Ancient atmospheric oxygen found in iron ore deposits

It thus provides a new explanation for the formation of so-called iron oxide-apatite deposits, which are among the world’s most important sources of iron and rare-earth elements.At the same time, they establish a link between the development of the Earth’s atmosphere, the evolution of photosynthetic life and the formation of key mineral resources.

“We demonstrate that iron oxide-apatite deposits contain oxygen once derived from the ancient atmosphere. This shows that the assimilation of ancient salts by magma and the enrichment of the Earth’s atmosphere with oxygen played a key role in the formation of these deposits,”explains Dr Stefan Peters, Head of Mineralogy at the LIB’s Museum of Nature Hamburg.

Oxygen as a testimony to the Earth’s history

Using high-precision oxygen isotope analyses, the researchers examined magnetite from iron ore deposits in Sweden and other regions of the world. In doing so, they discovered an unusual signature: some of the oxygen did not originate directly from the magma, but from ancient salt deposits. These so-called evaporites had incorporated and preserved oxygen from the atmosphere billions of years ago. When they were later incorporated by rising magma, they supplied the oxygen that oxidised the iron, thereby facilitating the formation of the ore deposits.

Photosynthesis as a key to the formation of iron ore

For the first time, the study links the formation of these major mineral deposits to the evolution of Earth’s atmosphere and the rise of photosynthetic microorganisms.

“It’s quite a fascinating story: these iron ore deposits would probably never have existed without photosynthesis,”explains Stefan Peters.

The results suggest that the oxygenation of the atmosphere not only enabled the development of complex life, but also influenced the formation of important iron ore deposits. Furthermore, the measurements show that changes in the atmosphere over billions of years can still be detected in the rocks today.

New isotope method reveals ancient oxygen

The discovery was made using high-precision analyses of so-called triple oxygen isotopes. This method makes it possible to trace the origin of oxygen back billions of years and to reveal even the smallest isotopic differences.

The publication is the result of a collaboration with researchers from the LIB, the University of Göttingen, Uppsala University (Sweden), the Instituto de Geociencias (CSIC-UCM) in Madrid and Clausthal University of Technology.

Publication:

Peters, S.T.M., Feng, D., Troll, V.R. et al. Formation of iron oxide-apatite deposits triggered by magmatic assimilation of evaporitic sulfate. Nat Commun17, 5930 (2026). https://doi.org/10.1038/s41467-026-75189-0