Mineral chemistry of apatite, amphibole, biotite, and magnetite from the Masjeddaghi porphyry Cu-Au deposit, NW Iran: petrogenetic and metallogenic implications

Rahnama Z. Hassanpour S. Savard D. Shah Z.
2025 Frontiers Media SA

Frontiers in Earth Science
2025 #13

The Masjeddaghi porphyry Cu-Au deposit is situated in the Alborz-Azarbaijan structural zone of northwest Iran. Chemical compositions of rock-forming (biotite, amphibole) and accessory minerals (magnetite, apatite) in the potassic to propylitic altered diorite porphyry of Masjeddaghi serve as key indicators of magmatic-hydrothermal mineralization. In situ LA-ICP-MS was conducted to analyze trace element contents of selected magnetite-bearing samples, while EMPA analyzed biotite, amphibole, and apatite compositions. The mineral compositions show a parental magma with calc-alkaline features, suggesting a source comprised of both subduction mantle-derived and crust-derived materials, and the Masjeddaghi mineralizing magmas have a relatively elevated ƒO₂ and are classified as oxidized I-type magmas. The calculated temperature ranges are constrained by Al-in-amphibole geothermometry, saturation temperature of apatite, and the Ti-in-biotite geothermometer (830°C–877°C) (845°C-918°C) and (723°C–782°C), respectively, whereas the Al-in-amphibole geobarometry exhibits formation pressure (120–186 MPa; relating to depths ranging from 4 to 10 km) and H₂O_melt content at time of crystallization (4.10–4.46 wt%), indicating formation of a hydrous calc-alkaline magma from a deep magmatic reservoir. The intrusion of oxidized hydrous mafic magma from a deeper magma source likely promoted wide magma mixing and prolonged fractional crystallization within the evolved dioritic magma chamber, resulting in exsolution of the ore-forming fluids and the formation of the Masjeddaghi deposit. Copyright

amphibole , apatite , biotite , Iran , magnetite , Masjeddaghi porphyry Cu-Au deposit

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ANGLO REM CA Exploration Mining Ltd, Astana, Kazakhstan
Department of Geology, Payame Noor University, Tehran, Iran
LabMaTer, UQAC Laboratory, Université du Québec à Chicoutimi, Saguenay, QC, Canada
School of Mining and Geosciences, Nazarbayev University, Astana, Kazakhstan

ANGLO REM CA Exploration Mining Ltd
Department of Geology
LabMaTer
School of Mining and Geosciences

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