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, Högdahl, Karin, Harris, Chris, Millet, Marc-Alban, Chinnasamy, Sakthi Saravanan, Kooijman, Ellen, Nilsson, Katarina P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Uppsala universitet, Mineralogi, petrologi och tektonik 2019
• Subjects: Geology; Geologi; Kiruna
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-382552; https://doi.org/10.1038/s41467-019-09244-4

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 lowtemperature 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 d56Fe and d18O ratios that overlap with the volcanic and plutonic reference materials (> 800 degrees C), whereas similar to 20%, mainly vein-hosted and disseminated magnetite, match the low-temperature reference samples (<= 400 degrees C). Thus, Kiruna-type ores are dominantly magmatic in origin, but may contain latestage hydrothermal magnetite populations that can locally overprint primary hightemperature magmatic signatures.