Progress in mineralogical quantitative analysis of rock samples: application to quartzites from Denali National Park, Alaska Range (USA)

Abstract

This work deals with the determination of the mineralogical composition of three quartzite samples, selected as case study to verify the viability and accuracy of various experimental techniques commonly used in geometallurgy and petrography for the determination of the mineralogical composition of rock samples. The investigated samples are from the North-Eastern side of the Denali National Park (Alaska Range, USA). The mineralogical phase abundance of the samples was determined by digitally assisted optical modal point counting, scanning electron microscopy (SEM) + energy dispersive spectroscopy (EDS) modal and digital image analysis, normative calculation from bulk chemistry calculation, and modal Rietveld X-ray powder diffraction. The results of our study indicate that the results provided by modal optical and SEM digitalized counting seem less accurate than the others. The determination with EDS mapping was found to be inaccurate only for one sample. Agreement was found between the X-ray diffraction estimates and bulk chemistry calculation. For both modal optical and SEM digitalized counting, the statistics was probably insufficient to provide accurate results. The estimates obtained from the various methods are compared with each other in the attempt to attain general indications on the precision, accuracy, advantages/disadvantages of each method.

Factor Analysis of XRF and XRPD Data on the Example of the Rocks of the Kontozero Carbonatite Complex (NW Russia). Part II: Geological Interpretation

“…Three methods are capable of providing accurate determinations of the mineralogical phase composition: (1) point-counting techniques using optical microscopy (optical modal analysis), supplemented by image digitalization and analysis and the application of electron microscopy techniques; (2) modal X-ray powder diffraction (XRPD); (3) normative calculation from bulk chemical data. Reviews and comparisons of these and related methods have been published in many articles; for example, see [1][2][3]. Though highly advantageous, each method has limitations.…”

“…For a small sample of rocks (up to several tens of samples), it is preferable to use a combination of all three methods. They effectively complement each other, which guarantees a good result [3]. When processing extensive collections of samples-for example, when exploring deposits-the assessment of mineral contents by the uniform application of all three methods becomes a laborious task.…”

“…Crystals 2020, 10, x FOR PEER REVIEW 8 of 17 3. GROUP III has a peak intensity of less than a quarter of the maximum peak height (in Figure 5B,C, the elements related to this group are green-colored); 4.…”