate-type Ni-laterites
Dissolution kinetics of Ni-phyllosilicates from the Falcondo Deposit, Dominican Republic
Ni-phyllosilicates, commonly grouped under the name of "garnierites", are significant nickel ores found in hydrous silicate-type Ni-laterite deposits worldwide, formed by weathering of ultramafic rocks. Garnierites consist of one or more fine-grained nickelmagnesium phyllosilicates, including serpentine, talc, sepiolite, smectite and chlorite. They often occur as poorly crystalline micron-scale mixtures (e.g. Brindley, 1978)
Reactive transport model of the formation of oxide-type Ni-laterite profiles (Punta Gorda, Moa Bay, Cuba)
Oxide-type Ni-laterite deposits are characterized by a dominant limonite zone with goethite as the economically most important Ni ore mineral and a thin zone of hydrous Mg silicate-rich saprolite beneath the magnesium discontinuity. Fe, less soluble, is mainly retained forming goethite, while Ni is redeposited at greater depth in a Fe(III) and Ni-rich serpentine (serpentine II) or in goethite, where it adsorbs or substitutes for Fe in the mineral structure. Here, a 1D reactive transport model, using CrunchFlow, of Punta Gorda oxide-type Ni-laterite deposit (Moa Bay, Cuba) formation is presented. The model reproduces the formation of the different laterite horizons in the profile from an initial, partially serpentinized peridotite, in 10(6) years, validating the conceptual model of the formation of this kind of deposits in which a narrow saprolite horizon rich in Ni-bearing serpentine is formed above peridotite parent rock and a thick limonite horizon is formed over saprolite. Results also confirm that sorption of Ni onto goethite can explain the weight percent of Ni found in the Moa goethite.Sensitivity analyses accounting for the effect of key parameters (composition, dissolution rate, carbonate concentration, quartz precipitation) on the model results are also presented. It is found that aqueous carbonate concentration and quartz precipitation significantly affects the laterization process rate, while the effect of the composition of secondary serpentine or of mineral dissolution rates is minor. The results of this reactive transport modeling have proven useful to validate the conceptual models derived from field observations
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