Source and Evolution of Ore-Forming Fluids in the Bafq Iron Oxide–Apatite Deposits, Central Iran: Insights from Sulfur Isotopes of Pyrite and Oxygen Isotopes of Magnetite

Esmaeili Zeini, Mobina; Alirezaei, Saeid; Azimzadeh, Amir Morteza

doi:10.22071/gsj.2026.578346.2247

Source and Evolution of Ore-Forming Fluids in the Bafq Iron Oxide–Apatite Deposits, Central Iran: Insights from Sulfur Isotopes of Pyrite and Oxygen Isotopes of Magnetite

Articles in Press

Document Type : Original Research Paper

Authors

Mobina Esmaeili Zeini ¹

Saeid Alirezaei ²

Amir Morteza Azimzadeh ³

¹ Department of water and mineral, Faculty of Earth science, Shahid Beheshti University of Tehran, Iran.

² Department of water and mineral Faculty of Earth science Shahid Beheshti University of Tehran. Iran.

³ , Division of Geosciences and Environmental Engineering, Luleå University of Technology, Luleå, Sweden

10.22071/gsj.2026.578346.2247

Abstract

Despite sharing several key features, the iron oxide–apatite deposits of the Bafq district display considerable variability in host rocks, wall rock alteration, and ore texture/mineralogy, and geochemical attributes, reflecting the complexity of the ore forming processes and the ore fluid sources. Here, oxygen and sulfur isotope composition of magnetite and pyrite from various ores are used to investigate the source and evolution of ore-forming fluids in the Bafq district. Massive and vein-type magnetites exhibit lowerδ¹⁸Ovalues, between0.7-4.4‰, consistent with crystallization from high-temperature magmatic fluids. Theδ¹⁸Ovalue of+3.9‰for the banded ore at Mishdovan indicates a significant contribution from high-temperature magmatic fluids. The presence of cumulative textures in the banded ore of Chadormalu, together with a δ¹⁸Ovalue of+2.5‰for magnetite, supports formation under high-temperature magmatic conditions. In contrast, the higher δ¹⁸Ovalues (up to+8‰) for magnetite from Gazestan and Lak-e-Siah suggest deposition from non-magmatic fluids, compatible with a sedimentary–diagenetic origin or sub-seafloor replacement. Theδ³⁴Svalues for pyrite from massive, brecciated, and vein-type ores range from+4‰to+30‰, indicating the involvement of non-magmatic sulfur sources. The broad range of oxygen and sulfur isotopic compositions suggests a multi-stage evolutionary model for mineralization, with contributions from both magmatic and non-magmatic fluid sources. This is supported by the fluid inclusion data.

Keywords

Oxygen isotope

Sulfir isotope

Magnetite

Pyrite

Iron oxide-apatite deposits

Bafq

Central Iran

Subjects