Occurrence of iron in industrial granitic pegmatite

Granitic pegmatite is used as raw material for industrial minerals in the production of feldspar and quartz for glass, ceramic and porcelain. One of the most important quality parameters in the feldspar is the content of iron (Fe). At the Lillesand plant, Norway, pegmatite is floated to produce quartz, albite and microcline products. Fe is mostly removed through flotation and magnetic separation, but some Fe is still present in the final products, the amount depending on the raw material source. Rietveld X-ray Diffraction (XRD), Point counting by optical microscopy, and Electron Microprobe Analysis (EPMA) combined with image analysis of Back-Scatter Electron (BSE) images was used to quantify the mineralogy and to map the distribution Fe in the pegmatites. The study showed that Fe is present as mineral inclusions in feldspar, in addition to its occurrence in minor mineral components such as mica and chlorite. The frequency of Fe-mineral inclusions was higher in albite than in microcline, and they were often associated with micro-fractures and areas of alteration. These findings reveal a potential for reducing total Fe₂O₃ in the microcline products.