Development of process mineralogy for optimization and increased value of the mineral production in Sibelco Nordic

Abstract

Process mineralogy is a term well known to the mining industry considering high income products like precious minerals and metals, but for lower income products like industrial minerals the term is not so familiar or commonly used. The purpose has been to apply process mineralogical methodology for characterizing and quantifying granitic pegmatite used for industrial mineral products like quartz, feldspar and muscovite.

The first part included the development of Rietveld X-ray diffraction (XRD) methods for quantification of the main mineralogy of granitic pegmatites from two pegmatite deposit areas; Glamsland (Norway) and Limbergsbo (Sweden). This Rietveld XRD method was tested against other known quantification methods like X-ray fluorescence (XRF) and element to mineral conversion based on mineral chemistry data achieved from Electron Probe Micro Analyser (EPMA). The result of the comparison was that Rietveld XRD was an accurate and precise quantification method. Also because the method is mathematically based, the analyses were reproducible and the handling of the method was user friendly not demanding an expert interpretation for every sample analysed.

The second part of the project included a characterization of the mineralogy. The methods used were XRF, the newly developed Rietveld XRD methods, Point Counting using an optical microscope (PC), Image Analysis (IA) and Mineral Liberation Analysis (MLA) using the Scanning Electron Microscope (SEM), and mineral chemistry and element mapping of certain elements using the EPMA. The main perspective was to characterize the mineralogy of the granitic pegmatite from Glamsland and Limbergsbo deposits, with a special focus on feldspar and the defined quality parameters. The quality parameters were different for the two deposit areas. For the Glamsland deposit area the main quality parameter was content of iron (Fe), and also types of feldspar. Quartz was not considered due to documented quality parameters for the products confirming Fe content to be stable and low (0.01 Wt. %). During the analysis it was discovered that the feldspars (microcline and albite) had several inclusions of contaminating minerals, in addition to microtextures like graphic granite, perthites and anti-perthites. The albite investigated was more exposed to alteration than microcline, and had a higher content of contaminating mineral inclusions. For albite and microcline in two of the raw materials investigated elevated levels of Fe2O3 was observed in the mineral chemistry.

The reason for this was that Fe was able to enter the crystal lattice in feldspar influencing the chemical assays. For the Limbergsbo deposit the quality parameters covered content of iron (Fe) and also fluorine (F) in the pegmatites. During the analysis it was discovered that content of both Fe and F was present in muscovite, a discovery that lead to further analysis of muscovite. The results of these extra analyses were that at least three types of muscovite were present in the pegmatite, a Fe-rich type, an F-rich type, and more regular muscovite.

The methods included in this project have proved to cover several kinds of information of the materials investigated, and in summary provide important chemical, mineralogical and textural knowledge. As process mineralogical methods for exploration, the different methods can be used in combinations well suited for the deposits which are to be investigated. For industrial companies to be able to utilize a deposit in the best way both considering cost efficiency and environmental aspects the most important step is thoroughly exploration of the deposit area before opening. This should be done to reveal the geological settings like structural geology and process mineralogy. Based on the knowledge received from the exploration, it is then possible to develop an enrichment process best fitted for refining of the raw materials. The findings from an exploration can also be used to set up quality control management procedures covering daily quality control of the material and periodically quality controls. These periodically quality controls can reveal changes in the mineralogy and distribution of contaminating elements, an information that can be used to update the methods used for daily quality control management.