Garnierites and garnierites: Textures,mineralogy and geochemistry of garnierites in the Falcondo Ni-laterite deposit,Dominican Republic |
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| Institution: | 1. Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Catalonia, Spain;2. Department of Mineralogy and Petrology, Universidad de Granada, Andalusian Institute of Earth Sciences (IACT, UGR-CSIC), Campus Fuentenueva s/n, 18071 Granada, Spain;3. Department of Earth and Environmental Sciences, The George Washington University, 20052 Washington D.C., USA;4. Falcondo Glencore, Box 1343, Santo Domingo, Dominican Republic;1. Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin 541004, China;2. Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA 16802, USA;3. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an 710061, China;4. Shanxi Key Laboratory of Accelerator Mass Spectrometry Technology and Application, Xi''an AMS Center, Xi''an 710061, China;1. Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain;2. School of Environmental and Technology (SET), University of Brighton, Cockroft Building, Lewes Road, BN4 2GJ Brighton, United Kingdom;3. Centres Científics i Tecnològics, Universitat de Barcelona, Lluís Solé i Sabarís, 1-3, 08028 Barcelona, Spain;1. Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain;2. Department of Earth and Environmental Sciences, The George Washington University, Washington, DC 20052, USA;3. Institute of Geology, Academy of Sciences, v.v.i., Rozvojova´ 269, 16500 Praha 6, Czech Republic;4. Departamento de Geología, Instituto Superior Minero Metalúrgico de Moa, Las Coloradas s/n, Moa, Holguín, Cuba;5. Falcondo Glencore Nickel, Box 1343, Santo Domingo, Dominican Republic;1. Laboratoire GéoRessources, rue Jacques Callot, BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex, France;2. EOST, 1 rue Blessig, 67084 Strasbourg Cedex, France;3. CEREGE, Aix-Marseille Université, CNRS, IRD, CdF, CEREGE, BP 80, 13545 Aix en Provence, France;4. Geosciences Montpellier, CNRS UMR5243, Université de Montpellier, Place E. Bataillon, 34095 Montpellier, France;5. Service de la Géologie de Nouvelle-Calédonie, Direction de l''industrie, des Mines et de l''Énergie, 1ter rue Unger, BP M2, 98849 Nouméa Cedex, New Caledonia |
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| Abstract: | Garnierites (Ni–Mg-bearing phyllosilicates) are significant ore minerals in Ni-laterites of the hydrous silicate-type. In the Falcondo Ni-laterite deposit (Dominican Republic), garnierites are found within the saprolite horizon mainly as fracture-fillings and thin coatings on joints. Field observations indicate an important role of active brittle tectonics during garnierite precipitation. Different greenish colours and textures can be distinguished, which correspond to different mineral phases, defined according to X-ray diffraction (XRD) and electron microprobe (EMP) analyses: a) talc-like (10 Å-type), b) serpentine-like (7 Å-type), c) a mixture of talc- and serpentine-like, and d) sepiolite-like types. Compositional data indicate continuous Mg–Ni solid solution along the joins lizardite–népouite (serpentine-like), kerolite–pimelite (talc-like) and sepiolite–falcondoite (sepiolite-like). In general, talc-like garnierite is dominant in Falcondo Ni-laterite and displays higher Ni contents than serpentine-like garnierites. EMP analyses showing deviations from the stoichiometric Mg–Ni solid solutions of serpentine and talc are best explained by talc- and serpentine-like mixing at the nanoscale. A detailed textural study by means of quantified X-ray element imaging provides a wealth of new information about the relationships between textural position, sequence of crystallization and mineral composition of the studied garnierite samples. These results indicate several stages of growth with variable Ni content, pointing to recurrent changes in the physical–chemical conditions during garnierite precipitation. In addition, our detailed mineralogical study of the Falcondo garnierites revealed that the different types identified have characteristic H2O content and SiO2/MgO ratios, which play important roles during the pyrometallurgy process. |
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