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Trace-element chemistry of magnetite from the Malmberget apatite-iron deposit
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
2008 (English)Conference paper, Oral presentation only (Other academic)
Abstract [en]

Iron is the most used metal and it is mined from several different types of deposits. Those of a chemical-sedimentary origin dominate, but also deposits of hydrothermal or magmatic origin are important in some parts of the world. Due to an expanding market of iron ore and increased customer demands on product quality the producers has to meet this with a more detailed knowledge of their resources, including trace element composition of the iron oxides.Sweden is Europe's most important producer of iron ore with two large underground mines in Kiruna and Malmberget operated by LKAB. Both deposits are apatite iron ores, an ore type that is common in northern Sweden but rare in other parts of the world. These two world class deposits have a similar origin and were formed by magmatic-hydrothermal process at 1.89-1.88 Ga. However, the Malmberget ore is more strongly affected by later metamorphose, deformation and intrusion of granitic rocks.More than 20 different tabular to stock shaped ore bodies are known at Malmberget, occupying an area of 2.5 x 5km. The Malmberget deposit was probably from the beginning a more or less continuous ore lens which were exposed for at least two phases of folding and metamorphism. By strong ductile deformation it was torn into several lenses that today occupy a large-scale fold structure were the individual ore bodies stretches parallel to the fold axis, which plunge 40º-50º towards SSW. Due to the strong metamorphic overprinting of the area, the ore minerals are recrystallised, coarse grained, and elongated in the direction of the lineation of the rocks.The iron ore minerals are both magnetite (Fe3O4) and hematite (Fe2O3) with magnetite as the only iron oxide in most major ore bodies. Hematite dominates some minor ore bodies and is mixed with magnetite in others. The main gangue minerals are apatite, amphibole, pyroxene, feldspars, quartz and biotite. Among the accessory minerals are pyrite, chalcopyrite, titanite, zircons and calcite most common. Each ore body is characterised by its own mineral, chemical and textural properties. Magnetite belongs to the spinel group of minerals and besides the ferrides it may also contain Al and Mg substituting for Fe. Apatite iron ores, including the Malmberget deposit, are characterized by magnetite chemistry different to most other iron deposits. They typically have high vanadium content similar to magmatic segregations of magnetite in mafic rocks but a Ti content that is between magmatic and sedimentary iron deposits. Microprobe analyses of magnetite of different textures and from different ore types indicate that magnetite is not uniform in composition and the content of e.g. Al and Mg seem to be largely controlled by local chemical conditions with Al most enriched in ore of breccia style while Mg is highest in magnetite from massive ore.

Place, publisher, year, edition, pages
2008.
National Category
Geology
Research subject
Ore Geology
Identifiers
URN: urn:nbn:se:ltu:diva-28359Local ID: 2231f900-c842-11dd-941d-000ea68e967bOAI: oai:DiVA.org:ltu-28359DiVA, id: diva2:1001555
Conference
International Geological Congress : 06/08/2008 - 14/08/2008
Note
Godkänd; 2008; 20081212 (luncec)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-03-26Bibliographically approved

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