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

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 (