Characterization of a chalcopyrite from Brazil by Mössbauer spectroscopy and other physicochemical techniques

We studied a chalcopyrite from a Cu ore deposit in Rio Grande do Sul, Brazil, by Mössbauer spectroscopy at room temperature and 110 K. Supporting methods to check for sample purity and to characterize further sample properties were slow-scanning X-ray powder diffraction and optical and microprobe analyses of polished sections of selected grains. Chemical analyses obtained using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer showed the sample to consist of homogeneous and essentially stoichiometric chalcopyrite (CuFeS₂). Mössbauer spectra taken at both the above temperatures consist of asymmetric magnetically ordered patterns with unequal intensities of the line pairs 1–6 and 2–5, pointing to the existence of non-equivalent or multiple Fe sites. Least-squares fittings evidenced that the resonance intensity ratio of subspectrum with lower quadrupole shift (indicative of a more symmetric environment) to that with higher shift is 69:31, at room temperature, and 68:32, at 110 K. Rietveld refinement of the XRD data indicates the existence of tetragonal [a = 0.52855(1) and c = 1.0412(1) nm] and cubic [a ₀ = 0.5273(2) nm] modifications in a proportion of 74:26, in good agreement with the Mössbauer data. The saturation magnetization of the sample was 32.7 J/(T kg), confirming the oxidation state of Fe as trivalent and pointing to little to no spin canting.     

STUDIES OF BRAZILIAN METEORITES XIV. MINERALOGY,PETROLOGY, AND CHEMISTRY OF THE CONQUISTA,MINAS GERAIS,CHONDRITE

The Conquista chondrite consists of major olivine, low-Ca pyroxene (both ortho- and twinned clino-), troilite and metallic nickel-iron; minor glassy to microcrystalline material and pigeonite; and accessory chromite, high-Ca clinopyroxene and hydrous ferric oxides that formed by terrestrial weathering of metallic nickel-iron. Results of microscopic, electron microprobe, and bulk chemical studies, particularly the compositions of olivine (Fa_17.2) and low-Ca pyroxene (Fs_15.4); the contents of metallic nickel-iron (18.5%) and total iron (25.83%); and the ratios of Fe°/Fe_total (0.64), Fe°/Ni° (9.59) and Fe_total/SiO₂ (0.69) indicate H-group classification. The pronounced, well-developed chondritic texture; the slight compositional variations in constituent phases; the high Ca contents of pyroxene and the presence of pigeonite, glassy to microcrystalline interstitial material rich in alkalis and SiO₂, and of twinned low-Ca clinopyroxene suggest that Conquista is of petrologic type 4.