Evaluating the Origin of Magnetite and Sulfide Phasess from Gol-Gohar Iron Ore Deposit (Sirjan): Constrains from O and S Isotope Data

Gol-Gohar iron mine in Sirjan with general tonnage of 1135 milion tons, is one of the most important iron sources in Iran. The main ore minerals in this ore deposit consist of magnetite and subordinate hematite. δ18O of magnetite ranges from 3.8‰ to 4.8‰, while the calculated δ18O of the fluids that are in isotopic equilibrium with magnetite, varies between 10‰ and 11.3‰. Such isotopic attributes indicates that magnetite originated from magmatic fluids that were also equilibrated with sources enriched in 18O. This theory completely corresponds with the breaciated environment of Gol-Gohar ore deposit and the presence of metamorphosed sedimentary and igneous rocks with high δ18O amounts. Magnetite in Gol-Gohar iron, particularly in lower levels, is associatd with sulfide phases, so that the amount of sulfur increases with depth. The main sulfide phase in Gol-Gohar ore is pyrite that occupies the spaces between the magnetite grains and occurs as narrow veinletss. The δ34S values of pyrite (23.46‰-25‰) are similar to those of seawater sulfate (~30‰) and evaporative sulfates (10-30‰) and thus suggest pyrite originated likely from such sources. Texture and pertogrephic studies also show that sulfides were deposited after the formation of magnetite ore in Gol-Gohar.