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Mineralogical Characterization of Ni-Bearing Smectites from Niquelândia, Brazil
- Eliana Satiko Mano, Laurent Caner, Sabine Petit, Arthur Pinto Chaves, André Sampaio Mexias
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- Journal:
- Clays and Clay Minerals / Volume 62 / Issue 4 / August 2014
- Published online by Cambridge University Press:
- 01 January 2024, pp. 324-335
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Nickel-lateritic ore is the most common source of nickel in Brazil. The Niquelândia deposit, located in State of Goias, is one of the most famous deposits due to the large amounts of nickel associated with both oxidized and mainly silicated ores. The terms oxidized and silicated ores are used to specify two different ores formed exclusively by oxides and silicate (clay) minerals, respectively. The aim of the present study was to characterize thoroughly the silicated ore to identify the Ni-bearing clay minerals and their crystal chemistry in support of developing a better mineral-processing method or optimizing the current one to improve Ni recoveries. X-ray diffraction, chemical analyses, scanning electron microscopy, and Fourier transform infrared (FTIR) spectroscopy demonstrated that nickel is associated with Ni-rich stevensite and to a lesser extent with Fe-rich montmorillonite. The crystal chemistry performed by FTIR spectroscopy revealed that Ni is present in the octahedral positions, substituting for Mg or Fe, which results in significant chemical and layer-charge heterogeneity in the samples. This heterogeneity seems to be responsible for reduction in Ni recoveries during the hydrometallurgical process.
Spatial and temporal evolution of hydrothermal alteration at Lavras do sul, Brazil: Evidence from dioctahedral clay minerals
- Everton Marques Bongiolo, Patricia Patrier-Mas, André Sampaio Mexias, Daniel Beaufort, Milton Luiz Laquintinie Formoso
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- Journal:
- Clays and Clay Minerals / Volume 56 / Issue 2 / April 2008
- Published online by Cambridge University Press:
- 01 January 2024, pp. 222-243
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TheAu-Cu (±Pb, Zn, Ag) prospects of Lavras do Sul, southernmost Brazil, arehosted in Neoproterozoic granitic and volcanogenic rocks. Mineralization occurs in structurally controlled N40°W to E-W quartz veins; sericite (±chlorite) and sulfides are the main secondary minerals in associated wall rocks.
In the present contribution we use petrography (optical microscopy and scanning electron microscopy (SEM)), mineralogy (X-ray diffraction (XRD) with polytypes, FWHM, decomposition of diffraction patterns), and crystal chemistry of samples from several prospects to document the spatial and temporal evolution of sericitic alteration of veins and wall rocks associated with gold.
Hexagonal, coarse-grained 2M1 phengite-rich alteration (± illite) is best developed with coarse-grained primary growth (comb) quartz + pyrite ± Au veins and altered wall rock from the western portion of the granitic complex (phyllic alteration). Pure phengite was recognized by narrow XRD profiles (FWHM ⩽ 0.2°2θ CuKα) of the <5 µm particle-size fraction, non-expandable d001 X-ray reflections and interlayer charge (IC) >0.9 per O10(OH)2.
Towards the eastern zones of the granitic complex and in the volcanogenic rocks, wider XRD profiles (FWHM values ⩾ 0.2°2θ CuKα) were decomposed. They contain mixtures of coarse- to fine-grained, lath-like crystals of both 2M1 and 1M illite (non-expandable d001 X-ray reflections, IC between 0.85 and 0.89 per O10(OH)2) with expandable d001 reflections associated with lath-like, fine-grained crystals of ordered (R ⩾ 1) illite-rich I-S (80–90% of illite; IC of ∼0.8 per O10(OH)2), and minor amounts of regularly ordered (R = 1), illite-rich I-S mixed layers (75% of illite; IC of ∼0.74 per O10(OH)2). The dioctahedral clay association of illite + illite-rich I-S mixed layers (intermediate argillic alteration) is best developed in quartz + pyrite ± Au veins, breccias, and wall-rock alteration from the eastern portion of the granitic complex and in the volcanic area. Quartz from veins and breccias has fine-grained primary growth, recrystallization, and replacement textures, similar to those in epithermal deposits.
The overall distribution of the dioctahedral clays indicates that the study area represents a fracture-controlled, tilted, porphyry to epithermal deposit, with telescoping alteration features observed in the east of the mining district. Deeper levels of exposure of a large hydrothermal system are observed in the west of the mining district, as shown by higher-rank dioctahedral minerals (phengite) that crystallize at relatively high temperatures (Tphe ≈ 300°C, phyllic alteration) associated with coarse-grained, primary-growth quartz veins, similar to those observed in porphyry deposits. On the other hand, shallower levels of exposure are observed in the east of the study area, associated with abundant, lower-rank dioctahedral clay minerals (illite + illite-rich I-S mixed layers, intermediate argillic alteration) that crystallize at relatively lower temperatures (TI-S ≈ 120–200°C).
Available data show that gold is associated with phengite, but that lower-rank, overprinting alteration characterized by illite-I-S may have locally modified the original gold grades.