DETERMINATION OF THE IRON VALENCE STATE IN PICROILMENITES WITH USE OF X-RAY ELECTRON MICROPROBE AND X-RAY-FLUORESCENCE ANALYSES
This study was carried out to estimate the possibility to determine the iron valence state in picroilmenite using L- and K-series of X-ray spectrum. Analyzed samples of kimberlites have been taken out from pipes Udachnaya, Mir and some others. The measurements were realized with the XRF spectrometer S4 Pioneer and the EMP analizer JXA-8200. Ratios of intensities of Kb2,5/Kb1,3 and Lb/La1,2 lines were used as the analytical signal. Thus estimated values if FeO contents were compared with data of wet chemistry analyses and stoichiometric calculations. Results of stoichiometric calculations are usable only for rough estimations of iron valence state. Its determination in picroilmenite with the X-ray micro-analysis should be based on the Lb/La2,5 ratio. In this case, the relative standard deviation of FeO content was 6.8 %. Precisions of XRF analyses of picroilmenite by L- and/or K-series are very close, that is why both ILb/ILa1,2 and IKb2,5/IKb1,3 ratios may be used to determine the iron valence ratio. The relative standard deviation of FeO content did not exceed 5.5 %. The XRF method is preferable to determine the iron valence state in samples with mass no less than 1 g, for it is faster and cheaper in the sample preparation, than the wet chemistry. The XRF method allows to make determinations in local areas of 1-10 mkm across with precision comparable with the XRF analysis.