Mineralogical, chemical and textural characterisation of the Malmberget iron ore deposit for a geometallurgical model

Sammanfattning: The northern Norrbotten ore province is an intensely mineralised area and has traditionally been a very important mining district. It contains Fe, Cu-Au, Au, and Ag deposits ranging from world-class ore deposits to small and uneconomic ones (Martinsson 2004). The most important are the Kiruna and Malmberget iron ores and the Aitik Cu-Au deposit.The cross-discipline approach called geometallurgy connects two different but closely related areas in the mining industry, namely geology and mineral processing. It involves understanding and measurements of the ore properties significant for its successful processing. Geometallurgy takes both the geological and mineral processing information to create a spatially-based (3D) predictive model for product management in mining operations (Lamberg, 2011).This case study investigates how to establish a geometallurgical model using the Malmberget iron ore deposit as a case study. A mineralogical approach (Lamberg 2011) was selected meaning that the focus is on mineralogy, and therefore parameters like modal mineralogy, mineral textures, mineral associations, mineral grain sizes and their relation to liberation characteristics are important. The main effort is to deliver a geological model which gives quantitative rather than descriptive information to be used in a process submodel.The ore characterisation (Papers I and II) gives new information on the chemical composition of minerals, mineralogical composition of both ore and host rocks, as well as the variation within the individual ore bodies. This sets a firm basis for the quantitative methods developed for routine analysis of modal mineralogy (Paper III) and mineral textures (Paper IV). Also, this increases the understanding regarding the primary origin and metamorphic evolution of the deposit, which is important since the origin of the apatite iron ore of the Kiruna type is still controversial.Based on the modal composition, preliminary geometallurgical (GEM) ore types were established for the Malmberget ore body. Each of these GEM-types describes quantitatively: the minerals present, their chemical composition, rules how to calculate the modal composition from routine chemical assays (element to mineral conversion, EMC rules) and a textural archetype in a library of archetypes. Using these GEM-types it is possible to calculate the modal mineralogy and the liberation distribution for every geological unit from the sample level to GEM-types to be further used in building a GEM block model of the ore.The applicability of the geological model was tested by developing a liberation based process model of simple one stage dry magnetic separation for the GEM-types. The model returns the metallurgical response, in terms of grade and recovery, of each of the developed GEM-types. The model was validated with another ore sample representing the same archetype from a different ore body and with a different grade. The model forecasted the recovery and concentrate grade within 2%-unit accuracy.This is the first published study where a full predictive geometallurgical model is entirely based on the mineralogy. The approach is a generic approach and valid not only for iron ores but also for other metallic mines.