Magmatic origin of giant ‘Kiruna-type’ apatite-iron-oxide ores in Central Sweden
Creator:
Jonsson, E., Troll, V. R, Högdahl, K., Harris, C., Weis, F., Nilsson, P. K. & Skelton, A.
Subject:
Grängesberg apatite iron ore, Kiruna-type, Oxygen isotopes, REE-minerals
Publisher:
Nature, Scientific Report
Date:
Wednesday, April 10, 2013
Format:
Article
Source:
http://www.nature.com/articles/srep01644
Language:
English
Coverage:
Distant File:
Description:
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 δ18O values between −0.4 and +3.7‰, while the 1.90−1.88 Ga meta-volcanic host rocks have δ18O 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 (δ18Omgt > +0.9‰, i.e. ortho-magmatic). A smaller group of magnetites (δ18Omgt ≤ +0.9‰), in turn, equilibrated with high-δ18O, 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.