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 ?(18)O values between -0.4 and +3.7‰, while the 1.90-1.88?Ga meta-volcanic host rocks have ?(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 (?(18)Omgt > +0.9‰, i.e. ortho-magmatic). A smaller group of magnetites (?(18)Omgt ? +0.9‰), in turn, equilibrated with high-?(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.

SUBMITTER: Jonsson E 

PROVIDER: S-EPMC3622134 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature