Iron Oxides of Fazendao Deposit, East Border of Quadrilatero Ferrifero, Minas Gerais, Brazil

摘要

The iron oxides highly influence the soil structure and aggregation of mineral particles in soil. They also play an important role in some economical variables, as those related to the use of land for agriculture practices or mineral exploitation, in ore mining activities. About 60 % of all industrial activities on iron processing in Brazil is based on ores mined in the geodomain of Quadrilatero Ferrifero, state of Minas Gerais, Brazil. Samples of a mining area for iron, the Fazendao Deposit in the east border of Quadrilatero Ferrifero have been studied in an attempt to contribute to a better understanding of the key chemical and mineralogical pathways related to the formation and transformation of iron oxides, involving hematite. From powder diffraction patterns, it is confirmed that hematite is the main mineralogical phase in all samples. The total iron contents were found to range between 65.15 and 70.00 mass%. The saturation magnetization values, σ =6.9 and 2.1 J T~(-1) kg~(-1), are significantly measurable only for the two samples showing some evidences of magnetite. 298 K-Moessbauer data confirmed the dominant occurrence of hematite in all samples, along with magnetite for the two samples showing non-zero magnetization. 110K-Moessbauer data indicate that the hematite in all samples undergoes the Morin transition (TM≈260 K), as expected for the relatively pure oxide. Maghemite could not be detected in any sample. New numerical analysis are now being performed, using Rietveld refinement of XRD data, in an attempt to obtain crystallographic results that could indicate more reliable evidences about the mechanisms of formation of hematite, particularly in the magnetic samples, for which the precursor is presumably magnetite.