Characterization of granites by 57Fe Mössbauer spectroscopy

Abstract

Characterization of granites by 57Fe Mössbauer spectroscopyTwo granite complexes in Egypt, a sodic type and an aluminous type are characterized by Mössbauer spectroscopy. Mössbauer spectra (MS) of the sodic granite show a major doublet of ferric (Fe3+) iron that is attributable to octahedral coordination (M1) sites plus/minus a tetrahedron Fe3+ doublet plus/minus a doublet of ferrous (Fe2+) iron on the M1 sites plus/ minus another Fe2+ (M1) doublet and a sextet of Fe3+. The sextet is attributed to α-Fe2O3 (hematite) and the other Fe components are due to NaCaFeSi2O6 (aegirine-augite) plus/minus minor contributions from (Ca2(Mg, Fe)5(Si, Al)8O22(OH)2 (magnesium-hornblende). Changes in the quadrupole splitting and width line of Fe2+ ions are likely composition-related. The MS of the aluminous-type granite, on the other hand, shows evidence only of single doublets containing Fe2+ or Fe3+ in the octahedral M1 sites, with parameters that remain almost constant. This consistency implies that the existing minerals - K(Mg, Fe2+)3 (Al, Fe3+)Si3O10(OH, F)2 (biotite), (Mg, Fe)6(Si, Al)4O10(OH)8 (clinochlore), (Na, K)Ca2(Fe, Mg)5(Al, Si)8O22(OH)2 (ferrohornblende and magnesiohornblende) - have similar iron positions. The intensity of iron oxidized (Fe3+/ΣFe) for the sodic granite is 79.1 to 100% and for the aluminous granite, 28.4 to 38.2%. The observed Fe3+/ΣFe differences between the two granites are source-related and consistent with distributions of other redox-sensitive elements.

Characterization of barren, granitic soils from the Nubian Desert (SW Egypt) by 57Fe Mössbauer spectroscopy

“…XRD patterns for the bulk samples of Soil A and Soil B, with mineral identifications, are given in Figure 2 along with XRD data for the parent granites from Hassan (2009). In the soil samples, quartz was identified by XRD as the major component.…”

“…The ICP-MS results are listed in Table 1 along with the chemical data of the parent granites from Hassan (2005Hassan ( , 2009). Soil A is richer in magnesium oxide than Soil B and poorer in total iron (as ferric) and potassium oxide.…”

“…These granites consist of microcline, quartz and albite plus some iron-bearing silicates, including aegirine-augite and aegirine ± minor riebeckite. Typical of the peralkaline acidic rocks often found in ring complexes and dikelike intrusions in Egypt (List et al 1989), they characteristically contain high abundances of iron (mainly ferric), uranium, thorium, neodymium, cerium, zirconium, yttrium, niobium and samarium (Hassan 2009(Hassan , 2010. Radiometrically, Soil B has up to eight times more total field -ray radiation than Soil A, but no obvious mineralization.…”

Trace elements and REE enrichment at Seboah Hill, SW Egypt

“…Results of loss-on-ignition (LOI) and major-element analyses of the radioactive vein, granite, and rhyolite samples from Seboah Hill are listed in Table 4, along with Fe 3+ /∑Fe of the samples from Hassan (2009bHassan ( 2010. The LOI values ranging from 0.3-2.0wt% represent the loss of H 2 O in the main.…”

Note on the stable isotope values of vein calcite in the El-Seboah peralkaline granite (SW Egypt)

“…Both veins display enriched total gamma-ray radiation (up to three orders of magnitude more than the host granite), with vein I having high radiation counts. The radioactivity in the area is due mainly to thorium and, to a lesser extent, uranium (Hassan 2005(Hassan , 2009(Hassan , 2010. The nearest carbonate outcrop to the site of the veins is Sinn el-Keddab plateau ~ 80 kilometers to the north (Fig.…”