Crystal chemistry of barian titanian phlogopite from a lamprophyre of the gargano promontory (Apulia, Southern Italy)

This study is focused on a barian titanian phlogopite found in an alkaline ultramafic dyke transecting Mesozoic limestones of the Gargano Promontory (Apulia, Italy). The rock containing the barian titanian phlogopite, an olivine-clinopyroxene-rich lamprophyre with nepheline and free of feldspars, has been classified as monchiquite. The present study combines chemical analyses, single crystal X-ray diffraction and Raman spectroscopy. Chemical variations suggest that the entry of Ba into the phlogopite structure can be explained by the exchange Ba + Al = K + Si. The crystal structure refinement indicates that the Ti uptake is consistent with the Ti–oxy exchange mechanism. The structural parameters associated with the oxy substitution mechanism are extremely enhanced and rarely reported in natural phlogopite: (a) displacement of M2 cation toward the O4 site (~0.7); (b) M2 octahedron bond-length distortion (~2.5); (c) very short c cell parameter (~10.14 Å). Raman analysis showed most prominent features in the 800–200 cm−1 region with the strongest peaks occurring at 773 and 735 cm−1. Only a weak, broad band was observed to occur in the OH-stretching region. As concerns the origin of the barian titanian phlogopite, the rock textural features clearly indicate that it crystallized from pockets of the interstitial melt. Here, Ba and Ti enrichment took place after major crystallization of olivine under fast-cooling conditions, close to the dyke margin

TEM-EDS microanalysis: Comparison among the standardless, Cliff & Lorimer and absorption correction quantification methods

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.ultramic.2023.113845Available quantification methods for energy dispersive X-ray microanalysis in transmission electron microscopy, such as the standardless method (SLM), the Cliff-Lorimer approximation (CLA) and the absorption correction method (ACM), are compared. As expected, the CLA and ACM give superior results with respect to the SLM. As far as absorption can be considered negligible, CLA and ACM perform similarly. However, starting from mass-thickness of the order of 22 × 10−6 g/cm2, absorption become significant and the ACM gives better results. More accurate analyses can be obtained with the ACM if distinct kO/Si factors are determined for light and heavy minerals, respectively, placing a divide at 2.90 g/cm3. Caution must be used when k-factors are derived indirectly from minerals with very different structure/chemistry, suggesting that separate k-factors data sets are required for accurate EDS quantification, at least for the major and diverse broad classes of minerals. Element diffusion of monovalent cations and channelling effects may represent a complication, especially in very anisotropic minerals such as phyllosilicates, where these two phenomena may occur together

Arsenic behavior during the treatment of refractory gold ores via POX: Characterization of Fe-AsO4-SO4 precipitates

Abstract Arsenic is a common contaminant in refractory gold ores/concentrates and it's accepted that total pressure oxidation (POX) is the most appropriate technology to treat these due to their refractoriness and ability to stabilize arsenic via ferric arsenate compounds (Fe-As). However, information gaps about the behavior and stability of the various Fe-As's formed at high temperatures in downstream gold processing steps remain and may have significant practical implications. This paper focuses on the precipitation behavior of arsenic during autoclaving of various arsenopyrite containing ore concentrates from around the world. The first portion involved the precipitation of different synthetic precipitates at POX conditions found in the gold industry by varying Fe/As ratios in the feed solutions. Mineralogical characterization results showed that arsenate-containing basic ferric sulphate (As-BFS), basic ferric arsenate sulphate (BFAS), and ferric arsenate sub-hydrate (FAsH) formed. In the second portion, five pyrite/arsenopyrite concentrates received from gold mines around the world were submitted to batch POX and mineralogical analysis. We observed that the mechanism of precipitation for pyrite/arsenopyrite concentrates appears to be different vs. synthetic solutions. Upon processing of the gold concentrates under POX, the initial Fe/As ratio in the concentrates was retained to the final generated residues. The major Fe-As's generated in the POX residues from the concentrates were As-BFS and BFAS, while non-As containing ferric phases included hematite and some small fraction of jarosite. Finally, we observed that as the Fe/As molar ratio in the concentrate feed increased, the amount of As-BFS decreased while that of BFAS increased

High-temperature study of basic ferric sulfate, FeOHSO 4

AbstractWe report in this paper a new crystal-chemical study of synthetic basic ferric sulfate FeOHSO4. The structure solution performed by the Endeavour program, from new X-ray powder diffraction (XRPD) data, indicated that the correct space group of the monoclinic polytype of FeOHSO4 is C2/c. Selected Area Electron Diffraction (SAED) patterns are also consistent with this structure solution. The arrangement of Fe and S atoms, based on linear chains of Fe3+ octahedra cross-linked by SO4 tetrahedra, corresponds to that of the order/disorder (OD) family. The positions of the hydrogen atoms were located based on DFT calculations. IR and Raman spectra are presented and discussed according to this new structure model. The decomposition of FeOHSO4 during heating was further investigated by means of variable temperature XRPD, thermogravimetry, and differential thermal analysis as well as IR and Raman spectroscopies