title: Magmatic origin of giant 'Kiruna-type' apatite-iron-oxide ores in central Sweden.
abstract: Iron is the most important metal for modern industry and Sweden is by far the largest iron-producer in Europe, yet the genesis of Sweden's main iron-source, the 'Kiruna-type' apatite-iron-oxide ores, remains enigmatic. We show that magnetites from the largest central Swedish 'Kiruna-type' deposit at Grängesberg have δ(18)O values between -0.4 and +3.7‰, while the 1.90-1.88 Ga meta-volcanic host rocks have δ(18)O values between +4.9 and +9‰. Over 90% of the magnetite data are consistent with direct precipitation from intermediate to felsic magmas or magmatic fluids at high-temperature (δ(18)Omgt > +0.9‰, i.e. ortho-magmatic). A smaller group of magnetites (δ(18)Omgt ≤ +0.9‰), in turn, equilibrated with high-δ(18)O, likely meteoric, hydrothermal fluids at low temperatures. The central Swedish 'Kiruna-type' ores thus formed dominantly through magmatic iron-oxide precipitation within a larger volcanic superstructure, while local hydrothermal activity resulted from low-temperature fluid circulation in the shallower parts of this system.
authors.affiliation: Department of Earth Sciences, CEMPEG, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Jonsson
authors.forename: Valentin R
authors.initials: VR
authors.lastname: Troll
authors.forename: Karin
authors.initials: K
authors.lastname: Högdahl
authors.forename: Chris
authors.initials: C
authors.lastname: Harris
authors.forename: Franz
authors.initials: F
authors.lastname: Weis
authors.forename: Katarina P
authors.initials: KP
authors.lastname: Nilsson
authors.forename: Alasdair
authors.initials: A
authors.lastname: Skelton