Determination of the Mineral Composition of the Lake Bottom Sediments by X-Ray Diffraction Method and Physico-Chemical Modelling

The paper reports comparison of three approaches to define the contents of minerals and mineral groups in the carbonate-silicate lake bottom sediments. The two approaches are based on the method of X-ray powder diffraction. The first one treats with the Rietveld Method in the software DIFFRAC Plus diffractometer D8 Advance (PDF-2 database). The second one uses the method of reference intensities (corundum ratios) and optimization of the model powder patterns from the X-ray phase standards of PDF-2 database and equations of the element balance with regularization of the least square functional. The third approach of physic-chemical modeling selects probable single mineral and multi-component phases through modelling the sold solutions, and it uses the data on the element composition obtained by XRF technique, as well as the data of X-ray diffraction on the qualitative mineral composition. Thirty samples of bottom sediment cores taken in the Zun-Torey Lake in East Siberia were analyzed by the three approaches described herein. The contents of mineral groups (feldspars, quartz, clay minerals and carbonates) varied within the range 10-40 mass %. The discrepancies between obtained results show the standard deviation ranging from 2 to 9 mass %. A relative standard deviation commonly provides the value below 30 %, so such determinations could be considered quantitative ones. With regard to the acquired data, it is hard to prefer this or that approach. Available data was employed to assess the error of X-ray phase powder analysis in measuring the abundance of mineral groups in the carbonate-silicate sedimentary rocks in the absence of reference materials to compare with certified mineral composition