Global Fe-O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores

• Published in: Nature Communications
• Main Authors: Troll, Valentin R., Weis, Franz A., Jonsson, Erik, Andersson, Ulf B., Majidi, Seyed Afshin, Hogdahl, Karin, Harris, Chris, Millet, Marc-Alban, Chinnasamy, Sakthi Saravanan, Kooijman, Ellen, Nilsson, Katarina P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Research 2019
• Subjects: Kiruna
• Online Access: https://orca.cardiff.ac.uk/id/eprint/119344/; https://doi.org/10.1038/s41467-019-09244-4; https://orca.cardiff.ac.uk/id/eprint/119344/7/s41467-019-09244-4.pdf

Kiruna-type apatite-iron-oxide ores are key iron sources for modern industry, yet their origin remains controversial. Diverse ore-forming processes have been discussed, comprising low-temperature hydrothermal processes versus a high-temperature origin from magma or magmatic fluids. We present an extensive set of new and combined iron and oxygen isotope data from magnetite of Kiruna-type ores from Sweden, Chile and Iran, and compare them with new global reference data from layered intrusions, active volcanic provinces, and established low-temperature and hydrothermal iron ores. We show that approximately 80% of the magnetite from the investigated Kiruna-type ores exhibit δ56Fe and δ18O ratios that overlap with the volcanic and plutonic reference materials (> 800 °C), whereas ~20%, mainly vein-hosted and disseminated magnetite, match the low-temperature reference samples (≤400 °C). Thus, Kiruna-type ores are dominantly magmatic in origin, but may contain late-stage hydrothermal magnetite populations that can locally overprint primary high-temperature magmatic signatures