Mineralography, paragenesis sequence, and sulfur isotopic composition of Baba-Ali and Galali iron ore deposits from the Sanandaj-Sirjan zone, northwest Iran

The northern part of the Sanandaj-Sirjan zone hosts important iron deposits formed during the Mesozoic magmatism. The Baba-Ali and Galali ore deposits occurred on the border of Hamedan, Kermanshah, and Kurdistan provinces. Ores in these deposits include magnetite together with pyrite, pyrrhotite, chalcopyrite, and hematite. The petrographic studies show at least two generations of magnetite and one generation of pyrite in the Baba-Ali, and one generation of magnetite and pyrite in the Galali ore deposits. The supergene processes replaced the magnetite with hematite, goethite, and limonite in the surface parts of the deposits. Field and mineralographic evidence show that the studied ore deposits are of skarn type. The δ34S values of pyrite from the Baba-Ali and Galali deposits range from +6.8 to +13.3‰ and +6.1 to +7.3‰ respectively, and calculated δ34SH2S of the mineralizing fluid range from +7.8 to +14.3 ‰ and +7.1 to +8.3‰, respectively. The δ34S values of the Baba-Ali and Galali ore deposits are higher than the magmatic source values for the skarn deposits. Therefore, these positive values indicate the incorporation of sulfur from both magma and host/wall rocks. The igneous bodies of the studied area are mainly composed of mafic to felsic intrusive rocks, which formed as a result of magmatism resulting from the subduction of the Neo-Tethys oceanic crust beneath the Central Iran Microcontinent (CIM) during the Late Jurassic-Early Cretaceous time. Due to the emplacement of dioritic magmas within the carbonate rocks of the region, iron mineralization (magnetite) of the skarn type has occurred with the metamorphism of the host rocks.