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)

Distribution and speciation of Ni in sepiolite-falcondoite- type 'garnierite' by EXAFS

Ni-laterites represent one of the main Ni sources worldwide, with about 40% of the annual production (Gleeson et al., 2003). A problem in laterites is to find a reliable system to control the exact partitioning of Ni among the different minerals in the lateritic profile, because laterite profiles are generally constituted by fine-grained minerals. The determination of Ni-sorption mechanisms during the process of lateritization arises as a very important target from both the mining and environmental point of view (e.g. RoquéRosell et al., 2010)

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

The supergene origin of ruthenian hexaferrum in Ni-laterites

For two decades, the nature of Fe-rich, oxygen-bearing, Ru-Os compounds found in the supergene environment has been debated. Ru-Os-Fe-oxides and nano-intergrowths of ruthenium with magnetite have been proposed. We applied FE-SEM, EMPA, mu-Raman spectroscopy and synchrotron tts-lXRD to Ru-Os-Fe compounds recovered from Ni-laterites from the Dominican Republic. The results demonstrate that a significant portion of Fe exists in a common structure with the Ru-Os alloy, that is, ruthenian hexaferrum. This mineral occurs both as nanoparticles and as micrometric patches within a matrix of Fe-oxide(s). Our data suggest that supergene ruthenian hexaferrum with a (Ru-0.4(Os, Ir)(0.1)Fe-0.5)(Sigma 1.0) stoichiometry represents the most advanced weathering product of primary laurite within Ni-laterites from the Dominican Republic