Data for: Mineralogy and genesis of rare Al-phosphate minerals in weathered itabirite and iron ore from the Quadrilátero Ferrífero, Minas Gerais, Brazil

Published: 7 February 2020| Version 1 | DOI: 10.17632/s3k585nbvv.1
Contributors:
Carlos Spier,
Avish Kumar,
Aline Nunes

Description

The files contain powder and micro XRD, and microprobe analyses for rare, secondary phosphates (augelite, senegalite, turquoise) formed by chemical weathering of carbonate veins in itabirite and iron ore on the Quadrilatero Ferrífero, Minas Gerais, Brazil. To obtain samples as pure as possible of the different phosphate minerals for XRD analyses, small fragments (~1.0 cm long) were crushed below 1mm and ultrasonic washed with distilled water. Two different materials were examined: (i) a thin (~2 mm) film of phosphate minerals that line and cement P-bearing concretions (Fig. 2i and g), (ii) a brownish, very porous material, containing phosphate minerals that occur underneath the thin film (Fig. 2f and h). Fragments below 1 mm of both materials were handpicked using a binocular microscope, trying to avoid contamination with hematite. In addition to powder XRD, 35 in situ micro-XRD analyses were performed to identify secondary phosphate phases in polished thin sections. XRD data were collected using a Rigaku SmartLab XRD equipped with a 9 kW Cu rotating anode source, operated at 45 kV and 200 mA. A parabolic multilayer X-Ray mirror parallel-optics system with a polycapillary optics attachment produced a high-intensity point focus on the sample. A 0.2 collimator was used to reduce the beam diameter to 200 µm. Diffraction patterns were recorded by continuous scans from 5 to 70° 2Ɵ, with a step size of 0.02° at a scan rate of 2° per minute. The resulting patterns for both powder and microdiffraction were imported into Diffrac EVA version 4.2, where phases were identified using the PDF-4 2019 ICDD database. Quantitative chemical analyses of the major and minor elements of secondary phosphates were carried out on selected samples using electron microprobe in wavelength dispersive mode (EMPA-WDS) using a JEOL JXA-8200, at the CMM-UQ. Operating conditions were 15 kV, 15 nA and beam diameter of 10 μm. Natural and synthetic standards used were: apatite for P (TAP; Kα), wollastonite for Ca (PETJ; Kα) and Si (TAP; Kα), spinel for Mg (TAP; Kα) and Al (TAP; Kα), Fe2O3 for Fe (LIF; Kα), Cu metal for Cu (LIF; Kα), ZnO for Zn (LIF; Kα), spessartite for Mn (LIF; Kα), Bananb02 for Ba (PET; lα), Bi metal for Bi (PETJ; mα), SrTiO3 for Sr (TAP, lα) and InAs for As (TAP, lα). H2O was calculated by imposing the closure to 100 wt. %.

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