Mineralogical, chemical and textural properties of the Malmberget iron deposit : a process mineralogically characterisation

Sammanfattning: This thesis combine two different but closely connected disciplines in a mining process to each other, ore geology and process mineralogy by studying mineralogical-textural features of the ore and the ore concentrate in an apatite iron ore deposit in Malmberget, Sweden. Apatite iron ore deposits (Kiruna type) exist in a few places around the world and the two most important deposits are mined by LKAB at Kiruna and Malmberget. Their contribution to the global iron ore market is minor but on a local scale these high grade deposits have a large economical importance. Three different ore bodies from the Malmberget deposit are included in the study; Hens, ViRi and Fabian. Each of these three ore bodies has characteristic mineralogy, chemical and textural properties. The first paper (Paper І) describes the metamorphic influence on the ore, particular the chemical and textural effects on the ore minerals. The ore bodies Fabian and ViRi have a similar mineralogy by the occurrence of Ti-minerals, pyrite and chalcopyrite as common minor components. Hematite is only present in Hens ore body. Magnetite from the different ore bodies and ore types show a chemical variation of the minor elements V2O3, TiO2, Al2O3, and MgO. Our data support a model with the massive ore formed from an iron oxide melt while the ore breccia is part of the same ore forming system but of hydrothermal origin. The second and third paper is about process mineralogy. Paper two (Paper ІІ) characterise the mineralogical properties of an apatite iron ore body in a quantitative manner by using an automated SEM based system QEMSCAN®. Two major ore types were used; massive ore and ore breccia. Each ore type was crushed and split in the fractions 150 µm, 75 µm and 38 µm. The results show a rather distinct difference between these two ore types, both in the mineralogy but particularly in their textural properties. The particle liberation of magnetite is high for massive ore, being much lower for ore breccia and has a decreasing liberation in finer fractions in each ore type. This has to do with grain size, mineralogy and textures of the magnetite and the gangue minerals. The mineral associations of ore breccia are more diverse than of massive ore by the presence of more binary and complex magnetite bearing particles. Ore breccia is an ore type where some of the magnetite bearing associations will cause an increasing amount of silica in the concentrate or iron content to the tailings. Paper three (Paper ІІІ) shows that is possible to find traceability in a concentration process by identifying significant mineralogical signatures in the ore and in the concentrate. Two possibly useful mineralogical signatures were found. The first is a rather simple association between magnetite and apatite existing as mixed grain and the second is a complex texture with smaller magnetite grains as inclusions in feldspars grains. These signatures can probably be used as a fingerprint for different ore types, particle fractions and grinding circuit which can create traceability in the process. The results from these two instruments show some differences, QEMSCAN® compared to PTA generate analysis which being more accurate and precise due to the amount of data in each sample.