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Boletín de la Sociedad Geológica Mexicana Volumen 72, núm. 3, A050620, 2020 |
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The Loma de Hierro Ni-laterite deposit (Venezuela): Mineralogical and chemical composition
El depósito de lateritas Ni de Loma de Hierro (Venezuela): Composición química y mineralógica
Cristina Domènech1,*, Salvador Galí2, Josep M. Soler3, Marite P. Ancco2, Williams Meléndez4,
José Rondón5, Cristina Villanova-de-Benavent2, Joaquín A. Proenza2
1 Grup MAiMA, Mineralogia Aplicada, Geoquímica i Geomicrobiologia, Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Catalunya, Spain.
2 Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Catalunya, Spain.
3 Institute of Environmental Assessment and Water Research, IDAEA-CSIC, 08034 Barcelona, Catalunya, Spain.
4 Instituto de Ciencias de la Tierra, Universidad Central de Venezuela, Av. Minerva, 1015, Caracas,Venezuela.
5 Instituto Nacional de Geología y Minería, Av. Lecuna, Parque Central, Torre Oeste,1015, Caracas,Venezuela.
* Corresponding author: (C. Domènech) This email address is being protected from spambots. You need JavaScript enabled to view it.
How to cite this article:
Domènech, C., Galí, S., Soler, J. M., Ancco, M. P., Meléndez, W., Rondón, J., Villanova-de-Benavent, C., Proenza, J. A., 2020, The Loma de Hierro Ni-laterite deposit (Venezuela): Mineralogical and chemical composition: Boletín de la Sociedad Geológica Mexicana, 72 (3), A050620. http://dx.doi.org/10.18268/BSGM2020v72n3a050620
Abstract
Nickel laterite deposits developed on ultramafic rocks have traditionally been a significant source of Ni and Co and recently of Sc. Although the Loma de Hierro deposit (Venezuela) has been in operation for more than 50 years, it lacks detailed studies on the mineralogical and geochemical composition of the lateritic profile. In this study, we present a geochemical and mineral description of the main carrier phases of Ni and Co in a complete profile of the deposit. The selected weathering profile has been developed from a partially serpentinized harzburgitic protolith and has a well-developed saprolitic horizon covered by a thin limonitic horizon. The geochemical signature of the profile is characterized by a significant Mg and Si decrease towards the top of the saprolite, with a clearly visible Mg discontinuity. The main Ni-bearing minerals are secondary serpentine (1–4 wt.% NiO) and kerolite-pimelite-dominated garnierite mixtures with serpentine (18–22 wt.% NiO). Limonite is rich in goethite (0–1.85 wt. % NiO), gibbsite, and Mn-oxy-hydroxides. The latter have intermediate compositions between lithiophorite and asbolane (2–13 wt.% CoO). The highest Sc grades (40–68 ppm) were observed in the limonite with amounts positively correlated with Fe content. Rare earth elements are mainly concentrated in the upper part of the saprolite horizon (60–80 ppm), while they have a lower content in the limonite (7–45 ppm). In this horizon, rare earth elements are clearly associated with Fe, indicating adsorption and/or coprecipitation. This association was not observed in the saprolite, suggesting that other minerals (e.g., clay minerals) are controlling their concentration; more information is needed to identify the rare earth element-bearing minerals. The lateritic profile of Loma de Hierro can be classified as representative of hydrated Mg silicate deposits, and was formed in a context of continuous tectonic uplift and a low water table conditions favoring the development of a thick saprolitic horizon and the precipitation of kerolite-pimelite-dominated garnierites.
Keywords: Nickel, cobalt, Loma de Hierro, laterite, critical metals.
