The main source of magnetite (Fe2+Fe3+2O4) is magnetite-bearing banded iron formations (BIF) and the key economic parameters for magnetite ore being economic are the crystallinity of the magnetite, the grade of the iron within the banded iron formation host rock and the contaminant elements, which exist within the magnetite concentrate. Occasionally granite and ultrapotassic igneous rocks segregate magnetite crystals and form masses of magnetite suitable for economic concentration. A few iron ore deposits, notably in Chile, are formed from volcanic flows containing significant accumulations of magnetite phenocrysts. Chilean magnetite iron ore deposits within the Atacama Desert have also formed alluvial accumulations of magnetite in streams leading from these volcanic formations. Some magnetite skarn and hydrothermal deposits have been worked in the past as high-grade iron ore deposits requiring little beneficiation.Magnetite skarn deposits are an important source of iron ore around the globe such as the huge Kachar and Sarbai deposits in Kazakhstan or the Savage River deposit in Tasmania. This style of iron ore deposit forms from metasomatic reaction during intrusion of igneous rocks into calc-silicate sediments. Mineralisation is generally in the form of large coarsely crystallised magnetite lenses and is often associated with trace elements such as copper, gold, cobalt, nickel, zinc or lead. Other sources of magnetite iron ore include metamorphic accumulations of massive magnetite ore such as at Savage River, Tasmania, formed by shearing of ophiolite ultramafics.Another, minor, source of iron ores are magmatic accumulations in layered intrusions, which contain a typically titanium-bearing magnetite often with vanadium.Lower-grade sources of iron ore generally require beneficiation, using techniques like crushing, milling, gravity or heavy media separation, screening and silica froth flotation to improve the concentration of the ore and remove impurities. The results, high-quality fine ore powders, are known as fines. Although magnetite ores require a more time-consuming beneficiation process, and thereby require more money spent by the mining company, the final products have significantly fewer impurities than the products of hematite ores.A number of magnetite-bearing iron ores (lump, fines and pellet feed) have been characterised using ore sorting, optical microscopic point counting, quantitative X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe micro-analysis (EPMA) techniques. Lump magnetite ore was sized and manually sorted using a classification based on mineral content, magnetism and other physical properties. Magnetite fines and pellet feed were sized and point-counted quantitatively under an optical microscope using an ore classification based on mineralogy, texture and liberation characteristics._x000D_
The liberation characteristics of magnetite ores with sizing were also studied._x000D_
A number of stages in the oxidation of magnetite to martite (hematite) via maghemite and hydration of martite (hematite) to goethite have been observed in both BIF and skarn ores. Hydration of magnetite directly to goethite was also observed. Ore group abundance data were used to compare lump, fines and magnetite pellet feed derived from BIF and skarns. Gangue minerals were identified using optical, XRD, SEM and EPMA techniques to improve the fundamental understanding of the occurrence and form of gangue minerals in different ore types. The main gangue minerals include silicates (quartz, amphiboles, mica, garnet), carbonates and sulfides._x000D_
The form and occurrence of gangue minerals in different ore types has been described and compared to enable optimisation of beneficiation flow sheets. Characterisation of magnetite-bearing lumps and fines allows comparison of magnetites ores from different origins and facilitates valuable information related to the production of lump or fine ore products. Characterisation of magnetite pellet feed facilitates evaluation of pellet feed on iron ore sinter quality._x000D_
*This is an abstract only. No full paper was prepared for this abstract.* CITATION:Hapugoda, S, Manuel, J R, Lu, L, Peterson, M J and Donskoi, E, 2013. Characterisation of magnetite iron ore, in Proceedings Iron Ore 2013 , pp 259-260 (The Australasian Institute of Mining and Metallurgy: Melbourne).