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Nat Commun. 2019 Apr 12;10(1):1712. doi: 10.1038/s41467-019-09244-4.

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

Author information

1
Section for Mineralogy, Petrology and Tectonics, Department of Earth Sciences, Uppsala University, Villavägen 16, 75236, Uppsala, Sweden. valentin.troll@geo.uu.se.
2
Section for Mineralogy, Petrology and Tectonics, Department of Earth Sciences, Uppsala University, Villavägen 16, 75236, Uppsala, Sweden.
3
Swedish Museum of Natural History, Dept. of Geosciences, Frescativägen 40, 114 18, Stockholm, Sweden.
4
Department of Mineral Resources, Geological Survey of Sweden, Villavägen 18, Box 670, 75128, Uppsala, Sweden.
5
Luossavaara-Kiirunavaara AB, Research & Development, FK9, 981 86, Kiruna, Sweden.
6
Geological Survey of Iran, Meraj St, Azadi Sq, Tehran, 138783-5841, Iran.
7
Geology and Mineralogy, Åbo Akademi University, Domkyrkotorget 1, 20500, Turku, Finland.
8
Department of Geological Sciences, University of Cape Town, Rondebosch, 7701, South Africa.
9
School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff, CF10 3AT, UK.
10
National Institute of Technology Rourkela, Department of Earth & Atmospheric Sciences, NIT Rourkela, Odisha, 769008, India.
11
Indian Institute of Technology (IIT) Bombay, Department of Earth Sciences, Powai, Mumbai, 400076, India.
12
Swedish Ministry of Enterprise and Innovation, Division for Business, Mäster Samuelsgatan 70, 10333, Stockholm, Sweden.

Abstract

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.

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